460 



PHYSIOLOGY OF GONADS 



specific examples must be presented in order 

 to avoid the dangers of generalization. 



In the rabbit copulation triggers a neuro- 

 humoral mechanism which releases gonado- 

 trophin from the pituitary which subse- 

 quently induces ovulation in 10 to 12 hours. 

 The ruptured follicles form corpora lutea 

 which have a functional span of about 28 

 days if pregnancy ensues but only 14 days if 

 the mating is infertile. Crystals of estrogen 

 implanted into a corpus luteum of a rabbit 

 will cause its persistence while other corj^ora 

 lutea regress (Hammond and Robson, 1951 ). 

 This suggests that either estrogen makes the 

 corpus luteum more sensitive to pituitary 

 maintenance (Hammond, 1956) or estrogen 

 protects the corpus luteum from luteolytic 

 action. In the cat, copulation induces ovula- 

 tion about 25 hours after mating; the cor- 

 pora lutea function for 36 days after an in- 

 fertile mating, but gestation lasts 62 to 64 

 days. The ferret ovulates about 30 hours 

 after copulation and the corpora lutea are 

 functional for 42 days, w^hether the mating 

 is fertile or infertile (Brambell, 1956 1. 



In the unmated rat and mouse ovulation 

 is spontaneous, but the resulting corpora lu- 

 tea are nonfunctional and begin to regress 

 within 2 days. After copulation the corpora 

 lutea persist for 18 days if impregnation has 

 occurred, but for only 12 days after an in- 

 fertile mating. Copulation probably results 

 in the release of enough additional gonado- 

 trophin (LH or LTH) to activate the cor- 

 pora lutea. In rats and mice the pituitary 

 hormone, prolactin, is luteotrophic (LTH) 

 (Desclin, 1949; Everett, 1956). These spe- 

 cies have functional corpora lutea through- 

 out lactation— actually two sets, that of 

 pregnancy and that of the postpartum ovu- 

 lation. Using the rat and taking weight and 

 levels of ovarian enzymes as measures of ac- 

 tivity, these corpora lutea were studied by 

 Meyer and McShan and their associates and 

 the results summarized in a ic\'i('\v (]\Ieyer 

 and McShan, 1950). They found that "the 

 weight of the corpora lutea of pregnancy in- 

 creased greatly during the latt(>r half and 

 that the amount of enzymes per corjius lu- 

 teum was also greater. With some caution, 

 they concluded that these corpora lutea are 

 more highly functional during this phase of 

 pregnancy than during the first half. 



Not only copulation, but also injection of 



estrogen at estrus is followed by the forma- 

 tion of functional corpora lutea. The estro- 

 gen maintenance of corpora lutea in rabbits 

 and mice is offset by hypophysectomy 

 (Hohn and Robson, 1949); presumably, 

 therefore, maintenance is mediated through 

 the anterior })ituitary. Reece and Turner 

 (1937) showed that estrogen stimulates the 

 rat i^ituitary to produce prolactin so the lat- 

 ter may be the luteotrophic agent in this 

 s]:)ecies. Moore and Nalbandov (1955) found 

 that prolactin is luteotrophic in sheep. To 

 date this is the only species other than the 

 rat and mouse in which prolactin has been 

 shown to have luteotrophic activity. 



In the guinea pig, monkey, man, and 

 many other species, ovulation and the for- 

 mation of functional corpora lutea are spon- 

 taneous. Copulation is not known to have 

 any neurohumoral influence in these species. 

 The corjiora lutea of the human female func- 

 tion for 2 to 3 months in pregnancy and for 

 only 12 to 14 days in. an infertile cycle. Berg- 

 man ( 1949 ) states that the duration of the 

 luteal i^hase is limited to a maximum of 16 

 days. In the rhesus monkey the functional 

 life has been estimated to be about 13.5 days 

 in the normal cycle, and approximately 30 

 days when pregnancy intervenes (Hisaw, 

 1944) . In the bitch, ovulation is spontaneous 

 and the corpora lutea remain functional for 

 6 weeks irrespective of mating or pregnancy. 

 In the lactating African elephant the cor- 

 pora lutea degenerate soon after parturition 

 (Perry, 1953) ; in the lactating domestic cat 

 they not only persist, l)ut they become ''re- 

 juvenated" (Dawson, 1946). 



As a general statement, it can be said that 

 the functional span of the corpora lutea is 

 cithei' adequate to permit implantation or 

 it is prolonged by copulation (as in rats and 

 mice) so that imjilantation can occur. But 

 inasmuch as imj:)lantation occurs in many 

 species, including man, about the sixth day 

 after ovulation and fertilization, the margin 

 of safety is not great and a delay in the se- 

 cretion of chorionic gonadotrophin by the 

 tro])hoblast must reduce the chances of a 

 successful pregnancy. 



Ill some species, e.f/., rats, mice, rabbits, 

 an ill felt ih' mating prolongs the life of the 

 corpora hitea. This prolonged interval of 

 functional luteal activity is known as pseu- 

 doj)regnancy. As Everett has noted in his 



