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  • Title: Evidence for a positive feedback interaction between progesterone and luteinizing hormone in the induction of ovulation in the hen, Gallus domesticus.
    Author: Johnson PA, Johnson AL, van Tienhoven A.
    Journal: Gen Comp Endocrinol; 1985 Jun; 58(3):478-85. PubMed ID: 4007483.
    Abstract:
    Two experiments were conducted to test the hypothesis that progesterone (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. Aminoglutethimide phosphate (AGP), 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 branchial vein cannula 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. Atresia 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)
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