Role of endothelial NO in the vasorelaxing effects induced by H2S in conductance and resistance rat arteries

L Testai1, A Martelli1, V D\'Antongiovanni1, MC Breschi1, E Duranti2, A Virdis2, S Taddei2, C Blandizzi2, V Calderone1. 1University of Pisa, Dept. of Psychiatry, Neurobiology, Pharmacology and Biotechnologies, via Bonanno, 6, I-56126 Pisa, Italy, 2University of Pisa, Dept. of Internal Medicine, Via Roma, I-56126 Pisa, Italy

Hydrogen sulphide (H2S) is presently known to act as an endogenous mediator, generated in mammalian tissues from cysteine by cistathionine β-synthase (CBS) and cistathionine γ-lyase (CSE) [1]. H2S plays important roles in controlling the homeostasis of cardiovascular system, where it mediates vasorelaxing effects both in conductance and resistance arteries [1]. Accordingly, an impaired endogenous production of H2S is thought to contribute to the pathogenesis of hypertension [2]. The vascular effects of H2S are mediated mainly by opening of ATP-sensitive potassium channels (KATP), but additional mechanisms cannot be excluded [1]. Interestingly, a possible cross-talk between H2S and nitric oxide (NO) has been suggested. On one hand, some experimental reports indicate that the inhibition of NO-synthase (NOS) or endothelium removal can attenuate the H2S-induced relaxation. On the other hand, a negative feedback regulation between these two gaseous mediators and a H2S-induced inhibition of the L-Arginine/NOS/NO pathway have been proposed [3]. Furthermore, it has been hypothesized that H2S may act as a scavenger of NO, to produce an unidentified nitrosothiol [4]. Taken together, these conflicting data suggest a fine, but not yet exhaustively investigated, link between NO and H2S. This study was aimed at assessing the vasoactive effects of the H2S-donor NaHS, and evaluating the link between H2S and the L-Arginine/NOS/NO pathway in conductance (rat thoracic aorta) and resistance (rat mesenteric and coronary arteries) vascular beds. The study was carried out on male Wistar rats (300-350 g); data are expressed as mean±SEM from n>6 experiments and as been analysed by ANOVA and Student t test. In endothelium-denuded thoracic aortae, NaHS 300μM reduced the vasocontractile efficacy of noradrenaline (NA) or angiotensin II (AngII) by 18±3% and 28±6% respectively. By contrast, in endothelium-intact preparations, NaHS did not affect NA-induced contractions. In endothelium-intact aortae, the H2S-induced inhibitory effects were restored by inhibition of NO biosynthesis with L-NAME (inhibition of NA-induced contraction = 21±3%). In perfused hearts, AngII reduced the coronary flow (66±5% of the basal one); NaHS 100μM completely reversed this effect leading the coronary flow to 126±4%. The effect of NaHS was completely antagonized by L-NAME. In mesenteric resistance vessels, NaHS 100μM reduced (by 54±17%) the vasoconstriction induced by NA, and again this effect was fully antagonized by L-NAME. Moreover, NaHS abolished almost completely the vasoconstriction evoked by AngII (by 92±6%), but, surprisingly, such an effect was not affected by L-NAME (NaHS-induced reduction = 94±3%). In conclusion, these results suggest that the H2S-induced vasorelaxing activity can be linked in a complex and variable way to NO pathways, depending both on the vascular district and the nature of vasoconstrictor agent.

Acknowledgements: This work was supported by the “Regional Health Research Program 2009” grant issued by Regione Toscana, Italy.

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