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.