Differential sensitivities of the prostacyclin and nitric oxide biosynthetic pathways to cytosolic calcium in bovine aortic endothelial cells

A Review of the Actions of Endogenous and Exogenous Vasoactive Substances during the Estrous Cycle and Pregnancy in Rats

Vascular endothelium plays a key role in regulating cardiovascular homeostasis by controlling the vascular tone. Variations in sex hormones during the reproductive cycle of females affect the homeostasis of the cardiovascular system. Also, the evidence shows that estrogens show a cardioprotective effect. On this basis, this study describes some vascular responses induced by vasoactive substances during the estrous cycle in rats. We obtained the information available on this topic from the online databases that included scientific articles published in the Web of Science, PubMed, and Scielo. Many investigations have evaluated the vasoactive response of substances such as acetylcholine and norepinephrine during the estrous cycle. In this review, we specifically described the vascular response to vasoactive substances in rats during the estrous cycle, pregnancy, and in ovariectomized rats. In addition, we discussed the existence of different signaling pathways that modulate vascular function. The knowledge of these effects is relevant for the optimization and development of new treatments for some vascular pathologies.

Protective effect of N-acetylcysteine against oxygen radical-mediated coronary artery injury

The present study investigated the protective effect of N-acetylcysteine (NAC) against oxygen radical-mediated coronary artery injury. Vascular contraction and relaxation were determined in canine coronary arteries immersed in Kreb's solution (95% O2-5% CO2), incubated or not with NAC (10 mM), and exposed to free radicals (FR) generated by xanthine oxidase (100 mU/ml) plus xanthine (0.1 mM). Rings not exposed to FR or NAC were used as controls. The arteries were contracted with 2.5 microM prostaglandin F2alpha. Subsequently, concentration-response curves for acetylcholine, calcium ionophore and sodium fluoride were obtained in the presence of 20 microM indomethacin. Concentration-response curves for bradykinin, calcium ionophore, sodium nitroprusside, and pinacidil were obtained in the presence of indomethacin plus Nomega-nitro-L-arginine (0.2 mM). The oxidative stress reduced the vascular contraction of arteries not exposed to NAC (3.93 +/- 3.42 g), compared to control (8.56 +/- 3.16 g) and to NAC group (9.07 +/- 4.0 g). Additionally, in arteries not exposed to NAC the endothelium-dependent nitric oxide (NO)-dependent relaxation promoted by acetylcholine (1 nM to 10 microM) was also reduced (maximal relaxation of 52.1 +/- 43.2%), compared to control (100%) and NAC group (97.0 +/- 4.3%), as well as the NO/cyclooxygenase-independent receptor-dependent relaxation provoked by bradykinin (1 nM to 10 microM; maximal relaxation of 20.0 +/- 21.2%), compared to control (100%) and NAC group (70.8 +/- 20.0%). The endothelium-independent relaxation elicited by sodium nitroprusside (1 nM to 1 microM) and pinacidil (1 nM to 10 microM) was not affected. In conclusion, the vascular dysfunction caused by the oxidative stress, expressed as reduction of the endothelium-dependent relaxation and of the vascular smooth muscle contraction, was prevented by NAC.

Simvastatin increases endothelial nitric oxide synthase and ameliorates cerebral vasospasm resulting from subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Endothelial nitric oxide synthase (eNOS) activity is decreased after subarachnoid hemorrhage (SAH). Simvastatin increases eNOS activity. We hypothesized that simvastatin would increase eNOS protein and ameliorate SAH-induced cerebral vasospasm.

METHODS

Mice were treated with subcutaneous simvastatin or vehicle for 14 days and then subjected to endovascular perforation of the right anterior cerebral artery or sham surgery. Three days later, neurological deficits were scored (5 to 27; 27=normal), and middle cerebral artery diameter and eNOS protein were measured. The study was repeated, but simvastatin treatment was started after SAH or sham surgery.

RESULTS

In SAH mice, simvastatin pretreatment increased middle cerebral artery diameter (SAH-simvastatin=74+/-22 micro m, SAH-vehicle=52+/-18 micro m, P=0.03; sham-simvastatin=102+/-8 micro m, sham-vehicle=105+/-6 micro m). Pretreatment reduced neurological deficits (SAH-simvastatin=25+/-2, SAH-vehicle=20+/-2, P=0.005; sham-simvastatin and sham-vehicle=27+/-0). Simvastatin pretreatment also increased eNOS protein. Simvastatin posttreatment caused a modest increase in middle cerebral artery diameter in SAH mice (SAH-simvastatin=56+/-12 micro m, SAH-vehicle=45+/-4 micro m, P=0.03; sham-simvastatin=92+/-13 micro m, sham-vehicle=99+/-10 micro m) and reduced neurological deficits (SAH-simvastatin=21+/-1, SAH-vehicle=19+/-2, P=0.009). Simvastatin posttreatment did not significantly increase eNOS protein.

CONCLUSIONS

Simvastatin treatment before or after SAH attenuated cerebral vasospasm and neurological deficits in mice. The mechanism may be attributable in part to eNOS upregulation.

