Role of nitric oxide in isoprenaline and sodium nitroprusside-induced relaxation in human hand veins.
(9/3024)
AIMS: Recent reports, largely in animal models, have suggested that either inhibition of nitric oxide (NO) synthase or endothelium removal in arteries inhibits the response to isoprenaline, a beta-adrenoceptor agonist, and also enhances the response to sodium nitroprusside, a nitrovasodilator. This in vivo study was designed to determine whether N(G)-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthesis, influences relaxation of human hand veins mediated by isoprenaline or by sodium nitroprusside. METHODS: Using the dorsal hand vein technique, full dose-response curves to bradykinin (0.27-278 ng min(-1), n=6), isoprenaline (2.12-271 ngmin(-1), n=8) and sodium nitroprusside (0.01-634 ng min(-1) n=7) were generated on separate occasions before and after L-NMMA co-infusion (50 microg min(-1)). RESULTS: In veins preconstricted with the alpha1-adrenoceptor-selective agonist phenylephrine, the three vasodilators induced maximal responses (Emax) of 119+/-35, 72+/-18 and 103+/-17%, respectively. L-NMMA inhibited relaxation to bradykinin by 64% (P=0.014) but did not influence relaxation induced by isoprenaline. The sensitivity to sodium nitroprusside was significantly enhanced by L-NMMA co-infusion (concentration shift of 2.3, P=0.031). CONCLUSIONS; We conclude that in human veins, spontaneously released NO does not play a major role in isoprenaline-induced relaxation. Our results also suggest that the effects of sodium nitroprusside in this vascular bed may be attenuated by endothelium-derived NO. (+info)
Hemodynamic basis for the acute cardiac effects of troglitazone in isolated perfused rat hearts.
(10/3024)
Troglitazone is a thiazolidinedione used for the treatment of NIDDM and potentially for other insulin-resistant disease states. Troglitazone has recently been shown to increase cardiac output and stroke volume in human subjects. These actions are thought to be mediated by the reduction of peripheral resistance, but a potential direct effect on cardiac function has not been studied. Therefore, we investigated the direct cardiac hemodynamic effects of troglitazone in isolated perfused rat hearts. Five groups of hearts were studied. Hearts were tested under isovolumetric contraction with a constant coronary flow, and troglitazone (0.2, 0.5, and 1.0 micromol) was administered by bolus injection. Peak isovolumetric left ventricular pressure (LVPmax), peak rate of rise of LVP (dP/dt(max)), and peak rate of fall of LVP (dP/dt(min)) were significantly increased 1 min after troglitazone administration in a dose-dependent manner, while the heart rate (HR) and coronary perfusion pressure (CPP) were significantly decreased (P < 0.05). HR was then fixed by pacing and/or CPP was fixed with nitroprusside to eliminate any effect of the two variables on the action of troglitazone. With constant HR and/or constant CPP, the effect of troglitazone on LVPmax, dP/dt(max), and dP/dt(min) was still unchanged. In addition, the positive inotropic, positive lusitropic, and negative chronotropic actions of troglitazone were not influenced even when hearts were pretreated with prazosin, propranolol, or nifedipine. In conclusion, troglitazone has direct positive inotropic, positive lusitropic, negative chronotropic, and coronary artery dilating effects. The inotropic and chronotropic actions of troglitazone are not mediated via adrenergic receptors or calcium channels. These findings have important clinical implications for diabetic patients with congestive heart failure. (+info)
Abnormal flow-mediated epicardial vasomotion in human coronary arteries is improved by angiotensin-converting enzyme inhibition: a potential role of bradykinin.
(11/3024)
OBJECTIVES: This study was performed to determine whether angiotensin converting enzyme (ACE) inhibition improves endothelium-dependent flow-mediated vasodilation in patients with atherosclerosis or its risk factors and whether this is mediated by enhanced bradykinin activity. BACKGROUND: Abnormal coronary vasomotion due to endothelial dysfunction contributes to myocardial ischemia in patients with atherosclerosis, and its reversal may have an antiischemic action. Previous studies have shown that ACE inhibition improves coronary endothelial responses to acetylcholine, but whether this is accompanied by improved responses to shear stress remains unknown. METHODS: In 19 patients with mild atherosclerosis, metabolic vasodilation was assessed during cardiac pacing. Pacing was repeated during separate intracoronary infusions of low-dose bradykinin (BK) and enalaprilat. Endothelium-dependent and -independent vasodilation was estimated with intracoronary BK and sodium nitroprusside respectively. RESULTS: Enalaprilat did not alter either resting coronary vascular tone or dilation with sodium nitroprusside, but potentiated BK-mediated dilation. Epicardial segments that constricted abnormally with pacing (-5+/-1%) dilated (3+/-2%) with pacing in the presence of enalaprilat (p = 0.002). Similarly, BK at a concentration (62.5 ng/min) that did not alter resting diameter in the constricting segments also improved the abnormal response to a 6+/-1% dilation (p < 0.001). Cardiac pacing-induced reduction in coronary vascular resistance of 27+/-4% (p < 0.001) remained unchanged after enalaprilat. CONCLUSIONS: Thus ACE inhibition: A) selectively improved endothelium-dependent but not-independent dilation, and B) abolished abnormal flow-mediated epicardial vasomotion in patients with endothelial dysfunction, in part, by increasing endogenous BK activity. (+info)
Endothelium-dependent relaxation by acetylcholine is impaired in hypertriglyceridemic humans with normal levels of plasma LDL cholesterol.
