Boosting Testosterone via Aromatase Inhibition
by Dan Gwartney, MD
Double-dipping is a term used in the business world and refer to situations that provide additional revenue with no additional work. An example of double-dipping is a waste recycler charging a customer to pick up sorted trash (paper, aluminum, etc.) and then selling the materials to a recycling plant for additional income. Though the extra income rarely doubles the amount of money generated, it always improves the company’s bottom line. Wise business operators always look for ways to double-dip. In many cases, the benefits go even further. Consider the waste company— not only have they generated two sources of income from the same operation, but they’ve decreased their cost by not having to pay dump fees for the recycled waste.
Double-Dipping In Bodybuilding
There are rare opportunities for double-dipping in bodybuilding as well. Human growth hormone (GH) offers the double-dipping effects of both burning fat and building lean mass.1,2 Clenbuterol has a mildly anabolic effect, but is also a potent thermogenic agent.3 Clearly, combining both anabolic and lipolytic (fat reducing) effects has made both of these drugs extremely popular among bodybuilders. There’s another double-dipping opportunity that’s often overlooked. In part, this is due to the relatively new entrance of the latest generation of this class of products. Supply also affects their popularity; as well, they don’t provide as much bang for the buck as anabolic steroids. Regardless, this class of drug is still highly regarded and sought after among more experienced and sophisticated bodybuilders. The class of drug is aromatase inhibitors. Aromatase is a complex of enzymes that convert androgens (testosterone, androstenedione and many anabolic steroids) into estrogenic hormones.4 Estrogens are hormones that impart female sexual characteristics, increase bone density, affect blood clotting and promote fat and water retention. Most bodybuilders are familiar with some of the effects of estrogens, causing bloating or gynecomastia (the development of breast tissue under the male nipple).5,6 There are two primary estrogens, estradiol and estrone, with estradiol (E2) being the more active of the two forms.
Prior to the development of the latest aromatase inhibitors, bodybuilders had few choices for reducing the estrogenic load of a cycle. Often, they tailored their cycles to include both aromatizing and non-aromatizing steroids, tapering down on the amount of the more effective (relative to mass and strength) aromatizing steroids if bloating arose. In preparation for a competition, aromatizing steroids were often removed from the cycle to improve the hardened appearance onstage. If gynecomastia appeared, there were few effective options. Cytadren (aminoglutethimide) is a non-specific inhibitor of steroid formation.7,8 Though it was usually regarded as being a cortisol suppressing agent, it also had moderate anti-aromatase activity at low doses. Nolvadex® (tamoxifen) is a mixed estrogen agonist-antagonist. Though tamoxifen did reduce gynecomastia in some cases, it worsened it in others. Tamoxifen also increases sex hormone binding globin, reducing the bioavailability of steroid hormones; it’s also been noted to increase estrogen levels ironically.9,10 Clomid (clomifene citrate) also works at the level of the estrogen receptor, but its use was usually reserved for restoring natural testosterone production at the end of a cycle.11
Age-Related Testosterone Declines
Though medical science has no interest in bodybuilding, many discoveries relate to the sport. In the matter of aromatase inhibition, breast cancer research has been extremely valuable. Breast cancers are typically responsive to female sex hormones (estrogens and progesterone). Therapies that reduce estrogen levels in the body and especially in tumors, have been actively investigated and developed by the pharmaceutical industry. This has resulted in the development of effective anti-aromatase drugs. Several drugs in this class have been developed, including the most recent generation of aromatase inhibitors, anastrazole and letrozole. Bodybuilders are familiar with anastrazole and letrozole by the trade names Arimidex® and Femara®.12,13 Arimidex is more commonly encountered and has been used with great effectiveness in treating steroid-induced gynecomastia. It’s also believed to provide a tighter, harder appearance. Femara is less commonly encountered but is believed to be slightly more effective for the steroid-using bodybuilder.
