Effects of Dl- and l-propranolol, labetalol, and phentolamine on rabbit iris blood flow determined by hydrogen clearance method.

In rabbits anesthetized with urethane, blood flow in the iris and the eye lid was 104.0 to 120.0 and 96.6 to 112.4 ml/min/100 g tissue (determined by the hydrogen clearance method), respectively. Dl-propranolol (1.0 mg/kg, i. v.) or phentolamine (0. 5 mg/kg, i. v.) decreased blood flow in both iris and eye lid to a similar degree, and also decreased blood pressure. Neither saline solution (0.5 ml/kg, i. v.) nor d-propranolol (1.0 mg/kg, i. v.) changed blood flow in both iris and eye lid and blood pressure. Labetalol (1.0 mg/kg, i. v.) decreased blood flow in the iris markedly and that in the eye lid moderately with a moderate decrease in blood pressure ; blood pressure/iris blood flow ratio increased significantly without changes in blood pressure/eye lid blood flow ratio. None of the drugs tested changed pupil size of the anesthetized rabbits. It is suggested that labetalol decreases iris blood flow because of blood pressure decrease plus other mechanisms that might be different from alpha- and beta-adrenergic blockade.