A probe for a histaminergic component of drinking in the rat

Systemic antagonism of H1 or H2 receptors for histamine attenuated drinking elicited by SC 20 mg/kg histamine in adult male Sprague-Dawley rats. The H1 antagonist dexbrompheniramine (DXB; 0.5-16 mg/kg) and the H2 antagonist cimetidine (C; 0.5-100 mg/kg) each inhibited drinking elicited by histamine when given IP 10 min prior to SC histamine: The lowest doses to produce a statistically significant inhibition of drinking were 2 mg/kg DXB and 32 mg/kg C. While 1 mg/kg DXB alone or 16 mg/kg DXB plus 16 mg/kg C virtually abolished drinking elicited by histamine (1.25-20 mg/kg) in a dose-response study. In addition, such combined antagonism of H1 and H2 receptors failed to elicit drinking in the absence of exogenous histamine and failed to inhibit drinking elicited by deprivation from water for 7 or 24 hr. Because combined systemic antagonism of H1 and H2 receptors can specifically and completely inhibit drinking elicited by exogenous histamine, these findings provide a probe for a histaminergic component of drinking in the rat.