Though most research on these drugs relates to breast cancer therapy, there have been several interesting studies on aromatase inhibition in human males. One such study was recently published in the Journal of Clinical Endocrinology and Metabolism, reporting some very interesting results.14 There were also several comments in the discussion that hold potential value to bodybuilding, though that aspect wasn’t addressed for obvious reasons. The purpose of this study was to test whether the age-related decline in testosterone is due to an increased suppressive effect of estrogens on the hypothalamic-pituitary axis. To briefly review, natural testosterone production is regulated via a negative-feedback loop, involving the testes and two regions of the brain— the hypothalamus and the pituitary gland. Testosterone production occurs in the testes under the stimulation of a protein hormone released by the pituitary called leutinizing hormone (LH). LH, in turn, is released from the pituitary under stimulation of a hypothalamic hormone called gonadotropin-releasing hormone (GnRH). The hypothalamus is called the master gland because it monitors the body and regulates the activity of the endocrine glands by means of its releasing hormones. In the case of testosterone, when the hypothalamus detects that androgen levels are too high, it temporarily shuts down GnRH release. When GnRH levels drop, the pituitary stops releasing LH and the testes are no longer stimulated to produce testosterone. Once testosterone levels drop, GnRH surges, causing LH and subsequently testosterone levels to pick back up. For reasons not clearly understood, the body isn’t designed to maintain a steady, even level of testosterone. Rather, it produces testosterone in wave-like surges, with peaks and valleys in the blood levels of testosterone. Even more interesting is the fact that the hypothalamus doesn’t only detect testosterone, but also its metabolites estradiol and dihydrotestosterone (DHT).15,16
The researchers designed a study whereby they could measure whether older men were more sensitive to estrogen suppression of testosterone production as compared to young adult men. To test this, they measured several hormones, including LH and testosterone (T) in two groups of men, old versus young. It’s known that T production decreases with age, resulting in a 50 percent reduction of bioavailable T.17 It’s believed that this reduction is due to cellular changes in the testes, changes in the regulatory function of the brain and increased negative feedback (or suppression).18 It’s also known that aromatase activity increases with age and overall fat content increases, combining to maintain estrogen levels even in the face of decreasing T levels.19 This results in a markedly lower T:E2 ratio, with E2 representing estradiol levels. This altered ratio is likely responsible for many of the changes experienced by men with age.
Initially, it appeared as though there was little difference between the two groups, as the older and younger men had similar LH and total T values. However, the older men had much higher sex hormone binding globin (SHBG), which traps circulating T, keeping it from being metabolized, but also preventing it from having any biological activity. This resulted in significantly lower free or bioavailable T levels and markedly lower free T:free E2 ratios.14 The subjects were then given 2.5 milligrams per day of letrozole (Femara) for 28 days and retested. The aromatase inhibitor produced “a remarkable and comparable elevation” of both GnRH and T in both groups. Letrozole increased LH and T 339 percent and 146 percent respectively in the younger group; LH and T increased 323 percent and 99 percent in the older group. Letrozole also reduced E2 levels by 46 percent in young men, and 62 percent in the older subjects. SHBG also dropped significantly in both groups, with the T:E2 and free T:free E2 ratios rising sharply in response. Despite the robust response to aromatase inhibition, the study failed to show any evidence of older men experiencing a greater suppressive effect of estrogens on natural testosterone production. In fact, the younger men demonstrated a greater response to aromatase inhibition relative to the suppressive effects of estrogens on the hypothalamus and pituitary gland. While it remains to be seen what accounts for the hormonal changes older men experience, it’s clear that inhibiting aromatase might restore some of the youthful hormonal values.
“Natural” Supraphysiologic Testosterone Levels
Thus far, the study has been valuable in that it clearly demonstrates that healthy men, both young and old, can safely tolerate short-term aromatase inhibition and experience hormonal changes that would be beneficial to those involved in bodybuilding. As noted earlier, there were several comments in the discussion that are worthy of further regard.
One issue that impaired the study, but was very noteworthy was the observation that the effect of letrozole persisted for much longer than anticipated. Subjects were originally scheduled to have a 14-day washout period, where they didn’t receive either drug or placebo before beginning the second phase of the study. However, after the 14-day break, it was discovered that the subjects who received letrozole were still experiencing the effects of the drug with markedly higher T.14 This is somewhat surprising, as letrozole has a half-life of approximately two days, so one would presume 14 days would be sufficient to eliminate the drug from the system.20 It’s possible that the daily dose regimen allowed levels to build up higher than anticipated. In fact, a separate study looking at obese men with low T levels showed that 2.5 mg given three times a week was sufficient to restore normal T levels.21 It’s possible that letrozole wouldn’t need to be dosed daily to provide adequate protection against aromatization.
The degree of T elevation experienced by the younger and older men was quite pronounced. In fact, both groups ended up with T levels at or above the upper limit of normal for young men.14 This would suggest that suppressing aromatase could allow a steroid-free bodybuilder to experience “natural” supraphysiologic testosterone levels. This would be roughly equivalent to receiving 250 to 300 milligrams of testosterone enanthate per week.
