Basal Plasma Glucagon Levels of Man*

The isolated perfused rat liver can serve as a bioassay system for glucagon, capable of detecting 10 mmug of this agent. Seven 15-ml plasma specimens obtained from different healthy volunteers after an overnight fast were assayed in this system; glucagon could not be detected in any of them, indicating concentrations significantly below 0.67 mmug per ml in all subjects. The effects of administering small doses of glucagon to patients were consistent with these results; imposition of increments to plasma glucagon concentration below 1 mmug per ml induced distinct and sustained increases in blood glucose. Observations of the biologic effects of glucagon, together with data on the rate of its inactivation by the liver, suggest that the basal concentration of this hormone in peripheral plasma probably does not exceed 0.1 mmug per ml.