Beta-adrenergic receptor subtypes in iris-ciliary body of rabbits.

Direct comparison of drug interaction with intraocular relative to extraocular beta-adrenergic receptors was used to test the hypothesis that the receptors in ocular tissues are of the beta 2-subtype. Potencies for the displacement of 3H-dihydroalprenolol radioligand binding to membranes obtained from rabbit-iris ciliary bodies by beta-adrenoceptor agonists was in the order: isoproterenol greater than or equal to epinephrine greater than salbutamol greater than terbutaline greater than tazolol greater than norepinephrine. Similar radioligand displacement by beta-adrenoceptor antagonists was in the order of potency: alprenolol greater than or equal to bupranolol = oxprenolol = timolol = propranolol greater than ICI 118,551 = IPS 339 much greater than betaxolol greater than metoprolol. Finally, for the above beta-adrenoceptor antagonists, a highly significant correlation was obtained for displacement of radioligand to ocular tissues (pKi values) relative to antagonism (pA2 values) of isoproterenol-induced guinea-pig tracheal relaxation but not guinea-pig atrial chronotropic effects. Consequently, the above three observations reinforce the notion that rabbit-iris ciliary bodies contain beta-adrenergic receptors predominantly of the beta 2-subtype.