Hydrogen sulphide induced-dual vascular effect involves arachidonic acid cascade in rat mesenteric arterial bed

Emma Mitidieri, Roberta d’Emmanuele di Villa Bianca, Ciro Coletta, Giuseppe Cirino, Raffaella Sorrentino. Department of Sperimental Pharmacology, University of Naples Federico II, 80131 Naples, Italy.

Hydrogen sulphide (H2S) is a gaseous transmitter produced in various mammalian tissues from L-cysteine by the actions of cysthationine β-synthase (CBS) and/or cysthationine-γ-lyase (CSE). CBS is predominantly localised within the central nervous system and CSE within vascular tissues such as aorta and mesenteric artery. Recently, it has also been reported that CSE is present in vascular endothelial cells and that CSE gene deletion induces hypertension in mice, leading to the suggestion that H2S could be an endothelium-derived hyperpolarizing factor (EDHF). To address this idea we have evaluated the effects of sodium hydrogen sulphide (NaHS), an H2S donor, on the mesenteric arterial bed.

Bolus injections of NaHS(10 µmol L-1-1mmol L-1) were made into isolated perfused rat mesenteric arterial beds preconstricted with methoxamine (100 µmol L-1). In various experiments, indomethacin, L-NAME and apamin and charibdotoxin respectively, cyclooxygenase, nitric oxide synthase, calcium-dependent potassium channel inhibitors, were used to evaluate the contribution of EDHF to H2S responses. In additional experiments, 4-(4-octadecylphenyl)-4-oxobutenoic acid or proadifen were used respectively as PLA2 and cytochrome P450 inhibitors. An immunofluorescence study for cPLA2 involvement in NaHS was also conducted.

NaHS caused increases in perfusion pressure (vasoconstriction) at lower doses (10 µmol L-1 and 100 µmol L-1) and decreases (vasodilatation) at higher doses (1 mmol L-1). NaHS-induced vasodilatations were unaffected by L-NAME but were inhibited by apamin or charibdotoxin (n = 5; p<0.01). Inhibition of PLA2 abolished the vasoconstricting and vasodilating effects of NaHS (n = 5; p<0.01), while inhibition of cytochrome P450 reduced NaHS-induced vasodilatations (n = 5, p<0.01). Immunofluorescence showed NaHS caused cPLA2 to migrate towards the nucleus, consistent with enzyme activation.

Our data suggest that H2S may activate PLA2 causing the release of arachidonic acid, associated with transient vasoconstriction followed by vasodilatation. This vasodilatation may well depend upon an arachidonic acid metabolite of cytochrome P450. As EDHF activity has been also attributed to a cytochrome P450 derivative of arachidonic acid H2S may be involved in the signalling pathway leading to EDHF production.