DISSOCIATION BETWEEN THE POTENCY AND REVERSIBILITY OF THE INSULINOTROPIC ACTION OF TWO MEGLITINIDE ANALOGUES

The non-sulphonylurea hypoglycaemic agent repaglinide is about one order of magnitude less potent, in terms of insulinotropic efficiency, than S3075, another meglitinide analogue. In the present study, the effects of these two drugs upon86Rb outflow,45Ca efflux and insulin release from prelabelled rat pancreatic islets were investigated in a perifusion system. At a concentration of 10μM, which is sufficient to evoke a maximal secretory response in incubated islets, both agents inhibited86Rb efflux from islets perifused in the absence ofD-glucose, and stimulated both45Ca efflux and insulin release from islets perifused in the presence of 6mMD-glucose. The stimulation of45Ca efflux from prelabelled islets was suppressed in the absence of extracellular Ca2+. The cationic and secretory response to repaglinide differed, however, from that evoked by S3075, in persisting for at least 20min after removal of the drug from the perifusion medium, whilst the changes in86Rb outflow,45Ca efflux and insulin release caused by S3075 were rapidly reversible. These findings indicate that there is no parallel between the insulinotropic efficiency of distinct meglitinide analogues, and the reversibility of their functional effects. Since a comparable dissociation was recently documented in the case of hypoglycaemic sulphonylureas, the present observations reinforce the view that distinct molecular determinants may rule the relative insulinotropic potency of sulphonylureas and structurally related meglitinide analogues, on one hand, and the reversibility of their biological action, on the other hand.