Temporal Relationship Between Estradiol, Estrone and Progesterone Secretion in the Ovarian Venous Blood and LH in the Peripheral Plasma of Cyclic Hamsters

Ovarian venous blood levels of estradiol estrone and progesterone were measured in 66 hamsters at various stages of the estrous cycle to determine the relationship between the secretory pattern of these hormones and the peripheral plasma levels of LH. There were no significant differences observed in blood flow rate at any stage of the estrous cycle. Designating the day of vaginal discharge as Day 1 estradiol level was lowest on Day 2 but increased over 200% after 14:00 hours of Day 3 and remained unchanged during proestrus (Day 4). The concentration of estrone which was lower than estradiol did not fluctuate significantly during the cycle. Progesterone concentrations were highest on Day 1 and gradually declined to the lowest values before the critical period on Day 4 (p< .01). The concentration and output increased after the ovulatory surge of LH and ovulation. LH levels remained unchanged (p< .05) until after the critical period on Day 4 when they rose sharply. Since only estradiol showed a rise preceding the ovulatory surge of LH the data support an earlier hypothesis that estradiol and not estrone and progesterone provides a "trigger" for releasing ovulating hormone during the hamsters estrous cycle.