Concentration-dependent Relaxation Of Arteries Research Articles

Abstract 11591: Mechanism of Finerenone-Induced Vasorelaxation in Arteries From Human Visceral Adipose Tissue

Introduction: Inadequate perfusion has emerged as a main determinant of adipose tissue (AT) dysfunction in obesity, sparking interest about possible ways to improve it. Among several mechanisms, mineralcorticoid receptor (MR) signaling has been shown to play a key role in the cross-talk between AT and the vasculature. Hypothesis: This study, therefore, tested the vasoactive properties of finerenone, a nonsteroidal MR antagonist, in arteries harvested from human AT. Methods: Small arteries (<1 mm in diameter) were isolated from visceral AT and studied ex vivo in a wire myograph. After vessels had been contracted, changes in vascular tone were determined under different experimental conditions. Results: Finerenone elicited a concentration-dependent relaxation in arteries of obese individuals contracted with the thromboxane A2 analogue U46619 (n=9; P<0001 vs. baseline); the steroidal MR antagonist potassium canrenoate, by contrast, did not induce any vasorelaxation (n=3; P>0.05). The relaxing effect of finerenone on U46619-induced constriction was not different in arteries from lean (n=3) and obese subjects (P=0.155). Mechanistically, the vasorelaxing response to finerenone was not influenced by pre-incubation with the nitric oxide (NO) synthase inhibitor L-NAME (n=4; P=0.19 vs. saline), hence ruling out an involvement of NO. Interestingly, finerenone was also able to relax arteries contracted with endothelin-1 (n=7; P<0.001) or with high-K + solution (n=4; P<0001), as well as those contracted with the L-type Ca 2+ -channel agonist BayK8644 (n=5; P=0.007); similarly, the calcium-channel blocker nifedipine induced relaxation of arteries contracted with BayK8644 (n=3; P<0.001). Conclusions: Finerenone induces NO-independent vasorelaxation in arterioles from human visceral AT, likely through antagonism of L-type Ca2 + -channels. This finding identifies a novel action of finerenone to improve AT perfusion, thereby potentially expanding the emerging observations about the cardiovascular benefits of this agent.

In vitro Effects of the Organophosphorus Pesticide Malathion on the Reactivity of Rat Aorta

Background and Purpose: There is a remarkable paucity of studies analyzing the role of the endothelium-derived relaxing factors on the vascular effects of organophosphates. This study was carried out to evaluate the vascular effects of malathion and the role of nitric oxide (NO) and prostacyclin (PGI₂). Methods: Vascular reactivity measuring isometric forces in vitro (‘organ chambers') and flow cytometry (cells loaded with DAF-FM DA) were used. Results: In rat thoracic aorta segments contracted with phenylephrine (Phe) (10^-7 mol/l), malathion (10^-10 to 10^-5 mol/l) induced concentration-dependent relaxation in arteries with intact endothelium (n = 7; p < 0.05). Malathion-mediated relaxation was blocked by N-nitro-<smlcap>L</smlcap>-arginine methyl ester (<smlcap>L</smlcap>-NAME; 10^-4 mol/l), a nonspecific NO synthase inhibitor, and/or indomethacin (10^-5 mol/l), a nonspecific cyclooxygenase inhibitor (n = 10, p < 0.05). In thoracic aorta rings, with and without endothelium, Phe (10^-10 to 10^-5 mol/l) evoked concentration-dependent contraction, which was reduced in the presence of malathion. In rings with or without endothelium, incubated with malathion, <smlcap>L</smlcap>-NAME and indomethacin, the Phe-induced contraction was restored. The role of NO was confirmed using flow cytometry. Malathion evokes endothelium-dependent relaxation through the M₁ muscarinic receptor, since this relaxation was clearly blocked by atropine (M₁ and M₂ blocker) and pirenzepine (M₁ blocker), but was less blocked by gallamine (M₂ blocker) or 4-DAMP (M₃ blocker). Conclusions: These findings suggest that the organophosphate compound effects on vascular reactivity depend of NO and PGI₂.

Differential mechanisms of endothelium-dependent vasodilator responses in human myometrial small arteries in normal pregnancy and pre-eclampsia.

Pre-eclampsia is a pregnancy-specific disorder associated with hypertension and proteinuria, characterized by alterations in endothelial cell function. In the present study we have compared responses to the endothelium-dependent vasodilator, bradykinin, in small myometrial arteries from normal pregnant and non-pregnant women and women with pre-eclampsia, in order to assess the relative contributions of nitric oxide, endothelium-derived hyperpolarizing factor (EDHF) and prostanoids in mediating endothelium-dependent vasodilatation. Bradykinin-induced concentration-dependent relaxation in arteries isolated from the three subject groups did not differ with regard to sensitivity or maximum response. Responses to bradykinin in all three groups were unaffected by cyclo-oxygenase inhibition alone, and were similarly unaffected by partial depolarization. The nitric oxide synthase (NOS) inhibitor, N-nitro-l-arginine methyl ester, significantly attenuated the responses to bradykinin in arteries from non-pregnant women and almost abolished responses in arteries from women with pre-eclampsia. However, in arteries from normal pregnant women, bradykinin-induced responses were maintained in the presence of NOS inhibition. Inhibition of NOS combined with partial depolarization abolished responses to bradykinin in these vessels. These results support the suggestion that, in the absence of NO, an EDHF can mediate vasodilator responses to bradykinin during normal pregnancy, an effect not apparent in arteries from non-pregnant women or women with pre-eclampsia. The up-regulation of EDHF-type function may represent a vascular adaptation to normal pregnancy that is absent in pre-eclampsia, and this might contribute to the clinical features of the disease.

