Effects of adrenergic agonists upon regional ocular blood flow in normal and ganglionectomized rabbits

Radioactive microspheres were used to measure changes in regional ocular blood flow 30–45 min after the topical application of epinephrine, norepinephrine, phenylephrine, and isoproterenol, to both normal and ganglionectomized rabbits. In normal animals, epinephrine (4%), phenylephrine (8%), and norepinephrine (4%), in order of decreasing potency, caused significant reductions in blood flow to the iris and ciliary processes. Isoproterenol (4%) had no significant effect in these tissues. Ganglionectomized eyes received much lower drug concentrations (0·1% in all cases), and displayed a different order of responsiveness: phenylephrine caused a larger reduction in flow than epinephrine, and norepinephrine failed to provoke statistically significant change. None of the drugs affected choroidal blood flow in either normal or ganglionectomized animals, but retinal blood flow in ganglionectomized eyes was significantly reduced by phenylephrine or isoproterenol administration. Additional experiments, addressing epinephrine's effects at 3 hr after administration, demonstrated a restoration of flow to the ciliary processes and an increased iridial blood flow in both normal and ganglionectomized animals. This was accompanied by an increased flow to the choroid, and a reduced retinal blood flow in the ganglionectomized state.