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Effect of Consecutive Injections of Synthetic Gonadotropin Releasing Hormone on LH Release in the Anestrous and Ovariectomized Ewe^{1, 2,}

Abbott Laboratories, North Chicago, Illinois 60064

Abstract

Four experiments were conducted to examine LH secretion in the anestrous and ovariectomized ewe to one or more intramuscular injections of synthetic gonadotropin releasing hormone (GnRH). In the anestrous ewe mean peak level of LH was 65 ±11 ng/ml after the initial injection of GnRH, but declined abruptly following a series of injections given at 24- or 48-hr. intervals. Increases in serum LH did not exceed 8 and 12 ng/ml, respectively, after the initial high response. Successive injections of GnRH at 96-hr, intervals resulted in LH release similar to that occurring after the initial dose of the releasing hormone. However, a linear decline in LH release occurred at an interval of 72 hr. between consecutive injections. Pituitary levels of LH and FSH were not influenced by GnRH treatment. Estrogen did not induce an LH surge in the anestrous ewe which had received GnRH for 7 consecutive days.

The LH response to GnRH in the ovariectomized ewe was rapid, reaching near-peak levels at 20 minutes.

¹ This research was supported in part by Contract No. NIH-NICHD-72 2722 with the National Institutes of Health, Department of Health, Education, and Welfare.

² The authors wish to thank Mr. R. L. Gendrich for his review of this manuscript and assistance with the statistical analysis of the data.