INSULIN AND CYCLIC AMP RELEASE BY ISOLATED-INCUBATED ISLETS OF LANGERHANS

There is general agreement that glucose-induced insulin release is mediated by a complex mechanism (Randle & Hales, 1972). It has also been postulated that cyclic AMP might play an important role in this process. However, conflicting results have been reported about the effect of glucose on cyclic AMP levels in the islets of Langerhans (Charles, Fanska, Schmid, Forsham & Grodsky, 1973; Cooper, Ashcroft & Randle, 1973). Since it has been shown that cyclic AMP release from the liver rather than its intracellular concentration is better related to some meta-bolic effects (Exton & Park, 1972), we felt that a similar correlation might exist in the \g=b\cell. The release of both insulin and cyclic AMP by isolated islets was measured in the presence of various glucose concentrations. Isolated islets were obtained from normal mice (C3HS strain) by collagenase digestion(Lacy & Kostianovsky, 1967). Ten islets were carefully selected and placed in tubes containing 0-2 ml Krebs-Ringer bicarbonate buffer, pH 7-4, with bovine serum albumin, 5 mg/ml, a pro¬ tease inhibitor (Trasylol: Bayer, 1000 kallikrein international units/ml) and glucose (0-6 or 3 mg/ml). This buffer was previously gassed with a mixture of 95%02: 5%C02 while a constant atmosphere of this gas mixture was maintained within the tubes throughout the incubation period. The incubation was carried out for 60 min at 37 °C in a shaking incubator