Particularities of vascular reactivity of the conjunctiva and iris in rats.

Considering that the conjunctiva and iris are developed from different embryological origins, an analysis of any possible differences in the density and type of adrenoceptors between these two areas was tried. An experimental study on male adult Wistar rats was performed. Six groups (six rats per group) were used by recording the iris and conjunctival vessels after eye instillations with solutions of adrenaline 0.1%, isoprenaline chlorhydrate 0.00002% and distilled water. The image analyze were carried out using VirtualDub 1.5.1 and Adobe PhotoShop 6.0., measuring the variations of the vessels diameters before and after the solutions instillations at fixed time intervals. The means of each eye values were compared with the control value using a statistical significance T test. The analysis of the two groups treated with adrenaline 0.1% showed a different reactivity of the vessels from the conjunctiva and iris, respectively. The iris vessels performed a gradual vasoconstriction. On the contrary, the conjunctival vessels showed initially mild, but significant vasodilatation, while vasoconstriction started later and was not as intense as for the iris vessels. The iris vessels treated with isoprenaline 0.00002% showed no significant changes in the vascular diameters. On the contrary, the conjunctival vessels showed a significant vasodilatation. The differences in the vascular reactivity of the two ocular areas (conjunctiva and iris) to vasoactive amines (epinephrine, isoprenaline) support the idea that beta 2 adrenergic receptors are present only in conjunctiva vessels but not in iris vessels, while alpha adrenoceptors are present in both vascular territories.

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.