Effect upon Insulin Secretion of Physiologic Doses of Glucagon Administered via the Portal Vein

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Abstract
Rapid endoportal injections of glucagon in a dose (1 ug.) which does not elevate the arterial glucagon concentration beyond the physiologic range caused a prompt rise in both mean arterial glucose and pancreaticoduodenal insulin concentration to a peak six minutes later. Hyperglycemia of similar magnitude produced by intravenous glucose infusion failed to elicit as great a rise in insulin release. With smaller doses of glucagon a more variable response was observed; however, in some dogs doses of glucagon which were too small to cause a significant change in arterial glucagon concentration did cause a rise in both glucose and insulin levels. It is concluded that glucagon administered in physiologic doses via the portal venous system elicits a greater rise in insulin release than can be attributed to the concomitant hyperglycemia and, as suggested by others, does possess the qualifications of a potentiator of insulin secretion.