REPRODUCTIVE ENDOCRINOLOGY IN BIRDS 



1101 



an increase of testicular size in hypophysec- 

 toraized birds (Chu, 1940; Nalbandov, 

 Meyer and McShan, 1946; Lofts and Mar- 

 shall, 1956j. 



Bioassays of avian pituitaries have shown 

 that the different gonadotrophic hormones 

 found in mammals are also present in avian 

 pituitaries. FSH and LH were shown to be 

 present by Witschi, Stanley and Riley 

 (1937) and by Leonard (1937), and Bur- 

 rows and Byerly (1936) demonstrated the 

 presence of prolactin in the pituitaries of 

 the fowl, particularly in the pituitary of 

 broody hens. The experiments which proved 

 that the avian pituitary contains these three 

 gonadotrophic hormones have been con- 

 firmed many times. The response of the 

 avian gonads to the purified hormones has 

 already been discussed in connection with 

 replacement therapy experiments. The ap- 

 plication of this response in bioassay meth- 

 ods will be discussed in a separate section. 



The LH portion of the gonadotrophic 

 complex seems to be the only hormone which 

 can restore the function of the Leydig cells. 

 The restoration or the resumption of sper- 

 matogenesis in an inactive testis can be in- 

 duced in hypophysectomized and in intact 

 individuals of certain avian species by hor- 

 mones other than gonadotrophins. Chu 

 (1940) demonstrated that the germinal epi- 

 thelium of the hypophysectomized pigeon 

 can be maintained by testosterone injec- 

 tions, whereas Chu and You (1944) showed 

 that spermatogenesis can be induced in such 

 pigeons after the germinal epithelium has 

 degenerated and the tubules contain sper- 

 matogonia and Sertoli cells only. Pfeiffer 

 (1947) subsequently observed that testos- 

 terone will enhance further spermatogenesis 

 in sparrows. Passer domesticus, provided 

 spermatocytes were present. Wolf son and 

 Harris (1959) could maintain gonadal ac- 

 tivity of slate-colored j uncos, J unco hye- 

 inalis, and white-throated sparrows, Zono- 

 trichia albicollis, when illumination was 

 reduced from 16 to 8 hours per day. Li the 

 controls gonadal activity decreased. Cler- 

 mont and Benoit (1955) could not increase 

 the size of the testes of either juvenile or 

 adult drakes during the sexual rest period, 

 nor could testicular size be maintained when 

 the drakes were subjected to a sharp de- 



crease in daily illumination. The species dif- 

 ferences which seem to exist in intact birds 

 do not prove that such differences will exist 

 in hypophysectomized birds. Chu and You 

 (1944), for instance, demonstrated that tes- 

 tosterone does not stimulate the testes of 

 immature or of adult but sexually quiescent 

 male pigeons. The hypothesis that androgen 

 stimulates the testes of hypophysectomized 

 ducks needs to be tested. 



Doses of androgen capable of inducing 

 spermatogenesis in hypophysectomized male 

 pigeons cause degeneration of the germinal 

 epithelium and a decrease in testicular size 

 when given to intact males (Chu, 1940). 

 Breneman and Mason (1951) found that 

 physiologic doses of androgen are followed 

 by a reduction of gonadotrophic potency. 

 This inhibition was implied in the statement 

 by Kumaran and Turner (1949c) that the 

 same dose of androgen acts as an inhibitor 

 of spermatogenesis at one age but stimulates 

 it at a later age. They suggested that, in the 

 fowl, androgen stimulates only the trans- 

 formation of secondary spermatocytes; 

 higher doses of androgen inhibit the FSH 

 required for the transformation of spermato- 

 gonia to spermatocytes, and no spermato- 

 cytes are available when androgen is given 

 at too early an age. Pfeiffer 's data (1947) 

 for the sparrow and Chu's data (1940) for 

 intact young and adult pigeons also support 

 this concept, but the concept is not consistent 

 with the action of androgen in the hypophy- 

 sectomized pigeon in which only spermato- 

 gonia are present. Further investigation as 

 to what distinguishes the immature testis 

 from the testis of the hypophysectomized 

 pigeon is needed to resolve this question. 



The testis is also under control of the third 

 hormone found in the avian pituitary, pro- 

 lactin. This hormone reaches its highest con- 

 centration during incubation of the eggs by 

 the parents. It has been found in the pitui- 

 taries of the domestic fowl (Burrows and 

 Byerly, 1936; Saeki and Tanabe, 1955), pi- 

 geons (Schooley and Riddle, 1938) , the Cali- 

 fornia gull, Larus californicus (Bailey, 

 1952), and pheasants, Phasianus colchicus 

 (Breitenbach and Meyer, 1959). Its physi- 

 ologic effects are many. In the male it causes 

 a decrease in comb size, a decrease in tes- 

 ticular size, a decrease in tubule diameter, 



