Endothelium-dependent vasoconstriction in isolated vessel grafts: a novel mechanism of vasospasm?

Endothelium-dependent contraction: The non-classical action of endothelial prostacyclin, its underlying mechanisms, and implications

Although commonly thought to produce prostacyclin (prostaglandin I₂ ; PGI₂ ) that evokes vasodilatation and protects vessels from the development of diseases, the endothelial cyclooxygenase (COX)-mediated metabolism has also been found to release substance(s) called endothelium-derived contracting factor(s) (EDCF) that causes endothelium-dependent contraction and implicates in endothelial dysfunction of disease conditions. Various mechanisms have been proposed for the process; however, the major endothelial COX metabolite PGI₂ , which has been classically considered to activate the I prostanoid receptor (IP) that mediates vasodilatation and opposes the effects of thromboxane (Tx) A₂ produced by COX in platelets, emerges as a major EDCF in health and disease conditions. Our recent studies from genetically altered mice further suggest that vasomotor reactions to PGI₂ are collectively modulated by IP, the vasoconstrictor Tx-prostanoid receptor (TP; the prototype receptor of TxA₂ ) and E prostanoid receptor-3 (EP3; a vasoconstrictor receptor of PGE₂ ) although with differences in potency and efficacy; a contraction to PGI₂ reflects activities of TP and/or EP3 outweighing that of the concurrently activated IP. Here, we discuss the history of endothelium-dependent contraction, evidences that support the above hypothesis, proposed mechanisms for the varied reactions to endothelial PGI₂ synthesis as well as the relation of its dilator activity to the effect of another NO-independent vasodilator mechanism, the endothelium-derived hyperpolarizing factor. Also, we address the possible pathological and therapeutic implications as well as questions remaining to be resolved or limitations of our above findings obtained from genetically altered mouse models.

Superior vasodilation of human pulmonary vessels by vardenafil compared with tadalafil and sildenafil: additive effects of bosentan

OBJECTIVES

Pulmonary arterial hypertension is characterized by pulmonary vascular proliferation and remodelling, leading to a progressive increase in pulmonary arterial resistance. Vasodilator properties of 3 different phosphodiesterase (PDE)-5 inhibitors alone and in combination with an endothelin (ET) receptor antagonist were compared in an ex vivo model.

METHODS

Segments of human pulmonary arteries (PAs) and pulmonary veins (PVs) were harvested from lobectomy specimens. Contractile forces were determined in an organ bath. Vessels were constricted with norepinephrine (NE) to determine the effects of sildenafil, tadalafil and vardenafil and with ET-1 to assess the effects of bosentan.

RESULTS

All 3 PDE-5 inhibitors had no relevant effect on the basal tone of the vessels. Both sildenafil and vardenafil significantly (P < 0.0001) reduced the responses of the vessels to NE, whereas tadalafil was effective only in PA (P = 0.0009) but not in PV (P = 0.097). Sildenafil relaxed NE-preconstricted PV (P < 0.0001) but not PA (P = 0.143). Both tadalafil and vardenafil relaxed PA and PV significantly. Vardenafil appears to be the most potent of the PDE-5 inhibitors tested. Furthermore, we analysed the combination of bosentan and vardenafil in PA. Bosentan and vardenafil reduced ET-1 and NE induced vasoconstriction stronger than vardenafil alone (P ≤ 0.049).

CONCLUSIONS

Vardenafil caused the most consistent antihypertensive response in this ex vivo model. However, ET receptor antagonism appears to be an even more potent mechanism. A combination therapy using vardenafil and bosentan turned out to be an effective combination to lower vessel tension in PA.

Increased role of E prostanoid receptor-3 in prostacyclin-evoked contractile activity of spontaneously hypertensive rat mesenteric resistance arteries