Insulin inhibits acetylcholine responses in rat isolated mesenteric arteries via a non-nitric oxide nonprostanoid pathway

Hyperinsulinemia is a risk factor for hypertension and arteriosclerosis. The mechanism by which it contributes to disease progression is not known. The present study examines the effects of insulin on endothelium-derived relaxing factors. Segments of rat mesenteric arterioles and aorta were set up for isometric recordings. The effect of insulin (1 mU/mL) on acetylcholine responses was examined with and without nitro-L-arginine, indomethacin, KCl (40 mmol/L), and apamin+charybdotoxin. Incubation with insulin (maximum response to acetylcholine 90.9+/-8.7% versus 90.7+/-4.5% for before versus after insulin, respectively), nitro-L-arginine, indomethacin, or high K(+) alone had no effect on these responses in mesenteric arterioles. Apamin+charybdotoxin significantly blunted responses to acetylcholine. When coincubated with nitro-L-arginine but not with indomethacin or high K(+), insulin blunted the maximum response to acetylcholine (from 84.8+/-8.2% to 40.7+/-10.2% for before versus after insulin, respectively; P<0.01). When coincubated with apamin+charybdotoxin, insulin had no further effect. Coadministration of indomethacin with nitro-L-arginine had no greater effect than did nitro-L-arginine alone. The addition of insulin, together with nitro-L-arginine and indomethacin, significantly decreased the maximal response to acetylcholine from 96.6+/-5.3% to 52.9+/-10.8% (P<0.01). In the aorta, nitro-L-arginine abolished acetylcholine responses. Coadministration with insulin had no further effect. We conclude that insulin attenuates acetylcholine responses mediated by endothelium-derived hyperpolarizing factor in small but not large arteries. This effect of insulin is apparent only when NO is blocked and may be important in the development of hypertension or arteriosclerosis when reduced NO function has been reported.

Effects of SK&F 96365 and mefenamic acid on Ca2+ influx in stimulated endothelial cells and on endothelium-derived hyperpolarizing factor-mediated arterial hyperpolarization and relaxation

This study was undertaken to assess how Ca2+ influx into endothelial cells via Ca2+-permeable nonselective cation channels (NSCCs) is important in vascular responses mediated by endothelium-derived hyperpolarizing factor (EDHF). In cultured porcine aortic endothelial cells, the sustained increases in the intracellular Ca2+ concentration ([Ca2+]i) elicited by bradykinin and cyclopiazonic acid, which were strongly dependent on the presence of extracellular Ca2+, were suppressed by the NSCC blockers, SK&F 96365 and mefenamic acid. In porcine coronary artery with intact endothelium, bradykinin elicited a rapid fall in the membrane potential, followed by sustained hyperpolarization with a slow decay. In the presence of SK&F 96365 or mefenamic acid, the peak amplitude was severely reduced and the decay phase of hyperpolarization to bradykinin was greatly accelerated, which was apparently similar to the response obtained in Ca2+-free medium. Cyclopiazonic acid caused sustained hyperpolarization in an extracellular Ca2+-dependent manner, an effect which was markedly diminished by SK&F 96365 and mefenamic acid. In rings of coronary artery precontracted with U46619, bradykinin and cyclopiazonic acid produced endothelium-dependent relaxations even in the presence of N(G)-nitro-L-arginine and indomethacin. SK&F 96365 and mefenamic acid significantly attenuated the relaxant responses. These results indicate that the increase in [Ca2+]i of endothelial cells due to Ca2+ entry via NSCCs plays a crucial role in the maintenance of the EDHF-mediated vascular responses.

EDHF mediates flow-induced dilation in skeletal muscle arterioles of female eNOS-KO mice

Vasodilation to increases in flow was studied in isolated gracilis muscle arterioles of female endothelial nitric oxide synthase (eNOS)-knockout (KO) and female wild-type (WT) mice. Dilation to flow (0-10 microl/min) was similar in the two groups, yet calculated wall shear stress was significantly greater in arterioles of eNOS-KO than in arterioles of WT mice. Indomethacin, which inhibited flow-induced dilation in vessels of WT mice by approximately 40%, did not affect the responses of eNOS-KO mice, whereas miconazole and 6-(2-proparglyoxyphenyl)hexanoic acid (PPOH) abolished the responses. Basal release of epoxyeicosatrienonic acids from arterioles was inhibited by PPOH. Iberiotoxin eliminated flow-induced dilation in arterioles of eNOS-KO mice but had no effect on arterioles of WT mice. In WT mice, neither N(omega)-nitro-L-arginine methyl ester nor miconazole alone affected flow-induced dilation. Combination of both inhibitors inhibited the responses by approximately 50%. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) alone inhibited flow-induced dilation by approximately 49%. ODQ + indomethacin eliminated the responses. Thus, in arterioles of female WT mice, nitric oxide and prostaglandins mediate flow-induced dilation. When eNOS is inhibited, endothelium-derived hyperpolarizing factor substitutes for nitric oxide. In female eNOS-KO mice, metabolites of cytochrome P-450, via activation of large-conductance Ca2+-activated K+ channels of smooth muscle, mediate entirely the arteriolar dilation to flow.

In eNOS knockout mice skeletal muscle arteriolar dilation to acetylcholine is mediated by EDHF

The mechanisms that account for acetylcholine (ACh)-induced responses of skeletal muscle arterioles of mice lacking endothelial nitric oxide (NO) synthase (eNOS-KO) were investigated. Isolated, cannulated, and pressurized arterioles of gracilis muscle from male eNOS-KO (74.1 +/- 2.3 microm) and wild-type (WT, 87.2 +/- 2.1 microm) mice developed spontaneous tone accounting for 63 and 61% of their passive diameter (116.8 +/- 3.4 vs. 143.2 +/- 2.8 microm, respectively) and dilated dose-dependently to ACh (10(-9)-10(-7) M). These dilations were significantly smaller in vessels of eNOS-KO compared with WT mice (29.2 +/- 2.0 microm vs. 46.3 +/- 2.1 microm, at maximum concentration) but responses to the NO donor, sodium nitrite (NaNO(2), 10(-6)-3 x 10(-5) M), were comparable in the vessels of the two strains. N(G)-nitro-L-arginine (L-NNA, 10(-4) M), an inhibitor of eNOS, inhibited ACh-induced dilations by 60-90% in arterioles of WT mice but did not affect responses in those of eNOS-KO mice. In arterioles of eNOS-KO mice, dilations to ACh were not affected by indomethacin but were essentially abolished by inhibitors of cytochrome P-450, clotrimazole (CTZ, 2 x 10(-6) M) or miconazole (MCZ, 2 x 10(-6) M), as well as by either high K(+) (40 mM) or iberiotoxin [10(-7) M, a blocker of Ca(2+)-dependent K(+) channels (K(Ca) channels)]. On the other hand, in WT arterioles CTZ or MCZ inhibited ACh-induced dilations only by approximately 10% and only in the presence of L-NNA. These results indicate that in arterioles of eNOS-KO mice, endothelium-derived hyperpolarizing factor (EDHF), synthesized via cytochrome P-450, accounts entirely for the mediation of ACh-induced dilation via an increase in K(Ca)-channel activity. In contrast, in arterioles of WT mice, endothelium-derived NO predominantly mediates ACh-induced dilation in which participation of EDHF becomes apparent only after inhibition of NO synthesis.

