- Plasma GH and cortisol responses were examined in unanesthetized adult male rhesus monkeys infused with approximately 30 ml (8.3 ml/kg) of arginine monohydrochloride (Arg 0.5 g/kg), 0.9% saline (NS) or Dextran 75 and following 15 ml infusions of acid-saline (AS), or somatostatin (GHRIH 30 mug/kg). None of the infusions were accompanied by GH elevations. Rebound GH elevations occurred after each 30 ml infusion and after GHRIH but not after 15 ml AS. Although the amplitude of GH responses were not significantly different (p greater than 0.05), responses to Arg and dextran were significantly delayed as compared to responses following NS and GHRIH which did not differ from each other. Both of the latter responses occurred within 15 min of infusion completion. The delay following dextran was significantly longer than that following Arg (p less than 0.05). Since the volume of saline and the dosage of Arg were equivalent to those used in the standard intravenous Arg test, results suggest that effects of infusion volume upon GH secretion and upon GH responses to Arg warrant examination in the human. In addition, it is suggested that GH responses to NS and to dextran are mediated via an intravascular volume control mechanism and that GHRIH may be released upon activation of such a mechanism. GH elevations may represent rebound responses upon termination of GHRIH secretion.