Evidence for a positive feedback interaction between XXXX and luteinizing hormone in the induction of ovulation in the hen, Gallus domesticus.

@entity1420 @entity14214 @entity35535 @entity1146 @entity12743
Two experiments were conducted to test the hypothesis that @entity1420 (P4) acts to induce a preovulatory rise of luteinizing hormone (LH) by initiating a true positive feedback interaction between P4 and LH. In each experiment, ten hens were stereotaxically implanted with a third ventricle cannula. @entity35535 ( @entity14214 ), an inhibitor of steroidogenesis, was administered (200 mg iv) to hens at 10 and 6 hr (Experiment 1) and 10 and 7 hr (Experiment 2) before an expected C1 ovulation. A 20-micrograms injection of P4 (n = 5) or the vehicle (n = 5) was made intraventricularly at 6 hr (Experiment 1) or 7 hr (Experiment 2) before the expected ovulation. Blood samples were taken via @entity12743 at regular intervals after the injection. In Experiment 1, four of five P4-treated hens ovulated, and no atretic follicles were found in any of the five P4-treated hens, including the one which did not ovulate. Ovulations were always accompanied by preovulatory LH peaks. By comparison, none of the vehicle-injected animals ovulated and in four of five hens the largest follicle was determined to be atretic. No ovulations occurred in Experiment 2 for either the P4- or vehicle-injected hens. @entity1146 of the largest follicle occurred in all five hens in the P4-treated group and four of five hens of the vehicle-treated group. The difference in results between Experiment 1 and Experiment 2 can be explained assuming that the steroidogenesis-inhibiting action of the initial AGP injection in Experiment 1 (at 10 hr before ovulation) had diminished prior to the second AGP treatment (at 6 h before ovulation).(ABSTRACT TRUNCATED AT 250 WORDS)
