15.08 Drugs and the hormones of male reproduction

The main male sex hormone testosterone is used to treat androgen deficiency. Androgen deficiency is associated with testicular failure caused by cryptorchidism (failure of one or both testes to descent into scrotum), orchitis (inflammation of the testes), orchidectomy (surgical removal of one or both testes). Androgen deficiency can also be due to insufficiency of the pituitary-hypothalamic axis or in delayed male puberty.

For a longer action, the enanthate ester of testosterone is used, and it is administered intramuscularly every 1-4 weeks. Adverse effects are mainly related to route of administration, and with intramuscular can be bleeding, infection and extrusion.

Androgens are anabolic agents stimulate the formation and maintenance of muscular and skeletal proteins. For these reasons, the anabolic steroids have become drugs of abuse in sport but this is not discussed in this eChapter.

Benign prostatic hyperplasia (BPH) is excessive growth of the prostate gland, which surround the urethra and obstructs the bladder to make urination difficult. In severe prostatic hyperplasia, surgery to remove part or the entire prostate may be necessary. Prior to this, a₁-adrenoceptor blocker such as prazosin or tamsulosin, which is the first example of an uroselective blocker, that is a selective a₁-adrenoceptor blocker, which additionally shows selectivity for a_1A-adrenoceptors (which are found on the prostate) over a_1B-adrenoceptors, which are found of blood vessels. Tamsulosin is discussed in eChapter 7.

The other drug used to treat BPH is finasteride, which is a 5α-reductase inhibitor. In the prostate gland, testosterone is metabolised to 5α-dihydotestosterone, which is more potent than testosterone as an androgen, and promotes prostrate grown. The enzyme responsible for this metabolism is 5α-reductase, and consequently inhibition of the enzyme with finasteride prevents the growth of the prostate.