ioi8 



HANDBOOK OF PHYSIOLOGY 



NEl'ROPHYSIOLOGY II 



ous and vascular components of the stalk for gonado- 

 trophic secretion. Shirley & Nalbandov (315) have 

 obtained similar results in the hen. Donovan & Harris 

 (81) observed that stalk section in the ferret was 

 followed by the development of light-induced estrus 

 if regeneration of the hypophysial portal vessels was 

 allowed to occur. If such regeneration was prevented 

 no estrous response to light was seen and the repro- 

 ductive organs were found to be atrophic. There was 

 no difference in size or vascularity of the pituitary 

 gland in the two groups. Thomson & Zuckerman 

 (329) had previously found that regeneration of the 

 portal vessels may occur in the ferret but thought that 

 such regeneration was not necessary for the light- 

 induced estrous response. Fortier et al. (107) studied 

 rabbits after pituitary stalk section. Again, those ani- 

 mals with well-marked portal vessel regeneration 

 showed normal ovaries and some accepted the male 

 and ovulated. The group in which vascular regenera- 

 tion was nearly or completely prevented had ovaries 

 and reproductive tracts indistinguishable from the 

 hypophysectomized control group. The volumes of 

 the pituitary glands in these two stalk-sectioned 

 groups were not significantly different (table i). From 

 the above results it may be concluded that the central 

 nervous system, acting via the hypophysial portal 

 vessels, a) maintains gonadotrophic secretion at its 

 normal level (as demonstrated by ovarian weight and 

 size, the onset and maintenance of estrus in the ferret 

 and rabbit, and the cycles of estrus in the rat), since 

 if the pituitary stalk is effectively cut no demonstrable 

 secretion of gonadotrophic hormone occurs (i.e. the 

 reproductive organs are indistinguishable from those 

 of hypophysectomized animals) ; and h) mediates re- 

 flex changes in gonadotrophic secretion dependent on 

 environmental stimuli (light-induced estrus in the 

 ferret, the pseudopregnancy response to sterile coitus 

 in the rat and the o\'ulatory response after coitus in 

 the rabbit). 



The functional activity of the adenohypophysis is 

 very markedly reduced if it is transplanted to a site 

 in the body remote from its normal position, and in 

 this respect the anterior pituitary differs sharply from 

 the gonads, thyroid and adrenal cortex. The evidence 

 for this statement has been recently reviewed (23, 

 156). Although some gonadotrophic activity was 

 ascribed to pars distalis tissue placed ia the testis, 

 anterior chamber of the eye, thigh muscle and other 

 sites in several earlier studies (177, 231, 232, 260, 

 304, 305), the methods that were used for checking 

 the completeness of the initial "hypophysectomy must 

 be held open to doubt. More recent workers among 



whom may be mentioned Westman & Jacobsohn 

 (353), Greer et al. (134), Cheng et al. (54), McDer- 

 mott et al. (237), Fortier (105) and Harris & Jacob- 

 sohn (161) have all reported that gonadal atrophy 

 follows transplantation of the pituitary gland to a site 

 remote from the sella turcica. The most convincing 

 evidence that pituitary tissue, isolated from the in- 

 fluence of the hypothalamus, still possesses some 

 residual gonadotrophic activity comes from the ex- 

 periments of Everett (92, 93) who made autotrans- 

 plants of the pituitary into the kidney of the rat and 

 found evidence for some secretion of iuteotrophic 

 hormone but not of follicle-stimulating or luteinizing 

 hormone. The question then arises as to the cause of 

 the difference in functional ability of transplants of 

 the gonads, thyroid and adrenal cortex as compared 

 with that of anterior pituitary transplants. One pos- 

 sible explanation appeared to be that gonadal, thy- 

 roidal or adrenal cortical tissue would receive its 

 physiological stimulus (in the form of gonadotrophic, 

 thyrotrophic or adrenocorticotrophic hormone) via 

 the general circulation wherever it was placed in the 

 body. On the other hand if anterior pituitary tissue is 

 normally activated by some humoral stimulus passing 

 to the gland lj\ the hypophy.sial portal circulation, 

 then if the gland is transplanted away from the site 

 of these particular vessels a loss of activity might be 

 expected. This view was put to the test by Harris & 

 Jacobsohn (161) who grafted anterior pituitary tissue, 

 in hypophysectomized rats, either on to the surface of 

 the temporal lobe of the brain, where it became vas- 

 cularized by the cortical vessels of the cerebrum, or 

 on to the tuber cinercum of the hypothalamus, where 

 it became vascularized by the hypopiiysial portal 

 vessels (fig. 5). In the case of the temporal lobe grafts, 

 no estrous cycles were observed and post mortem 

 the ovaries and reproductive tracts were found to be 

 completely atrophic. In contrast were the findings in 

 the animals with grafts under the tuber cinereum in 

 which normal reproductive activity (including regular 

 estrous cycles, pregnancy and lactation) was observed 

 to return in a large proportion of cases. It was con- 

 cluded from these experiments that good vasculariza- 

 tion irrespective of the source of the blood is not 

 sufficient to render anterior lobe tissue functional; 

 some additional factor is necessary and this factor is 

 present when the blood supply is derived, at least in 

 part, from the hypophysial portal system. 



The study of pituitary grafts placed under the tuber 

 cinereum of hypophysectomized recipients (161) fur- 

 nished some data on two further points of interest 



