Molecular and Cellular Endocrinology (1995) 115 177. COS 1 cells were transfected with human AR DNA with the CMV promoter. The authors state that the DNA sequence responsible for downregulation of the AR is encoded within the AR DNA, not the promoter region. Dexamethasone [a glucocorticoid drug similar to cortisol] was observed to result in downregulation of AR mRNA relative to zero dexamethasone level. Androgen also had this effect, but did not result in lower levels of androgen receptors. This was attributed to increase in androgen receptor half life caused by androgen administration. The observed androgen downregulation effect relative to zero androgen ended at a concentration of 0.1 nanomolar of androgen (methyltrienolone) – higher doses, to 100 nanomolar, resulted in no further downregulation of AR mRNA production.
While this list is not complete, I am not omitting any studies that appear to have any better evidence – indeed, any evidence at all – that supraphysiological levels of androgen result in downregulation, relative to normal androgen levels, of the AR The above is a reasonably complete picture of the research evidence that might be used to support the bodybuilding theory of AR downregulation. When analyzed closely, no scientific study provides support for that theory.
Scientific evidence indicating that a biochemical mechanism for upregulation does exist
Even in the above evidence which apparently (at first sight) might seem in favor of downregulation, it was sometimes seen that actual levels of the AR increased, even going from zero to normal (rather than normal to supraphysiological.) This is upregulation of the receptor, since as we recall, regulation is the control of the number of receptors, and this control may be achieved by change in the half life of the receptors. Increased half life of the receptor, all else being equal, or perhaps with change in half-life overcoming other factors, can yield higher receptor numbers. Kemppainen et al. (J Biol Chem 267 968) demonstrated that androgen increases the half life of the AR, which is an upregulating effect.
Endocrinology (1990) 126 1165. In fibroblasts cultured from human genital skin which contained very low amounts of 5-alpha reductase, 2 nanomolar tritium-labeled testosterone [which is sufficient to saturate ARs] produced a 34% increase in androgen receptors as measured by specific AR binding, the best assay method known, and 20 nanomolar tritium-labeled testosterone produced an increase of 64% in number of ARs.
Note: 20 nanomolar free testosterone is approximately 400 times physiological level (normal level in humans is approximately 0.05 nanomolar).
J Steroid Biochemistry and Molecular Biology (1990) 37 553. In cultured adipocytes, methyltrienolone and testosterone demonstrated marked upregulation of AR content upon administration of androgen. 10 nanomolar methyltrienolone increased AR content (as measured by binding to radiolabeled androgen) by more than five times, relative to zero androgen.
J Steroid Biochemistry and Molecular Biology (1993) 45 333. In cultured smooth muscle cells from the penis of the rat, mRNA production was found to be upregulated by high dose testosterone (100 nanomolar) or DHT. When 5-alpha reducatase was inhibited by finasteride, thus blocking metabolism to DHT, AR mRNA production was downregulated in response to testosterone. Blockage of the aromatization pathway to estrogen by fadrozole eliminated this downregulation effect. Estradiol itself was found to downregulate AR mRNA production in these cells.
Endocrinol Japan (1992) 39 235. One nanomolar DHT was demonstrated to increase AR protein by over 100% within 24 hours, relative to zero androgen level. The half life of the AR was demonstrated to increase from 3.3 h to 7.5 h as a result of the androgen administration.
Endocrinology (1996) 137 1385. 100 nanomolar testosterone was found to increase AR levels in vitro in muscle satellite cells, myotubes, and muscle-derived fibroblasts.
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Conclusions from Scientific Research
As androgen levels decrease from normal to zero, production of AR mRNA may increase in some tissues. However, the number of ARs does not necessarily increase, because the half life of the ARs decreases with lower concentrations of androgen.
As androgen levels increase from normal to supraphysiological, numbers of ARs in some tissues have been shown to increase. Such an increase is upregulation. The increase may be due primarily or entirely to increase in half-life of the AR resulting from higher androgen level.
There is no scientific evidence to support the popular view that AAS use might be expected to result in downregulation of the AR relative to receptor levels associated with normal androgen levels.
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Conclusions from Bodybuilding Observations
I find it rather unreasonable to think that the most likely thing is that athletes who have been on high dose AAS for years, and are far more massive than what they could be naturally, and who are maintaining that mass or even slowly gaining more, could possibly have less androgen receptor activity than natural athletes or low-dose steroid users.
It might, hypothetically, be possible that their AR activity is the same, and the extra size due to steroids is due entirely to non-AR mediated activities of the androgens. However there is no evidence for that and it seems unlikely.
I believe the most logical possibility is that these athletes are experiencing higher activity from their androgen receptors than natural athletes, or low dose steroid users, are experiencing. Since the majority of androgen receptors are occupied at quite moderate levels of AAS, the explanation cannot be simply that a higher percentage of receptors is occupied, with the receptor number being the same. That would not allow much improvement. In contrast, upregulation would allow substantial improvement, such as is apparently the case (unless non-AR mediated activities are largely or entirely responsible for improved anabolism, which would be an entirely unsupported hypothesis.)
Upregulation in human muscle tissue, in vivo, is not directly proven but seems to fit the evidence and to provide a plausible explanation for observed results.
I leave the matter, however, to the reader. Weigh the evidence, and decide if downregulation, as popularly advocated, is supported by science, or by what is experienced in bodybuilders
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