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The present study examined the ovarian progesterone levels in rats during the normal 5-day oestrous cycle and in rats with an experimentally induced delayed or advanced ovulation. Ovarian androgen and oestrogen concentrations were also studied in rats with an advanced ovulation.

The ovarian progesterone concentrations during the normal cycle showed two peaks: one during metoestrus and dioestrus 1 and the second during the afternoon of pro-oestrus.

Rats treated with pentobarbitone sodium (35 mg/kg body weight) at 13.00 h on the day of pro-oestrus showed no increase in ovarian progesterone levels on that day, but did show an increase during the afternoon of the next day.

Rats injected intraperitoneally with an ovulation-inducing bolus of human chorionic gonadotrophin (hCG; 20 i.u.) at 15.00 h on the day before pro-oestrus (dioestrus 2) showed increased ovarian progesterone levels as early as 0·5 h after hCG injection. Lowered levels of ovarian androgen and oestrogen values compared with saline-injected rats were first found 2 and 6 h respectively after hCG injection.

In conjunction with data obtained previously these findings show that normal, delayed and advanced ovulations are preceded by an increase in ovarian progesterone concentrations and a subsequent decline in ovarian androgen and oestrogen levels.

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				B.-Y. Chern, Y.-H. J. Chen, L.-S. Hong, and P. S. LaPolt Ovarian Steroidogenic Responsiveness to Exogenous Gonadotropin Stimulation in Young and Middle-Aged Female Rats Experimental Biology and Medicine, September 1, 2000; 224(4): 285 - 291. [Abstract] [Full Text]