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Serum LH in Ewes Treated with Synthetic Luteinizing Hormone-Releasing Hormone/Follicle Stimulating Hormone-Releasing Hormone (LH-RH/FSH-RH) at Three Periods of Anestrus^{1, 2, 3,}

Washington State University⁴, Pullman 99163

Abstract

Ten anestrous ewes were assigned at random to two equal groups. Treatments consisted of a single intramuscular injection of either 50 µg synthetic luteinizing horome-releasing hormone/follicle stimulating hormone-releasing hormone (LH-RH/FSH-RH) in acidified saline or an equivalent volume of acidified saline. Blood samples were collected via jugular puncture immediately preceding and at 30 min intervals after treatment for a subsequent 8 hours. The previously described treatments were repeated three times at 45-day intervals and were designated as early (May 7), mid (June 21) and late (August 5) anestrus. Each ewe received the same treatment for all three stages of anestrus. All ewes were laparotomized before and after treatment to determine ovulation rate. Each serum sample was assayed for LH by a radioimmunoassay and the pretreatment samples for the LH-RH/FSH-RH group were quantitated for total estrogens by a radioimmunoassay. The mean heights of the peak LH found after LH-RH/FSH-RH treatment in early, mid and late anestrus were 70.8 ± 16.7, 64.8 ± 13.2 and 93.6 ± 20.0 ng/ml, respectively, and were significantly higher than control values. Pituitary responsiveness to LH-RH/FSH-RH was not different at the three stages of anestrus as indicated by lack of significant differences among mean peak serum LH concentrations. Mean serum total estrogen concentrations before treatment with LH-RH/FSH-RH were not significantly altered due to stage of anestrus. Endogenous estrogen levels before treatment did not appear to affect the response to LH-RH/FSH-RH as suggested by a correlation coefficient of r = –.243 between estrogen levels before treatment and peak serum LH response to LH-RH/FSH-RH. The circulating levels of estrogens in the anestrous ewes were very low and were measured at the lower limit of assay sensitivity. Thus lack of significant correlation between pretreatment endogenous estrogen levels and response to LH-RH/FSH-RH may not indicate lack of estrogen effect. One ewe out of five ovulated after LH-RH/FSH-RH treatment at each stage of anestrus compared to no ovulation in the saline treated ewes. None of the ewes including those which ovulated exhibited estrus after LH-RH/FSH-RH treatment.

¹ Scientific Paper 4085 College of Agriculture Research Center, Washington State University. Project 0137.

² The authors thank Dr. L. E. Reichert for LH used for iodination; Dr. W. White for antiovine LH serum, Dr. T. D. Nett and Dr. V. L. Estergreen for antiestrogen serum, Dr. Y. Baba of Sankyo Co. Limited of Japan for synthetic LH-RH/FSH-RH, Dr. A. Arimura and Dr. A. V. Schally for determining potency of LH-RH/FSH-RH and the Endocrine Study Section NIH for NIH-LH-S16 used for standards.

³ This study was supported in part by USPHS Grant from National Institute of Child Health and Human Development AM 06192.

⁴ Department of Animal Sciences.