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Pituitary and Blood Plasma Levels of Gonadotropin after Ovariectomy of Heifers¹

Michigan State University, East Lansing 48823

Abstract

Pituitary and blood plasma gonadotropins were determined in 25 heifers killed at 3, 7, 15, 30 or 60 days after ovariectomy. Relative to unoperated controls, pituitary weight was unaffected, but pituitary FSH was doubled at 60 days after ovariectomy. Pituitary prolactin remained unchanged for 7 days, increased 60% at 30 days and returned to control levels at 60 days, while pituitary LH generally declined following ovariectomy. Levels of plasma prolactin declined 3 days after ovariectomy and fluctuated greatly during the next 2 months, but never significantly exceeded control levels. In contrast, plasma LH increased within 3 days, and plateaued 30 and 60 days after castration at levels twice those of unoperated controls. While levels of pituitary and plasma prolactin were generally positively related after ovariectomy comparable levels of LH were generally negatively related.

¹ Agricultural Experiment Station Journal Article No. 5149. Supported by U.S.P.H.S. research grant No. HD-03039.

² Animal Reproduction Laboratory, Dairy Department.

³ Present address: Reproduction Research, The Upjohn Company. Kalamazoo, Michigan 49001.

⁴ Present address: Animal Science Department. Rutgers University, New Brunswick, N. J. 08903.