Though the goal of aromatase inhibition is to reduce estrogen conversion of androgens, it’s not necessary to completely remove estrogens from the body. There are case reports of men and women who were born without any aromatase activity due to genetic mutation. These individuals are not particularly robust specimens. They are typically very tall (due to a failure to close the growth plates of the bone), have fragile skeletons due to low bone mineral density and in the case of males, are fully mature sexually. Females experience pubertal failure with virilization (male characteristics— facial hair, clitoromegaly, etc). Males also have macroorchidism, a term describing abnormally large testes. Thus, complete suppression of aromatase would not be of benefit to the bodybuilder long term. Fortunately, the degree of suppression appeared to be only partial in the letrozole study. Both groups still retained approximately 40 to 50 percent of their original estrogen levels, though it remains to be seen if such values would lead to an increased risk of osteoporosis.
Reducing Side Effects, Increasing Testosterone
The authors compared the results of other aromatase inhibition studies in males, using either anastrazole (Arimidex) or letrozole (Femara).14 The estrogen-reducing effect seen in this study is in agreement with other letrozole studies. While anastrazole also has a potent estrogen lowering effect, its potency is less than that of letrozole. Comparing several studies, using different dosing schedules, it appears that letrozole is capable of lowering estrogen levels 40 to 60 percent, while anastrazole (commonly dosed at one milligram per day) lowered estrogen 30 to 50 percent. It’s important to note that these figures represent blood levels and there’s some debate as to the importance of tissue levels, rather than circulating levels of estrogen. Even in that regard, letrozole is considered superior. Also discussed were the comparable results between letrozole and clomiphene citrate (Clomid).23 Clomid is used at the end of cycles to aid in restoring natural testosterone production. In considering this comment, and the fact that Femara (letrozole) is used in some fertility drug protocols, it appears that letrozole could be used in place of Clomid for off-cycle recovery.11 This would be particularly beneficial when used along with human chorionic gonadotropin (hCG), as hCG is known to raise estrogen levels in men, even as they are attempting to restore their testosterone producing ability.24
An unrelated study suggested another mechanism whereby aromatase inhibition helps resolve feminizing side effects. In studying the cellular effects of aromatase inhibitors versus tamoxifen on breast cancer cells, it was determined that aromatase inhibition led to a reduction of progesterone receptors in the tissue.25 In contrast, tamoxifen increased progesterone receptor density. Progesterone is another female steroid hormone, and is believed by some to be due for the uncommon cases of nandrolone-induced gynecomastia.26 It remains unclear as to why older men suffer the hormonal changes associated with age. Certainly, it is known that older men have a higher aromatase activity and greater fat mass leading to higher estrogen levels, higher SHBG leading to lower bioavailability of T, functional and cellular changes in the testes and brain leading to less orderly signaling and lower T response, and a greater degree of inhibition by DHT and T. Though enhanced estrogenic suppression of the hypothalamus and pituitary isn’t the culprit causing older men to have lower testosterone and free T:free E2 ratios, by suppressing estrogen formation through aromatase inhibition, many of the changes are corrected. For the bodybuilder, this is of significant note, as it proves once again the utility of this class of drug for the steroid using bodybuilder and offers the non-steroid using bodybuilder an option to consider for increasing testosterone to mildly supraphysiologic levels. Aromatase inhibitors are on the banned substance list for the IOC (Olympics), so competitive athletes need to be aware of organizational restrictions.
Aromatase inhibitors give bodybuilders a chance to double-dip as the drug reduces estrogenic side effects and increases testosterone levels. By reducing SHBG, testosterone and other steroids would have a greater bioavailability though they would clear the system more quickly. Gynecomastia, water retention and fat accumulation could be more easily controlled.
While these effects are clearly attractive to bodybuilders, they also hold value to aging men. Hopefully, in the interest of the growing aging population, further research will be conducted to investigate the role of this class of drugs in combating the ravages of aging and age-associated diseases.
1. Kim KR, Nam SY, et al. Low-dose growth hormone treatment with diet restriction accelerates body fat loss, exerts anabolic effect and improves growth hormone secretory dysfunction in obese adults. Horm Res, 1999;51(2):78-84.
2. Stacy JJ, Terrell TR, et al. Ergogenic AIDS: human growth hormone. Curr Sports Med Rep, 2004 Aug;3(4):229-33.
3. Maltin CA, Delday MI, et al. Clenbuterol, a beta-adrenoreceptor agonist, increases relative muscle strength in orthopaedic patients. Clin Sci, 1993 Jun;84(6):651-4.
4. Richards JA, Petrel TA, et al. Signaling pathways regulating aromatase and cyclooxygenases in normal and malignant breast cells. J Steroid Biochem Mol Biol, 2002 Feb;80(2):203-12.
