Hypothalamic Regulation of Growth Hormone Secretion

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Abstract
To investigate neural control of growth hormone (GH) secretion, the effect of hypothalamic lesions on resting GH plasma concentrations and GH response to insulin-induced hypoglycemia was studied in squirrel monkeys. Plasma GH was determined by radioimmunoassay using a human growth hormone system. In 9 control animals with small lesions in the frontal cortex, hypoglycemia induced by the intravenous injection of insulin, 0.15 U/kg body wt, led to an acute rise in GH. Of 16 animals with lesions in various basilar brain structures, 8 had either markedly reduced or completely blocked GH responses to hypoglycemia. Anatomical analysis of the site of the lesions suggests that the anterior median eminence, central median eminence and pituitary stalk mediate reflex GH discharge. Resting levels of GH were not altered by hypothalamic lesions, a finding which is indicative of a reasonable degree of autonomy of basal GH secretion. During the first hr. of the insulin tolerance test, blood sugar changes had a similar magnitude of response in animals with and animals without hypothalamic damage. These results indicate that the GH which is discharged reflexly during the 1st hr. of the insulin tolerance test is probably not an essential part of the mechanism for the immediate restitution of the blood sugar.