The Effect of Subcutaneous Administration of Synthetic Luteinizing Hormone Releasing Factor on Plasma Gonadotropins and Prolactin in the Rat

Abstract

Summary

The effect of subcutaneous injection of synthetic LRF was evaluated in normal and castrated rats under tribromoethanol (TBE) anesthesia. The procedure of anesthetization with TBE followed by injection and bleeding produced no change in plasma LH in intact males, but a decline followed by a rebound to initial levels in castrates. FSH levels showed a delayed rise in the intact animals and a decline followed by return to initial values in the castrates. In both intact and castrate animals, prolactin levels declined acutely and remained low throughout the experiment. Subcutaneous administration of LRF produced a dose-related acute release of LH in intact and castrate males. The response was prolonged compared to that observed in previous studies following intravenous administration of the peptide. Minimal and delayed FSH release occurred following high doses of 100 or 500 ng of the peptide in intact animals, but dose-related increases of considerable magnitude took place in the castrates. In general, responses in terms of FSH release were more sluggish than those obtained with LH. The peptide had no clear effect on the release of prolactin in these animals as judged by its failure to alter plasma prolactin concentration. It is concluded that subcutaneous administration of LRF is a convenient way to provoke gonadotropin release and that the responses are quite prolonged, mimicking the effects observed following infusion of the peptide.

The authors thank Drs. C. P. Fawcett and L. Krulich for supervision of the radioimmunoassays. The skillful technical assistance of Mrs. Glenda Roberts, Sue Cohen, and Thelma Criddle is gratefully acknowledged. We thank Miss Cheri Reimann for secretarial assistance.