5. Bouraima H, Lireux B, et al. Major hyperestrogenism in a feminizing adrenocortical adenoma despite a moderate overexpression of the aromatase enzyme. Eur J Endocrinol, 2003 Apr;148(4):457-61.
6. Babigian A, Silverman RT. Management of gynecomastia due to use of anabolic steroids in bodybuilders. Plast Reconstr Surg, 2001 Jan;107(1):240-2.
7. Forrest AR. Aromatase inhibitors in breast cancer. N Engl J Med, 2003 Sep 11;349(11):1090.
8. Carella MJ, Dimitrov NV, et al. Adrenal effects of low-dose aminoglutethimide when used alone in postmenopausal women with advanced breast cancer. Metabolism, 1994 Jun;43(6):723-7.
9. Derman O, Kanbur NO, et al. The effect of tamoxifen on sex hormone binding globulin in adolescents with pubertal gynecomastia. J Pediatr Endocrinol Metab, 2004 Aug;17(8):1115-9.
10. McDermott MT, Hofeldt FD, et al. Tamoxifen therapy for painful idiopathic gynecomastia. South Med, J 1990 Nov;83(11):1283-5.
11. Homburg R. Clomiphene citrate – end of an era? A mini-review. Hum Reprod, 2005 Aug;20(8):2043-51.
12. Rhoden EL, Morgentaler A. Int J Imp Res, 2004 Feb;16(1):95-7.
13. Wickman S, Dunkel L. Inhibition of P450 aromatase enhances gonadotropin secretion in early and midpubertal boys: evidence for a pituitary site of action of endogenous E. J Clin Endocrinol Metab, 2001 Oct;86(10):4887-94.
14. T’Sjoen GG, Giagulli VA, et al. Comparative assessment in young and elderly men of the gonadotropin response to aromatase inhibition. J Clin Endocrinol Metab, 2005;90:5717-22.
15. Hayes FJ, Seminara SB, et al. Aromatase inhibition in the human male reveals a hypothalamic site of estrogen feedback. J Clin Endocrinol Metab, 2000;85:3027-35.
16. Canovatchel WJ, Volquez D, et al. Luteinizing hormone pulsatility in subjects with 5-alpha-reductase deficiency and decreased dihydrotestosterone production. J Clin Endocrinol Metab, 1994 Apr;78(4):916-21.
17. Gray A, Berlin J, et al. An examination of research design effects on the association of testosterone and male aging: results of a meta-analysis. J Clin Epidemiol, 1991;44:671-84.
18. Kaufman JM, Vermeulen A. Declining gonadal function in elderly men. Ballieres Clin Endocrinol Metab, 1997;11:289-309.
19. Vermeulen A, Kaufman JM, et al. Estradiol in elderly men. Aging Male, 2002;5:98-102.
20. Sioufi A, Gauducheau N, et al. Absolute bioavailability of letrozole in health postmenopausal women. Biopharm Drug Dispos, 1997;18:779-89.
21. de Boer H, Vershoor L, et al. Letrozole normalizes serum testosterone in severely obese men with hypogonadotropic hypogonadism. Diabetes Obes Metab, 2005;7:211-5.
22. Morishima A, Grumbach MM, et al. Aromatase deficiency in male and female siblings caused by a novel mutation and the physiological role of estrogens. J Clin Endocrinol Metab, 1995 Dec;80(12):3689-98.
23. Tenover JS, Matsumoto AM, et al. The effects of aging in normal men on bioavailable testosterone and luteinizing hormone secretion: response to clomiphene citrate. J Clin Endocrinol Metab, 1987;65:1118-26.
24. Conte D, Romanelli F, et al. Aspirin inhibits androgen response to chorionic gonadotropin in humans. Am J Physiol, 1999 Dec;277(6 Pt 1):E1032-7.
25. Miller WR, Anderson TJ, et al. Aromatase inhibitors: Cellular and molecular effects. J Steroid Biochem Mol Biol, 2005 May;95:83-9.
26. Llewellyn W. Deca-durabolin (nandrolone decanoate). Anabolics, 2005. Body of Science Press, Jupiter, FL, 2005:109-12.
