1128 



SUBMAMMALIAN VERTEBRATES 



1953; Das and Nalbandov, 1955; Opel and 

 Nalbandov, 1958j . Whether or not the avian 

 pituitary is required for this "maturation" 

 of the ovary has not been determined and 

 not enough data are available for a com- 

 parison of birds hypophysectomized at dif- 

 ferent ages and given similar treatments. In 

 all cases in which ovarian development has 

 been obtained in chickens, large amounts of 

 gonadotrophins, equivalent to 10 to 20 pitui- 

 taries from 12- 14-week-old "broilers," had 

 to be used. If one assumes that the pitui- 

 taries came half from males and half from 

 females, and that female pituitaries have 

 half the potency of male pituitaries (com- 

 parison of data of Breneman and Mason, 

 1951; and Breneman, 1955), then the 18 to 

 20 avian pituitaries per day are equivalent 

 to 270 to 300 I.U. gonadotrophin per day be- 

 cause according to Phillips (1959), 1 pitui- 

 tary of a "broiler" rooster = 1 mg. dried 

 powder = 20 I.U. PMS. Mammalian gon- 

 adotrophin injections, equivalent to 500 rat 

 units of FSH (Nalbandov and Card, 1946) 

 or to 100 to 200 rat units PMS (Fraps, Riley 

 and Olsen, 1942) were needed to stimulate 

 follicles in adult intact hens. In contrast to 

 the rather low sensitivity of the ovary with 

 respect to follicular growth, stands the ex- 

 treme sensitivity to LH for induction of 

 ovulation. Fraps, Fevold and Neher (1947) 

 showed that 1 fjig. LH prepared from chicken 

 pituitaries was capable of inducing prema- 

 ture ovulations in 50 per cent of the hens. 



The effect of gonadotrophin injections into 

 intact female birds other than chickens 

 seems to depend on the species used. Red- 

 billed weavers (Witschi, 1935), European 

 gold finches, Carduelis elegans (Vaugien, 

 1956), green finches, Chloris chloris, bunt- 

 ings and canaries, Serinus canaria (Vaugien, 

 1957), and house sparrows. Passer domesti- 

 cus (Riley and Witschi, 1938; Witschi and 

 Riley, 1940; Vaugien, 1954 j can be stimu- 

 lated to lay eggs during the nonbreeding 

 season by injections of about 100 to 150 

 I.U. PMS every 3 days for 3 weeks. In con- 

 trast to those of chickens, the follicles of 

 these birds show normal gradations in size 

 (Riley and Witschi, 1938; Witschi and 

 Riley, 1940), and no separate LH injections 

 are required for ovulation (Witschi, 1935; 

 Vaugien, 1954, 1957). The lack of ovarian 



response in the robin, Erithacus r. rubecula, 

 observed by Schildmacher (1939), may be 

 explained by the low dosage used. If one ex- 

 cludes possible differences between species 

 with respect to the dosage required to obtain 

 ovarian stimulation, the generalization can 

 be made that intact songbirds differ from 

 chickens in their response in the following 

 ways. 



1. Regular gradation of follicular size is 

 obtained even with rather massive doses of 

 PMS. 



2. Ovulations occur "spontaneously" and 

 do not require separate LH injections. It 

 seems, thus, that a comparative approach to 

 the problem of follicle-size gradation might 

 prove to be profitable, as might an investiga- 

 tion of the endocrine regulation of ovulation 

 in song birds. 



Administration of the third gonadotrophic 

 hormone, prolactin (the luteotrophic hor- 

 mone of mammals), inhibits FSH secretion 

 and results in cessation of laying and in 

 atresia of the follicles (Bates, Lahr and 

 Riddle, 1935; Bates, Riddle and Lahr, 1937) . 

 Juhn and Harris (1956) reported, however, 

 that prolactin counteracts the inhibition of 

 laying by exogenous progesterone. This ef- 

 fect is rather surprising for it would assign 

 to prolactin a true gonadotrophic function 

 which is contrary to its effects in roosters 

 and female pigeons (Bates, Lahr and Riddle, 

 1935; Bates, Riddle and Lahr, 1937). Fur- 

 ther investigations are needed to establish 

 whether prolactin affects male and female 

 chickens differently. 



Assays of the pituitaries from chickens 

 (Burrows and Byerly, 1936; Saeki and Ta- 

 nabe, 1956; Nakajo and Tanaka, 1956), 

 pheasants, Phasianus colchicus Breitenbach 

 and Meyer, 1959), and California gulls 

 (Bailey, 1952) reveal that the prolactin con- 

 tent is maximal when the eggs are being in- 

 cubated. Prolactin content decreases when 

 the chicks are hatched, although the hen is 

 still caring for the young. Strong lights or 

 electric shocks to the head interrupted 

 broodiness and decreased the prolactin con- 

 tent of the anterior pituitary, especially of 

 the caudal lobe (Nakajo and Tanaka, 1956) . 

 As we noted in the section on the male, the 

 data from a limited number of species sug- 

 gest that prolactin may be required for in- 



