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

Insulin and GH secretion patterns were surveyed in four adolescent male baboons 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 pr...