Enhancing Fat Loss Through Beta-Adrenergic Mediated Stimulation
Enhancing Fat Loss Through Beta-Adrenergic Mediated Stimulation
by Robbie Durand
In a previous column, the topic of beta-2 agonists and their effects on muscle hypertrophy were discussed along with the pros and cons of using the drug. The beta adrenergic receptors are regulated not only by the catecholamines epinephrine and norepinephrine, but also by the thyroid hormones cortisol and testosterone. Research has shown that testosterone administration promotes a rapid and dose dependent up-regulation of the fat cell beta-receptors, which enhance lipolysis (i.e., fat mobilization).8 Not only are catecholamines involved in protein synthesis rates and muscle hypertrophy, but they’re major sources of human fat metabolism. Basal metabolic rate increases as much as seven to 15 percent with increased catecholamines. 31 When trying to get ripped up, stimulating catecholamines through the use of supplements can enhance resting metabolic rate. Remember, the largest fraction of total energy expenditure doesn’t come from exercise, but from your resting energy expenditure (approximately 65 to 75 percent). So if you had to pick the organ requiring the largest metabolic rate, which one would it be? Heart and kidneys have the highest (440 kcal/kg day), then liver (240 kcal/kg day), muscle (13 kcal/kg day) and finally fat (4.5 kcal/kg day).
Catecholamines can increase resting metabolic rate through multiple pathways and are important for weight regulation. In fact there are some researchers who believe obesity may be due to “catecholamine resistance” similar to diabetics suffering from “insulin resistance.” In a study by Lonnqvist et al.,33 65 subjects were divided in two groups: those who were sensitive to catecholamines and those who weren’t. Both groups were subjected to an exercise stress protocol (i.e., 30 minutes at two-thirds of their maximum aerobic power) in combination with mental stress (i.e., color words), which can significantly enhance catecholamine secretion. The subjects who were classified as “catecholamine resistant” had a 50 percent reduction in the lipolytic response to exercise and mental stress, despite a 50 percent increased plasma noradrenaline (norepinephrine) response and a 350 percent increased plasma adrenaline (epinephrine) response. Interestingly, the cardiac responses to the exercise and mental stress were virtually identical between the groups. Catecholamines have an effect on causing metabolic changes in adipose tissue. There are two types of fat cells in the body: white adipose tissue and brown adipose tissue. Both are heavily influenced by the sympathetic nervous system (has an active "stimulating" function), whereas the parasympathetic nervous system (has mainly a “relaxing” function) plays a minor role in adipose tissue lipolysis. The metabolic activity and biochemical properties of the two tissues are vastly different. It’s been reported that brown adipose tissue has a 10-fold higher metabolic activity than white adipose tissue.24 See Figure 1 for a biochemical breakdown between the two types of adipose tissues.
Brown and White Adipose Tissue
White adipose tissue serves three functions: heat insulation, mechanical cushion and, a source of energy. It could also serve fourth function: making you look like a “fat-ass.” When white adipose tissue is mobilized as an energy source, triglycerides are broken down into free fatty acids from their glycerol backbone allowing them to enter circulation and be used as an energy source. On the other hand, brown adipose tissue, which derives its color from a rich supply of blood vessels for oxygen supply and abundant source of mitochondria, is found in different locations depending upon the species and/or age of the animal. Brown adipose tissue releases fatty acids in the cell. For example, rats have more brown adipose tissue than humans.1,12 In newborn babies, brown fat makes up about five percent of the body mass and is located on the back, along the upper half of the spine and toward the shoulders. Brown fat is of great importance to babies because it helps protect against lethal cold exposure as it’s important for regulating body temperature via non-shivering thermogenesis. Shivering thermogenesis is created in the muscle by shivering or contacting. For example, when you’re cold your muscles start contracting to generate heat. In brown adipose tissue, heat production is increased without muscle involvement. Brown adipose tissue is heavily influenced by catecholamines; interestingly when catecholamines are blocked, brown adipose tissue is reduced, whereas chronic catecholamine production increases hypertrophy of brown adipose tissue.1 The mechanism of heat generation is related to the metabolism of the mitochondria. Mitochondria from brown adipose tissue have a specific carrier called uncoupling proteins that transfer protons from outside to inside without subsequent production of ATP. Basically this means in contrast to other cells, including white adipocytes, brown adipocytes utilize substrates to generate heat rather than ATP. The mitochondria are larger in brown adipose tissue as well as more abundant compared to white adipose tissue.11 During the adult life span in humans, brown adipose tissue becomes metabolically less active, although cold exposure can activate it. As mentioned previously, brown adipose tissue uses 60 percent of the extra oxygen used in non-shivering thermogenesis-induced cold-acclimated animals.3
