To understand why methasterone has had a reputation as a “potent” oral steroid, it is not enough to say that it “activates androgen receptors”. It is important how the structure of the molecule determines its fate in tissues, what happens after binding to the receptor and how this signal reaches the synthesis of muscle protein. The editors break down the mechanism of action step by step — and honestly note where direct data on methasterone ends and extrapolation from other androgens begins.
Molecular structure as a key to the mechanism
Methasterone is dihydrotestosterone (DHT) with two methyl groups: at the 2-alpha and 17-alpha positions. DHT in itself is the strongest natural ligand of the androgen receptor, but in skeletal muscles it is quickly inactivated, so its direct anabolic action there is limited.
The reason is the enzyme 3-alpha-hydroxysteroid dehydrogenase, which is abundant in muscle tissue. It reduces the 3-keto group of DHT, turning it into the less active androstanediol. That is why DHT has a strong effect on the prostate and skin, but not so noticeably on the muscles.
The methyl group in the 2-alpha position, according to pharmacologists, sterically hinders the work of this enzyme. The same principle is embedded in drostanolone. Therefore, the molecule keeps the active 3-ketoform longer in the muscles and can more effectively interact with the receptors there.
The 17-alpha-methyl group performs another function — it protects the molecule from oxidation in the liver and provides oral activity. The editors write more about this in the article about the oral bioavailability of methasterone.
| Modification | Site of action | Probable consequence |
|---|---|---|
| 5α-reduced core (as in DHT) | All tissues | No aromatization, no enhancement via 5α-reductase |
| 2α-methyl | Skeletal muscles | Slowing down of 3α-HSD inactivation |
| 17α-methyl | Liver | Oral activity, but also hepatotoxicity |
Androgen receptor: from binding to gene
Androgen receptor is a protein from the family of nuclear receptors. In an inactive state, it is in the cytoplasm of the cell in a complex with heat shock proteins. When the androgen enters the cell and binds to it, the receptor changes conformation, is freed from companion proteins and forms dimers.
Next, the complex moves to the nucleus, where it binds to specific areas of DNA — androgen response elements. There, it attracts coactivators and starts the transcription of target genes. This process takes hours, and its physiological effects accumulate over days and weeks.
Different androgens differently change the shape of the receptor and, accordingly, differently attract coactivators. This is one of the reasons why two steroids with similar affinity can have different action profiles in different tissues. As far as the editors know, no such detailed molecular studies have been published for methasterone.
Important: receptor affinity is not the same as clinical “potency”. The final effect also depends on the concentration in the tissue, the rate of metabolism and binding to blood transport proteins.
How the signal is converted into protein synthesis
In skeletal muscle, androgen receptor activation affects several processes simultaneously. The first is an increase in the synthesis of muscle protein, in particular the contractile proteins actin and myosin. Studies with testosterone have shown that androgens increase the rate of fractional protein synthesis in muscle.
The second process is activation of satellite cells, muscle stem cells. They divide and merge with existing fibers, adding new nuclei. This allows the fibers to grow larger than would be possible with the number of nuclei available. Bhasin's work showed a dose-dependent increase in the number of satellite cells when taking testosterone.
The third aspect is the effect on catabolism. Androgens, according to experimental work, can counteract the catabolic action of glucocorticoids, although the exact contribution of this mechanism in humans is still debated.
For methasterone, there are no direct data on protein synthesis in humans. It is logical to assume that it works through the same pathways as other androgens, but quantitative estimates such as "how many times stronger" have no scientific basis.
- Strengthening the synthesis of contractile proteins.
- Activation and proliferation of satellite cells.
- May counteract catabolic signals.
- Effect on erythropoiesis (formation of erythrocytes).
Anabolic and androgenic index: what it means
In old reference books, methasterone is attributed a very high ratio of anabolic to androgenic activity. These data were obtained in the classic Hershberger test: in castrated rats, the weight gain of the levator ani muscle and the prostate or seminal vesicles was compared.
The problem is that the levator ani muscle in rats is a specific androgen-sensitive tissue that poorly reflects the response of large skeletal muscles in humans. Current pharmacologists, particularly in the review by Kicman (2008), emphasize the limited value of this test for predicting effects in humans.
In addition, "low androgenicity" in rats does not guarantee the absence of androgenic effects in humans. DHT derivatives, on the other hand, can significantly affect the skin, hair follicles and lipid metabolism.
Therefore, the editors advise to perceive the numbers of the anabolic index as a historical artifact, and not as a practical characteristic of the drug.
What the mechanism does not explain
Mechanism of action describes how a molecule triggers a biological response, but does not address safety concerns. The same receptors that stimulate muscle growth are located in the heart, blood vessels, liver, skin, brain and gonads.
Because of this, the anabolic effect cannot be "separated" from the systemic effect. Activation of the androgen receptor in the hypothalamus and pituitary gland inhibits the production of gonadotropins, in the liver it changes the synthesis of lipoproteins, in the bone marrow it stimulates the formation of erythrocytes.
Also, the mechanism does not explain individual variability. Genetic differences in the androgen receptor (for example, the length of the CAG repeats) and metabolic enzymes affect how a person responds to androgens.
Finally, any conclusions about methasterone are limited by the fact that no human clinical studies have been conducted. All we know is chemistry, animal tests and clinical cases of complications.
Editorial conclusions
Methasterone acts through the androgen receptor in the same way as other androgens, and its features are due to two methyl groups: 2-alpha slows inactivation in muscles, 17-alpha provides oral activity.
The drug's high "anabolicity" is based on animal tests with low predictive value for humans.
The same mechanism that triggers protein synthesis operates in the heart, liver, and pituitary gland, so anabolic effects are inseparable from systemic risks.
To complete the picture, we recommend our materials on the side effects of methasterone, its effects on the cardiovascular system and the hypothalamus-pituitary-testes axis.
References
- Kicman AT. Pharmacology of anabolic steroids. Br J Pharmacol. 2008;154(3):502â521.
- Bhasin S, Woodhouse L, Casaburi R, et al. Testosterone dose-response relationships in healthy young men. Am J Physiol Endocrinol Metab. 2001;281(6):E1172âE1181.
- Sinha-Hikim I, Artaza J, Woodhouse L, et al. Testosterone-induced increase in muscle size in healthy young men is associated with muscle fiber hypertrophy. Am J Physiol Endocrinol Metab. 2002;283(1):E154âE164.
- Vida JA. Androgens and Anabolic Agents: Chemistry and Pharmacology. New York: Academic Press; 1969.
- Hartgens F, Kuipers H. Effects of androgenic-anabolic steroids in athletes. Sports Med. 2004;34(8):513â554.
- Nieschlag E, Behre HM, Nieschlag S (eds). Testosterone: Action, Deficiency, Substitution. 4th ed. Cambridge University Press; 2012.
