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Secretion of Prostaglandin F₂ in Cycling and Pregnant Ewes^{1, 2,}

Colorado State University⁶, Fort Collins 80523

Abstract

Indwelling cannulas were placed into a branch of the uterine vein and into the utero-ovarian vein of 10 nonpregnant ewes and into the utero-ovarian vein only of eight pregnant ewes. Blood samples were collected into chilled, heparinized tubes at 3-hr intervals from days 11 to 14 (three pregnant and five cycling ewes) or from days 14 to 17 (five pregnant and five cycling ewes) after estrus. Levels of prostaglandin (PG) F₂ were determined by radioimmunoassay. No significant difference was noted in mean levels of PGF₂ in the utero-ovarian vein between cycling (9.1 ± .6 ng/ml, n=458) and pregnant (8.1 ± .1 ng/ml, n=386) ewes. However, there was more variation (P<.01) in levels of PGF₂ in cycling ewes than in pregnant ewes. This was reflected by a greater number (P<.01) of peaks (any value greater than two standard deviations above the daily mean) of PGF₂ in cycling ewes than in pregnant ewes (32 vs 12). There was no significant difference in magnitude of peaks between cycling (41.3 ± 5.1 ng/ml) and pregnant (25.3 ± 7.4 ng/ml) ewes. It is suggested that decreased numbers of peaks of PGF₂ may be involved in the mechanism responsible for luteal maintenance in pregnant ewes.

¹ The authors are indebted to Dr. Kenneth Kirton of the Upjohn Co., Kalamazoo, Michigan, for supplying the antiserum to prostaglandin F₂ and for the prostaglandin F₂-tham salt used as a standard for the radioimmunoassay. The authors also wish to express their gratitude to Mr. Vaughn Cook for his excellent technical assistance throughout these experiments. The critical review of this manuscript by Dr. Lloyd Faulkner is also greatly appreciated.

² Supported in part by NIH contract 69-2134 and a grant from G. D. Searle and Co.

³ NIH postdoctoral fellow.

⁴ Present address: U.S. Range Livestock Experiment Station, Miles City, Montana 59301.

⁵ Present address: Department of Endocrinology, Cook Country General Hospital, Chicago, Illinois 60612.

⁶ Department of Physiology and Biophysics.

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