[Show abstract][Hide abstract] ABSTRACT: Endothelium-dependent dilatation is mediated by 3 principal vasodilators: nitric oxide (NO), prostacyclin (PGI2), and endothelium-derived hyperpolarizing factor (EDHF). To determine the relative contribution of these factors in endothelium-dependent relaxation, we have generated mice in which the enzymes required for endothelial NO and PGI2 production, endothelial NO synthase (eNOS) and cyclooxygenase-1 (COX-1), respectively, have been disrupted (eNOS-/- and COX-1-/- mice).
In female mice, the absence of eNOS and COX-1 had no effect on mean arterial blood pressure (BP), whereas BP was significantly elevated in eNOS-/-/COX-1-/- males compared with wild-type controls. Additionally, endothelium-dependent relaxation remained intact in the resistance vessels of female mice and was associated with vascular smooth muscle hyperpolarization; however, these responses were profoundly suppressed in arteries of male eNOS-/-/COX-1-/- animals. Similarly, the endothelium-dependent vasodilator bradykinin produced dose-dependent hypotension in female eNOS-/-/COX-1-/- animals in vivo but had no effect on BP in male mice.
These studies indicate that EDHF is the predominant endothelium-derived relaxing factor in female mice, whereas NO and PGI2 are the predominant mediators in male mice. Moreover, the gender-specific prevalence of EDHF appears to underlie the protection of female eNOS-/-/COX-1-/- mice against hypertension.
[Show abstract][Hide abstract] ABSTRACT: Myogenic constriction describes the innate ability of resistance arteries to constrict in response to elevations in intraluminal pressure and is a fundamental determinant of peripheral resistance and, hence, organ perfusion and systemic blood pressure. However, the receptor/cell-type that senses changes in pressure on the blood vessel wall and the pathway that couples this to constriction of vascular smooth muscle remain unclear. In this study, we show that elevation of intraluminal transmural pressure of mesenteric small arteries in vitro results in a myogenic response that is profoundly suppressed following ablation of sensory C-fiber activity (using in vitro capsaicin desensitization resulted in 72.8+/-10.3% inhibition, n=8; P<0.05). Activation of C-fiber nerve endings by pressure was attributable to stimulation of neuronal vanilloid receptor, TRPV1, because blockers of this channel, capsazepine (71.9+/-11.1% inhibition, n=9; P<0.001) and ruthenium red (46.1+/-11.7% inhibition, n=4; P<0.05), suppressed the myogenic constriction. In addition, this C-fiber dependency is likely related to neuropeptide substance P release and activity because blockade of tachykinin NK1 receptors (66.3+/-13.7% inhibition, n=6; P<0.001), and not NK2 receptors (n=4, NS), almost abolished the myogenic response. Previous studies support a role for 20-hydroxyeicosatetraenoic acid (20-HETE) in myogenic constriction responses; herein, we show that 20-HETE-induced constriction of mesenteric resistance arteries is blocked by capsazepine. Together, these results suggest that elevation of intraluminal pressure is associated with generation of 20-HETE that, in turn, activates TRPV1 on C-fiber nerve endings resulting in depolarization of nerves and consequent vasoactive neuropeptide release. These findings identify a novel mechanism contributing to Bayliss' myogenic constriction and highlights an alternative pathway that may be targeted in the therapeutics of vascular disease, such as hypertension, where enhanced myogenic constriction plays a role in the pathogenesis.
Full-text · Article · Dec 2004 · Circulation Research
[Show abstract][Hide abstract] ABSTRACT: Endothelium-derived hyperpolarising factor (EDHF) is an important regulator of vascular tone; however, its identity is still unclear. Several different molecules have been suggested, the most recent of which is the 22-amino acid peptide C-type natriuretic peptide (CNP). CNP induces hyperpolarisation and relaxation of rat mesenteric resistance artery vascular smooth muscle through activation of natriuretic peptide receptor subtype C (NPR-C) and the same potassium channels as EDHF. In addition, this peptide is released from endothelial cells of the perfused rat mesenteric bed in response to endothelium-dependent vasodilators. Thus, CNP is likely to play a vital role in regulation of vascular tone. In addition, since there is evidence that up-regulation of EDHF occurs where normal endothelium function has been compromised, modulation of this pathway represents a novel target for therapeutics in the treatment of inflammatory cardiovascular pathologies characterised by endothelial dysfunction.
