MAMMALIAN REPRODUCTIVE CYCLE 



511 



arachnoid space under the temporal lobe of 

 the brain, and beneath the renal capsule — 

 all distant from the hypothalamus. 



Transplantation of the pars distalis into 

 sites close to the hypothalamus, on the other 

 hand, is characteristically followed by 

 maintenance of the female reproductive 

 tract and essentially normal sex functions. 

 Greep (1936) found that re-implantation 

 of hypophyses into the (presumably) emp- 

 tied capsule was frequently followed in both 

 male and female rats by return of virtually 

 normal reproductive powers. Females ex- 

 hibited cycles and even went through suc- 

 cessful pregnancy and lactation. The result 

 observed in male rats was confirmed by 

 Cutuly (1941a). The obvious difficulty of 

 establishing completeness of hypophysec- 

 tomy has been the only criticism of these 

 instructive experiments. This fault has been 

 eliminated by an improved procedure de- 

 vised by Harris and Jacobsohn (1952). Hy- 

 pophysectomy was performed by the para- 

 pharyngeal route, after which the tissue to 

 l)e grafted was introduced by a transtem- 

 poral approach to a site immediately be- 

 neath the median eminence. This permitted 

 later histologic search for remnants of the 

 original gland in its capsule. In many cases, 

 including all in which the graft comprised 

 several hypophyses from the animal's own 

 newborn young, entirely normal gonado- 

 trophic function was recorded. This included 

 resumption of regular estrous cycles, typi- 

 cally during the 2nd or 3rd postoperative 

 week. Several of the rats became pregnant 

 and delivered viable litters. In marked con- 

 trast, none of the grafts that were placed 

 under the temporal lobe gave any indication 

 of gonadotrophin secretion, although they 

 were as well preserved and richly vascular- 

 ized as the others. Explanation of the dif- 

 ference seems to be that grafts under the 

 median eminence acquire blood supply from 

 regenerated hypophyseal portal veins and 

 iience a neurovascular linkage with the hy- 

 pothalamus. The importance of this rela- 

 tionship has been amply confirmed by Ni- 

 kitovitch-Winer and Everett (1957, 1958d) 

 in studies described below. 



In lieu of significant numbers of nerve fi- 

 bers entering the pars distalis (see Rasmus- 

 sen, 1938; Harris. 1948a I, the hypophyseal 



portal veins afford the most likely means 

 by which the gland is brought under hypo- 

 thalamic control. Recently it was demon- 

 strated in rats and monkeys that these ves- 

 sels have the power of rapid regeneration 

 after simple stalk-section (Harris, 1949, 

 1950a, b). This fact at once gives a ready 

 explanation of many of the discordant re- 

 sults of stalk-section experiments reported 

 in the past. Harris (1950b) explored in rats 

 the efficacy of various materials as barriers 

 to regeneration, with the result that numer- 

 ous examples of partial regeneration were 

 produced. Degree of recovery of gonado- 

 tropliic activity by the hypophysis was 

 strikingly correlated with degree of ana- 

 tomic vascular recovery. Restoration of nor- 

 mal ovarian function after simple interrup- 

 tion of the stalk, as reported in the guinea 

 pig by Dempsey (1939), in rats by Demp- 

 sey and Uotila (1940) , and in the human by 

 Dandy (1940), is thus explained by the as- 

 sumption that portal vein regeneration had 

 taken place. On the other hand, Westman 

 and Jacobsohn (1937-1938), who always 

 inserted a barrier of metal foil between the 

 median eminence and hypophyseal capsule, 

 consistently found ovarian atrophy, as did 

 Harris when portal vein regeneration was 

 completely obstructed. Attempting to prove 

 that the portal vessels are not essential in 

 regulating the hypophysis, Thompson and 

 Zuckerman (1954) stated that increased 

 illumination induced estrus in two ferrets 

 after stalk-section and in the absence of 

 demonstrable regeneration of portal vessels. 

 Donovan and Harris (1954), however, ex- 

 amining the histologic sections prepared 

 from 1 of the 2 animals, found many such 

 vessels that were uninfected. In their own 

 experimental series, an estrous response to 

 light was always associated with regenera- 

 tion of the portal veins. 



Greep and Barrnett (1951) rightly em- 

 phasized the prime importance of a good 

 vascular supply for recovery of function by 

 the pars distalis after either transplantation 

 or stalk-section. They pointed to the ex- 

 tensive central infarction and scarring that 

 characteristically followed stalk-section by 

 their technique, an obvious factor contribut- 

 ing to hypopituitarism. Harris (1950a I, 

 however, reported good function from sev- 



