Studies on the Mechanism of Growth Hormone and Thyrotropin Responses to Somatostatin Antiserum in Anesthetized Rats*

Abstract

An i.v. administration of 1 ml sheep antiserum to somatostatin (anti-SS) resulted in marked increases of both serum GH [growth hormone] and TSH [thyrotropin ], with a peak 10-20 min after administration in male rats anesthetized with urethane or pentobarbital. Administration of anti-SS had no effect on serum PRL [prolactin]. Ablation of the basal medial hypothalamus abolished the rises of both serum GH and TSH after anti-SS administration. Injection [i.v.] of 1 ml rabbit TRH [thyroliberin] antiserum (anti-TRH) decreased serum TSH levels 15 min after injection, whereas injection of normal rabbit serum did not affect TSH levels. Serum TSH levels did not rise after injection of anti-SS in rats pretreated with anti-TRH. Pretreatment with anti-TRH did not affect the basel serum GH levels nor the anti-SS-induced GH release. The enhanced secretion of GH and TSH after anti-SS injections was not blocked by pretreatment with indomethacin, an inhibitor of prostaglandin synthesis. GH and TSH responses to anti-SS require an intact basal medial hypothalamus; TSH response to anti-SS is mediated by hypothalamic TRH; and the GH response may be mediated by hypothalamic GH-releasing hormone which is not TRH or prostaglandin.