Reaction of Ovaries of Mature Female Rats to Injections of Oestrin. ∗

Abstract

Twenty-five mature female rats received daily injections of 200 rat units of a concentrated oestrus-inducing extract† for 8 to 15 days (a majority were for 12 days). Vaginal smears usually revealed a complete cornification of the vaginae for the first 3 to 5 days of the experiment which did not persist throughout the injection period except in 2 rats. At autopsy it was found that the ovaries of these rats presented a normal number of corpora lutea but that the corpora were greatly increased in size when compared with those of rats killed during the normal oestral cycle. They were, however, similar in appearance and size to the corpora lutea of rats killed during the latter half of pregnancy. The pituitary glands of the oestrin-injected rats were increased in weight. Their mean weight was 19.2 mg.; the range was from 12.5 to 27 mg., and all but 2 weighed above 15 mg. The mean pituitary weight of 143 normal cyclic female rats was 10.5 mg.

Serial sections of all ovaries and representative sections of the uteri and the vaginae were cut. For control material similar sections were made of the ovaries and the accessory organs of 30 female rats killed during the normal oestral cycle and from 25 rats killed during the latter half of pregnancy. The relative size of the corpora lutea in the various groups was obtained by measuring the 2 greatest diameters, in millimeters, of the sections of the corpora lutea with a micrometer eye-piece. The product of the 2 greatest diameters of the corpora was calculated and the average of the 5 greatest products thus obtained was considered as the size of the corpora lutea in the ovary.