TIMING OF LH RELEASE AND OVULATION IN THE POST PARTUM MOUSE

Summary. The time at which ovulation occurred in post partum mice under L14:D10 (lights on from 05.00 to 19.00 hours) was investigated. Ovulation tended to occur during the late part of the dark period and early part of the light period, but the exact time depended on the time of delivery. Mice that gave birth between 21.00 and 01.00 hours ovulated approximately 26 hr after delivery. The interval between delivery and ovulation decreased the later in the day that delivery occurred, until it became 12 to 13 hr for mice that gave birth between 17.00 and 21.00 hours. Barbital was administered at various intervals after delivery in an effort to determine the time of release of the lh responsible for ovulation. Although the data indicate that lh release tended to occur in most mice during the afternoon or early evening, there was no one time of day at which barbital was totally effective in blocking lh release for mice giving birth during different times of the entire 24-hr light and dark period.