Glucagon-free insulin in doses of 0.003 to 0.2 units per kilogram of body weight was infused into the pancreatic artery and portal vein during anesthesia or in fully recovered dogs. The changes in blood glucose concentrations were not significantly different between the two sites of infusion with any of the doses employed. These data indicate that insulin does not affect endogenous insulin secretion by a direct pancreatic mechanism. It may operate by reducing the blood glucose or via some other metabolic change. Similar experiments were conducted with glucagon (0.2 μg.) in anesthetized dogs. Glucagon infusion into the pancreas or liver failed to affect insulin or glucagon secretion as evidenced by peripheral venous glucose response.

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