PHYSIOLOGY OF ANTERIOR HYPOPHYSIS 



275 



hypophyseal tract. The central zone ex- 

 hibits, of course, abundant Goraori-positive 

 material. 



In 1957 Dawson presented morphologic 

 evidence of a closer neurovascular relation- 

 ship in the median eminence of frogs than 

 has yet been observed in mammals. Study- 

 ing the hypothalamo-hypophyseal relation- 

 ships at the level of the median eminence 

 in sections stained by modifications of the 

 chrome alum hemotoxylin-phloxine and the 

 aldehyde fuchsin methods, he found that of 

 the fibers from the preoptic tract a sur- 

 prisingly large number enter and end in the 

 median eminence and have a specific asso- 

 ciation with the vessels of the portal system. 

 The final simple nerve terminals (dilated 

 with secretion) and the selectively stained 

 secretory substance were arranged in radial 

 patterns about the capillaries. It has not 

 been determined whether the amount of neu- 

 rosecretory material accumulated about the 

 vessels in the primary plexus is of func- 

 tional significance, but Dawson noted a 

 specific cell type scattered along the portal 

 vessels as they enter the anterior lobe, and 

 felt that the "rather specific morphologic 

 pattern displayed" suggests a functional 

 interaction of some kind between nervous 

 components of the hypothalamus and glan- 

 dular units of the anterior pituitary gland, 

 mediated by way of the portal circulation. 



C. THE HYPOPHYSEAL PORT.\L 

 CIRCULATORY SYSTEM 



A systetH-~o^ hypophyseal portal vessels 

 which drain the tuber cinereum above and 

 supply the adenohypophysis below is pres- 

 ent throughout the reptiles, birds, and mam- 

 mals (Green, 1951). It is indicative of sig- 

 nificance that in all these forms the portal 

 vessels provide either the entire or the 

 major vascular supply to the adenohypophy- 

 sis. Wingstrand (1951a) found no afferent 

 vessels to the pars distalis other than portal 

 vessels in over 50 genera of birds. However, 

 Benoit and Assenmacher (1951b) state that 

 in ducks the pars distalis is inconstantly 

 supplied by a few twigs passing directly 

 from the superior hypophyseal arteries. 

 Crooke (1952) expressed the opinion that 

 the blood supply to the pars distalis in man 

 must be almost entirely by way of the 

 stalk vessels. In examination of over 300 



human jntuitaries, he found minute vessels 

 entering from the capsule in only 6 in- 

 stances. McConnell (1953) reached the con- 

 clusion that the pars distalis in man is 

 supplied entirely by the hypophyseal portal 

 vessels, a view which is substantiated by 

 the results from a recent critical study by 

 Xuereb, Prichard and Daniel (1954a). The 

 latter workers (1954b), however, made a 

 further observation wdiich is of cardinal sig- 

 nificance. They discovered a vascular link 

 between the neural lobe and the adenohy- 

 pophysis. Thus, in addition to the "long" 

 portal veins which drain the upper stalk 

 region and supply the sinusoidal network of 

 the anterior and lateral regions of the pars 

 distalis, they found a variety of "short" 

 portal vessels, which arise from an anasto- 

 motic link between the superior and inferior 

 hy])oi)hyseal arteries on the lower margin 

 of the infundibular stem. These "short" ves- 

 sels supply the jjosterior portion of the pars 

 distalis. It will be apparent, therefore, that 

 even though the pars distalis derives all of 

 its blood from the portal vessels, the source 

 of this blood is not limited to that from the 

 superior hypophyseal arteries as was pre- 

 viously thought, but can be supplied by the 

 inferior hypophyseal arteries as well. The 

 matter is of significance in that channels are 

 now known to exist whereby some blood 

 from the systemic circulation can reach the 

 pars distalis without having passed through 

 the primary plexus on the median eminence. 

 Consequently, when the long portal vessels 

 are severed, as in the transection of the 

 pituitary stalk, the possibility remains that 

 in some species collateral channels in the 

 form of these short portal veins continue 

 to sup])ly a portion of the pars distalis. 



From a study of the arrangement and 

 structure of the hypophyseal vasculature, 

 Wislocki and King (1936) inferred that the 

 flow of blood in the hypophyseal portal 

 veins was toward the anterior lobe and this 

 has now been confirmed by decisive evi- 

 dence from work on frogs (Green, 1947), 

 birds (Wingstrand, 1951a), rats (Green and 

 Harris, 1949; Barrnett and Greep, 1951), 

 and man (McConnell, 1953; Xuereb, Prich- 

 ard and Daniel, 1954a, b). In 1952 Nowa- 

 kowski, on the basis of his studies of the 

 cat, once more advanced the view that the 

 flow of blood in the portal system is toward 



