Non-homogeneous distribution of beta 1- and beta 2-adrenoceptors in various human tissues

The distribution of beta 1- and beta 2-adrenoceptor subtypes was determined in membranes obtained from the right atrium, abdominal fat pad, kidney, lung and liver of each of three human subjects. The number of each beta-adrenoceptor subtype was calculated by nonlinear least-squares computer analysis of the competition curve of (-) [125I]iodocyanopindolol (125I-CYP) binding, using beta 1-selective antagonist CGP 20712A and beta 2-selective antagonist ICI 118,551. Competition studies using CGP 20712A indicated that both beta 1- and beta 2-adrenoceptor subtypes coexist in all five tissues, with marked difference in the relative proportion of beta 1- and beta 2-adrenoceptors among these tissues. Most notably, the existence of beta 1-subtypes could be clearly shown in the lung (27%) and liver (18%); according to previous reports, beta 2-subtypes are found almost exclusively in the lung and liver in humans. Regarding the kidney, the present results (beta 2-subtypes: 68%) also differed from previous human data in that beta 1-subtypes predominated. Consistent results were obtained in experiments with ICI 118,551. These results provide a new insight into the mechanisms by which catecholamines regulate a particular beta-adrenergic function in these tissues.