Conditions for establishment of reflex ovulation in light estrous rats.

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Abstract
Continual anovulatory states associated with persistent vaginal cornification (light estrus) was induced by placing 4 day cycling rats under continuous lighting (LL). Uterine cervical stimulation was applied at arbitrary solar hours to light estrous rats showing continual vaginal estrus for more than 2 wk. The ovulation was induced between 14 and 16 h after the stimulation dissociating entirely with solar hours. Injection of anti-LHRH [luteinizing hormone releasing hormone] serum 5 min after the stimulation but not later than 20 min blocked this ovulation. Ovulation thus induced was always followed by pseudopregnancy with a continual leukocytic vaginal smear lasting 10.70 days. The change in concentrations of peripheral serum progesterone during this period was almost similar to that of normal pseudopregnancy except for extremely low levels observed at the start and end. Effectiveness of the cervical stimulation for induction of ovulation in light estrous rats was related to not only the duration of the light estrus but also the time after transfer to LL, suggesting that the neural mechanism of ovulation in light estrous rats shifted from that of spontaneous to reflex ovulators due to the extinction of the environmental photic cue.