HORMONES AND MATING BEHAVIOR 



1189 



hormones received endogenously or exog- 

 enously. 



In connection with the above described 

 findings in the guinea pig, i.e., the apparent 

 relatively higher threshold of vaginal epi- 

 thelium to estrogenic stimulation, and the 

 dependence of cornification on a small 

 amount of progesterone, three observations 

 on other species should be noted here. In 

 the ewe the hormonal recjuirements for the 

 vaginal changes characteristic of estrus and 

 the behavior changes are about the same 

 (Robinson, Moore and Binet, 1956). In 

 the cat vaginal cornification does not seem 

 to be dependent on progesterone (Ford, 

 1954). In the cat, in experiments with 

 amounts of two estrogens below 12 /tg. per 

 day, at which dosage the latent period to 

 mating exceeded 7 days, the appearance of 

 a fully cornified vaginal smear invariably 

 preceded the mating response (Michael and 

 Scott, 1957; Harris, Michael and Scott, 

 1958) . At high dose levels the occurrence of 

 mating preceded the vaginal smear change 

 by about 24 hours. A comparison of the 

 vaginal and central nervous system thresh- 

 olds to estrogenic stimulation must await 

 the results from measurements of the mean 

 rate of release at these sites which these 

 investigators appear to have undertaken. 



Estrogen and progesterone participate 

 in the induction of heat in the ewe, but the 

 sequence is different from that in rodents. 

 It is clear from studies of ewes at the be- 

 ginning of the breeding season (Schinckel, 

 1954a, b), from studies of anestrous ewes 

 given pregnant mare serum (PMS) and 

 progesterone (Dutt, 1953; Robinson, 1954b) , 

 and from experiments on spayed ewes given 

 estrogen and jirogesterone (Robinson, 1954a, 

 1955; Robinson, Moore and Binet, 1956) 

 that normal heat behavior is not displayed 

 unless treatment with an estrogen of en- 

 dogenous or exogenous origin is preceded by 

 progesterone. Progesterone, 12.5 mg., twice 

 daily for 3 days followed 2 days later by 

 1000 I.U. of PMS was an optimal treat- 

 ment when anestrous ewes were used (Rob- 

 inson, 1954b). When the effectiveness of 

 progesterone and estradiol was tested on 

 spayed ewes, 75 mg. of progesterone given 

 in 6 injections over 3 days followed 2 days 

 later by 38 jug. of estradiol induced heat in 



90% of the injected animals (Robinson, 

 1955 ». 



Except that estrogen and progesterone act 

 together in the induction of heat in labora- 

 tory rodents, the cow, and the ewe, the proc- 

 esses whereby this end is achieved are not 

 known. The subject is discussed in the sec- 

 tion on the mechanism of hormone action 

 (p. 1204) where the important studies of 

 Sawyer and Markee (1959), Sawyer and 

 p]verett (1959), and Kawakami and Sawyer 

 ( 1959a, b) are related to the problem. What 

 might be thought of as a complication is 

 that progesterone terminates estrus in the 

 ral)bit (Makepeace, Weinstein and Fried- 

 man, 1937; Sawyer and Everett, 1959), fer- 

 ret (Marshall and Hammond Jr., 1945), 

 sheep and goat (Phillips, Fraps and Frank, 

 1946), reduces the estrogen-induced sexual 

 activity of the rhesus monkey (Ball, 1941a) , 

 antagonizes the effect of estradiol on spayed 

 gilts (Day, Anderson, Hazel and Melampy, 

 1959), and, in large doses, antagonizes the 

 action of estrogen in ovariectomized cows 

 (Melampy, Emmerson, Rakes, Hanka and 

 Eness, 1957). We cannot reconcile such ac- 

 tions with its role as a priming substance in 

 the ewe beginning with the ovulation pre- 

 ceding heat. Sawyer and Everett (1959), 

 citing the study by Dutt (1953), refer to 

 such an estrus as one "that appears on the 

 'rebound' from progesterone treatment." 



The termination of estrus by progesterone 

 is not inconsistent with its action in helping 

 to stimulate heat. In the guinea pig, rat, 

 mouse, hamster, and cow the small amount 

 of progesterone produced in the developing 

 follicle about the beginning of the preovula- 

 tory swelling touches off the estrus-mecha- 

 nism, but the larger amounts produced about 

 the time of ovulation may be inhibitory. 

 Experimental evidence supporting this view 

 has recently been ]irovided by Sawyer and 

 Everett (1959) and by Kawakami and 

 Sawyer ( 1959a ) in their investigations 

 which are reviewed in more detail elsewhere 

 (p. 1206). 



A purified estrogen alone or an estrogenic 

 substance is said to be sufficient for the stim- 

 ulation of mating reactions in ovariecto- 

 mized cats (Bard, 1939; Maes, 1939; Michael 

 and Scott. 1957; Harris, Michael and Scott, 

 1958), dogs (Kunde, D'Amour, Carlson and 



