TRH-lnduced Growth Hormone (GH) Release in Rats of Both Sexes: Changes in Pituitary Response after Gonadectomy and During the Estrous Cycle

In both intact adult male and female rats anesthetized with tribromoe-thanol, the iv injection of thyrotropin-re-leasing hormone (TRH) evoked GH release within 2 min following the injection. The GH response to TRH was greater in males than in females and this response was significantly diminished by short-term (6 days) orchidectomy. In females, the GH response to TRH was maximal in estrus and minimal in diestrus day 2, showing intermediate values at proestrus and diestrus day 1. Long-term ovariectomy decreased the response. Pituitary GH content and concentration were higher in males than in females. Orchidectomy was followed by a significant decrease in pituitary GH values, whereas ovariectomy resulted in increased GH content and concentration. The results indicate that the gonads can modify pituitary GH response to TRH and, therefore, play a physiological role in modulating the stimulatory effect that the hypothalamus exerts on GH release through the secretion of substances with GH-releasing activity. We appreciate the technical assistance of Miss Helen Jameson. We also thank Miss Cheri Reimann for secretarial assistance.