152 P. L. Krohn 



It is now known, however, tliat grafts of any age often fail to 

 respond to a dose of gonadotrophin when the host's ovaries 

 remain in situ, a finding which is attributed by Lane and 

 Markee (1941) to differential take-up of the hormone by the 

 host glands which retain an intact normal blood supply. 



The anterior pituitary gland of a young animal also 

 develops more rapidly after it has been transferred into an 

 adult host. Harris and Jacobsohn (1951) found that pituitary 

 tissue which was transplanted from two-day-old female rats 

 to the sella turcica of their hypophysectomized mother, very 

 soon functioned like a normal mature gland and restored 

 normal cestrous cycles. Harris and Jacobsohn also found 

 that the pituitaries of newborn male rats were just as effective 

 in producing cestrous cycles in the female host. 



When ovaries are transplanted into adult males, however, 

 only follicular development takes place and no corpora lutea 

 are formed. The mature male pituitary apparently fails to 

 secrete the luteinizing hormone which is required for ovulation 

 and the formation of corpora lutea. There is, therefore, a 

 functional difference between mature male and female 

 pituitaries. By gonad transplantation studies Pfeiffer (1936) 

 was able to show that, at birth, the character of the hormone 

 production of the pituitary is still undetermined and can be 

 directed in one direction or the other by bringing the gland 

 under the influence of male or female gonads. Final determi- 

 nation has normally occurred before the age of puberty, after 

 which attempts to change the function of the gland are 

 unsuccessful. 



Pituitary transplants and the end of activity of the 

 ageing ovary 



Wiesner's preliminary observations (1932) indicate that 

 the ovaries of old rats, unlike those of women, are still capable 

 of responding to gonadotrophic stimuli, which, in ordinary 

 circumstances, the pituitary no longer provides. Compensa- 

 tory hypertrophy after unilateral gonadectomy did not occur 

 in either male or female rats which were over twenty-four 



