Gonadotrophin release induced by Gn-RH or progesterone in female rats maintained on high or low levels of feed intake

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Abstract
The effect was compared of high or low feed levels on the response of intact rats to injected Gn-RH [gonadotropin releasing hormone] and of ovariectomized rats to Gn-RH or progesterone. Rats on a low feed intake level are equally or perhaps more responsive to the gonadotropin-releasing action of progesterone than rats on a high feed intake level. The positive effect of progesterone is believed to play an essential role in inducing the ovulatory surge of gonadotropins. The responses to progesterone indicated that the cells involved in synthesis of the hypothalamic hormone(s) required for gonadotropin release and the pituitary cells which respond to Gn-RH all seem to be functioning adequately in rats on a low level of feed intake. The eventual cessation of estrous cycles is probably explained by a lack of the ovarian steroids required for the positive feedback effects which trigger an ovulatory release of hormone. This lack of adequate steroid secretion may reflect a failure of hypothalamic mechanisms which govern basal luteinizing hormone secretion.

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