1106 



SUBMAMMALIAN VERTEBRATES 



when progesterone is given in large doses 

 to laying hens. Apparently there exists a 

 species difference with respect to the effect 

 of progesterone for Kar (1949) reported an 

 increase of more than 75 per cent in testicu- 

 lar size when he administered 0.5 mg. 

 progesterone per day for 30 days. Histologic 

 examination showed that both tubules and 

 Leydig cells were stimulated by the hor- 

 mone. In this case, we might have an ex- 

 ample of a hormone which stimulates the 

 organ which secretes it, for Lofts and Mar- 

 shall (1959) showed that progesterone is 

 present in the tubules of hypophysectomized 

 pigeons. Whether or not progesterone has a 

 role in the regulation of the male pigeon's 

 breeding cycle needs to be determined. If 

 progesterone can stimulate the testes in the 

 absence of the pituitary, as is the case for 

 androgens (Chu and You, 1946) , one might 

 observe "cycles" in the absence of the an- 

 terior pituitary. 



6. Estrogen 



Two lines of indirect evidence suggest that 

 estrogen is secreted by the avian male. (1) 

 In some birds, as for instance in Colymbi- 

 formes, Piciformes, Phalaropodidae, and 

 Jacamidae in which the male incubates the 

 eggs, an incubation patch is formed just 

 before incubation starts. Experimentally 

 this incubation patch will only form under 

 the combined effect of estrogen and pro- 

 lactin (Bailey, 1952). (2) Estrogens have 

 been isolated from the feces of roosters 

 (Hurst, Kuksis and Bendell, 1957). 



As far as the author is aware no evidence 

 has been published in which the presence 

 of estrogen in the blood was demonstrated. 

 The indirect evidence, although presump- 

 tive, may have to be accepted to explain 

 some phenomenon in the reproduction of 

 birds. 



The effects of estrogen administration 

 have been studied extensively, both from an 

 endocrinologic point of view and from the 

 angle of practical applications in improving 

 the quality and efficiency of poultry pro- 

 duction. This subject has been reviewed ex- 

 pertly by Lorenz (1954) . Therefore, only the 

 aspects which involve the reproductive sys- 

 tem will be mentioned here. 



In young cockerels physiologic doses of 



estrogen will inhibit comb size, testicular 

 size, and gonadotrophin secretion (Brene- 

 man, 1953). The same author demonstrated 

 that comb growth is more sensitive to estro- 

 gen inhibition than testicular size. The 

 latter in turn is more sensitive than gon- 

 adotrophin content of the pituitary. The 

 difference in sensitivity between comb and 

 testes has been confirmed (Bird, Pugsley 

 and Klotz, 1947; Nalbandov and Baum, 

 1948; Boas and Ludwig, 1950). Lorenz 

 (1959) mentions that the pituitary becomes 

 less sensitive to estrogen-inhibition with in- 

 creasing age. Other effects of estrogen, e.g., 

 lipemia, still manifest themselves at doses 

 of estrogen which do not inhibit the pitui- 

 tary. The inhibition of the comb by estro- 

 gen may be mediated also by an additional 

 mechanism not involving the jiituitary. 

 Martin, Graves and Dohan (1955) surgi- 

 cally divided combs of capons in halves. 

 All half combs received 2 fxg. testosterone 

 propionate and the other half of each comb 

 received, in addition, 0, 80, 100, 160, or 

 200 yttg. estrone. The results showed that 

 the 100- and 200-fjig. levels inhibited comb 

 growth significantly. The lack of effect of 

 the IQO-fig. dose is puzzling, but the local 

 effect of estrogen seems a real one. These 

 experiments may mean that in adult hens, 

 in which the pituitary apparently has be- 

 come relatively insensitive to estrogen in- 

 hibition, large amounts of estrogen are re- 

 quired to inhibit the comb by local effect. 

 Apparently, the estro^en-androgen ratio in 

 the laying hen is not high enough to cause 

 such a regression. 



The question has been raised whether a 

 temporary estrogen inhibition of the pitui- 

 tary at a young age would have a ''carry- 

 over" effect at older age, manifesting itself in 

 delayed maturity, damage to testes, small 

 comlD, and decreased fertility. Reports in 

 the literature (Akpinar and Shaffner, 1953; 

 Eaton, Carson and Beall, 1955; Traps, Sohn 

 and Olsen, 1956) seem to indicate that estro- 

 gen inhibition may have a carry-over effect. 

 However, in these cases estrogen pellets 

 were implanted and the possibility exists 

 that the pellets were not completely ab- 

 sorbed before sexual maturity. This sug- 

 gestion receives support from the observa- 

 tion that estrogen administered as a paste 



