Abstract
It was shown 1 that 21- and 25-day-old rats responded to mare gonadotropic hormone with follicular growth, ovulation, and the formation of corpora lutea. Later it was shown 2 that in female rats 10 days old at the time of the injection the response consisted in a marked development of interstitial tissue. This divergence in results led us to study further the nature of the response dependent upon age.
Rats were divided into groups with age and size of the dose as the variables. Single doses of 2, 16, and 500 R. U. were given to rats 15, 18, 19, 21, and 25 days old at the time of injection with necropsy 120 hours after the injection. The ovaries and uteri were weighed and the ovaries of three rats in each group were sectioned serially. The response of the 15-day-old rats is comparable to that of 10-day-old rats and thus does not need further consideration.
A pure follicle stimulating response was obtained at all dosage levels with rats injected on the 18th day. Not a single corpus luteum was found in 26 rats injected at this age. Macroscopically enlarged pale translucent follicles were visible. Microscopic study shows that ovulation has not occurred and there is no evidence of the conversion of the granulosa into lutein tissue. There is, however, a marked development of interstitial tissue in rats receiving the larger amounts, which is in many ways similar to that found in the ovary of the rabbit in heat. In those receiving 2 R. U. the only detectable change is the growth of a few follicles.
Ovulation and the formation of corpora occurred in 3 of 18 rats injected on the 19th day of age, and the results in 21- and 25-day-old rats were comparable to those previously obtained.
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