THE PITUITARY BODY 



eration of gonadotropic hormone.''^ There is some evidence 

 that castration changes in the male pituitary are more readily 

 abolished by testicular hormone than are those in the pitui- 

 tary of the spayed female (Martins and Rocha, 1931).^' As 

 has already been shown, the pituitary of castrated rats con- 

 tains more gonadotropic hormone than that of normal males. 



From all the reported observations, which are too numer- 

 ous to cite, it appears that internal secretions of both the 

 tubules and the interstitial cells affect the pars glandularis. 



What is the significance of the data on the i?2te?relationship 

 between the pituitary and the gonads? — The experiments con- 

 sidered so far in this section clearly suggest that the interac- 

 tions of the gonadotropic hormone(s) and the internal secre- 

 tions of the gonads are important in the physiology of all 

 these structures in the normal animal. The rhythm of oes- 

 trous cycles, especially if repeated throughout the year, prob- 

 ably depends at least in part upon a pituitary-gonadal inter- 

 relationship. Smith and Engle (1927) stated that the periodic 

 liberation of gonadotropic hormone seemed best to account 

 for cyclic changes in the ovaries. Siegmund (1928) suggested, 

 on the basis of his experiments in mice, that the oestrous 

 rhythm might depend upon an antagonism between the fol- 

 licular hormone and the gonadotropic hormone (s). By im- 

 planting the pituitary of adult female guinea pigs into mice. 

 Smith and Engle (1929) demonstrated that the pituitary of 

 the guinea pig in oestrus contained less gonadotropic hormone 

 than when the guinea pig was in dioestrus (fifth to fourteenth 

 day of cycle). In similar experiments, Siegert used adult fe- 

 male rats, the pituitaries of which were imiplanted into imma- 

 ture rats; he too found that the pituitary of dioestrus con- 

 tained more gonadotropic hormone than that of oestrus. A 

 recent explanation of the oestrous cycle in the rat, in terms of 



'I* The utilization of hormone by the testes is, of course, also abolished. 



"" Similarly, oestrin appears to aboHsh the castration changes in the pituitary 

 more readily in spayed female rats than in castrated males. 



[156] 