Molecular keys to the problems of cerebral vasospasm

The mechanisms responsible for subarachnoid hemorrhage (SAH)-induced vasospasm are under intense investigation but remain incompletely understood. A consequence of SAH-induced vasospasm, cerebral infarction, produces a nonrecoverable ischemic tissue core surrounded by a potentially amenable penumbra. However, successful treatment has been inconsistent. In this review, we summarize the basic molecular biology of cerebrovascular regulation, describe recent developments in molecular biology to elucidate the mechanisms of SAH-induced vasospasm, and discuss the potential contribution of cerebral microcirculation regulation to the control of ischemia. Our understanding of the pathogenesis of SAH-induced vasospasm remains a major scientific challenge; however, molecular biological techniques are beginning to uncover the intracellular mechanisms involved in vascular regulation and its failure. Recent findings of microvascular regulatory mechanisms and their failure after SAH suggest a role in the development and size of the ischemia. Progress is being made in identifying the various components in the blood that cause SAH-induced vasospasm. Thus, our evolving understanding of the underlying molecular mechanism may provide the basis for improved treatment after SAH-induced vasospasm, especially at the level of the microcirculation.

Inhibitory effect of insulin on bradykinin-induced venodilation

BACKGROUND

Excessive insulin is one of the risk factors of hypertension and arteriosclerosis despite its vasodilative properties shown in recent studies. Although many vasoactive substances contribute and interact with each other in the development of hypertension, the interactions between insulin and other vasoactive substances have yet to be elucidated.

OBJECTIVE

To assess the effect of insulin on the action of bradykinin.

METHODS

The vasodilating effect of bradykinin was evaluated, with or without coadministration of insulin, in human dorsal hand veins of healthy volunteers. In cultured porcine aortic endothelial cells, the bradykinin-induced increase of intracellular calcium was also investigated before and after insulin administration.

RESULTS

Insulin significantly attenuated bradykinin-induced increase in intracellular calcium and venodilation in cultured endothelial cells and human dorsal hand veins, respectively.

CONCLUSIONS

These findings suggest that insulin attenuates the bradykinin-induced calcium elevation in endothelial cells and may decrease the production of vasodilative substances from endothelial cells, resulting in the reduction of vasodilation. This effect may contribute to the development of hypertension in patients with hyperinsulinaemia.

The effects of perhexiline on the rat coronary vasculature

The predominant site and mechanism(s) of perhexiline-induced coronary vasodilatation were investigated in the rat heart. Perhexiline was more potent in the Langendorff perfused heart than in the left anterior descending coronary artery (EC50; 0.27 microM, confidence limits 0.19-0.39: 2.7 microM, 2.0-3.4, respectively). Selective endothelial inactivation with Triton X-100 in the perfused heart, reduced the response to perhexiline 1 microM (76+8% to 30+3% of control). 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) 3 microM, Nomega-nitro-L-arginine 100 microM, or a combination of the latter with indomethacin 10 microM, had no significant effect on responses to perhexiline in the perfused heart. Unlike bradykinin-induced vasodilatation, responses to perhexiline were not inhibited by tetrabutylammonium 1 mM, or charybdotoxin 20 nM. SKF525A 5 microM inhibited both perhexiline and bradykinin responses, while apamin 1 microM and glibenclamide 3 microM inhibited neither. Perhexiline exerts partially endothelium-dependent coronary vasodilator effects in the rat, predominantly on small coronary arteries, which appear to be independent of nitric oxide (NO), prostacyclin and the endothelium-derived hyperpolarising factor (EDHF) released by bradykinin.

Effects of K+ channel openers on relaxations to nitric oxide and endothelium-derived hyperpolarizing factor in rat mesenteric artery

Relaxation of methoxamine-precontracted, endothelium-intact, rat mesenteric artery in the presence of NG-nitro-L-arginine methyl ester (L-NAME; 100 microM) and indomethacin (10 microM) is attributed to endothelium-derived hyperpolarizing factor (EDHF). The potency of carbachol in the presence (but not the absence) of L-NAME was reduced by levcromakalim and pinacidil, activators of ATP-sensitive K+ channels (KATP). EDHF-mediated relaxation to Ca2+ ionophore A23187 was unaffected by these compounds but was inhibited by verapamil at the level of the smooth muscle. Levcromakalim and pinacidil had the same effects at both reduced and standard levels of tone. Glibenclamide (10 microM), a KATP blocker, alone did not affect carbachol relaxations but abolished both relaxation to levcromakalim and pinacidil and their inhibitory action on EDHF released by carbachol. Levcromakalim inhibited the endothelium-dependent hyperpolarization of mesenteric arteries to carbachol but not to A23187. Thus, levcromakalim or pinacidil inhibit EDHF, but not nitric oxide, release by carbachol through an action on the endothelium.