No preview · Article · Nov 2004 · The International Journal of Biochemistry & Cell Biology
[Show abstract][Hide abstract] ABSTRACT: Endothelial dysfunction is a characteristic of, and may be pathogenic in, inflammatory cardiovascular diseases, including sepsis. The mechanism underlying inflammation-induced endothelial dysfunction may be related to the expression and activity of inducible nitric oxide synthase (iNOS). This possibility was investigated in isolated resistance (mesenteric) and conduit (aorta) arteries taken from lipopolysaccharide (LPS)-treated (12.5 mg/kg i.v.) or saline-treated iNOS knockout (KO) and wild-type (WT) mice. LPS pretreatment (for 15 h, but not 4 h) profoundly suppressed responses to acetylcholine (ACh) and significantly reduced sensitivity to the NO donor spermine-NONOate (SPER-NO) in aorta and mesenteric arteries of WT mice. This effect was temporally associated with iNOS protein expression in both conduit and resistance arteries and with a 10-fold increase in plasma NOx levels. In contrast, no elevation of plasma NOx was observed in LPS-treated iNOS KO animals, and arteries dissected from these animals did not express iNOS or display hyporeactivity to ACh or SPER-NO. The mechanism underlying this phenomenon may be suppression of eNOS expression, as observed in arteries of WT animals, that was absent in arteries of iNOS KO animals. These results clearly demonstrate that iNOS induction plays an integral role in mediation of the endothelial dysfunction associated with sepsis in both resistance and conduit arteries.
[Show abstract][Hide abstract] ABSTRACT: Endothelial cells in most vascular beds release a factor that hyperpolarizes the underlying smooth muscle, produces vasodilatation, and plays a fundamental role in the regulation of local blood flow and systemic blood pressure. The identity of this endothelium-derived hyperpolarizing factor (EDHF), which is neither NO nor prostacyclin, remains obscure. Herein, we demonstrate that in mesenteric resistance arteries, release of C-type natriuretic peptide (CNP) accounts for the biological activity of EDHF. Both produce identical smooth muscle hyperpolarizations that are attenuated in the presence of high [K(+)], the G(i) G protein (G(i)) inhibitor pertussis toxin, the G protein-gated inwardly rectifying K(+) channel inhibitor tertiapin, and a combination of Ba(2+) (inwardly rectifying K(+) channel blocker) plus ouabain (Na(+)K(+)-ATPase inhibitor). Responses to EDHF and CNP are unaffected by the natriuretic peptide receptor (NPR)-AB antagonist HS-142-1, but mimicked by the selective NPR-C agonist, cANF(4-23). EDHF-dependent relaxation is concomitant with liberation of endothelial CNP; in the presence of the myoendothelial gap-junction inhibitor 18alpha-glycyrrhetinic acid or after endothelial denudation, CNP release and EDHF responses are profoundly suppressed. These data demonstrate that acetylcholine-evoked release of endothelial CNP activates NPR-C on vascular smooth muscle that via a G(i) coupling promotes Ba(2+)ouabain-sensitive hyperpolarization. Thus, we have revealed the identity of EDHF and established a pivotal role for endothelial-derived CNP in the regulation of vascular tone and blood flow.
Full-text · Article · Mar 2003 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Responses to EDHF are usually characterised in the presence of nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibitors. The contribution of NO to endothelium-dependent relaxation in the presence of NOS inhibitors was assessed using NO scavengers with the objective of testing (i) whether any residual NO produces endothelium-dependent relaxation in a manner similar to EDHF and (ii) to identify the source of the residual NO.
Small rat hepatic and mesenteric arteries were mounted in a tension myograph for either isometric or membrane potential measurements.
Relaxation to ACh was unaffected by pre-treatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 300 microM), and indomethacin (Indo, 5 microM) in the absence or presence of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 microM), nitro-L-arginine (300 microM) or L-nitro-mono-methyl-arginine (L-NMMA, 300 microM). Addition of OxyHb (20 microM) or carboxy-PTIO (300 microM) produced a significant suppression of ACh-induced relaxations ( approximately 40%). In L-NAME+Indo treated arteries ACh-induced hyperpolarisation (delta16.3+/-2.1 mV, n=8) was significantly suppressed with the addition of OxyHb (Delta10.2+/-1.6 mV, n=12). ACh-induced relaxation, in the presence of L-NAME+Indo+OxyHb, was abolished by raised extracellular K(+), or the combination of charybdotoxin (CTX, 100 nM)+apamin (100 nM). In contrast whilst L-NAME+indo+barium+ouabain suppressed ACh-induced relaxation, the presence of OxyHb had no additional effect. Ultraviolet light induced a relaxation in arteries treated with L-NMMA+Indo (37.0+/-5.2%, n=9) which was sensitive to OxyHb (15.2+/-10.9%, n=4), and barium+ouabain (6.39+/-2.7%, n=4), but not CTX+apamin (37.8+/-2.4%, n=4).
