Histaminergic vasodilation of intracerebral arterioles in the rat.

Histamine from various sources is found in significant amounts around cerebral vessels and may play a significant role in controlling CBF. The effect of histamine on the intracerebral microcirculation has not been examined. We have used an in vitro technique for the isolation and cannulation of intracerebral arterioles from the rat to study the effect of histamine on the spontaneous tone developed by these vessels. Extraluminally administered histamine caused dose-dependent vasodilation of isolated intracerebral arterioles with a maximal dilation of 139 +/- 2.4% of control diameter. The dilation was blocked by the H2 receptor antagonist cimetidine, but was only incompletely attenuated by the H1 receptor blocker chlorpheniramine. Histamine effects a dilation of the spontaneous tone of intracerebral resistance vessels, which is mediated by H2 receptors.