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Relationships between LH and Estradiol-17β after Removal of Luteal Progesterone in the Ewe¹

West Virginia University², Morgantown 26506

Abstract

Three experiments were conducted to examine the relationship between systemic concentrations of luteinizing hormone (LH) and estradiol-17β (E₂) after withdrawal of progesterone in cycling ewes. In Exp. 1, ewes were assigned randomly to one of three treatments: laparotomy (C), removal of the luteal ovary (ULO), or ULO plus anesthesia with sodium pentobarbital for 6 h beginning 4 h after surgery. Anesthesia was used in an attempt to block the expected increase in tonic secretion of LH. Patterns of LH and E₂ in these three groups did not differ during the 24-h experimental period. In Exp. 2, a longer period of anesthesia was utilized. Forty-eight ewes were assigned at random to one of four treatments: C, ULO, lutectomy or an intrafollicular injection of prostaglandin F₂ (PGF₂). One-half of the ewes in each group were anesthetized with sodium pentobarbital from initiation of treatment (0 h) until 10 h after surgery. Sodium pentobarbital did not suppress the increases in LH and E₂ after progesterone withdrawal. The regression of concentrations of E₂ on concentration of LH was not significant. In Exp. 3, ewes were infused with either saline or dopamine after receiving an im injection of PGF₂. Tonic secretion of LH increased after 4 h in ewes infused with saline, but not in ewes infused with dopamine. Despite the suppression of LH, concentrations of E₂ increased in dopamine-treated ewes as in control ewes. Therefore, the initial increase in E₂ after a decline of progesterone in cycling ewes is independent of increases in LH.

¹ Published with the approval of the Director of the West Virginia Agr. and Forestry Exp. Sta. as Scientific Paper No. 1823. Supported by Hatch Project 224 (NE-72). The authors thank Dr. R. L. Butcher for the antisera for progesterone and estradiol-17β, Dr. G. D. Niswender for the ovine LH antisera (GDN #15), Dr. L. Reichert for the purified ovine LH (LER 1374-A) used for iodinations, and Dr. W. V. Thayne for assistance in the statistical analysis.

² Division of Anim. and Vet. Sci.