Are beta-adrenergic mechanisms involved in ocular hypotensive actions of adrenergic drugs?

Specific beta 1- and beta 2-adrenergic agonists and antagonists were studied for their effects on aqueous humor dynamics in a cat model. Tazolol (beta 1-agonist) reduced formation of aqueous humor more than outflow, while metoprolol (beta 1-antagonist) reduced outflow more than formation. Both salbutamol (beta 2-agonist) and butoxamine (beta 2-antagonist) inhibited aqueous humor formation and aqueous humor outflow to an equal extent. It is concluded that the adrenergic mechanism is functioning only slightly, if at all, in affecting the intraocular pressure. On the other hand, receptor binding experiments on iris-ciliary body showed clearly that there are 40-fold and 281-fold differences in binding affinity of D- and L-isomers of timolol and propranolol, respectively. These results indicate that the adrenergic receptor mechanism does exist in the eye tissues but that it does not control intraocular pressure significantly.