Effect of Hypophysectomy on the Ovary of Immature Rats

Abstract

We know that the immature gonad is largely independent of the pituitary. Malformations of the pituitary, such as those associated with anencephaly, do not influence the embryonic development of the ovary, although they inhibit the growth of the adrenal cortex very markedly. 1 It has also been shown that the anterior pituitary-like hormone is unable to produce follicle maturation and formation of corpora lutea in the ovary of the very young rat; its only effect at an age of 6-12 days is luteinization of theca cells. 2 It seemed of interest, therefore, to study the effect of hypophysectomy on immature rats. In previous experiments we saw that the immature follicles of young rats may persist a very long time after the removal of the pituitary, and although the follicular atresia in such animals is usually considerable the results of hypophysectomy are not very clear-cut because the number of follicles undergoing atresia is also very considerable in the normal immature rat. We thought that our recent observations 3 on the effect of hypophysectomy on the theca might be used to detect more obvious signs of pituitary deficiency in the immature rodent. We hypophysectomized 20 female rats 18 days of age and killed them at various intervals between the 10th and 25th days after operation. They all showed both normal and atretic follicles, and many typical thecal deficiency cells as described previously. 3 The chromatin of their nuclei aggregates in large, dark granules, leaving unstained spaces in between (Figs. 1 and 2).

It is interesting to note in this connection that the transformation of thecal cells into deficiency, cells occurs only around the atretic follicles, while the theca of normal follicles maintains its normal appearance (Fig. 2). The reason for this phenomenon is not known to us, but it seems that the living granulosa and ovum protect the theca. This observation reminds one of the fact that thecal lutein-ization as produced by the anterior pituitary-like hormone of pregnancy urine also appears most readily in thecal cells which are not in immediate contact with living granulosa cells.