Abstract
The fact that rats do not respond to anterior-pituitary-like hormone (A.P.L.) in the first days of life has been observed repeatedly, and the conclusion has been drawn that they should not be used as test objects for this hormone earlier than the 18th to the 21st day of life. In an attempt to find an explanation for this fact we injected a series of 30 rats daily with A.P.L., starting on the 6th day of life. Although no mature follicles or corpora lutea had been formed after 10 injections and the ovary did not differ macroscopically from that of an untreated rat of the same age, histological examination of this organ reveals very pronounced changes. The thecal cells were very much enlarged and assumed the appearance of corpus luteum cells, whereas the granulosa cells were not luteinized and no signs of ripening of the follicles could be detected. These experiments show that at a very early age A.P.L. is unable to induce follicular maturation or the formation of normal or atretic corpora lutea; however, it does lead to luteinization of the thecal cells and thereby to the formation of thecal corpora lutea. These structures are not very prominent and therefore they can be readily overlooked upon macroscopical examination. (Fig. 1.) Histologically they are composed of a peripheral ring of corpus luteum cells and a central part of a few rows of normal granulosa cells in the center of which the ovum is included. (Fig. 2.)
It is difficult to find a satisfactory explanation for these observations. It is remarkable, however, that the hypophysectomized rat shows a very similar ovarian reaction when treated with A.P.L. 1 In the absence of the pituitary we could never induce maturation of the follicles or luteinization of the granulosa cells with A.P.L., but the luteinization of the theca cells is very conspicuous.
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