Interactions between endothelium-derived relaxing factors in the rat hepatic artery: focus on regulation of EDHF

1. In rat isolated hepatic arteries contracted with phenylephrine, acetylcholine and the calcium ionophore A23187 each elicit endothelium-dependent relaxations, which involve both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). However, the contribution of prostanoids to these responses, and the potential interaction between EDHF and other endothelium-derived relaxing factors have not been examined. 2. In the presence of the NO synthase inhibitor N(G)-nitro-L-arginine (L-NOARG, 0.3 mM) and a mixture of charybdotoxin (0.3 microM) and apamin (0.3 microM), inhibitors of the target potassium (K) channel(s) for EDHF, acetylcholine and A23187 each induced a concentration-dependent and almost complete relaxation, which was abolished in the additional presence of indomethacin (10 microM). Thus, in addition to EDHF and NO, a relaxing factor(s) generated by cyclo-oxygenase (COX) contributes to endothelium-dependent relaxation in the rat hepatic artery. 3. The resting membrane potentials of endothelium-intact and endothelium-denuded vascular segments were -57 mV and -52 mV, respectively (P>0.05). In intact arteries, the resting membrane potential was not affected by L-NOARG plus indomethacin, but reduced to -47 mV in the presence of charybdotoxin plus apamin. Acetylcholine and A23187 (10 microM each) elicited a hyperpolarization of 13 mV and 15 mV, respectively. The hyperpolarization induced by these agents was not affected by L-NOARG plus indomethacin (12 mV and 14 mV, respectively), but reduced in the presence of charybdotoxin plus apamin (7 mV and 10 mV, respectively), and abolished in the combined presence of charybdotoxin, apamin and indomethacin. 4. The NO donor 3-morpholino-sydnonimine (SIN-1) induced a concentration-dependent relaxation, which was unaffected by charybdotoxin plus apamin, but abolished by the selective soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, 10 microM). SIN-1 (10 microM) did not alter the resting membrane potential in endothelium-denuded vascular segments. 5. The COX-dependent relaxation induced by acetylcholine was abolished following exposure to 30 mM KCl, but unaffected by glibenclamide (10 microM). The prostacyclin analogue iloprost induced a concentration-dependent relaxation, which was also abolished in 30 mM KCl and unaffected by the combined treatment with glibenclamide, charybdotoxin and apamin. Iloprost (10 microM) induced a glibenclamide-resistant hyperpolarization (8 mV with and 9 mV without glibenclamide) in endothelium-denuded vascular segments. 6. Exposure to SIN-1 or iloprost did not affect the EDHF-mediated relaxation induced by acetylcholine (i.e. in the presence of L-NOARG and indomethacin). Replacement of L-NOARG with the NO scavenger oxyhaemoglobin (10 microM) or the soluble guanylate cyclase inhibitor ODQ (10 microM) or methylene blue (10 microM), which all significantly inhibited responses to endothelium-derived NO, did not affect the acetylcholine-induced relaxation in the presence of indomethacin, indicating that endogenous NO also does not suppress EDHF-mediated responses. 7. These results show that, in addition to EDHF and NO, an endothelium-derived hyperpolarizing factor(s) generated by COX contributes significantly to endothelium-dependent relaxation in the rat heptic artery. Neither this factor nor NO seems to regulate EDHF-mediated responses. Thus, EDHF does not serve simply as a 'back-up' system for NO and prostacyclin in this artery. However, whether EDHF modulates the NO and COX pathways remains to be determined.

Conducted vascular responses: communication across the capillary bed

Conducted vasomotor responses are important for the effective distribution of blood flow, although the mechanism by which these responses are initiated is not well understood. ATP, a substance which is released from circulating red blood cells in response to low PO2 and low pH, two conditions which are associated with decreased supply relative to demand, has been shown to initiate conducted vasodilation following its intraluminal application in first and second order arterioles. Since such low PO2 and low pH conditions would most likely occur on the venous side of the vasculature, we evaluated the response of the arteriolar and capillary networks to application of ATP into venules in the Saran-covered hamster cheek pouch retractor muscle using in vivo video microscopy. Intraluminal application of 40 and 400 pl of 10(-6) M ATP resulted in dose-dependent increases in arteriolar diameter > 450 microm upstream from the site of application. These changes in arteriolar diameter were accompanied by significant increases in red blood cell flux. In capillaries, red blood cell flux doubled in response to ATP administration. Since NO was previously determined to be involved in the vascular response to intraluminal ATP in arterioles, we evaluated its role in these responses. We found that systemic administration of l-NAME prior to ATP application eliminated any conducted response and this effect of l-NAME was reversed by the systemic administration of l-arginine. These data suggest that ATP, which is released from red blood cells in response to low PO2 and low pH, conditions which would be found in the venular microvasculature, may serve a role in distributing perfusion in response to alterations in supply.

Mechanism of endothelium-dependent relaxation induced by thrombin in the pig coronary artery

The mechanism of thrombin-induced endothelium-dependent relaxation was investigated using fura-2 front-surface fluorometry. Thrombin induced an endothelium-dependent relaxation during U46619-induced contractions in pig coronary arterial strips. The relaxation consisted of two components: the early phasic component with a transient decrease in [Ca2+]i of smooth muscle and the subsequent sustained tonic component without [Ca2+]i decrease. The phasic relaxation was inhibited by a combination of N(omega)-nitro-L-arginine and K+-depolarization, while the tonic component was inhibited by either indomethacin or K+-depolarization. Thrombin induced a transient [Ca2+]i increase and nitric oxide (NO) production in pig aortic valvular endothelial cells, which expressed NO synthase as determined by reverse transcription and polymerase chain reaction. Thus, it was concluded that NO and hyperpolarizing factor were involved in the phasic component of thrombin-induced relaxation and that hyperpolarizing factor and prostacyclin were involved in the tonic component.