(12/3024)
OBJECTIVES: Patients with high triglyceride (of which very low density lipoproteins [VLDL] are the main carriers), but with normal low density lipoprotein (LDL) cholesterol levels, were examined for in vivo endothelium function status. BACKGROUND: Very low density lipoproteins inhibit endothelium-dependent, but not -independent, vasorelaxation in vitro. METHODS: Three groups were studied: 1) healthy volunteers (n = 10; triglyceride 1.24+/-0.14 mmol/liter, LDL cholesterol 2.99+/-0.24 mmol/liter); 2) hypertriglyceridemic (n = 11; triglyceride 6.97+/-1.19 mmol/liter, LDL cholesterol 2.17+/-0.2 mmol/liter, p < 0.05); and 3) hypercholesterolemic (n = 10; triglyceride 2.25+/-0.29 mmol/liter, LDL cholesterol 5.61+/-0.54 mmol/liter; p < 0.05) patients. Vasoactive responses to acetylcholine, sodium nitroprusside, noradrenaline, N(G)-monomethyl-L-arginine and postischemic hyperemia were determined using forearm venous occlusion plethysmography. RESULTS: Responses to acetylcholine (37 microg/min) were significantly dampened both in hypercholesterolemic (% increase in forearm blood flow: 268.2+/-62) and hypertriglyceridemic patients (232.6+/-45.2) when compared with controls (547.8+/-108.9; ANOVA p < 0.05). Responses to sodium nitroprusside (at 1.6 microg/min: controls vs. hypercholesterolemics vs. hypertriglyceridemic: 168.7+/- 25.1 vs. 140.6+/-38.9 vs. 178.5+/-54.5% increase), noradrenaline, N(G)-monomethyl-L-arginine and postischemic hyperemic responses were not different among the groups examined. CONCLUSIONS: Acetylcholine responses are impaired in patients with pathophysiologic levels of plasma triglycerides but normal plasma levels of LDL cholesterol. The impairment observed was comparable to that obtained in hypercholesterolemic patients. We conclude that impaired responses to acetylcholine normally associated with hypercholesterolemia also occur in hypertriglyceridemia. These findings identify a potential mechanism by which high plasma triglyceride levels may be atherogenic independent of LDL cholesterol levels. (+info)
Inhibition of hypoxia-inducible factor 1 activation by carbon monoxide and nitric oxide. Implications for oxygen sensing and signaling.
(13/3024)
It has been proposed that cells sense hypoxia by a heme protein, which transmits a signal that activates the heterodimeric transcription factor hypoxia-inducible factor 1 (HIF-1), thereby inducing a number of physiologically relevant genes such as erythropoietin (Epo). We have investigated the mechanism by which two heme-binding ligands, carbon monoxide and nitric oxide, affect oxygen sensing and signaling. Two concentrations of CO (10 and 80%) suppressed the activation of HIF-1 and induction of Epo mRNA by hypoxia in a dose-dependent manner. In contrast, CO had no effect on the induction of HIF-1 activity and Epo expression by either cobalt chloride or the iron chelator desferrioxamine. The affinity of CO for the putative sensor was much lower than that of oxygen (Haldane coefficient, approximately 0.5). Parallel experiments were done with 100 microM sodium nitroprusside, a nitric oxide donor. Both NO and CO inhibited HIF-1 DNA binding by abrogating hypoxia-induced accumulation of HIF-1alpha protein. Moreover, both NO and CO specifically targeted the internal oxygen-dependent degradation domain of HIF-1alpha, and also repressed the C-terminal transactivation domain of HIF-1alpha. Thus, NO and CO act proximally, presumably as heme ligands binding to the oxygen sensor, whereas desferrioxamine and perhaps cobalt appear to act at a site downstream. (+info)
Effects of temperature and preservation time on the pharmacological response of isolated vascular endothelial and smooth muscle function.