This study aimed to determine whether E prostanoid receptor-3 (EP3) is involved in prostacyclin (PGI₂)-evoked vasoconstrictor activity of resistance arteries and if so, how it changes under hypertensive conditions. Mesenteric resistance arteries from Wistar-Kyoto rats (WKYs) and spontaneously hypertensive rats (SHRs) were isolated for functional and biochemical studies. Here we show that in vessels from WKYs, PGI₂ or the endothelial muscarinic agonist ACh (which stimulates in vitro PGI₂ synthesis) evoked vasoconstrictor activity, which increased in SHRs. The thromboxane-prostanoid receptor (TP) antagonist SQ29548 partially removed the vasoconstrictor activity, and an increased contractile activity of PGI₂ resistant to SQ29548 was observed in SHRs. Interestingly, L798106, an antagonist of EP3 (whose expression was higher in SHRs than in WKYs), not only added to the effect of SQ29548 but also caused relaxation to PGI₂ more than that obtained with SQ29548. In accordance, EP3 deletion, which reduced PGI₂-evoked contraction, together with SQ29548 resulted in relaxation evoked by the agonist in mouse aortas. These results thus demonstrate an explicit involvement of EP3 in PGI₂-evoked vasoconstrictor activity in rat mesenteric resistance arteries and suggest that up-regulation of the receptor contributes significantly to the increased contractile activity evoked by PGI₂ under hypertensive conditions.

Neuronal nitric oxide synthase-derived hydrogen peroxide effect in grafts used in human coronary bypass surgery

Recently, H₂O₂ has been identified as the endothelium-dependent hyperpolarizing factor (EDHF), which mediates flow-induced dilation in human coronary arteries. Neuronal nitric oxide synthase (nNOS) is expressed in the cardiovascular system and, besides NO, generates H₂O₂ The role of nNOS-derived H₂O₂ in human vessels is so far unknown. The present study was aimed at investigating the relevance of nNOS/H₂O₂ signaling in the human internal mammary artery (IMA) and saphenous vein (SV), the major conduits used in coronary artery bypass grafting. In the IMA, but not in the SV, ACh (acetylcholine)-induced vasodilatation was decreased by selective nNOS inhibition with TRIM or Inhibitor 1, and by catalase, which specifically decomposes H₂O₂ Superoxide dismutase (SOD), which generates H₂O₂ from superoxide, decreased the vasodilator effect of ACh on SV. In the IMA, SOD diminished phenylephrine-induced contraction in endothelium-containing, but not in endothelium-denuded vessels. Importantly, while exogenous H₂O₂ produced vasodilatation in IMA, it constricted SV. ACh increased H₂O₂ production in both sets of vessels. In the IMA, the increase in H₂O₂ was inhibited by catalase and nNOS blockade. In SV, H₂O₂ production was abolished by catalase and reduced by nNOS inhibition. Immunofluorescence experiments showed the presence of nNOS in the vascular endothelium and smooth muscle cells of both the IMA and SV. Together, our results clearly show that H₂O₂ induced endothelium-dependent vascular relaxation in the IMA, whereas, in the SV, H₂O₂ was a vasoconstrictor. Thus, H₂O₂ produced in the coronary circulation may contribute to the susceptibility to accelerated atherosclerosis and progressive failure of the SV used as autogenous graft in coronary bypass surgery.

Herbal Prescription, DSGOST, Prevents Cold-Induced RhoA Activation and Endothelin-1 Production in Endothelial Cells

Herbal prescription, Danggui-Sayuk-Ga-Osuyu-Saenggang-tang (DSGOST), has long been used to treat Raynaud's phenomenon (RP) in traditional Chinese medicine (TCM). However, a biological mechanism by which DSGOST ameliorates RP is yet deciphered. In this study, we demonstrate that DSGOST inhibits cold-induced activation of RhoA, in both vascular smooth muscle cells (VSMC) and endothelial cells (EC), and blocks endothelin-1-mediated paracrine path for cold response on vessels. While cold induced RhoA activity in both cell types, DSGOST pretreatment prevented cold-induced RhoA activation. DSGOST inhibition of cold-induced RhoA activation further blocked α2c-adrenoreceptor translocation to the plasma membrane in VSMC. In addition, DSGOST inhibited endothelin-1-mediated RhoA activation and α2c-adrenoreceptor translocation in VSMC. Meanwhile, DSGOST inhibited cold-induced or RhoA-dependent phosphorylation of FAK, SRC, and ERK. Consistently, DSGOST inhibited cold-induced endothelin-1 expression in EC. Therefore, DSGOST prevents cold-induced RhoA in EC and blocks endothelin-1-mediated paracrine path between EC and VSMC. In conclusion, our data suggest that DSGOST is beneficial for treating RP-like syndrome.