Extraocular rectus muscles of the rabbit contain alpha 2- and beta 2-adrenergic receptors

Selective and non-selective adrenergic drugs were given to isolated extraocular rectus muscles (EOM) of rabbits to differentiate its postjunctional adrenergic receptors. Without precontraction none of the adrenergic agents had significant effects, but after cholinergic precontraction of the muscles a further contraction could be obtained with the non-selective agonists epinephrine, norepinephrine and isoproterenol, with the alpha 2-agonist B-HT 920, and with the beta 2-agonist terbutaline. No effect was seen from alpha 1- and beta 1-agonists. The presence of alpha 2- and beta 2-receptors was confirmed in experiments with selective and non-selective adrenergic antagonists. The lack of alpha 1-receptors in EOM and the absence of a hypertensive peak after topical alpha 2- and beta 2-agonists in vivo does not support the assumption that the initial rise in intraocular pressure (IOP) after topical epinephrine is produced by contraction of EOM.