Beta 1- and beta 2-adrenoceptor-mediated relaxation responses in peripheral arteries from spontaneously hypertensive rats at pre-hypertensive and early hypertensive stages.

Beta-adrenoceptor-mediated relaxation of isolated arteries from spontaneously hypertensive rats (SHR) was studied. The relaxation responses of the femoral arteries of pre-hypertensive SHR (PHSHR) to isoprenaline (ISO) and dibutyryl cyclic AMP were less than those of the age-matched tissues of rats of the Wistar-Kyoto strain (WKY). The responses of the mesenteric arteries of PHSHR to ISO and noradrenaline (NA) but not fenoterol (FEN) and forskolin were diminished when compared to those from the WKY tissues. The diminished relaxation response to ISO was observed in the SHR arteries with and without endothelial cells as compared to similar arteries from WKY. Relative potency ratios of ISO:FEN:NA and the Schild plot data for atenolol and butoxamine suggested that there were only beta 1-adrenoceptors and predominantly beta 2-adrenoceptors mediating relaxation in the femoral and mesenteric arteries, respectively. There was no difference in beta-adrenoceptor subtypes between the SHR and WKY arteries. The evidence in this study suggests that beta 1-adrenoceptor-mediated relaxation was diminished in the femoral and mesenteric arteries of PHSHR.