The general term for any one of a group of HORMONES which govern the development of the sexual organs and the secondary sexual characteristics of the male. TESTOSTERONE, the androgenic hormone formed in the interstitial cells of the testis (see TESTICLE), controls the development and maintenance of the male sex organs and secondary sex characteristics. In small doses it increases the number of spermatozoa (see SPERMATOZOON) produced, but in large doses it inhibits the gonadotrophic activity of the anterior PITUITARY GLAND and suppresses the formation of the spermatozoa. It is both androgenic and anabolic in action. The anabolic eﬀect includes the ability to stimulate protein synthesis and to diminish the catabolism of amino acids, and this is associated with retention of nitrogen, potassium, phosphorus and calcium. Doses in excess of 10 mg daily to the female may produce VIRILISM.
Unconjugated testosterone is rarely used clinically because its derivatives have a more powerful and prolonged eﬀect, and because testosterone itself requires implantation into the subcutaneous fat using a trocar and cannula for maximum therapeutic beneﬁt. Testosterone propionate is prepared in an oily solution, as it is insoluble in water; it is eﬀective for three days and is therefore administered intramuscularly twice weekly. Testosterone phenyl-propionate is a long-acting microcrystalline preparation which, when given by intramuscular or subcutaneous injection, is eﬀective for four weeks. Testosterone enantate is another long-acting intramuscular preparation. Mesterolone is an eﬀective oral androgen and is less hepatoxic: it does not inhibit pituitary gonadotrophic production and hence spermatogenesis is unimpaired. Testosterone undecanoate is also an eﬀective oral form.