A comparison of EDHF-mediated and anandamide-induced relaxations in the rat isolated mesenteric artery

1. Relaxation of the methoxamine-precontracted rat small mesenteric artery by endothelium-derived hyperpolarizing factor (EDHF) was compared with relaxation to the cannabinoid, anandamide (arachidonylethanolamide). EDHF was produced in a concentration- and endothelium-dependent fashion in the presence of NG-nitro-L-arginine methyl ester (L-NAME, 100 microM) by either carbachol (pEC50 [negative logarithm of the EC50] = 6.19 +/- 0.01, Rmax [maximum response] = 93.2 +/- 0.4%; n = 14) or calcium ionophore A23187 (pEC50 = 6.46 +/- 0.02, Rmax = 83.6 +/- 3.6%; n = 8). Anandamide responses were independent of the presence of endothelium or L-NAME (control with endothelium: pEC50 = 6.31 +/- 0.06, Rmax = 94.7 +/- 4.6%; n = 10; with L-NAME: pEC50 = 6.33 +/- 0.04, Rmax = 93.4 +/- 6.0%; n = 4). 2. The selective cannabinoid receptor antagonist, SR 141716A (1 microM) caused rightward shifts of the concentration-response curves to both carbachol (2.5 fold) and A23187 (3.3 fold). It also antagonized anandamide relaxations in the presence or absence of endothelium giving a 2 fold shift in each case. SR 141716A (10 microM) greatly reduced the Rmax values for EDHF-mediated relaxations to carbachol (control, 93.2 +/- 0.4%; SR 141716A, 10.7 +/- 2.5%; n = 5; P < 0.001) and A23187 (control, 84.8 +/- 2.1%; SR 141716A, 3.5 +/- 2.3%; n = 6; P < 0.001) but caused a 10 fold parallel shift in the concentration-relaxation curve for anandamide without affecting Rmax. 3. Precontraction with 60 mM KCl significantly reduced (P < 0.01; n = 4 for all) relaxations to 1 microM carbachol (control 68.8 +/- 5.6% versus 17.8 +/- 7.1%), A23187 (control 71.4 +/- 6.1% versus 3.9 +/- 0.45%) and anandamide (control 71.1 +/- 7.0% versus 5.2 +/- 3.6%). Similar effects were seen in the presence of 25 mM K+. Incubation of vessels with pertussis toxin (PTX; 400 ng ml-1, 2 h) also reduced (P < 0.01; n = 4 for all) relaxations to 1 microM carbachol (control 63.5 +/- 7.5% versus 9.0 +/- 3.2%), A23187 (control 77.0 +/- 5.8% versus 16.2 +/- 7.1%) and anandamide (control 89.8 +/- 2.2% versus 17.6 +/- 8.7%). 4. Incubation of vessels with the protease inhibitor phenylmethylsulphonyl fluoride (PMSF; 200 microM) significantly potentiated (P < 0.01), to a similar extent (approximately 2 fold), relaxation to A23187 (pEC50: control, 6.45 +/- 0.04; PMSF, 6.74 +/- 0.10; n = 4) and anandamide (pEC50: control, 6.31 +/- 0.02; PMSF, 6.61 +/- 0.08; n = 8). PMSF also potentiated carbachol responses both in the presence (pEC50: control, 6.25 +/- 0.01; PMSF, 7.00 +/- 0.01; n = 4; P < 0.01) and absence (pEC50: control, 6.41 +/- 0.04; PMSF, 6.88 +/- 0.04; n = 4; P < 0.001) of L-NAME. Responses to the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) were also potentiated by PMSF (pEC50: control, 7.51 +/- 0.06; PMSF, 8.00 +/- 0.05, n = 4, P < 0.001). 5. EDHF-mediated relaxation to carbachol was significantly attenuated by the K+ channel blocker tetraethylammonium (TEA; 1 mM) (pEC50: control, 6.19 +/- 0.01; TEA, 5.61 +/- 0.01; n = 6; P < 0.01). In contrast, TEA (1 mM) had no effect on EDHF-mediated relaxation to A23187 (pEC50: control, 6.47 +/- 0.04; TEA, 6.41 +/- 0.02, n = 4) or on anandamide (pEC50: control, 6.28 +/- 0.06; TEA, 6.09 +/- 0.02; n = 5). TEA (10 mM) significantly (P < 0.01) reduced the Rmax for anandamide (control, 94.3 +/- 4.0%; 10 mM TEA, 60.7 +/- 4.4%; n = 5) but had no effect on the Rmax to carbachol or A23187. 6. BaCl2 (100 microM), considered to be selective for blockade of inward rectifier K+ channels, had no significant effect on relaxations to carbachol or A23187, but caused a small shift in the anandamide concentration-response curve (pEC50: control, 6.39 +/- 0.01; Ba2+, 6.20 +/- 0.01; n = 4; P < 0.01). BaCl2 (1 mM; which causes non-selective block of K+ channels) significantly (P < 0.01) attenuated relaxations to all three agents (pEC50 values: carbachol, 5.65 +/- 0.02; A23187, 5.84 +/- 0.04; anandamide, 5.95 +/- 0.02; n = 4 for each). 7. Apamin (1mu M), a selective blocker of small conductance, Ca2+-activated, K+ channels (SKCa), 4-aminopyridine (1mM), a blocker of delayed rectifier, voltage-dependent, K+ channels (Kv), and ciclazindol (10mu M), an inhibitor of Kv and adenosine 5'-triphosphate (ATP)-sensitive K+ channels (KATP), significantly reduced EDHF-mediated relaxations to carbachol, but had no significant effects on A23187 or anandamide responses. 8. Glibenclamide (10mu M), a KATP inhibitor and charybdotoxin (100 or 300nM), a blocker of several K+ channel subtypes, had no significant effect on relaxations to any of the agents. Iberiotoxin (50nM), an inhibitor of large conductance, Ca2+-activated, K+ channels (BKCa), had no significant effect on the relaxation responses, either alone or in combination with apamin (1muM). Also, a combination of apamin (1muM) with either glibenclamide (10muM) or 4-aminopyridine (1mM) did not inhibit relaxation to carbachol significantly more than apamin alone. Neither combination had any significant effect on relaxation to A23187 or anandamide. 9. A combination of apamin (1muM) with charybdotoxin (100nM) abolished EDHF-mediated relaxation to carbachol, but had no significant effect on that to A23187. Apamin (1muM) and charybdotoxin (300nM) together consistently inhibited the response to A23187, while apamin (1muM) and ciclazindol (10muM) together inhibited relaxations to both carbachol and A23187. None of these toxin combinations had any significant effect on relaxation to anandamide. 10. It was concluded that the differential sensitivity to K+ channel blockers of EDHF-mediated responses to carbachol and A23187 might be due to actions on endothelial generation of EDHF, as well as its actions on the vascular smooth muscle, and suggests care must be taken in choosing the means of generating EDHF when making comparative studies. Also, the relaxations to EDHF and anandamide may involve activation of cannabinoid receptors, coupled via PTX-sensitive G-proteins to activation of K+ conductances. The results support the hypothesis that EDHF is an endocannabinoid but relaxations to EDHF and anandamide show differential sensitivity to K+ channel blockers, therefore it is likely that anandamide is not identical to EDHF in the small rat mesenteric artery.

