ADRENERGIC RECEPTORS OF THE BOVINE IRIS SPHINCTER

¹ College of Pharmacy, The Ohio State University, Columbus, Ohio

Bovine iris sphincter strips in vitro, under light tension (200 mg), slowly (2 to 3 hr) develop an inherent tone. In concentration-dependent fashion, (—)-isoproterenol, (—)-phenylephrine and theophyiline induced relaxation of this tissue. The ED5O values indicate that (—)-isoproterenol was some 300 times more active than (—)-phenylephrine. Sotalol (3 x 10^-7 M to 10^-5 M, 30 min) produced effective blockade of adrenergic inhibitory effects, whereas propranolol produced little or no blockade. It is suggested that inhibitory beta adrenergic receptors in this tissue discriminate between the two antagonists. The inhibitory effect of theophylline was not affected by either blocker. Phentolamine (10^-5 M, 30 min) potentiated slightly the effects of phenylephrine but did not affect the responses to isoproterenol. Although slight excitatory alpha adrenergic effects of phenylephrine could be demonstrated in the presence of sotalol, it appears that the bovine iris sphincter contains mainly inhibitory beta adrenergic receptors.