Effects of alpha 1 and alpha 2 activation of adrenergic receptors on aqueous humor dynamics.
Effects of phenylephrine (alpha 1-adrenergic agonist), prazosin (alpha 1-adrenergic antagonist), clonidine (alpha 2-adrenergic agonist), and yohimbine (alpha 2-adrenergic antagonist) on aqueous humor (AH) dynamics were studied with a cat eye model. Phenylephrine (130 microgram/ml) inhibited AH outflow (67% at 90 min. period) more than AH formation (26% at the same period) indicating the intraocular pressure (IOP) might be raised by the administration of phenylephrine. Prazosin (0.1 microgram/ml) produced effects opposite to those of phenylephrine (55% reduction of AH formation and 25% reduction of AH outflow at 3 hr. period) suggesting the alpha 1-adrenergic receptor is responsible for increases rather than decreases of IOP. Both clonidine (10 microgram/ml) and yohimbine (0.1-1.0 microgram/ml) inhibited AH formation (60% inhibition) more than AH outflow (no inhibition for clonidine and 40% inhibition for yohimbine) to lower IOP. The conventional theory of receptor antagonism does not seem to function at alpha 2-receptor sites.
D000818:Animals; D001082:Aqueous Humor / Q000378:metabolism*; D002415:Cats; D003000:Clonidine / Q000494:pharmacology; D007429:Intraocular Pressure / Q000187:drug effects*; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D015016:Yohimbine / Q000494:pharmacology
D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D003000:Clonidine; D011224:Prazosin