Clonidine.

Clonidine hydrochloride has been demonstrated to produce vasoconstriction in the anterior segment of the cat eye. The mode of this action has been found to be due to direct stimulation of alpha-adrenergic receptors. In the intact, enucleated, arterially perfused eye, clonidine was found to decrease the rate of aqueous humor production. We suggest that clonidine, like hydroxyamphetamine hydrobromide, phenylephrine hydrochloride, and dopamine hydrochloride, decreases aqueous humor formation by constriction of afferent ciliary process blood vessels.