EFFECT OF GONADAL STEROIDS ON HYPOTHALAMIC LUTEINIZING HORMONE RELEASING HORMONE (LH-RH) CONTENT IN GONADECTOMIZED RATS

PRAKONG CHOBSIENG

Summary: The amount of LH-RH in the hypothalamus and serum levels of gonadotrophins in rats under various experimental manipulations were determined by radioimmunoassay. There were no significant changes in hypothalamic LH-RH content during the period of the preovulatory gonadotrophin surge. Orchidectomy or ovariectomy decreased hypothalamic LH-RH content by 75-80% and simultaneously elevated serum levels of LH and FSH. Daily administration of testosterone 100 g/100 g body weight} or estradioI benzoate (EB; 5 g/100 g body weight) to orchidectomized rats for 7 days, increased hypothalamic LH-RH content and reduced gonadotrophin release. A single injection of EB (50 g/rat) to ovariectomized rats increased hypo thalamic LH-RH content three days later, while serum levels of LH and FSH fell. Testosterone and progesterone had no such effect. These results suggest a negative feedback action of testosterone and EB on gonadotrophin release via hypothalamic LH-RH release.

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Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 5, Thailand

Received 13 October 1976