The Main Side Effects of Catecholamines
Energy expenditure can be measured directly as heat production (thermogenesis), but is more commonly assessed indirectly as oxygen consumption.16 Based on the results of previous studies, brown adipose tissue is accepted as the major site for non-shivering thermogenesis. So how do you increase the metabolic activity of brown adipose tissue? Well, you can move to Antarctica and live in your posing trunks or you can increase norepinephrine activity. Norepinephrine stimulation of brown adipose tissue mimics the effects of cold-induced activation and promotes an increase in uncoupling chain protein-1 (UCP-1). UCP-1 causes heat generation and the burning of calories in the mitochondria, which are important for metabolic control. An increase in norepinephrine activity increases UCP-1 mRNA in brown fats, which is mediated by the ?-3 receptor and subsequent increase in cAMP levels.5 In fact, UCP-1 is the major gene being expressed in adipose tissue responsible for non-shivering thermogenesis.19
There’s a disease termed “phaeochromocytoma” which leads to high circulating norepinephrine levels in man. Pheochromocytoma is a rare tumor usually occurring in the adrenal glands. As a result of the tumor, the adrenal glands produce too much adrenaline. Imagine the benefit— you would never have to take Ripped Fuel or Hydroxycut. The downside is that there are a host of side effects from this disease. As mentioned previously, during maturation brown adipose tissue disappears with aging, however in patients with pheochromocytoma, brown adipose tissue, which normally disappears after infancy, becomes “reactivated,” which may lead to excessive weight loss. Catecholamines are potent thermogenic stimulators, however, one of the main side effects of catecholamines is that there are adverse reactions associated with their usage namely, tachycardia (fast beating heart), tremors and decreased serum K+ levels. This is mainly due to catecholamines binding to beta-1 and beta-2 receptors in heart and muscle. The beta-2 receptor is the most commonly expressed receptor in most cells, with an abundant source on white adipose tissue. A third type of beta-receptors called the ?-3 receptor was thought to be the new pharmaceutical cure-all for obesity as the ?-3 receptor is only located in adipose tissue and its activation doesn’t affect the nervous system.
Enhancing Fat Mobilization During Rest
Many researchers have hypothesized that the ?-3 receptor to alpha-2adrenoceptor ratio is the key to the regulation of thermogenesis and adipose tissue lipolysis. What’s so special about this combination? Stimulation of the alpha-2 adrenoceptors is anti-lipolytic. It basically halts fat mobilization from adipose tissue. alpha-2 adrenoceptors are distributed differently in men and women, as men tend to contain more alpha-2 adrenoceptors in their abdomen whereas women tend to have more alpha-2 adrenoceptors located in their hips and buttocks. So how important are alpha-2 adrenoceptors for fat lipolysis? Well when you take a fat biopsy of adipose tissue ratios from a person’s butt, which is the hardest body part for many bodybuilders to get ripped up, you will find a three- to 10-fold higher concentration of alpha-2 adrenoceptors to beta receptors.38 It’s been demonstrated that epinephrine has a higher binding affinity than norepinephrine for the ?-2 adrenoceptors.6 In addition, at low concentrations (i.e., rest), it’s been reported that alpha-2 adrenoceptors are activated. However during exercise, high NE levels stimulate alpha-receptors which activate lipolysis.39 In human fat cells, after alpha-agonist administration, there’s marked down regulation of the ?-receptors, yet there’s no down regulation of the alpha-2 adrenoceptors.7 In fact, even after long term alpha-2 adrenoceptors agonist’s administration, there seems to be no down regulation of the alpha-2 adrenoceptors.7 If you’re trying to get ripped up adding some yohimbine to the supplement stack might be advantageous as alpha-2 adrenoceptors inhibits adenylyl cyclase activity, which in turn inhibits cAMP and turns off lipolysis!!! Another little benefit to men is that administration of yohimbine has been shown to enhance penile erections because the penis has a high density of alpha-2 adrenoceptors. alpha-2 adrenoceptors have the opposite effect from the beta receptors on intracellular cAMP levels.
