INDUCED OVULATION IN ALBINO RATS EXPOSED TO CONSTANT LIGHT

Abstract

SUMMARY Adult female albino rats were exposed to constant illumination of moderate intensity for 55–65 days; at the end of this period more than 95% had no macroscopically visible luteal tissue in their ovaries and more than 90% were sexually receptive. In these animals ovulation was consistently induced by mating. The major component of the mating pattern responsible for the induction of ovulation was penile intromission. Mounting without intromission was much less effective and the occurrence or non-occurrence of ejaculation did not affect the incidence of ovulation. Non-sexual 'stressful' stimuli or the injection of progesterone also induced ovulation in about 50% of animals. However, adrenal progesterone was not required for either the maintenance of sexual receptivity or mating-induced ovulation since adrenalectomized rats exposed to constant light also mated and ovulated. The time-course of the secretion of luteinizing hormone (LH), determined by radioimmunoassay of plasma LH, also indicated that mating had effects on LH secretion independent of any action of progesterone. LH concentrations were high at 40 min and maximal at 60 min after mating but decreased thereafter while following the injection of progesterone the levels rose gradually and remained high until at least 360 min after the injection. Sodium pentobarbitone administration had little effect on LH secretion induced by mating but blocked ovulation in some animals. Mating-induced ovulation was not invariably associated with increased activity of the thyroid gland but an increase did occur when the mating stimulus was prolonged.