(14/3024)
In clinical transplantation and cardiovascular surgery, cold preservation is usually used because it is a simple method. However, the established temperature is by no means exact. The aim of this study was to find the optimum storage temperature for preservation of the vasculature by observing the pharmacological endothelium and smooth muscle response. The thoracic aorta of 36 male Wister rats were studied in organ baths: as fresh control after 24 hours, 48 hours and 72 hours of storage at 0.5 degree C, 4 degrees C and 8 degrees C in Krebs-Henseleit bicarbonate (KHB) solution. Acetylcholine (Ach) was used to elicit endothelium-dependent relaxation, and sodium nitroprusside (SNP) to elicit smooth muscle-dependent relaxation. The contractility caused by Phenylephrine (Ph) was influenced by time but before 48 hours it was not influenced by preservation temperature. Significant responsive deterioration by Ach and SNP was seen after 24 hours of storage at 0.5 degree C as compared with storage at 4 degrees C. The endothelium-dependent relaxing function and smooth muscle-dependent relaxing function were best preserved at 4 degrees C and 8 degrees C. These results indicate that precise temperature control is necessary for vessel preservation in clinical situations. (+info)
Ceramide generation in nitric oxide-induced apoptosis. Activation of magnesium-dependent neutral sphingomyelinase via caspase-3.
(15/3024)
Sodium nitroprusside (SNP), a NO donor, has been recognized as an inducer of apoptosis in various cell lines. Here, we demonstrated the intracellular formation of ceramide, a lipid signal mediator, in SNP-induced apoptosis in human leukemia HL-60 cells and investigated the mechanisms of ceramide generation. The levels of intracellular ceramide increased to, at most, 160% of the control level in a time- and dose-dependent manner when the cells were treated with 1 mM SNP. SNP also decreased the sphingomyelin level to approximately 70% of the control level and increased magnesium-dependent neutral sphingomyelinase (N-SMase) activity to 160% of the control activity 2 h after treatment. Neither acid SMase nor magnesium-independent N-SMase was affected by SNP. Caspases are thought to be key enzymes in apoptotic cell death. Acetyl-Asp-Glu-Val-Asp-aldehyde, a synthetic tetrapeptide inhibitor of caspases, inhibited magnesiumdependent N-SMase, ceramide generation, and apoptosis. Moreover, recombinant purified caspase-3 increased magnesium-dependent N-SMase in a cell-free system. These results suggest that the findings that SNP increased ceramide generation and magnesium-dependent N-SMase activity via caspase-3 are interesting to future study to determine the relation between caspases and sphingolipid metabolites in NO-mediated signaling. (+info)
Endothelium-derived relaxing, contracting and hyperpolarizing factors of mesenteric arteries of hypertensive and normotensive rats.
(16/3024)
Differences in the acetylcholine (ACh)-induced endothelium-dependent relaxation and hyperpolarization of the mesenteric arteries of Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were studied. Relaxation was impaired in preparations from SHRSP and tendency to reverse the relaxation was observed at high concentrations of ACh in these preparations. Relaxation was partly blocked by NG-nitro-L-arginine (L-NOARG, 100 microM) and, in the presence of L-NOARG, tendency to reverse the relaxation was observed in response to higher concentrations of ACh, even in preparations from WKY. The relaxation remaining in the presence of L-NOARG was also smaller in preparations from SHRSP. The tendency to reverse the relaxation observed at higher concentrations of ACh in preparations from SHRSP or WKY in the presence of L-NOARG were abolished by indomethacin (10 microM). Elevating the K+ concentration of the incubation medium decreased relaxation in the presence of both indomethacin and L-NOARG. Relaxation in the presence of L-NOARG and indomethacin was reduced by the application of both apamin (5 microM) and charybdotoxin (0.1 microM). This suggests that the relaxation induced by ACh is brought about by both endothelium-derived relaxing factor (EDRF, nitric oxide (NO)) and hyperpolarizing factor (EDHF), which activates Ca2+-sensitive K+ channels. Electrophysiological measurement revealed that ACh induced endothelium-dependent hyperpolarization of the smooth muscle of both preparations in the presence of L-NOARG and indomethacin; the hyperpolarization being smaller in the preparation from SHRSP than that from WKY. These results suggest that the release of both NO and EDHF is reduced in preparations from SHRSP. In addition, indomethacin-sensitive endothelium-derived contracting factor (EDCF) is released from both preparations; the release being increased in preparations from SHRSP. (+info)