SARMs act via androgen receptor signaling and may be androgen agonists or antagonists, depending on the target tissues and their modulating effects on the coactivators or coinhibitors of the androgen receptor. An example of a steroid SARM is 7a-methyl 19 nor-testosterone (MENT). MENT is believed to be aromatized to an active estrogen but is not converted to a 5-a-reduced product. In rodents and monkeys, MENT has a greater stimulatory effect on skeletal muscle relative to the prostate (103-104). A clinical study showed that MENT could maintain sexual function and muscle mass in hypogonadal men. MENT is being developed as a long-acting implant (105). Other nonsteroidal orally active SARMs, which have potent actions on muscle and brain but little or substantially lower stimulatory effect on the prostate, are being developed by several pharmaceutical companies (106,107). SARMs may inhibit the synthesis and secretion of the gonadotropins, and, thereby, testosterone production will be markedly reduced. If so, after SARMs administration serum testosterone levels may be low, and clinicians may encounter difficulty in assessing adequate androgen replacement in the absence of measurable serum testosterone concentrations.
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