Progesterone levels measured every two hours in the cyclic hamster.
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.
D000818:Animals; D002642:Chick Embryo; D003338:Corpus Luteum / Q000502:physiology; D006224:Cricetinae; D003624:Darkness; D004971:Estrus; D005260:Female; D008027:Light; D003341:Luteolysis; D011247:Pregnancy; D011359:Proestrus; D011374:Progesterone / Q000097:blood*; D011863:Radioimmunoassay
D011374:Progesterone