1136 



SUBMAMMALIAN VERTEBRATES 



suited in complete atrophy of the ovaries 

 without any apparent effect on ACTH or 

 thyroid-stimulating hormone (TSH) secre- 

 tion as judged from adrenal and thyroid 

 weights and histology (Shirley and Nal- 

 bandov, 1956b) . Thus the ovaries resembled 

 those of hypophysectomized hens. The thy- 

 roids and adrenals were not affected by in- 

 terruption of the portal vessels, whereas 

 their weights were drastically reduced in 

 hypophysectomized birds. 



Assenmacher (1958) reported that sec- 

 tioning the portal vessels caused testicular 

 atrophy and prevented compensatory hyper- 

 trophy after hemicastration, light-induced 

 increase in testicular size, and cyclic activ- 

 ity such as that found in drakes even when 

 kept in total darkness. His data do not in- 

 dicate that thyroid weight or histology were 

 affected, but the adrenal weights were 

 slightly lower than in the controls. The evi- 

 dence from the experiments with these two 

 species can be interpreted in two ways. One 

 is that destruction of the portal vessels pre- 

 vents the transmission of the NSM to the 

 anterior pituitary. The second interpretation 

 is that sectioning the portal vessels inter- 

 rupts the blood supply to the anterior pitu- 

 itary, and thus causes ischemia. This latter 

 interpretation deserves emphasis in view of 

 Wingstrand's (1951) statement that the 

 pars distalis has no blood supply other than 

 the portal vessels. Indeed, sectioning of the 

 hypophyseal stalk resulted in "a profound 

 increase in fibrotic tissue as well as a de- 

 crease in the number of the usual cell types" 

 (Shirley and Nalbondov, 1956b). Assen- 

 macher (1958) stated that sectioning portal 

 vessels caused atrophy of the central part of 

 the caudal lobe but did not affect the ce- 

 phalic lobe (the cephalic lobe may still have 

 received some blood from the few anterior 

 portal vessels that are indicated in Assen- 

 macher's drawings). Zuckerman (1955) has 

 emphasized the importance of the second in- 

 terpretation in view of the observed infarcts 

 in the pituitary. Benoit and Assenmacher 

 (1959) have presented evidence that the in- 

 farct per se is not the factor causing testicu- 

 lar atrophy, but that sectioning the portal 

 vessels causes a qualitative difference in 

 the vascularity of the anterior pituitary. 

 First, similar infarcts, obtained when the 



portal vessels regenerated or were incom- 

 pletely cut, did not impede testicular re- 

 sponse to light nor did they cause atrophy 

 of the testes. Second, the lack of infarcts in 

 the cephalic lobe should allow production of 

 enough gonadotrophin to stimulate the 

 testes, inasmuch as in intact drakes the 

 cephalic and caudal lobes have equal 

 gonadotrophic potencies. Third, the infarcts 

 observed after sectioning of the portal ves- 

 sels leave more than 20 per cent of the gland 

 intact. Previous experiments had shown 

 that, even when 80 per cent of the pituitary 

 was removed during attempted hypophysec- 

 tomies, testicular degeneration did not oc- 

 cur, therefore 20 per cent of the gland was 

 sufficient to maintain the testes. 



3. Sectioning the hypothalamico-hypo- 

 physeal tract in the median eminence with- 

 out damag(> to the portal system results 

 in genital atrophy and lack of gonadal stim- 

 ulation by light (Assenmacher, 1958; As- 

 senmacher and Benoit, 1958; Benoit and 

 Assenmacher, 1959). 



Another line of evidence stems from the 

 correlations between activity of the neuro- 

 secretory cells and the experimentally in- 

 duced gonadal activity observed by Oksche, 

 Laws, Kamemoto and Farner (1959). An 

 increase in daily illumination from 8 to 20 

 hours increased body and testicular weight 

 of white crowned sparrows. Simultaneously, 

 the amount of NSM in the hypothalamic 

 nuclei and the median eminence decreased. 

 During the dark hours of the day, NSM 

 reaccumulates in these areas. This evidence 

 seems rather convincing, but it should be 

 pointed out that a variety of treatments af- 

 fect the activity of the neurosecretory cells 

 and the accumulation of NSM (Legait, 

 1959). The findings obtained with the white 

 crowned sparrows are suggestive, but they 

 cannot be regarded as proof. 



Finally, anticholinergic and antiad- 

 renergic drugs can block "spontaneous" 

 (Zarrow and Bastain, 1953; van Tienhoven, 

 Nalbandov and Norton, 1954) as well as 

 progesterone-induced ovulations (Zarrow 

 and Bastian, 1953; van Tienhoven, Nal- 

 bandov and Norton, 1954; van Tienhoven, 

 1955), although Zuckerman (1955) and 

 Moore (1958) have questioned the inter- 

 pretation that these drugs act specifically by 



