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DIURNAL COMPONENT IN THE RESPONSE BY THE MOUSE TO GONADOTROPHIN

Summary.: The uterine weight and ovulation responses of immature intact and hypophysectomized mice from two lighting regimes have been studied after injection of gonadotrophin. The results indicate diurnal variation in ovarian response: the response to gonadotrophin was greater when it was administered during the second half of the light phase of the daily light cycle than at any other time.

Pregnant mice were fasted for 36- to 48-hr periods beginning at 06.00 hours or 18.00 hours on the 2nd, 3rd or 4th day after mating. Diurnal variation in the proportion of pregnancies failing was demonstrated. The effect was not attributable to differences in loss of body weight during fasting, and could be prevented by injections of human chorionic gonadotrophin (HCG).

The numbers of eggs ovulated by adult di-oestrous mice treated with HCG were studied after 36- or 48-hr fasts commencing at 06.00 hours or 18.00 hours 2 days before an injection of HCG. Fasting reduced numbers of ovulations, but the effect was influenced by the time of day when the fast began. Reversal of the lighting regime resulted in a reversal of the pattern.