Endocrine Mechanisms 



743 



structures functionally important in the female. The progestins function pri- 

 marily in providing adequately for the intimate relationship between the 

 parent and developing young. The principal naturally occurring substance 

 in each class is: (1) androgen— testosterone; (2) estrogen— estradiol; and 

 (3) progestin— progesterone, which have the chemical structures shown. 



CH, 

 OH OH C=0 



c/V\/ 



Testosterone 



Estradiol 



Progesterone 



Just as these three classes of hormones show a basic similarity to one an- 

 other in their chemical organization, so is there also considerable functional 

 overlapping, and, in many instances, a ready conversion within the body 

 from one tvpe to another. These facts have made the acquisition of knowl- 

 edge of their normal function somewhat difficult. 



ANDROGENS. Androgen is a term used to describe all those compounds 

 whose biological actions resemble in general those of testosterone. The pri- 

 mary function of androgens is to stimulate the development and activity of 

 the male accessory reproductive organs. They are also responsible in part 

 for differences in the conformation of the male body, the lower pitch of the 

 human male voice, the characteristic distribution of hair, male pugnacious 

 assertiveness, and many special male secondary sex characteristics such as 

 the swollen clasping digits of the male frog, the comb of the cock, the crest 

 of the newt, and the nuptial coloration and gonopodal appendages of cer- 

 tain viviparus fishes. Many of these are characters the presence of which is 

 largely restricted to the breeding season. 



The various androgens differ from one another in their overall potency 

 and their relative effects on the numerous individual characters within the 

 body and these differences in turn may vary from species to species. This 

 complicates greatly the problem of the roles of androgens within the body. 



The testes comprise the principal sources of androgens; the principal one 

 is testosterone. This organ, furthermore, shows the capacity to extract less 

 potent androgens from the circulating blood and convert them to substances 

 of increased potency. Numerous observations have indicated the interstitial 

 glandular cells to be the specific source. Reduction or disappearance of the 

 seminal epithelium following x-radiation, ligation of the vasa efferentia, or in 

 cryptorchidism has been reported to cause no atrophy of the interstitial 

 glandular tissue and no loss of androgenic potency. In the newt, Triton 

 cristatus, there is no interstitial glandular tissue in the testes until the ap- 

 proach of the breeding season. At this time certain portions of the semin- 



