Somatostatin: A Physiological Role in the Regulation of Growth Hormone Secretion in the Adolescent Male Baboon*

Abstract

Insulin and GH [growth hormone] secretion patterns were surveyed in 4 adolescent male baboons [Papio cynocephalus] before and after active immunization against cyclic somatostatin. Before immunization, an ultradian GH rhythm with an interpeak interval of 4.1 .+-. 0.33 (SE) h was observed during a 12 h daylight sampling period. The rhythm was characterized by 2- to 12-fold increases in serum GH concentration; each burst was maintained over 3.15 .+-. 0.25 h. After immunization, baseline serum GH concentration was increased and episodic bursts of GH secretion were markedly diminished. The total integrated areas over 12 h did not differ between the control and postimmunization studies. A comparison of the autocorrelation analyses of GH secretion before and after active immunization revealed that the immunization procedure effected a disruption of the synchronous ultradian GH rhythm observed before treatment. Basal plasma insulin and glucose concentrations were observed in overnight-fasted subjects. There was no apparent effect of the immunization procedure on the mean plasma concentrations of either insulin or glucose. The immunization procedure did not alter patterns of the plasma insulin and glucose concentrations observed during i.v. arginine infusion or glucose tolerance testing. Blood-borne somatostatin contributes significantly to the physiological regulation of GH secretion in the adolescent male baboon; however, it was not possible to obtain evidence to support the hypothesis that circulating somatostatin is important in the dynamics of insulin/glucose regulation in this primate species.