Hypotensive effect of labetalol on intraocular pressure in rabbits: in relation to its alpha- and beta-adrenergic blocking action on the cardiovascular system.
Rabbits anesthetized with urethane were used. Labetalol was found to be about 3.7 times less potent than phentolamine in blocking phenylephrine-induced vasopressor response, and about 7.6 times less potent than propranolol in blocking isoproterenol-induced vasodepressor response. Labetalol (0.3, 1.0 and 2.5 mg/kg, i.v.) decreased both intraocular pressure (IOP) and mean arterial blood pressure (BP) significantly, and also decreased IOP/BP ratio. Propranolol (1.0 and 2.5 mg/kg, i.v.) reduced both IOP and BP slightly without affecting the IOP/BP ratio. Phentolamine (1.0 mg/kg, i.v.) reduced both IOP and BP significantly, but it did not alter the IOP/BP ratio. When both propranolol (1.0 mg/kg, i.v.) and phentolamine (1.0 mg/kg, i.v.) were injected at the same time, IOP and BP were reduced with a decrease in IOP/BP ratio. These findings suggest that labetalol is effective in decreasing the IOP, although the mechanism of the drug action cannot be explained simply by alpha- and beta-adrenergic blockade.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D004983:Ethanolamines / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D007429:Intraocular Pressure / Q000187:drug effects*; D007741:Labetalol / Q000494:pharmacology*; D008297:Male; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*
D004983:Ethanolamines; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D011433:Propranolol; D007741:Labetalol; D010646:Phentolamine