Mechanisms underlying the vasorelaxant effect of trans-4-methoxy-β-nitrostyrene in the rat mesenteric resistance arteries

Abstract

Mechanisms underlying the vasorelaxant effects of the synthetic nitro compound, trans-4-methoxy-β-nitrostyrene (T4MN) were studied in isolated small resistance arteries from spontaneously hypertensive rats (SHRs). T4MN caused vasorelaxation in endothelium-intact third-order branches of the mesenteric artery pre-contracted with noradrenaline (NA). This effect was unchanged by indomethacin and atropine but was significantly reduced by endothelium removal, L-NAME, LY294002, glybenclamide, TEA, apamin, TRAM 34, or by the association of apamin and TRAM 34. Pretreatment with the sGC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) reduced the T4MN-induced relaxation in endothelium-intact, but not in denuded preparations. Incubation of small resistance arteries with T4MN increased nitric oxide (NO) production, an effect that was blocked by L-NAME. In Ca²⁺-free medium, T4MN inhibits the contractions induced by (i) NA, (ii) exogenous calcium through receptor- or voltage-operated Ca²⁺ channels and (iii) those evoked by Ca²⁺ influx through stores-operated Ca²⁺ channels activated by thapsigargin-induced Ca²⁺ store depletion. In contrast, T4MN was inert against the transient contraction induced by caffeine in Ca²⁺-free medium. In conclusion, T4MN induced effective vasorelaxant effects in isolated small resistance arteries from SHRs. This vasorelaxation seems to be mediated partly by an endothelium-dependent mechanism involving activation of Akt/eNOS/NO pathway and partly by an endothelium-independent mechanism through activation of sGC/cGMP/PKG pathway in vascular smooth muscle, leading to inhibition of Ca²⁺ influx from the extracellular milieu and IP₃-sensitive intracellular Ca²⁺ release as well as activation of potassium channels.

Keywords: NO/cGMP pathway; Small resistance arteries; Spontaneously hypertensive rats; Trans-4-methoxy-β-nitrostyrene; Vasorelaxation.