Influencing vascular reactivity in vivo by histaminergic agonists and antagonists.

The eye is a target organ for the action of several topical or systemic drugs. The aim of the present study is to analyze the differences in reactivity between the iris and conjunctiva vessels after the topical administration of histamine and histamine receptor blockers respectively. Using a novel non-invasive technique for the quantification of the vascular diameters in the eye vessels, the response of these vessels to histamine, to H1 receptor blocker promethazine, and to H2 receptor blocker ranitidine versus vehicle (control) was analyzed. The results show differences in reactivity between iris and conjunctiva vascular territories. This data suggest that the population of histamine receptors differs between these two vascular areas.