Lack of effects of indomethacin on estradiol feedback control of luteinizing hormone in ovariectomized ewes

• Published in: Domestic animal endocrinology Vol. 10; no. 1; p. 15
• Main Authors: Bettencourt, C M, Moffatt, R J, Keisler, D H
• Format: Journal Article
• Language: English
• Published: United States 01-01-1993
• Subjects: Analysis of Variance; Anestrus - drug effects; Anestrus - metabolism; Animals; Drug Implants; Drug Interactions; Estradiol - administration & dosage; Estradiol - pharmacology; Feedback - drug effects; Female; Gonadotropin-Releasing Hormone - pharmacology; Indomethacin - administration & dosage; Indomethacin - pharmacology; Injections, Intramuscular - veterinary; Luteinizing Hormone - blood; Ovariectomy - veterinary; Pituitary Gland - drug effects; Pituitary Gland - metabolism; Random Allocation; Sheep - metabolism
• ISSN: 0739-7240
• DOI: 10.1016/0739-7240(93)90004-U

We tested the hypothesis that indomethacin, a potent inhibitor of prostaglandin synthesis, would modify estradiol's effects on tonic and surge concentrations of LH in chronically ovariectomized ewes during the anestrous season. Ewes (n = 21) were assigned randomly to one of four treatments: Vehicle+Blank (n = 5); Indomethacin+Blank (n = 6); Vehicle+Estradiol (n = 5); or Indomethacin+Estradiol (n = 5). On d=0 (hr = 0), ewes began to receive i.m. injections of either indomethacin (4 mg/kg body weight) or corn oil every 8 hr for 9 d. Blood samples were collected every 12 min for 6 hr beginning at -6 hr, +18 hr, and on day 8 (relative to initial injections of indomethacin or vehicle) to assess tonic patterns of secretion of LH. At +24 hr, ewes received blank- or estradiol-containing Silastic implants and were bled hourly for 48 hr. On day 9, ewes received 50 micrograms of GnRH i.v. and were bled hourly for 8 hr. Serum samples were assayed for LH. Indomethacin had no effect on the following parameters of LH secretion: 1) mean concentrations (ng/ml; 8.4 +/- .7 vs 8.9 +/- .8; P > .1), 2) pulse frequency/6 hr (4.5 +/- .4 vs 4.1 +/- .4; P > .1) or 3) pulse amplitude (ng/ml; 15.3 +/- 1.1 vs 14.9 +/- 1.2; P > 1). Estradiol elicited a surge of LH which began 18.9 +/- 1.7 hr after implant insertion, reached a mean peak concentration of 95.3 +/- 20.1 ng/ml, and did not differ with respect to indomethacin treatment (P > .1).