Abstract
It has been postulated that propranolol lowers the intraocular pressure by adrenergic neurone block. However, in the isolated iris of albino rabbits, there was only a small degree of cocaine-sensitive (i.e., neuronal) accumulation of 3H-(-)-propranolol, and none at all after pretreatment of the animals with reserpine. Moreover, after preloading of the iris with 3H-(-)-propranolol, veratridine failed to release any labelled material. Hence, any adrenergic neurone blocking action of propranolol is highly unlikely. Albino and pigmented irides were first exposed to 3H-(-)-propranolol and then washed out. The results and their compartmental analysis indicated an extensive binding of 3H-(-)-propranolol in or at pigment cells; the binding is characterized by a low dissociation constant. It is very likely that the initial binding and the subsequent slow dissociation from pigment cells explains the long duration of action of beta-adrenoceptor antagonists in human therapy.
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