Serum Gonadotropin Concentrations and Ovarian Response in Ewes Treated with Analogs to LH-RH/FSH-RH2

Abstract

One-hundred-twelve anestrous Columbia ewes were used in three experiments to evaluate biological potency of three analogs to LH-RH/FSH-RH. Either one or a combination of the following characteristics were utilized in the different experiments to evaluate biological potency of these analogs: Serum LH, serum FSH, ovulation rate or conception. In experiment 1, 32 ewes were assigned randomly to a 2 X 4 factorial experiment. Each ewe received either .5, 5, 50 or 500 µg of des Gly¹⁰-LH-RH ethylamide or LH-RH/FSH-RH. Peak serum LH concentration was significantly greater in ewes treated with .5 µg analog than in the ewes treated with .5 µg LH-RH/FSH-RH. The peak serum LH concentrations did not differ significantly between the analog or LH-RH/FSH-RH treated ewes in any of the other treatment groups. Peak concentrations of FSH did not differ among the groups of ewes treated with LH-RH/FSH-RH or analog at any of the respective doses. However, there was a greater number (P<.05) of ovulations in the ewes treated with des gly¹⁰-LH-RH-ethylamide than in ewes treated with LH-RH/FSH-RH. Experiment 2 consisted of five ewes treated with 500 µg des-gly¹⁰-LH-RH-ethylamide and five ewes treated with saline. All ewes were artificially inseminated 12 hr post-injection. There was a greater number of ovulations (P<.05) in the ewes treated with the analog than in the ewes treated with saline. However, none of these ewes conceived. In experiment 3, 70 ewes were used to compare the effects of the analogs D-Ala⁶ des Gly¹⁰-LH-RH ethylamide and D-Leu⁶. des Gly¹⁰-LH-RH-ethylamide with those of LH-RH/FSH-RH. Comparisons indicated an increase (P<.05) in total LH released, mean peak LH and duration of the LH release in ewes treated with either .5, 5, 50 µg D-Ala⁶ and D-Leu⁶ analog as compared to ewes receiving corresponding doses of LH-RH/FSH-RH. However, total LH released was not significantly different when the ewes treated with 500 µg of either analog were compared with those treated with LH-RH/FSH-RH. The amount of D-Ala⁶, D-Leu⁶ or LH-RH/FSH-RH which released 50% of the total LH released by the 500 µg dose (effective dose 50) was calculted as 2.4, 5.4 and 100 µg, respectively. The analogs were nine, four, and three times more potent in total LH releasing ability when compared to LH-RH/FSH-RH at the .5, 5 and 50 µg doses, respectively. These results indicated that the maximal pituitary response was obtained with 50 µg of the D-Ala⁶ or D-Leu⁶ analog but that 500 µg of LH-RH/FSH-RH was required before maximal LH release was attained. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science.