EFFECTS OF UREMIC PLASMA ON ALPHA-ADRENOCEPTOR AND BETA-ADRENOCEPTOR SUBTYPES

Responsiveness of adrenergic receptors is decreased in patients on mai ntenance hemodialysis. In this study we investigated whether uremic pl asma might affect adrenergic receptors. For this purpose we determined the effects of uremic plasma obtained from 10 patients on hemodialysi s treatment (mean age 61 +/- 3 years, dialysis frequency 3 x 4 h/week, duration of treatment 3 +/- 1 years) before and at the end of the 4-h our dialysis treatment on binding of radioligands to beta(1)- and beta (2)- as well as alpha(1)- and alpha(2)-adrenoceptors. Plasma from 6 he althy volunteers served as control; the plasmas were studied in three dilutions: undiluted, 1:1 (v/v) and 1:4 (v/v) with saline diluted. Pla sma from healthy control did not significantly affect the number of be ta(1)- and beta(2)- or alpha(1)- and alpha 2-adrenoceptors. On the oth er hand, uremic plasma significantly decreased the number of beta(1)- and beta(2)-adrenoceptors; this inhibitory effect was also observed wh en plasma obtained at the end of the 4-hour dialysis treatment was inv estigated. On the other hand, uremic plasma did not significantly decr ease the number of alpha(1)- and alpha(2)-adrenoceptors. We conclude t hat in patients on maintenance hemodialysis, the presence of inhibitor y substance(s) in uremic plasma could be - at least partly - responsib le for the beta-adrenoceptor hyporesponsiveness; the mechanism leading ot alpha-adrenoceptor hyporesponsiveness, however, remains to be eluc idated.