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Plasma Progestins in Anestrous Ewes Treated with D-Leu⁶ Des GlyNH¹₂ ⁰-LHRH Ethylamide^{1 ,2,}

Washington State University^,3, Pullman 99164 VA Hospital and Tulane University School of Medicine^,4, New Orleans 70140

Abstract

Peripheral plasma progestin levels were used to assess luteal function in 13 anestrous ewes following induction of ovulation by use of D-Leu⁶-des GlyNH¹₂ ⁰-LHRH ethylamide (D-Leu⁶ LHRH). Progestin levels in jugular vein plasma were measured by competitive protein binding and compared to plasma progestin levels in these same ewes following natural ovulation. The number of ovulations in each ewe was determined by the presence of corpora lutea (CL) at laparotomy. Eight of 13 ewes ovulated after D-Leu⁶ LHRH treatment. In ewes which failed to ovulate (n=5), progestin levels remained <1 ng/ml. In treated ewes with one CL (n=3) and two CL (n=5), progestin levels increased from <1 ng/ml on Day 1 to 4.5 ± .5 (mean ± SE), and 5.4 ± .1 ng/ml, respectively, on Day 9, and decreased to <1 ng/ml on Day 15. In cycling ewes with one CL (n=4) and two CL (n=9), progestin levels remained at approximately 1 ng/ml on Days 0 through 3, and then increased slowly to 4.9 ± 1.0 and 4.9 ± .8 ng/ml on Days 9 and 11, respectively. In both cases progestin levels gradually declined to <3 ng/ml on Day 15. Progestin levels across days were similar in ewes that ovulated after treatment with D-Leu⁶ LHRH and in ewes that ovulated during the natural cycle. These data indicate that CL formed after D-Leu⁶ LHRH-induced ovulation are functional and appear comparable in terms of progestin secretion to CL formed after natural ovulation.

¹ Scientific Paper No. 4645. College of Agriculture Research Center, Washington State University, Pullman. Projects 0120 and 0137.

² The authors would like to thank J. K. Hillers for statistical advice in analyzing these data.

³ Department of Animal Sciences.

⁴ Endocrine and Polypeptide Labs.

⁵ Present address: Department of Animal Sciences, Ohio State University, Columbus 43210.