THE PITUITARY BODY 



tropic hormone from the anterior pituitary as shown by 

 ovulation in an animal like the rabbit. Other peripheral 

 nerves like those of the sympathetic system may be part of 

 an afferent arc, but their significance is not clear. 



Great interest has been shown in the hormonal control of 

 the secretion of gonadotropic hormones, especially as far as 

 the internal secretions of the ovaries and testes may here be 

 important. There is much data to suggest that surges or re- 

 cessions of secretion by the anterior pituitary causing the 

 growth or decay of gonadal activity (e.g., oestrous cycles) 

 may be related to the absence or presence of internal secre- 

 tion (s) of the gonads such as oestrogen from the ovaries. 

 The regulation of the secretion of gonadotropic hormones by 

 the pars glandularis may well depend upon a delicate, com- 

 plex mechanism, partly hormonal and partly nervous. xAlso 

 it is probable that the relative importance of the nervous 

 system and of hormones of the gonads varies in different 

 animals. The reader can easily diagrammatize a self-regulat- 

 ing physiological unit consisting of the pars glandularis, the 

 gonads, and the nervous system. However, he cannot safely 

 picture this unit in any detail. The known hormones char- 

 acteristic of the gonads vary enormously in their apparent 

 "regulating" (usually depressing) effect on the formation of 

 gonadotropic hormone by the anterior pituitary. Oestrogens 

 far excel androgens in potency; progesterone (from the corpus 

 luteum) appears to be of slight importance. 



The relation of adrenal cortical secretion to the phase of 

 pituitary physiology under discussion is obscure because so 

 many variables affect experimentation. Thyroid secretion per- 

 haps is not of great significance; its usual effect, if any, is 

 to lessen the action of follicle-stimulating hormone. How 

 much regulation of the liberation of gonadotropic hormones 

 by the pars glandularis is effected by the gland's own lacto- 

 genic hormone can be judged better when experiments have 

 been performed with the recently isolated lactogenic prin- 

 ciple. 



[122] 



