Actions of Androgens

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Chapter: Essential pharmacology : Androgens and Drugs for Erectile Dysfunction

Testosterone is responsible for all the changes that occur in a boy at puberty: Growth of genitals—penis, scrotum, seminal vesicles, prostate.


ACTIONS

 

1. Sex Organs And Secondary Sex Characters (Androgenic)
 

Testosterone is responsible for all the changes that occur in a boy at puberty:

Growth of genitals—penis, scrotum, seminal vesicles, prostate.

Growth of hair—pubic, axillary, beard, moustache, body hair and male pattern of its distribution. Thickening of skin which becomes greasy due to proliferation and increased activity of sebaceous glands—especially on the face—frequently the duct gets blocked, infection occurs resulting in acne. Subcutaneous fat is lost and veins look prominent.

Larynx grows and voice deepens.

Behavioral effects are—increased physical vigour, aggressiveness, penile erections. Male libido appears to be activated by testosterone directly as well as by estradiol produced from testosterone. Testosterone is also important for the intrauterine development of the male phenotype; relatively large amounts are produced by the foetal testes during the first half of intrauterine life.

 

2. Testes

 

Moderately large doses cause testicular atrophy by inhibiting Gn secretion from pituitary. Still larger doses have a direct sustaining effect and atrophy is less marked. Testosterone is needed for normal spermatogenesis and maturation of spermatozoa. High concentration of testosterone attained locally in the spermatogenic tubules by diffusion from the neighbouring Leydig cells stimulates spermatogenesis.

 

3. Skeleton And Skeletal Muscles (Anabolic)

 

Testosterone is responsible for the pubertal spurt of growth in boys and to a smaller extent in girls. There is rapid bone growth, both in thickness as well as in length. After puberty, the epiphyses fuse and linear growth comes to a halt. There is evidence now that estradiol produced from testosterone, and not testosterone itself, is responsible for fusion of epiphyses in boys as well as girls. Moreover, estradiol appears to supplement the effect of testosterone on bone mineralization. Testosterone also promotes muscle building, especially if aided by exercise. There is accretion of nitrogen, minerals (Na, K, Ca, P, S) and water—body weight increases rapidly, more protoplasm is built. Appetite is improved and a sense of well being prevails. Testosterone given to patients prone to salt and water retention may develop edema.

 

4. Erythropoiesis

 

Testosterone also accelerates erythropoiesis by increasing erythropoietin production and probably direct action on haeme synthesis.

 

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