Synergistic interaction between endothelium-derived NO and prostacyclin in pulmonary artery: potential role for K+ATP channels

1. The aim of the present study was to assess interactions between nitric oxide (NO) and prostacyclin (PGI2) during endothelium-dependent relaxations evoked by bradykinin, calcium ionophore (A23187) and acetylcholine in canine isolated pulmonary artery. 2. Relaxations to low concentrations of bradykinin and A23187 were abolished by combined inhibition of NO-synthase (by N omega-nitro-L-arginine methyl ester L-NAME, 30 microM) and cyclo-oxygenase (indomethacin, 10 microM), suggesting mediation by NO and PGI2. The individual contributions of NO and PGI2 to the dilator responses were quantified by use of areas above the separate indomethacin-insensitive and L-NAME-insensitive components of the concentration-effect curves, respectively. Individually, NO and PGI2 accounted for only 53 +/- 5% and 16 +/- 9% of total bradykinin-induced relaxation, and 46 +/- 10% and 20 +/- 9% of total A23187-induced relaxation, suggesting that NO and PGI2 acted synergistically to cause endothelium-dependent relaxation. 3. Relaxation to low concentrations of acetylcholine was abolished by L-NAME but not affected by indomethacin, suggesting the response was mediated solely by NO with no interaction from PGI2. 4. Glibenclamide (1 microM), an inhibitor of ATP-sensitive potassium (K+ATP) channels, inhibited responses to bradykinin or A23187 but did not affect relaxations evoked by acetylcholine. Glibenclamide did not affect endothelium-independent relaxations to PGI2 or the NO-donor, 3-morpholinosydnonimine (SIN-1). 5. With bradykinin, glibenclamide attenuated total relaxation by 49 +/- 8%, but did not alter the individual NO and PGI2-mediated components of the response. Glibenclamide abolished the synergistic interaction between endothelium-derived NO and PGI2. 6. At high concentrations, bradykinin, A23187 or acetylcholine caused endothelium-dependent relaxation that was insensitive to L-NAME + indomethacin. With bradykinin or A23187, this component of relaxation was inhibited by glibenclamide, whereas with acetylcholine, glibenclamide had no effect. 7. The synergistic interaction between endothelium-derived NO and PGI2 in canine pulmonary artery is mediated by activation of K+ATP channels, presumably by an endothelium-derived hyperopolarizing factor (EDHF). The pattern of endothelial dilator mediators and the presence of this synergistic interaction is dependent on the nature of the endothelial stimulus.

Sources of Ca2+ in relation to generation of acetylcholine-induced endothelium-dependent hyperpolarization in rat mesenteric artery

