1090 



SUBMAMMALIAN VERTEBRATES 



hormone as shown by gradually increasing 

 comb size. 



Breneman and Alason (1951) estimated 

 the cumulative androgen secretion of White 

 Leghorn cockerels between the age of 10 

 and 40 days as ecjuivalent to 614.90 /x.g. 

 testosterone propionate (TP) for the 30- 

 day period. Such a high rate of secretion 

 in an immature male indicates early secre- 

 tory activity of the Leydig cells and sup- 

 ports the obser^'ations of Kumaran and 

 Turner (1949aj. 



The response of the comb to androgen 

 administration is influenced by a number 

 of variables : 



1. Dorfman (1950) investigated the sen- 

 sitivity of the comb of baby chicks to vari- 

 ous doses of androgen and found that, if 

 the sensitivity of the White Leghorn is 

 taken as 100 per cent, the Rhode Island 

 Red had a sensitivity of 10 per cent and 

 the Barred Rock of 1.8 per cent. Jaap and 

 Robertson (1953) established that inbred 

 lines within a breed may vary in their coml) 

 response to androgen. Campos and Shaffner 



(1952) selected males and females from a 

 nonpedigreed stock and established that 

 the offspring of such matings differed be- 

 tween sire families as well as between dam 

 families within sire families. It is thus im- 

 portant to randomize thoroughly any 

 chicks used for androgen bioassay. 



2. Forced exercise of cockerels reduced 

 the response of the comb to a given dose 

 of testosterone without affecting body or 

 adrenal weight ( Wong, Lavenda and Haw- 

 thorne, 1954). This experiment suggests 

 that differences in the results of the bio- 

 assay between laboratories might in some 

 cases be explainable by differences in the 

 voluntary exercise the birds obtain. 



3. As in other bioassays, the route of 

 administration of the hormone is important. 

 Generally intraperitoneal injections result 

 in a smaller response than do those given 

 subcutaneously (Bernstorf, 1957). The dif- 

 ference may be explainable by inactivation 

 of the hormone after intraperitoneal ad- 

 ministration (Bernstorf, 1957). When the 

 hormone is applied locally on the comb, 

 special care should be taken to use the 

 same volume, for Jaap and Robertson 



(1953) showed that the concentration of 



the hormone is more important tlian the 

 total amount. 



4. Light has been reported to inhibit the 

 response of the capon or the immature 

 cockerel comb to a given dose of androgen 

 (Womack, Koch, Domm and Juhn, 1931; 

 Koch and Gallagher, 1934; Caridroit and 

 Regnier, 1944; Wong and Hawthorne, 

 1954 ». However, in the experiments of 

 Womack, Koch, Domm and Juhn (1931) 

 the results ascribed to differences in light 

 can also be explained on the basis of differ- 

 ences in temperature, whereas in Koch and 

 Gallagher's experiment, there was no dif- 

 ference in comb response of capons kept in 

 the dark or under light. Inhibition of 

 response occurred only if birds were first 

 kept in the dark and then subjected to 

 light. As Lamoreux (1943) pointed out, 

 birds under these conditions show increased 

 activity, which, as was indicated above, 

 may inhibit the response of the comb to 

 exogenous androgen. Caridroit and Regnier 

 (1944) used only 3 capons and no controls; 

 it was assumed, however, that comb size 

 had equilibrated during the previous sev- 

 eral months of treatment. Their hypothesis 

 that thyroid activity increased in the dark, 

 and in turn caused a greater response to 

 exogenous androgen, was not substantiated 

 by measurements of thyroid activity before 

 or after exposure to darkness. In the experi- 

 ment of W^ong and Hawthorne (1954), in- 

 vestigation showed that light inhibited re- 

 sponse at only 1 of 4 levels of androgen 

 tested. An analysis of variance for the total 

 experiment, instead of the reported series 

 of individual "t" tests for each level of 

 androgen, reveals that light did not affect 

 the assay; neither the main effect of light 

 nor the androgen-light interaction was sig- 

 nificant ip > 0.05). On the basis of the 

 evidence cited, the claim for an effect of 

 light on the androgen bioassay should be 

 given the Scottish verdict "not proven." 



Lamoreux (1943) showed in a carefully 

 conducted experiment in which temperature 

 and light were controlled variables, that 

 neither visible nor ultraviolet light affected 

 comb size significantly, but that increased 

 temperature caused an increase of the comb 

 size. In contrast Leroy (1956, 1958) found 

 that combs of birds raised in darkness 



