1100 



SUBMAMMALIAN VERTEBRATES 



tuberis is connected with a large number of 

 nonmedullatecl fibers from the preoptic re- 

 gion, the possibility exists that areas of the 

 preoptic region influence the anterior pitui- 

 tary by way of the nucleus tuberis. Experi- 

 mental evidence indicating that the nervous 

 system can influence the avian anterior pi- 

 tuitary will be discussed later. 



The evidence summarized in Table 18.2 

 makes it seem logical that the avian pitui- 

 tary exercises the same control over the 

 general reproductive processes that the rep- 

 tilian, amphibian, and mammalian pitui- 

 taries do. Only a few of the numerous ex- 

 periments offering proof of this assumi^tion 

 will be mentioned here. 



The endocrine function of the avian an- 

 terior pituitary has been investigated by the 

 classical methods such as ablation of the 

 gland, replacement therapy, bioassays of the 

 gland, and purification of the hormones. The 

 aspects which concern the male will be dis- 

 cussed here whereas those [pertaining to the 

 female will be discussed in another section 

 of this chapter. 



Removal of the anterior pituitary leads to 

 a sharp decrease in testicular size (Benoit 

 and Aron, 1934a; Chu, 1940; Chu and You, 

 1946; Nalbandov, Meyer and McShan, 1946, 

 1951; Coombs and Marshall, 1956; Assen- 

 macher, 1958; Lofts and Marshall, 1959), to 

 a decrease in tubule diameter (Chu, 1940; 

 Chu and You, 1946; Nalbandov, Meyer and 

 McShan, 1946, 1951 ; Coombs and Marshall, 

 1956; Assenmacher, 1958; Lofts and Mar- 

 shall, 1959) , to a decrease in tubule diameter 

 (Chu, 1940; Chu and You, 1946; Nalbandov, 

 Meyer and McShan, 1946; Coombs and 

 Marshall, 1956; Lofts and Marshall, 1956), 

 to steatogenesis of the tubules (Coombs and 

 Marshall, 1956, Lofts and Marshall, 1959), 

 and, as a consequence of decreased Leydig 

 cell activity, to a decrease in comb size 

 (Nalbandov, Meyer and McShan, 1946, 

 1951), and to atrophy of the vas deferens 

 (Chu, 1940). 



The effect of hypophysectomy on the his- 

 tology of the Leydig cells is somewhat con- 

 troversial. Chu (1940) remarked that the 

 Leydig cells of hypophysectomized pigeons 

 were healthy in appearance but poor in 

 staining reaction, whereas Coombs and 

 Marshall (1956) stated that the interstitium 



of hy]5ophysectomized roosters became ex- 

 hausted but that a new generation of Leydig 

 cells with a sudanophilic and a cholesterol- 

 positive staining reaction arose in the ab- 

 sence of the pituitary. This observation 

 seems jmrticularly puzzling in view of the 

 experiments (Nalbandov, Meyer and Mc- 

 Shan, 1951) in which it was found that the 

 combs of hyi)ophysectomized roosters could 

 only be maintained for a limited time with 

 mammalian gonadotrophins. This was not 

 due to antihormone production. The comb 

 of such roosters could respond, however, for 

 an indefinitely long time to avian pituitary 

 extracts. Histologic examination of the in- 

 terstitium during these experimental treat- 

 ments revealed two types of Leydig cells, a 

 nonsecretory type which could be converted 

 into the secretory type by avian gonado- 

 trophin, and a secretory type which could 

 be stimulated to secrete androgen by avian 

 or mammalian LH. These experiments led 

 Nalbandov, Meyer and McShan (1951) to 

 the conclusion that a "third gonadotrophic 

 hormone" may be secreted by the avian pi- 

 tuitary or that avian and mammalian LH 

 are qualitatively different. In any event the 

 experiments support the hypothesis that re- 

 placement therapy stimulates the Leydig 

 cells. The observation of cyclic phenomena 

 in the Leydig cells by Coombs and Marshall 

 (1956) does not seem reconcilable with the 

 histologic studies made by Nalbandov, 

 :\Ieyer and McShan (1951). 'The following 

 observation by Coombs and Marshall (1956) 

 may offer an explanation. "... the hypophy- 

 sectomized bird was killed after only 17 days 

 and before there was any reduction in comb 

 size, so as to examine an early stage of 

 metamorphosis" (italics mine). According 

 to Nalbandov and Card (1943b), the reduc- 

 tion in comb size is obvious 6 days after 

 hypophysectomy. The cyclic phenomena of 

 the Leydig cells observed by Coombs and 

 ^larshall (1956) may thus be the result of 

 traces of anterior pituitary left during the 

 operation. 



Various gonadotroi:)hic hormone prej^a ra- 

 tions, all containing FSH, have proven to be 

 effective in causing an increase in diameter 

 of the seminiferous tubules, re-initiation of 

 spermatogenesis, loss of cholesterol-positive 

 material from the lumen of the tubules, and 