Beta-3 Agonists: A Great Start With a Poor Finish…
So what makes the beta-3 receptor so special? Gene studies of mass populations have shown that there’s strong evidence linking body mass index (BMI) and the beta-3 gene, which indicates that the beta-3 gene expression is a strong candidate for obesity.19 The beta-3 receptor has a low-binding affinity for epinephrine, yet a high binding affinity for norepinephrine.4 beta-3 receptors have a lower binding affinity for epinephrine compared to ?-1 and ?-2 receptors, however beta-3 receptors have a higher binding affinity for noradrenaline than ?-2 receptors, yet a lower binding affinity than ?-1. Administration of a beta-3 agonist has no effect on stimulating catecholamine release, which is quite different from many of the obesity drugs found on the market.12 White adipose tissue has a scarce number of beta-3 receptors, but a much larger number of beta-1 and beta-2 receptors.12 Another interesting feature about the beta-3 receptor is that in rat studies it’s highly resistant to down regulation, as are beta-2 receptors.32 The obesity treatment hypothesized by researchers was that if the beta-3 receptor is hard to down regulate and produces significant thermogenesis it might be a practical approach to stimulating fat loss. So here’s the study that started the beta-3 craze. Healthy volunteers were administered a dose of ephedrine, which stimulates all three beta- receptors in fat (beta-1, beta-2, beta-3), however they also administered nadolol. Nadolol inhibits both the beta-1 receptors, located chiefly in cardiac muscle and the beta-2 receptors, located chiefly in the bronchial and vascular musculature. What they found was nothing short of amazing. Even though beta-1and beta-2 receptors were blocked, there was a 43 percent increase in thermogenesis, which was entirely mediated by the beta-3 receptor. So the race was on…developing a beta-3 agonist could increase thermogenesis without the side effects of nervousness and tremors because beta-3 receptors are only located on adipose tissue.
The Mystery of White Adipose Tissue
In rats, the ?-3 agonist administration was a tremendous success; beta-3 agonist administration caused significant reductions in abdominal fat pads and a host of other beneficial mediators of fat lipolysis and was also found to be a potent anti-diabetic agent. beta-3 agonist in mice or rats approximates doubling of total body energy expenditure after an acute dose.14 beta-3 agonist administration also caused increases in hormone sensitive lipase (HSL) activity gene expression and also increases in uncoupling chain protein 1 (UCP-1) in adipose tissue. HSL is the major rate-limiting enzyme in adipose tissue lipolysis. By increasing HSL activity in adipose tissue more fatty acids are transported out of adipose to be used as an energy source. In fact, there’s an immediate increase in HSL gene activity that occurs with fasting.17 Your body is basically saying, “There’s no food coming so start mobilizing more adipose tissue as an energy source!”
So as stated before, there are very few beta-3 receptors located on white adipose tissue and there are very few brown adipocytes in humans, so how is there a decrease in white adipose tissue if there are few receptor sites? In fact, many studies have suggested that there’s an induction of brown adipose tissue into white adipose cell.20,21 That’s right!! White adipocytes tissue starts developing brown adipose tissue characteristics. Interestingly, beta-3 agonists have the ability to induce UCP-1 gene expression in white adipose tissue as well as brown adipose tissue.19 One study documented that four weeks of ?-3 agonists administration caused a 62-percent increase in UCP-1 expression at week two and a 132-percent increase at week four.25 UCP-1 is the major source of thermogenesis in brown adipose tissue. Take away UCP-1 and all you have is worthless brown adipose cells with no metabolic activity. Mice that are genetically engineered to be UCP-1 deficient suffer extreme hypothermia (i.e. decreased body core temperature) and are cold insensitive. Conversely mice that over-express UCP1 are hyperphagic (eat excessively) and obesity resistant.15,16 Here was a really cool experiment, which documents how UCP-1 regulates the brown adipose cell. Researchers took adipocytes from mice that were genetically modified so they didn’t produce UCP-1 or UCP-1 deficient mice. They exposed the brown adipocytes to norepinephrine, which is a potent stimulator of UCP-1, and guess what happened? Nothing!!! The brown adipocytes didn’t increase thermogenesis, demonstrating that UCP-1 is the major source of thermogenesis in adipose tissue.25
Did Someone Hear a Toilet Flush…
Okay…here’s where you hear a big toilet flush for ?