Effect of domperidone on the release of insulin after intravenous glucose load in man.

To determine whether the blockade of the dopaminergic system is capable of modifying glucose-induced insulin release in man, the responses of insulin to an iv glucose load were measured at various domperidone infusion rates. The infusion of 5 micrograms/kg/min of domperidone increased significantly plasma insulin levels during the acute phase of glucose-induced insulin release and lowered plasma glucose values at 50 and 60 min; the k of glucose disappearance improved significantly. At lower domperidone infusion rates the acute increment of insulin after glucose load was indistinguishable from the response observed at 5 micrograms/kg/min until 0.5 microgram/kg/min, while similar responses in control and experimental tests were observed at 0.25 microgram/kg/min. A group of subjects was submitted to an arginine load in order to establish whether the effect observed with domperidone was specific for the glucose-induced insulin release; but, this time, we did not observe any significant effect during the domperidone-induced dopaminergic blockade. Furthermore, we also measured the plasma prolactin levels, to see whether the specific and well known effect of domperidone on prolactin release matches with the effect on beta-cell function. As far as prolactin is concerned, we observed a dose response effect of domperidone infusion, with a detectable elevation of prolactin at infusion rate of 0.25 microgram/kg/min. Since domperidone is a specific antagonist of dopamine D2-receptors, we propose that dopamine might exert a specific inhibiting effect on glucose-induced insulin release through this class of dopamine receptors.