1. The aim of the present study was to identify the sources of Ca2+ contributing to acetylcholine (ACh)-induced release of endothelium-derived hyperpolarizing factor (EDHF) from endothelial cells of rat mesenteric artery and to assess the pathway involved. The changes in membrane potentials of smooth muscles by ACh measured with the microelectrode technique were evaluated as a marker for EDHF release. 2. ACh elicited membrane hyperpolarization of smooth muscle cells in an endothelium-dependent manner. The hyperpolarizing response was not affected by treatment with 10 microM indomethacin, 300 microM NG-nitro-L-arginine or 10 microM oxyhaemoglobin, thereby indicating that the hyperpolarization is not mediated by prostanoids or nitric oxide but is presumably by EDHF. 3. In the presence of extracellular Ca2+, 1 microM ACh generated a hyperpolarization composed of the transient and sustained components. By contrast, in Ca(2+)-free medium, ACh produced only transient hyperpolarization. 4. Pretreatment with 100 nM thapsigargin and 3 microM cyclopiazonic acid, endoplasmic reticulum Ca(2+)-ATPase inhibitors, completely abolished ACh-induced hyperpolarization. Pretreatment with 20 mM caffeine also markedly attenuated ACh-induced hyperpolarization. However, the overall pattern and peak amplitude of hyperpolarization were unaffected by pretreatment with 1 microM ryanodine. 5. In the presence of 5 mM Ni2+ or 3 mM Mn2+, the hyperpolarizing response to ACh was transient, and the sustained component of hyperpolarization was not observed. On the other hand, 1 microM nifedipine had no effect on ACh-induced hyperpolarization. 6. ACh-induced hyperpolarization was nearly completely eliminated by 500 nM U-73122 or 200 microM 2-nitro-4-carboxyphenyl-N, N-diphenylcarbamate, inhibitors of phospholipase C, but was unchanged by 500 nM U-73343, an inactive form of U-73122. Pretreatment with 20 nM staurosporine, an inhibitor of protein kinase C, did not modify ACh-induced hyperpolarization. 7. These results indicate that the ACh-induced release of EDHF from endothelial cells of rat mesenteric artery is possibly initiated by Ca2+ release from inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ pool as a consequence of stimulation of phospholipid hydrolysis due to phospholipase C activation, and maintained by Ca2+ influx via a Ni(2+)- and Mn(2+)-sensitive pathway distinct from L-type Ca2+ channels. The Ca(2+)-influx mechanism seems to be activated following IP3-induced depletion of the pool.

Hypoxic dilatation of porcine small coronary arteries: role of endothelium and KATP-channels

1. The aim of the present study was to determine the cellular mechanims and potential mediators involved in hypoxic dilatation of porcine small coronary arteries. 2. Small coronary arteries were isolated from a branch of the left anterior descending artery of porcine hearts, cannulated with glass micropipettes and studied in a perfusion myograph system. At a transmural pressure of 40 mmHg, the arteries had an internal diameter of 167.8 +/- 6.6 microns (n = 37). 3. In arteries contracted with acetylcholine (ACh), hypoxia (0% O2, 30 min) caused dilatation (86.9 +/- 6.7% relaxation, n = 6) in vessels with endothelium but constriction in endothelium-denuded vessels. 4. Hypoxic vasodilatation occurring in arteries with endothelium was abolished by the KATP channel inhibitor, glibenclamide (0.44 microM), but was not affected by inhibition of nitric oxide synthase (L-NAME, 44 microM) or cyclo-oxygenase (indomethacin, 4.4 microM). 5. Bradykinin evoked endothelium-dependent relaxation that was inhibited by L-NAME (44 microM) but not glibenclamide 0.44 microM). Cromakalim (0.1-0.3 microM), a KATP channel opener, caused relaxation that was inhibited by glibenclamide, but was not affected by L-NAME (44 microM) and/or indomethacin (4.4 microM). 6. Endothelium-removal inhibited vasodilatation evoked by cromakalim, but increased vasodilator responses to the NO donor, SIN-1 (10(-8) to 10(-5) M). 7. These results indicate that hypoxia acted directly on vascular smooth muscle of small coronary arteries to cause contraction. However, this effect was overwhelmed by endothelium-dependent relaxation in response to hypoxia. This relaxation was most likely mediated by release of an endothelium-derived factor, distinct from nitric oxide or prostacyclin, that activated smooth muscle KATP-channels.

Dynamic regulation of intracellular Ca2+ concentration in aortic endothelial cells

In non-excitable cells, a Ca2+ entry pathway is opened after the depletion of intracellular Ca2+ store sites. We have tried to estimate the sensitivity of this pathway to Ca2+ release using bovine aortic endothelial cells. Single application of a high concentration (30 microM) of ATP released almost all stored Ca2+ in Ca(2+)-free extracellular solution, whereas a low concentration of ATP (30 nM) produced a partial (57.3 +/- 3.0%) release of Ca2+. By 10 min of Ca2+ re-perfusion, the Ca2+ store site was reloaded to 97.1% of its initial filling state. When thapsigargin was applied to this cell in Mn2+ solution, Mn(2+)-induced quenching of fura-2 dye started when 19.3 +/- 5.3% of Ca2+ release, produced by 30 nM ATP, had occurred. Therefore, Ca2+ release required for Mn2+ entry was estimated as 11.1 +/- 3.0% of stored Ca2+. These results indicate that intracellular Ca2+ concentration is controlled dynamically by simultaneously occurring Ca2+ release and entry in bovine aortic endothelial cells.

Nitric oxide attenuates the release of endothelium-derived hyperpolarizing factor

BACKGROUND

The contribution of the endothelium-derived hyperpolarizing factor (EDHF), proposed to be a cytochrome P450-derived metabolite of arachidonic acid, to endothelium-dependent dilatation under physiological conditions has yet to be established, because its effect can be detected only after inhibition of NO synthase and cyclooxygenase. The possibility that NO exerts a feedback inhibition on EDHF formation was studied in isolated perfused arterial segments.

METHODS AND RESULTS

Under combined blockade of NO synthase and cyclooxygenase, the EDHF-mediated vasodilatation elicited by receptor-dependent agonists in rabbit carotid and porcine coronary arteries was significantly attenuated by the NO donors C87-3786 and CAS 1609. The endothelium-independent dilatation elicited by isoproterenol was not altered by either NO donor. In NG-nitro-L-arginine-treated carotid artery segments, C87-3786 significantly attenuated the acetylcholine-induced increase in 6-keto-prostaglandin F1 alpha release, which was taken as an index of arachidonic acid liberation. In parallel experiments using cultured human endothelial cells, C87-3786 attenuated the Ca2+ response to bradykinin. The release of EDHF from a luminally perfused porcine coronary artery was detected by recording the membrane potential of downstream-situated cultured rat aortic smooth muscle cells. The NO donor C87-3786 had no effect on the hyperpolarization elicited by preformed EDHF but markedly inhibited its release from bradykinin-stimulated donor segments.

