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Reductions in hydrogen sulfide (H 2 S) production have been implicated in the pathogenesis of vascular dysfunction in animal models of hypertension; however, no studies have examined a functional role for H 2 S in contributing to microvascular dysfunction in hypertensive (HTN) adults. We hypothesized that endogenous production of H 2 S would be reduced, impaired endothelium-dependent vasodilation would be mediated by reductions in H 2 S-dependent vasodilation, and vascular responsiveness to exogenous H 2 S (sodium sulfide) would be attenuated in HTN compared to normotensive adults. Fifteen normotensive (51±2 years; blood pressure, 116±3/76±3 mm Hg) and 14 HTN adults (57±2 years; blood pressure 140±3/89±2 mm Hg) participated. H 2 S biosynthetic enzyme expression (Western blot) and substrate-dependent H 2 S production (amperometric probe) were measured in cutaneous tissue homogenates. Red cell flux (laser Doppler flowmetry) was measured during graded perfusions of acetylcholine (ACh; 10 -6 -10 -1 mol/L) and sodium sulfide (10 -5 -10 1 mol/L) using intradermal microdialysis; the functional role of H 2 S was determined using pharmacological inhibition with aminooxyacetic acid (0.5 mmol/L). H 2 S biosynthetic enzyme expression and substrate-dependent H 2 S production were reduced in HTN adults (all P <0.05). ACh-induced endothelium-dependent vasodilation was blunted in HTN adults ( P =0.012). Aminooxyacetic acid attenuated ACh-induced vasodilation in normotensive adults (ACh, 1.31±0.13 versus ACh+aminooxyacetic acid, 1.07±0.09 flux/mm Hg; P =0.025) but had no effect on vasodilation in HTN adults (ACh, 1.16±0.10 versus ACh+aminooxyacetic acid, 1.37±0.11 flux/mm Hg; P =0.47). Sodium sulfide-induced vasodilation was not different between groups. Collectively, these findings indicate that while the microvasculature maintains the ability to vasodilate in response to exogenous H 2 S, reductions in endogenous synthesis and H 2 S-dependent vasodilation contribute to endothelial dysfunction in human hypertension., (© 2017 American Heart Association, Inc.)

Key Points: Hydrogen sulphide (H2 S) is vasoprotective, attenuates inflammation and modulates blood pressure in animal models; however, its specific mechanistic role in the human vasculature remains unclear. In the present study, we report the novel finding that the enzymes responsible for endogenous H2 S production, cystathionine-γ-lyase and 3-mercaptopyruvate sulphurtransferase, are expressed in the human cutaneous circulation. Functionally, we show that H2 S-induced cutaneous vasodilatation is mediated, in part, by tetraethylammonium-sensitive calcium-dependent potassium channels and not by ATP-sensitive potassium channels. In addition, nitric oxide and cyclo-oxygenase-derived byproducts are required for full expression of exogenous H2 S-mediated cutaneous vasodilatation. Future investigations of the potential role for H2 S with respect to modulating vascular function in humans may have important clinical implications for understanding the mechanisms underlying vascular dysfunction characteristic of multiple cardiovascular pathologies., Abstract: The present study aimed to identify the presence of cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulphurtransferase (3-MST), which endogenously produce hydrogen sulphide (H2 S), and to functionally examine the mechanisms of H2 S-induced vasodilatation in the human cutaneous microcirculation. CSE and 3-MST were quantified in forearm skin samples from 5 healthy adults (24 ± 3 years) using western blot analysis. For functional studies, microdialysis fibres were placed in the forearm skin of 12 healthy adults (25 ± 3 years) for graded infusions (0.01-100 mm) of sodium sulphide (Na2 S) and sodium hydrogen sulphide (NaHS). To define the mechanisms mediating H2 S-induced vasodilatation, microdialysis fibres were perfused with Ringer solution (control), a ATP-sensitive potassium channel (KATP ) inhibitor, an intermediate calcium-dependent potassium channel (KCa ) inhibitor, a non-specific KCa channel inhibitor or triple blockade. To determine the interaction of H2 S-mediated vasodilatation with nitric oxide (NO) and cyclo-oxygenase (COX) signalling pathways, microdialysis fibres were perfused with Ringer solution (control), a non-specific NO synthase inhibitor, a non-selective COX inhibitor or combined inhibition during perfusion of increasing doses of Na2 S. CSE and 3-MST were expressed in all skin samples. Na2 S and NaHS elicited dose-dependent vasodilatation. Non-specific KCa channel inhibition and triple blockade blunted Na2 S-induced vasodilatation (P < 0.05), whereas KATP and intermediate KCa channel inhibition had no effect (P > 0.05). Separate and combined inhibition of NO and COX attenuated H2 S-induced vasodilatation (all P < 0.05). CSE and 3-MST are expressed in the human microvasculature. Exogenous H2 S elicits cutaneous vasodilatation mediated by KCa channels and has a functional interaction with both NO and COX vasodilatatory signalling pathways., (© 2015 The Authors. The Journal of Physiology © 2015 The Physiological Society.)