Abstract
Summary
Four groups of unanesthetized hamsters were bled by cardiac puncture three times a day at 4-hr intervals for each day of the 4-day estrous cycle. Serum progesterone (P) was determined by RIA. On day 1 of the cycle (day of ovulation) there was a trend for excursions in P at 4-to 6-hr intervals; this was followed on day 2 by a relatively steady level of P of 6-8 ng/ml. P dropped drastically after 0200 of day 3, indicating the onset of luteolysis. A significant increase in P occurred at 1600 of day 3 which was presumably nonluteal in origin. A series of cyclic fluctuations in P began at 1600 of day 4 (proestrus) comparable to the pattern observed on day 1 of the cycle.
Kirk Ridley was supported as an Osborn Student Research Fellow. The research was supported by grants from NIH (HD00596) and the Ford Foundation. We acknowledge the excellent technical assistance of Mrs. Darlene Limback and Mrs. Diane Lawson.
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