Human ciliary process adrenergic receptor: pharmacological characterization.

To better understand the nature of interaction of various amines with adrenergic receptors in te human ciliary process, beta-adrenergic-stimulated adenylate cyclase activity was characterized in broken cell preparations of this tissue from donor eyes. Among various agonists, isoproterenol was the most potent activator of enzyme activity (Ka = 3.4 x 10(-7)M), followed in order by epinephrine (Ka = 2.7 x 10(-6)M), norepinephrine (Ka = 2.1 x 10(-5)M), and phenylephrine (Ka greater than 10(-4)M). Isoproterenol-stimulated enzyme activity was blocked by timolol (Ki = 3.4 x 10(-9)M), IPS 339 (Ki = 4.4 x 10(-9)M), H35/25 (Ki = 6.9 x 10(-7)M), and atenolol (Ki = 1.4 x 10(-5)M). These pharmacological characteristics indicate that the human ciliary processes contain a predominance of beta2-adrenergic receptors. The findings are relevant to physiological studies of aqueous humor secretion and to the potential development of adrenergic agents with greater specificity for the beta-adrenergic receptor.