Androgens: Pharmacological Actions

PHARMACOLOGICAL ACTIONS

Androgens produce both virilizing and protein anabolic actions (Table 63.1). The virilizing actions of testos-terone include irreversible effects that occur during em-bryogenesis, that is, those that induce differentiation of the central nervous system and male reproductive tracts, and the excitatory actions at puberty that are responsible for secondary sexual development. 

In addi-tion to the effects on male reproductive function, an-drogens influence a number of other systems, many of which are associated with masculinity. These actions in-clude the growth of male-pattern facial, pubic, and body hair, the lower vocal pitch resulting from a thickening and lengthening of the vocal cords, and a significant (30%) increase in the rate of long bone growth. 

Androgens also terminate long bone growth by induc-ing closure of the epiphyses. The degree of virilization and timing of puberty also affect peak bone density and risk of osteoporosis in males.

The protein anabolic actions of androgens on bone and skeletal muscle are responsible for the larger stature of males than females. Androgens induce some degree of anabolism in other tissues, including bone marrow, liver, kidney, and heart. They also have several other actions, not necessarily associated with maleness, such as lymphoid tissue regression during puberty.