PHYSIOLOGY OF ANTERIOR HYPOPHYSIS 



283 



tions. The fact that the pars distalis in rats 

 receives its blood from the portal veins and 

 that regeneration of these vessels means 

 restoration of nutrient supply to this organ, 

 would seem, on the face of it, to be a plaus- 

 ible explanation for resumption of secre- 

 tory activity following stalk transection. 

 However, there is strong evidence against 

 this possibility. Grafts of the pituitary 

 gland revascularized by vessels from other 

 than the median eminence lose their ability 

 to sustain ovarian functions other than 

 progestational (Harris and Jacobsohn, 

 1952; Everett, 1954, 1956; Nikitovitch- 

 Winer and Everett, 1957), and regain these 

 functions when vascular continuity with the 

 median eminence is restored (Nikitovitch- 

 Winer and Everett, 1957, 1958a, b). 



A series of recent reports has dealt with 

 the capacity of stalk-sectioned ferrets to 

 respond to the stimulus of added illu- 

 mination. Thomson and Zuckerman (1953, 

 1954) and Zuckerman (1955» claimed that 

 estrus supervened in 10 of 16 operated fer- 

 rets exposed to added illumination. In two 

 of the animals which responded, careful 

 study of serial sections of the operative site 

 after India ink perfusion revealed no vas- 

 cular connections between the pituitary and 

 the median eminence. Thus, the essential- 

 ity of the portal vessels and whatever hu- 

 mors they might convey for the regulation 

 of adenohypophyseal activities was called 

 into question. Donovan and Harris (1956), 

 on the contrary, found that stalk-transected 

 ferrets in which regeneration of the portal 

 vessels was-^recluded by a film barrier 

 between the severed ends of the stalk did 

 not exhibit light-induced estrus; 3 animals 

 lacking the barrier responded with early 

 estrus, but in each of them regeneration of 

 a vascular link with median eminence was 

 demonstrated. The question left unanswered 

 by the latter experiments is whether the 

 pituitaries in the animals which did not 

 respond actually had the capacity to re- 

 spond. Collateral evidence, such as reduced 

 adrenal weight and decreased thyroid ac- 

 tivity, suggests that the pituitaries may have 

 been functionally incapacitated for rea- 

 sons other than lack of a specific excitatory 

 agent of hypothalamic origin. Campbell and 

 Harris (1957) addressed themselves to this 

 problem by studying the volume change of 



the rabbit pituitary after dividing the stalk. 

 They found a reduction to 62-74 per cent of 

 the normal volume for the whole gland, 

 68-83 per cent for the pars distalis, and 26- 

 27 per cent for the neural lobe. Because the 

 extent of atrophy in operated animals was 

 the same with or without plate insertion, 

 they questioned the importance of ischemic 

 damage. The rabbit, however, seems an un- 

 fortunate choice for study of this problem 

 because Harris (1947) had already noted 

 that the anterior lobe in this species has 

 an arterial as well as a portal venous blood 

 supply. Moreover, volume changes are not 

 a crucial index of glandular competence. 

 Breckenridge and Keller (1948) found no 

 correlation between retention of sex func- 

 tions and the size of the anterior lobe 

 remnant in dogs which had been subjected 

 to complete removal of the stalk and partial 

 (graded) hypophysectomy. There was, how- 

 ever, a close correlation between mainte- 

 nance of the genital structures and retention 

 of normal cytoarchitecture of the remnant. 

 The arrangement of nervous and vascular 

 connections between the pituitary and the 

 brain in birds is such that it is possible to 

 section the infundibular stalk, leaving the 

 portal vessels intact, or contrariwise, divide 

 the vessels leaving the stalk undamaged, 

 or by appropriate incision segregate the 

 median eminence from the hypothalamus 

 without disturbing either the portal vessels 

 or the stalk. These experimental procedures 

 have been carried out on the duck (Benoit 

 and Assenmacher, 1953; Assenmacher and 

 Benoit, 1953a, b). Stalk transection alone 

 did not alter gonadal maturation in ani- 

 mals exposed to added illumination, but the 

 response was completely blocked by section- 

 ing either the median eminence or the 

 anterior portal vessels ; in birds these vessels 

 supply the cephalic lobe of the pars dis- 

 talis. In spite of the impaired secretion of 

 gonadotrophins, the functional capacity of 

 the anterior lobe tissue was otherwise ade- 

 quate as evidenced by the fact that the 

 thyroids and adrenals were fully main- 

 tained. After severing both stalk and portal 

 vessels in laying hens, Shirley and Nalban- 

 dov (1956a, b) observed gonadal atrophy, 

 but no change in either the thyroids or 

 adrenals. Benoit and his associates and 

 Shirley and Nalbandov strongly favor the 



