A species difference between hamster and rat in the effect of oestrogens on growth of large preantral follicles

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Abstract
Intact or hypophysectomized 23 day old hamsters and rats were injected s.c. with 2 mg diethylstilboestrol (DES) or 1 mg estradiol cyclopentylpropionate (OECP) on days 23-25 and killed on day 26. Although serum estradiol was elevated to the same high levels by OECP, ovarian and uterine weights were increased in the rat by OECP or DES, whereas only the uterus responded in the hamster. This correlated with the ability of the estrogens to increase significantly the number of large preantral and antral follicles in the intact rat, but only the number of follicles with 2-3 layers of granulosa cells in the immature hamster. Qualitative study revealed that DES and OECP increased the number of large preantral follicles in the adult hypophysectomized rat, but were ineffective in the adult hamster. It is concluded that for the immature and adult hamster estrogens do not play a major role in the recruitment of large preantral follicles.