These findings suggest that NO contributes significantly to the "EDHF-like" response seen in rat small arteries and that the source of this NO may be preformed vascular stores.
No preview · Article · Feb 2003 · Cardiovascular Research
[Show abstract][Hide abstract] ABSTRACT: Myogenic tone is an important determinant of vascular tone and blood flow in small resistance arteries of certain vascular beds. The role of the endothelium in myogenic responses is unclear. We hypothesized that endothelium-derived NO release modulates myogenic constriction in small resistance arteries and that mesenteric small arteries from mice with targeted disruption of the gene for endothelial NO synthase (eNOS) (knockout mice) demonstrate greater myogenic tone than do wild-type mice. Third-order mesenteric arteries (approximately 200 micrometer) were isolated and mounted in a pressure myograph. Internal diameter was recorded over a pressure range of 10 to 80 mm Hg. Removal of the endothelium significantly (P<0.05) enhanced the magnitude of myogenic constriction in wild-type mice. Similarly, pretreatment of arteries with N(G)-nitro-L-arginine methyl ester (L-NAME; 300 micromol/L) produced a comparable significant (P<0.05) increase in myogenic tone, whereas indomethacin (5 micromol/L) had no effect. eNOS knockout arteries also exhibited myogenic constriction. Neither L-NAME nor indomethacin had any effect on myogenic tone in the arteries of eNOS knockout mice. However, blockade of potential endothelium-derived hyperpolarizing factor-like mechanisms via inhibition of K(+) flux using either apamin (100 nmol/L) with charybdotoxin (100 nmol/L), Ba(2+) (30 micromol/L) with ouabain (1 mmol/L), or 18alpha-glycyrrhetinic acid (100 micromol/L) significantly (P<0.01) enhanced myogenic constriction. This study demonstrates that basal endothelium-derived NO modulates myogenic tone in mesenteric small arteries of wild-type mice. However, eNOS knockout arteries display normal myogenic responsiveness despite the absence of basal NO activity. The data suggest that this compensatory effect is due to the activity of an endothelium-derived hyperpolarizing factor to normalize vascular tone.
[Show abstract][Hide abstract] ABSTRACT: Objectives: Responses to EDHF are usually characterised in the presence of nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibitors. The contribution of NO to endothelium-dependent relaxation in the presence of NOS inhibitors was assessed using NO scavengers with the objective of testing (i) whether any residual NO produces endothelium-dependent relaxation in a manner similar to EDHF and (ii) to identify the source of the residual NO. Methods: Small rat hepatic and mesenteric arteries were mounted in a tension myograph for either isometric or membrane potential measurements. Results: Relaxation to ACh was unaffected by pre-treatment with G N -nitro-L-arginine methyl ester ( L-NAME, 300 mM), and indomethacin (Indo, 5 mM) in the absence or presence of 1H-(1,2,4)ox- adiazolo(4,3-a)quinoxalin-1-one (ODQ, 1 mM), nitro-L-arginine (300 mM) or L-nitro-mono-methyl-arginine ( L-NMMA, 300 mM). Addition of OxyHb (20 mM) or carboxy-PTIO (300 mM) produced a significant suppression of ACh-induced relaxations ( ¯40%). In L-NAME1Indo treated arteries ACh-induced hyperpolarisation (D16.362.1 mV, n58) was significantly suppressed with the addition of OxyHb (D10.261.6 mV, n512). ACh-induced relaxation, in the presence of L-NAME1Indo1OxyHb, was abolished by raised 1 extracellular K , or the combination of charybdotoxin (CTX, 100 nM)1apamin (100 nM). In contrast whilst L-NAME1indo1barium1 ouabain suppressed ACh-induced relaxation, the presence of OxyHb had no additional effect. Ultraviolet light induced a relaxation in arteries treated with L-NMMA1Indo (37.065.2%, n59) which was sensitive to OxyHb (15.2610.9%, n54), and barium1ouabain (6.3962.7%, n54), but not CTX1apamin (37.862.4%, n54). Conclusions: These findings suggest that NO contributes significantly to the ''EDHF-like'' response seen in rat small arteries and that the source of this NO may be preformed vascular stores. 2002 European Society of Cardiology. Published by Elsevier Science B.V. All rights reserved.