Differential effects of selective alpha 1- and alpha 2-adrenoceptor agonists on intraocular pressure in the conscious rabbit.

In the present study the influence of topically applied selective alpha 1- and alpha 2-adrenoceptor agonists on intraocular pressure and the diameter of the pupil was investigated in conscious rabbits. Selective stimulation of the alpha 1-subtype of receptors induced an elevation in intraocular pressure, accompanied by mydriasis, whereas stimulation of the alpha 2-subtype caused a marked and dose-dependent ocular hypotensive response, which could be blocked by the selective alpha 2-adrenoceptor antagonist yohimbine. After application of the non-selective alpha-adrenoceptor agonist clonidine the alpha 2-adrenoceptor mediated decrease in IOP is probably counteracted by a pressor effect due to the stimulation of alpha 1-adrenoceptors.