Evidence against a humoral control mechanism in adrenal catecholamine secretion during insulin-induced hypoglycemia

The present study tested the hypothesis that a humoral control mechanism is involved in the enhanced adrenal catecholamine secretion during insulin-induced hypoglycemia. The experiments were carried out in anesthetized dogs in which neuronal and humoral components were simultaneously determined by measuring catecholamine output from the right innervated and the left acutely denervated adrenal gland, respectively. Different levels of hypoglycemia were induced by intravenous injection of insulin with doses of 0.075 (n = 6), 0.150 (n = 6), and 0.300 IU/kg (n = 6) in three separate groups of dogs. Catecholamine output in the right innervated gland increased dose dependently (P less than 0.05), reaching a maximum level 45 min after insulin administration. By contrast, catecholamine output from the left denervated adrenal gland remained unchanged at all doses tested. In sham-denervated animals (n = 7), catecholamine output from the left adrenal gland increased to a magnitude similar to that observed in the right innervated gland after insulin administration. Plasma glucose concentration significantly decreased in a dose-dependent manner, reaching a nadir 30 min after insulin administration. Maximum decreases in plasma glucose concentration could be strongly correlated with maximum increases in catecholamine output from the right innervated adrenal gland (r = -0.66, n = 18, P = 0.011), but not with those from the left denervated gland (r = -0.32, n = 18, P = 0.455). The present results do not support the functional existence of a humoral mechanism permitting the release of adrenal catecholamines during insulin-induced hypoglycemia.