INHIBITING EFFECT OF SOMATOSTATIN ON GROWTH HORMONE RELEASE INDUCED BY ISOPRENALINE OR CHLORPROMAZINE IN RATS

Recent studies in animals have demonstrated that growth hormone (GH) secretion is controlled by GH releasing factor (GHRF) and GH inhibiting factor (somatostatin). Somatostatin has not only been purified from the ovine hypothalamus, but also syn-thesized (Brazeau, Vale, Burgus, Ling, Butcher, Rivier & Guillemin, 1973). It has been demonstrated recently that synthetic somatostatin suppresses the spon-taneous secretion of GH and the increase in plasma GH induced by i.v. injection of pentobarbitone in the rat (Brazeau, Rivier, Vale & Guillemin, 1974). We have previously reported that a single i.v. injection of isoprenaline or chlorpromazine causes a significant increase in plasma GH in the rat (Kato, Dupre & Beck, 1973). In the present experiment, we examined the effect of synthetic somatostatin (kindly supplied by Dr N. Yanaihara) on the response of plasma GH to isoprenaline or chlorpromazine in rats. Wistar strain male rats, weighing 180\p=n-\220 g, were housed in an air-conditioned room with a lighting scheme of 14 h light and 10 h darkness. Test substances were injected intravenously under urethane anaesthesia (150 mg/100 g body wt, i.p.) int