-3 agonists. The research was overwhelming clear that beta-3 agonists can increase thermogenesis and reduce body fat in rats, but when humans were studied, the results were only marginal. When beta-3 agonists are administered acutely, there’s an increase in energy expenditure and lipolysis, with no effects on heart rate, catecholamines, or body core temperature.29 The problem is that long-term studies fail to show any change in fat lipolysis or changes in resting energy expenditure. When obese men were administered beta-3 agonists for 28 days, there was no change in 24-hour energy expenditure, body composition, catecholamines, or changes in fatty acid mobilization.12 The author concluded that unlike rat studies, which have shown beta-3 receptors to be resistant to down regulation, human beta-3 receptors are directly or indirectly down-regulated in response to beta-3 agonists. Another study, which lasted for 14 days, found no changes in resting energy expenditure or fat metabolism.30 Barbe et al.,27 investigated the effect of all beta-receptors (beta-1, beta-2 and beta-3) on a very low-calorie diet (382 calories a day) for 28 days. A microdialysis pump was inserted in the abdomen after 28 days on the low-calorie diet and three types of beta agonist drugs (i.e., Dobutamine beta-1 agonist], Terbutaline [beta-2 agonist] and CGP [partial-3 agonist]) were infused to measure changes to receptor sensitivity to fat tissue lipolysis. Results of the study concluded that there was a significant up-regulation of the beta-1 adrenergic pathway in adipose tissue. beta-2 receptors increased sensitivity to catecholamine, yet there were no changes in receptor number. There was only a mild increase in beta-3 receptor activity, further supporting that the beta-3 receptor is only weakly involved in the lipolytic process in humans. Another potential problem with ?-3 agonists is that brown adipose tissue decreases with age and beta-3 receptors are only sparsely located on white adipose tissue in humans (approximately 20 percent), whereas in rats, brown adipose tissue (approximately 90 percent) is abundant.31 Whether or not beta-3 agonists will be proven to be useful is debatable given the low receptor number found in human tissue. The research basically shows that beta-3 receptor is present in adipose tissue of both white and brown adipose tissue, yet its activation is only weakly involved in the lipolytic process in man. Based on the research, beta- receptors located on brown adipose tissue play a minor role in the lipolytic actions in humans, although highly thermogenic in rats. This effect is probably due to the fact that rats have a high abundance of brown adipose tissue compared to humans.24
Stimulating Fat Loss Through ?-Adrenergic System
In fat cells, it’s clearly established that agents increasing lipolysis also stimulate the beta-adrenergic system and increase cAMP levels. Catecholamines increase cAMP levels, whereas insulin decreases cAMP levels.22 No wonder ketogenic diets are so effective for getting ripped. Increases in cAMP increases lipolysis in both white and brown adipose tissue and also increases brown adipose tissue hypertrophy. In addition, UCP-1 is also stimulated by increasing cAMP levels.10 It seems that lipolysis is mainly dependent on the beta-1 and beta-2 receptors in adipose tissue; however these receptors are readily down-regulated.27 In fact, human fat cells have been shown to be 300 times more sensitive to Isoprenaline, which has beta-1 and beta-2 adrenoceptor activity, than beta-3 agonists.36 When it comes to supplements, that good ole ephedrine and caffeine stack was great for stimulating all three beta-receptors. For example, the caffeine, ephedrine and aspirin stack was so effective because ephedrine is a non-selective beta-agonist, while caffeine inhibited cAMP breakdown (keeps its activity high), and aspirin inhibited the negative feedback loop that reduces ?-agonist production. Ephedrine stimulates all three beta receptors located on adipose tissue. Researchers have suggested that beta-3 receptors may be a highly regulatory mechanism in fat cells after beta-1 and beta-2 receptors become desensitized. This may be the reason an increase in metabolic rate is seen after an ephedrine and caffeine stack is stopped, as subjects have been reported to continuously lose weight after discontinuation of caffeine and ephedrine.35 Another great thing about the caffeine-ephedrine stack is that it increases norepinephrine and norepinephrine and directly increases UCP-1 gene expression in both white and brown adipose tissue.24
In conclusion, researchers once believed thermogenesis never occurs in white adipose tissue. Today, new research is questioning the validity of that claim. For example, a group of UCP-1 genetically deficient mice were exposed to a dose of beta-3 agonists. Based on what we know about UCP-1 as a potent stimulator of thermogenesis, researchers thought nothing should happen. How wrong they were!! There was still an increase in metabolic rate and body temperature that occurred in the UCP-1-deficient animals, which was mediated by white adipose tissue.34 The results demonstrate that white adipose tissue has the capacity to increase thermogenesis through the ?-3 receptor despite no effect on UCP-1. When reviewing the literature, it seems that in conjunction with consuming thermogenic supplements, you should also increase your consumption of polyunsaturated fats, as one study reported that in comparison to saturated fats with equal calories, a diet high in polyunsaturated fats increased mitochondrial activity and higher UCP-1 content than with saturated fats.26 Researchers are looking into pharmaceutical drugs that can counteract obesity by increasing UCP-1 expression in other organs (i.e., white adipose tissue). Muscle might be the better alternative to increasing thermogenesis as muscle is the major site of free fatty acid utilization. Of the beta-1 and beta-2 receptors located in muscle, the ?-2 receptor is the only receptor sub-type of importance for the adrenergic regulation of lipolysis in skeletal muscle and blood flow.28 Another positive benefit of increasing epinephrine during exercise is that epinephrine will cause vasodilatation of muscle, causing greater muscle swelling (a.k.a. pump) primarily mediated thru beta-2 receptors located on skeletal muscle.
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