Interaction between hydrogen sulphide and nitric oxide in the regulation of vascular tone

1Jatinder S. Virdee, 1Shuaib Quraishi, 2Marika Collin, 2Chris Thiemermann 3Adrian J. Hobbs & 1Amrita Ahluwalia. 1Clinical Pharmacology & 2Experimental Medicine, William Harvey Research Institute, Barts & The London & 3Wolfson Institute for Biomedical Research, UCL.

Hydrogen sulphide (H2S) has recently been identified as a third gaseous, small-molecule signalling mediator in the vasculature in addition to NO and CO (Moore et al., [2003] Trends Pharmacol. Sci., 24, 609). However, the mechanisms underlying the vasodilator activithy of H2S remain unclear. Herein, we have investigated in vitro and in vivo the pathways involved in H2S-induced vasodilatation.  

Thoracic aortic rings of male Sprague Dawley rats (200-250g) were mounted in organ baths for isometric tension recording. Following equilibration rings were incubated with either the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 300μM), the guanylate cyclase inhibitor ODQ (5μM) or the cystathionine-β-lyase (CSE; H2S synthetic enzyme) inhibitor DL-propargylglycine (PAG; 1mM) or left as untreated control for 30 min. Tissues were then pre-contracted using PE (~EC80) and (1) concentration responses curves to the H2S donor, NaHS (0.1μM-10mM) constructed, or (2) tissues were incubated with lipopolysaccharide (LPS; 1 μg/ml) and tone monitored for the following 5h. In all cases, tissue was collected and snap frozen in liquid nitrogen for CSE mRNA expression determination using SyberGreen Quantitative PCR. Similarly, blood pressure (BP) vasodilator dose-response curves to NaHS (0.1-3mg/kg, i.v), or response to LPS (6mg/kg) were monitored in vivo in anaesthetised rats in saline control (1 ml/kg i.v) or L-NAME (1 mg/kg i.v.) treated animals. In some experiments PE was given as a continuous infusion, at a dose required to increase BP by 15-20 mmHg from baseline.

NaHS caused concentration-dependent relaxations (pEC50=5.47 ± 0.12; Emax=69.8 ± 3.55%, n=10) that were enhanced by L - NAME (pEC50=5.57 ± 0.08, Emax=89.7 ± 3.02%; n=10, P<0.001), ODQ (pEC50=5.66 ± 0.09, Emax=96.9 ± 3.6%; n=5, P<0.001) or endothelial denudation (pEC50=5.64 ± 0.07, Emax=87.5 ± 2.6%; n=6, P<0.001). LPS caused a maximum relaxation of 92.50 ± 1.65%, a response attenuated by L-NAME (25.8 ± 3.9%; n=15, P<0.001) or PAG (68.78 ± 2.4%; n=8, P<0.001). Quantitative PCR demonstrated a 3.6 ± 0.45 fold increase in CSE mRNA expression in LPS treated tissue compared to control (n=5, P<0.01), a response attenuated by L-NAME (2.1 ± 0.34 fold increase, n=6, NS). NaHS caused dose-dependent hypotension (Emax=17 ± 2mmHg, n=6) that was significantly (P<0.05) enhanced by L-NAME (Emax=34 ± 4mmHg, n=6).  

These data demonstrate that H2S plays an important role in LPS-induced relaxation of rat aortic tissue. This is in part due to elevation of CSE expression that is dependent on LPS-induced NO production. However, we also show an inhibitory role of endothelial-derived NO on H2S-induced relaxation of aortic preparations. These findings suggest a novel dual role for NO in regulating H2S bioactivity.  

J. Virdee is supported by a Wellcome Trust Vacation Scholarship.