EFFECTS OF PERGOLIDE AND DOMPERIDONE ON INSULIN AND GLUCOSE PLASMA-LEVELS AFTER A GLUCOSE-LOAD

Dopaminergic modulation of insulin secretion is still unclear and the results of experiments with various dopaminergic agonists and antagoni sts are conflicting. The effects of the D-1 and D-2 agonist, pergolide (1 mg orally) and the D-2 antagonist, domperidone (100 mg orally), on insulin and glucose plasma levels after a glucose load was explored i n eight healthy volunteers. Also studied were the combinations of domp eridone with either atenolol (100 mg orally) or nifedipine (10 mg subl ingually), and the glucose load with placebo pretreatment for the gene ration of control data. A cross-over randomized sequence design was fo llowed, allowing at least two weeks between the five study sessions. P er-golide pretreatment resulted in significantly higher glucose and in sulin blood levels. Pretreatment with domperidone and domperidone plus nifedipine (but not with the domperidone-atenolol combination) tended to increase the insulin levels, but this was not statistically signif icant. Against the background of extensive evidence from the literatur e, it may be postulated that stimulation of the D-1-receptor facilitat es insulin secretion, whereas that of the D-2-receptor inhibits glucos e disposal. The non-significant increase in insulin levels with D-2 bl ockade could have been due to the release of counter-regulatory hormon es, including dopamine, or have resulted from inactivation of K+ chann els in the beta-cell membranes.