BETA-2-ADRENOCEPTORS IN RAT-LIVER MICROCIRCULATION

1. Rat liver sinusoids were observed by a microscopic in vivo transillumination method. The diameter of liver sinusoids and intrasinusoid erythrocyte flow velocities were measured quantitatively by a close‐circuit television technique. 2. Both isoprenaline and the selective β2‐adrenoceptor agonist terbutaline produced a concentration‐dependent dilatation of liver sinusoids and slowed erythrocyte flow velocity. The effects of isoprenaline and terbutaline were antagonized by propranolol but not by the selective β1‐adrenoceptor antagonist atenolol. Propranolol alone produced constriction of the liver sinusoids and increased erythrocyte flow velocity; these effects were not produced by atenolol. 3. The percentage dilatations produced by isoprenaline alone, isoprenaline in the presence of phenoxybenzamine and isoprenaline in the presence of phenylephrine‐induced constriction were similar. 4. It is proposed that the β‐adrenoceptors in liver sinusoids are of the β2‐type, and their physiological role was to counteract constrictor responses produced by a‐adrenoceptor activity. Copyright © 1979, Wiley Blackwell. All rights reserved