Involvement of protein kinase C and Na+/K+-ATPase in the contractile response induced by myricetin in rat isolated aorta.

The role of PKC and Na+/K+-ATPase in the vascular smooth muscle responses induced by the bioflavonoid myricetin was investigated. KCl induced a concentration-dependent relaxation in arteries exposed to K+-free solution that was mainly mediated by an activation of Na+/K+-ATPase. Myricetin (50 microM) partially inhibited this vasorelaxant effect induced by KCl in intact rings, being unaffected in the endothelium-denuded rings. This inhibitory effect induced by myricetin was suppressed by the PGH2-TXA2 receptor antagonist, SQ 29,548, and the PKC inhibitor, staurosporine. Myricetin also induced an endothelium-dependent contractile response which was increased in the presence of PMA and reduced by staurosporine. In conclusion, myricetin both modulates Na+/K+-ATPase-induced vasodilatation acting as a functional inhibitor of Na+/K+-ATPase activity and activates protein kinases, including PKC, to induce contraction. These effects appear to be related to the activation of PGH2-TXA2 receptors on vascular smooth muscle by the TXA2 released from endothelium.NA:noradrenalineNA+/K+-ATPase pump:sodium-potassium-activated ATPasePKC:protein kinase CPMA:phorbol 12-myristate 13-acetateTXA2:thromboxane A2The role of PKC and Na+/K+-ATPase in the vascular smooth muscle responses induced by the bioflavonoid myricetin was investigated. KCl induced a concentration-dependent relaxation in arteries exposed to K+-free solution that was mainly mediated by an activation of Na+/K+-ATPase. Myricetin (50 microM) partially inhibited this vasorelaxant effect induced by KCl in intact rings, being unaffected in the endothelium-denuded rings. This inhibitory effect induced by myricetin was suppressed by the PGH2-TXA2 receptor antagonist, SQ 29,548, and the PKC inhibitor, staurosporine. Myricetin also induced an endothelium-dependent contractile response which was increased in the presence of PMA and reduced by staurosporine. In conclusion, myricetin both modulates Na+/K+-ATPase-induced vasodilatation acting as a functional inhibitor of Na+/K+-ATPase activity and activates protein kinases, including PKC, to induce contraction. These effects appear to be related to the activation of PGH2-TXA2 receptors on vascular smooth muscle by the TXA2 released from endothelium.

Magnesium removal impairs the regulatory role of rat endothelium.

Vascular endothelium has been shown to play an important role in the regulation of vascular tone and, hence, impairment of the endothelium may induce hypertension. Although magnesium (Mg) deficiency could induce hypertension, the role of Mg on the endothelium is unclear. We examined the effects of Mg removal on endothelium-dependent and -independent responses using ring preparations of femoral arteries obtained from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Norepinephrine (10(-9)-10(-4) M) evoked concentration-dependent contractions in arteries with endothelium. The maximal response was greater in SHR than in WKY. Removal of external Mg augmented the contraction in WKY but not in SHR. As a result, the contraction obtained in arteries with endothelium was identical in the two groups. Removal of the endothelium enhanced the contraction in both strains, with a greater response occurring in WKY than in SHR in Krebs, but not in Mg-free, solution. As a result, in arteries without endothelium, the contractions were identical in WKY and SHR both in Krebs and Mg-free solutions. Acetylcholine (10(-9)-10(-4) M) evoked concentration-dependent relaxation in arteries with, but not in those without, endothelium obtained from WKY and SHR. The relaxation did not differ between the two strains, nor was it altered by Mg removal. Thus, Mg removal impairs inhibitory function of the endothelium against contraction induced by norepinephrine, without affecting endothelium-dependent relaxation in response to acetylcholine, in the rat femoral artery. The effect of Mg removal is not apparent in SHR. The fact that after removal of external Mg the contraction in response to norepinephrine in arteries with endothelium is identical in WKY and SHR suggests that a normotensive artery with Mg deficiency may mimic a hypertensive artery through endothelial impairment.

Human placental syncytiotrophoblast microvillous membranes impair maternal vascular endothelial function.

To investigate the hypothesis that, should there be an increase in deported syncytiotrophoblast microvillous membrane fragments in pre-eclampsia, it may cause maternal vascular endothelial dysfunction. Syncytiotrophoblast microvillous membrane (STBM) vesicles, prepared from normal term placentae, were perfused through small subcutaneous arteries isolated from fat biopsies obtained at caesarean section. Endothelial function of these arteries was studied by determining acetylcholine-induced relaxation after preconstriction with noradrenaline. As controls, physiological buffer or red blood cell membranes in physiological buffer were used and endothelial function similarly estimated. Transmission electron microscopy was performed on arteries after perfusion. STBM vesicles, isolated from the placentae of three healthy women undergoing elective caesarean section for reasons unrelated to pre-eclampsia, were suspended in physiological buffer. Subcutaneous fat arteries were obtained from a separate group of 13 normotensive pregnant women, also undergoing elective caesarean section at term. Perfusion with red blood cell membranes or physiological buffer had no significant effect on the concentration dependent relaxation in arteries preconstricted with noradrenaline. However, after 2 h perfusion with STBM vesicles, arteries showed a significant reduction in relaxation to acetylcholine, indicative of altered endothelial function. Transmission electron microscopy of arteries perfused with STBM vesicles confirmed endothelial disruption. STBM vesicle perfusion specifically altered the relaxation response of preconstricted maternal subcutaneous fat arteries to acetylcholine, suggesting an alteration in endothelial dependent relaxation. Deported microvilli may therefore be capable of producing endothelial cell damage and endothelial dysfunction observed in the maternal syndrome of pre-eclampsia.