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The relationship between insulin and the glucose-glucagon feedback mechanism was studied by testing the effectiveness of various routes, doses and timing of insulin administration prior to and during a glucose tolerance test in Peking ducks made transiently diabetic by subtotal pancreatectomy. Insulin injections or infusions given either before, or only during the glucose load, did not restore the A-cell response to glucose. Yet, if given both before and during the glucose test, in conditions which mimic the physiological basal insulin level and its variations (with, initially, intramuscular injections of 0.2 IU/kg and 8 mug/kg glucagon, every six hours, and then an intravenous injection of 3.6 mU/kg plus an infusion of 0.9 mU/kg/minute for one hour), the normal glucagon response to glucose was re-established. Insulin must therefore be present, both before and during glucose stimulation, for glucose to be effective as an A-cell suppressor.

Prof. P.A. 13astenie) l~e~u le 80ctobre 1969Dextran.coated charcoal radioimmunoassay of glucagon Summary. A dextran-coated charcoal radioimmunoassay of glucagon is described. Antigen (1~1 or 12~I-glucagon, 0.060 ng) --antibody (rabbit antiserum 1 : 550, final dilution 1:6600) reactions reached equilibrium within 3 days at 4 ~ C. The use of a proteinase inhibitor (Trasylol) prevented incubation damage of the immunoreaetive glueagon. The sensitivity of the assay (< to 0.020 ng) corresponds to about 0.100 ng/ml of plasma. The precision, the reproducibility, the specificity of the assay and some problems related to the dextran-chareoal separation have been studied. Recovery of ghcagon added go plasma was approximatively 90%. The mean glucagon concentration measured in peripheral venous plasma was 0.208 ng/ml in normal human subjects after an overnight fast, 0.396 ng/ml in anaesthetized dogs after an overnight fast, 0.354 ng/ml in fed rats and 0.909 ng/ml in the overnightfasted duck. Up go now, the use of the assay seems go be restricted go studies of glueagon secretion in vitro since our antisermn cross-reacts with a material extracted from the duodenum. The relative contribution of this material in the plasma glucagon determinations remains, however, go be established.