Histamine-Induced Constriction and Dilatation of Rabbit Middle Cerebral Arteries in vitro: Role of the Endothelium

We studied the effects of histamine on perfused rabbit middle cerebral arteries in vitro. Intact and endothelium-denuded preparations were compared. Histamine caused concentration-dependent constrictions in intact vessels which were competitively inhibited by an H1 receptor antagonist. This constriction was potentiated by either H2-receptor blockade or endothelium denudation. The greatest potentiation was observed with intraluminal as opposed to extraluminal administration. The H1 receptor agonist pyridylethylamine induced similar concentration-dependent constriction in intact and denuded preparations. After pre-constriction, histamine, in the presence of an H1 receptor antagonist, dilated intact vessels to a maximum of 45.1 %, and endothelium-denuded vessels to a maximum of 22% (p 1 constrictory and H2 dilatory receptors, and that many of the H2 dilatory receptors are situated on the endothelial cells.