CONCLUSIONS

These findings indicate that under physiological conditions, the production of EDHF is damped by NO. Therefore, it follows that when NO synthesis is impaired, alleviation of this intrinsic inhibition may, at least in part, maintain endothelial vasodilator function.

Inhibition of nitric oxide synthesis in vascular smooth muscle by retinoids

1. These studies examine the effect of retinoids on interleukin 1 beta (IL-1 beta)-induced nitric oxide synthase (NOS) activity in cultured rat aortic vascular smooth muscle (VSM) cells and isolated rat aortic rings. 2. All-trans-retinoic acid (all-trans-RA, 0.1-10 microM) and its active analogues produced concentration-dependent inhibition of IL-1 beta (0.1-10 ng ml-1)-induced nitrite production in cultured VSM cells. In contrast, the inactive retinoid, Ro 14-6113 (0.1-10 microM), had no effect on IL-1 beta-induced nitrite production. 3. Since some of the actions of retinoids are mediated by induction of transforming growth factor beta (TGF-beta), its effect on inducible NOS activity in VSM cells was examined. TGF-beta produced concentration-dependent (0.1-10 ng ml-1) inhibition of IL-1 beta-induced nitrite production and the maximum effect (approximately 90% inhibition) was significantly greater than that seen with all-trans-RA (approximately 70% with 10 microM). However, an anti-TGF-beta antibody (50 micrograms ml-1) which blocked the effect of exogenous TGF-beta (5 ng ml-1) did not significantly reverse the inhibitory action of all-trans-RA (10 microM). 4. In addition to inhibiting IL-1 beta-induced nitrite production, all-trans-RA (10 microM) reduced substantially inducible NOS mRNA and protein levels in IL-1 beta-induced VSM cells (P < 0.01). 5. Incubation of isolated rat aortic rings with IL-1 beta (10 ng ml-1) caused a progressive resistance of the rings to the vasoconstrictor action of phenylephrine (10 nM to 10 microM). This effect was abolished by the addition of the nitric oxide synthase inhibitor L-NG-monomethyl-L-arginine (L-NMMA, 1 mM). All trans-RA (10 micro M) also markedly and significantly reversed this IL-1p-induced vascular hyporeactivity(P<0.01).6. These data show that all-trans-RA and other active retinoids are able to block cytokine-stimulated expression of inducible NOS in cultured VSM cells and isolated aortic rings.

Phorbol ester enhances activation of adenylate cyclase in bovine aortic endothelial cells

Endothelial cells possess beta-adrenoceptors linked to adenylate cyclase which may regulate several aspects of endothelial cell function. The potential for this second messenger system to be modulated by protein kinase C activity was investigated. Bovine aortic endothelial cells (BAECs) were cultured in the absence or presence of phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C. Basal and forskolin-, sodium fluoride (NaF)-, and isoproterenol-stimulated adenylate cyclase activity was measured in homogenates from BAECs. beta-adrenoceptor density on membranes from BAECs was measured by 125I-iodocyanopindolol binding. Sodium dodecylsulfate-polyacrylamide gel electrophoresis of immunoprecipitated proteins was used to identify phosphorylated proteins. Pretreatment of BAECs with 100 nM PMA for 30 min increased basal adenylate cyclase activity above control levels, and also increased enzyme activity stimulated by forskolin, NaF, or isoproterenol. Pretreatment of BAECs for 60 min with 100 nM staurosporine, an inhibitor of protein kinase C, prevented the enhancement of adenylate cyclase activity caused by PMA. Treatment of BAECs with PMA did not trigger phosphorylation of the inhibitory guanine nucleotide-binding protein, and there was no change in BAEC beta-adrenoceptor density following PMA pretreatment. Exposure of BAECs to ATP or bradykinin did not mimic the effects of phorbol ester. In conclusion, activation of protein kinase C by PMA enhanced adenylate cyclase activity in BAECs. However, ATP and bradykinin which activate endothelial cell surface receptors linked to phospholipase C did not mimic this effect.

Bradykinin-induced release of PGI2 from aortic endothelial cell lines: responses mediated selectively by Ca2+ ions or a staurosporine-sensitive kinase

1. Bradykinin (100 nM) triggers release of nitric oxide and prostacyclin from both AG07680A and AG04762 bovine cultured aortic endothelial cells. The exposure of these cells to bradykinin is in each case associated with a striking rise in intracellular calcium ion concentration. 2. Exposure of AG07680A cells to 250 nM ionomycin was followed also by a significant release of prostacyclin, whereas 250 nM ionomycin had no capacity to stimulate release of prostacyclin from AG04762 cells. 3. There was a similar concentration-dependent increase in intracellular calcium ion concentration on exposure of AG07680A and AG04762 cells to ionomycin. 4. Exposure of AG04762 cells for 10 min to staurosporine produced a concentration-dependent inhibition (IC50 = 107 +/- 14 nM) in bradykinin-stimulated prostacyclin release. There was no similar inhibitory effect of staurosporine in AG07680A cells. 5. Bradykinin (10 nM) triggered release of nitric oxide from both AG07680A and AG04762 cells, and the effect was not inhibited by 500 nM staurosporine. There was a similar ionomycin-dependent release of nitric oxide from both cell types. 6. These results identify a common pathway for bradykinin-dependent nitric oxide release from both AG07680A and AG04762 cells, involving increases in intracellular calcium ion concentration. In contrast, the bradykinin-dependent release of prostacyclin may involve one of two pathways (involving an increase in intracellular calcium or activation of a staurosporine-sensitive kinase), and the two pathways are selectively exploited in AG07680A and AG04762 cells, respectively.