Impairment of the low-affinity state beta1-adrenoceptor-induced relaxation in spontaneously hypertensive rats

Abstract

1 In hypertension, a decrease of the vascular beta-adrenergic relaxation has been described. However, the specific involvement of each beta-adrenoceptor (beta-AR) subtype, in particular the low-affinity state of beta1-AR, has not yet been evaluated. We investigated whether the low-affinity state of beta1-AR-induced relaxation was impaired in Spontaneously Hypertensive Rats (SHR). 2 The relaxant responses to CGP 12177 and cyanopindolol, low-affinity state beta1-AR agonists (with beta1-/beta2-AR antagonistic and partial beta3-AR agonistic properties) were evaluated on thoracic aortic rings isolated from 12-weeks-old Wistar Kyoto rats (WKY) and SHR. 3 In WKY, CGP 12177 and cyanopindolol produced an endothelium and nitric oxide (NO)-independent relaxation. CGP 12177-induced endothelium-independent relaxation was not modified either by beta1-, beta2-AR (nadolol) or beta3-AR (L-748337 or SR 59230A) antagonists but was significantly reduced by high concentrations of CGP 20712A (P<0.05). This relaxation was also reduced by adenylyl cyclase inhibitors, SQ 22536 or MDL 12330A. 4 In SHR, CGP 12177 produced mainly an endothelium and NO-dependent relaxation. This effect was not modified by nadolol, but was strongly reduced by beta3-AR blockade. Endothelium-independent relaxation to CGP 12177 was not altered by adenylyl cyclase inhibition, but was amplified in preparations from pertussis toxin-pretreated SHR. 5 The immunohistochemical analysis revealed an upregulation of beta3-AR in the endothelial layer of SHR aorta, whereas the beta3-AR-induced relaxation was not modified. 6 In conclusion, we demonstrated an impaired low-affinity state of the beta1-AR-induced relaxation and an upregulation of the beta3-AR in hypertension. Some clinical implications of those findings are discussed.

Figure 1

Concentration–response curves to CGP 12177 (a) and cyanopindolol (b) in WKY rats. Curves were performed in intact, denuded rings or in intact rings pretreated with 100 μM L-NMMA for 30 min.

Figure 2

Concentration–response curves to CGP 12177 in denuded aortic rings from WKY rats. Curves were performed in the absence or presence of 10 μM nadolol, 3 μM L-748337, 1 μM SR 59230A or 10 μM GCP 20712A. ^*P<0.05 vs CGP 12177 alone (the curve in the presence of nadolol is mostly obscured under the control one).

Figure 3

Concentration–response curves to CGP 12177 in denuded aortic rings from WKY rats. Curves were performed in the absence or presence of 200 μM SQ 22536, 30 μM MDL 12330A or after pretreatment of rats with 10 μg kg⁻¹ PTX during 3 days. ^*P<0.05 vs CGP 12177 alone.

Figure 4

Concentration–response curves to CGP 12177 in SHR rats. Curves were performed in intact, denuded rings or in intact rings pretreated with 100 μM L-NMMA. ^*P<0.05 vs CGP 12177 alone.

Figure 5

Concentration–response curves to CGP 12177 in intact aortic rings from SHR. Curves were performed in the absence or in the presence of 3 μM L-748337 or 10 μM nadolol. ^*P<0.05 vs CGP 12177 alone.

Figure 6

Concentration–response curves to CGP 12177 in denuded aortic rings from SHR. Curves were performed in the absence or in the presence of 200 μM SQ 22536 or after pretreatment of rats with 10 μg kg⁻¹ PTX during 3 days. ^*P<0.05 vs CGP 12177 alone.

Figure 7

β₃-AR expression in WKY and SHR aorta. Panel a: adjacent 10 μm thick sections were incubated with either von Willebrand factor antibody (vWf Ab) or rat β₃-AR antibody (rβ₃-AR Ab) or after preabsorption of rβ₃-AR Ab with the blocking peptide (rβ₃-AR Ab+B pept.). Panel b: the same rβ₃-AR Ab staining experiment was performed in WKY (W1–W5) and SHR (S1–S5) aorta. vWf and rβ₃-AR antibodies were revealed with peroxidase-conjugated second serum.

Figure 8

Concentration–response curves to SR 58611A in intact aortic rings from WKY rats or SHR.