Histaminergic mechanism for drinking elicited by insulin in the rat

Sprague-Dawley male albino rats showed in a dose-response study a maximal drinking response to a 5 U/kg dose of SC insulin in a 2-hr test. Drinking elicited by 5 U/kg insulin was reduced to baseline (i.e., no insulin) level by combined antagonism of H1 and H2 receptors for histamine using IP 1 mg/kg dexbrompheniramine plus 16 mg/kg cimetidine. Antagonism of histamine receptors in this fashion was specific for drinking elicited by histamine because such antagonism reduced to baseline level drinking elicited by 2.5 mg/kg SC histamine, but failed to inhibit drinking after 8- or 24-hr water deprivation or drinking after 0.63 mg/kg SC serotonin (5-HT). These results demonstrate a histaminergic mechanism for drinking elicited by exogenous insulin which is consistent with the published report that exogenous insulin can release gastric mucosal histamine in the rat. Moreover, because eating is known to elicit the release of endogenous insulin, the results reported here suggest a working hypothesis that endogenous insulin is a component for drinking around mealtime in the rat.