Extraocular rectus muscles of the rabbit contain α2-and β2-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 α2-agonist B-HT 920, and with the β2-agonist terbutaline. No effect was seen from α1-and β1-agonists. The presence of α2-and β2-receptors was confirmed in experiments with selective and non-selective adrenergic antagonists. The lack of α1-receptors in EOM and the absence of a hypertensive peak after topical α2-and β2-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.