Activation of nitric oxide synthase by beta(2)-adrenoceptors in human umbilical vein endothelium in vitro

1 Some animal studies suggest that beta-adrenoceptor-mediated vasorelaxatio n is in part mediated through nitric oxide (NO) release. Furthermore, in hu mans, we have recently shown that forearm blood flow is increased by infusi on of beta(2)-adrenergic agonists into the brachial artery, and the nitric oxide synthase (NOS) inhibitor N-G-monomethyl-L-arginine (L-NMMA) inhibits this response, 2 The purpose of the present study was to determine whether stimulation of human umbilical vein endothelial beta-adrenoceptors causes vasorelaxation a nd nitric oxide generation, and whether this might be mediated by cyclic ad enosine-3',5'-monophosphate (cyclic AMP). 3 Vasorelaxant responses were determined in umbilical vein rings to the non selective beta-adrenergic agonist isoprenaline and to the cyclic AMP analog ue dibutyryl cyclic AMP, following precontraction with prostaglandin F-2 al pha. 4 NOS activity was measured in cultured human umbilical vein endothelial so ils (HUVEC) by the conversion of [H-3]-L-arginine to [H-3]-L-citrulline, an d adenylyl cyclase activity by the conversion of [alpha-P-32]-ATP to [P-32] -cyclic AMP. 5 Isoprenaline relaxed umbilical vein rings, and this vasorelaxation was ab olished by beta(2)- (but not beta(1)-) adrenergic blockage, and by endothel ium removal or 1 mM L-NMMA. In addition, vasorelaxant responses to dibutyry l cyclic AMP were inhibited by 1 mM L-NMMA, with a reduction in E-max from 90.0 +/- 9.39 to 50.5 +/- 9.9% (P < 0.05). 6 Isoprenaline 1 mu M increased NOS activity in HUVEC (34.0 +/- 5.9% above basal. P < 0.001). Furthermore, isoprenaline increased adenylyl cyclase act ivity in a concentration-dependent manner, this response was inhibited by b eta(2) (but not beta(1)-) adrenergic blockade. Forskolin 1 mu M and dibutyr yl cyclic. AMP 1 mM each increased NOS activity in HUVEC, to a degree simil ar to isoprenaline 1 mu M. The increase in [H-3]-L-arginine to L-citrulline conversion observed with each agent wets abolished by coincubation with NO S inhibitors. 7 These results indicate that endothelial beta(2)-adrenergic stimulation an d cyclic AMP elevation activate the L-arginine/NO system, and give rise to vasorelaxation, in human umbilical vein.