Effects of withholding food for 0-72 h on mating, pregnancy rate and pituitary function in female rats.

Food was withheld from female rats for 0-72 h at various stages of the oestrous cycle. Withholding food for periods of 24 h ending at 12:00 h on the day of pro-oestrus reduced the mating rate from 61 to 25% (P less than 0.05) but not the pregnancy rate of those rats that mated. Fasting for 24 h ending at 18:00 h on the day of pro-oestrus reduced the pregnancy rate from 82 to 18% (P less than 0.05) without affecting the mating rate and a 48-h fast starting at 12:00 h on the day of pro-oestrus reduced the pregnancy rate from 82 to 25% (P less than 0.05). Withholding food for 23 h ending at 17:00 h on the day of pro-oestrus prevented the LH and prolactin surges normally present at 17:00 h on this day. The treatments had no apparent effect on the ability of the adenohypophysis to release LH in response to injections of GnRH. When ovariectomized female rats fasted for 0-72 h and given 2 injections of oestradiol dibenzoate to test the ability of the hypothalamus to respond to an increasing plasma oestradiol concentration by stimulating the release of LH, a fast for 24 h reduced and a fast for 72 h completely prevented LH release.