Background Experimental evidence suggests that flow-dependent dilatation of conduit arteries is mediated by nitric oxide (NO) and/or prostacyclin. The present study was designed to assess whether NO or prostacyclin also contributes to flow-dependent dilatation of conduit arteries in humans. Methods and Results Radial artery internal diameter (ID) was measured continuously in 16 healthy volunteers (age, 24±1 years) with a transcutaneous A-mode echo-tracking system coupled to a Doppler device for the measurement of radial blood flow. In 8 subjects, a catheter was inserted into the brachial artery for measurement of arterial pressure and infusion of the NO synthase inhibitor N ^G -monomethyl- l -arginine (L-NMMA; 8 μmol/min for 7 minutes; infusion rate, 0.8 mL/min). Flow-dependent dilatation was evaluated before and after L-NMMA or aspirin as the response of the radial artery to an acute increase in flow (reactive hyperemia after a 3-minute cuff wrist occlusion). Under control conditions, release of the occlusion induced a marked increase in radial blood flow (from 24±3 to 73±11 mL/min; P <.01) followed by a delayed increase in radial diameter (flow-mediated dilatation; from 2.67±0.10 to 2.77±0.12 mm; P <.01) without any change in heart rate or arterial pressure. L-NMMA decreased basal forearm blood flow (from 24±3 to 13±3 mL/min; P <.05) without affecting basal radial artery diameter, heart rate, or arterial pressure, whereas aspirin (1 g PO) was without any hemodynamic effect. In the presence of L-NMMA, the peak flow response during hyperemia was not affected (76±12 mL/min), but the duration of the hyperemic response was markedly reduced, and the flow-dependent dilatation of the radial artery was abolished and converted to a vasoconstriction (from 2.62±0.11 to 2.55±0.11 mm; P <.01). In contrast, aspirin did not affect the hyperemic response nor the flow-dependent dilatation of the radial artery. Conclusions The present investigation demonstrates that NO, but not prostacyclin, is essential for flow-mediated dilatation of large human arteries. Hence, this response can be used as a test for the l -arginine/NO pathway in clinical studies.

We have shown previously that preconditioning myocardium with four 5-minute episodes of ischemia and reperfusion dramatically limited the size of infarcts caused by a subsequent 40-minute episode of sustained ischemia. The current study was undertaken to assess whether the same preconditioning protocol slowed the loss of high energy phosphates, limited catabolite accumulation, and/or delayed ultrastructural damage during a sustained ischemic episode. Myocardial metabolites and ultrastructure in the severely ischemic subendocardial regions were compared between control and preconditioned canine hearts. Hearts (four to 10 per group) were excised after 0, 5, 10, 20, or 40 minutes of sustained ischemia. All groups had comparable collateral blood flow. Preconditioned hearts developed ultrastructural injury more slowly than controls; evidence of irreversible injury was observed after 20 minutes in controls but not until 40 minutes in preconditioned hearts. Furthermore, after 40 minutes of ischemia, irreversible injury was homogeneous in controls but only focal in preconditioned myocardium. Preconditioning reduced starting levels of ATP by 29%. Nevertheless, it also slowed the rate of ATP depletion during the episode of sustained ischemia, so that after 10 minutes of ischemia, preconditioned hearts had more ATP than controls. However, after 40 minutes, ATP contents were not significantly different between groups. Preservation of ATP resulted from reduced ATP utilization and was not due to increased ATP production. Accumulation of purine nucleosides and bases (products of adenine nucleotide degradation) was limited in preconditioned myocardium. Accumulation of glucose-1-phosphate, glucose-6-phosphate, and lactate also was reduced markedly by preconditioning, due to reduced rates of glycogen breakdown and and anaerobic glycolysis. We propose that preconditioning reduces myocardial energy demand during ischemia, which results in a reduced rate of high energy phosphate utilization and a reduced rate of anaerobic glycolysis. Either preservation of ATP or reduction of the cellular load of catabolites may be responsible for delaying ischemic cell death.

Endothelin-1 is an endothelium-derived vasoconstrictor peptide. Its circulating levels are below those known to evoke direct vascular effects. To study whether low concentrations of endothelin-1 potentiate the effects of other vasoconstrictor hormones, we suspended isolated human internal mammary and left anterior descending coronary artery rings in organ chambers for isometric tension recording. In mammary artery rings, the contractions to norepinephrine (3 x 10(-8) M) were potentiated by threshold (3 x 10(-10) M) and low concentrations (10(-9) M) of endothelin-1 (96 +/- 35% and 149 +/- 58% increase from control; p less than 0.01 and 0.001; n = 6). The inhibitor of endothelial nitric oxide formation L-NG-monomethyl arginine did not affect the potentiating effects of the peptide. The calcium antagonist darodipine (10(-7) M) prevented the potentiation of the response to norepinephrine evoked by endothelin-1. Similarly, contractions to serotonin (10(-7) or 3 x 10(-8) M) were amplified by endothelin-1 (3 x 10(-10) M) in the mammary (30 +/- 9%) and in the coronary arteries (59 +/- 25%). Endothelin-1 (10(-9) M) further potentiated the response (57 +/- 23% in mammary and 87 +/- 26% in coronary arteries; p less than 0.05; n = 7 and 3). The sensitivity of mammary arteries to calcium chloride was markedly enhanced in the presence of endothelin-1 (3 x 10(-10) M; concentration shift, eightfold; p less than 0.01; n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Background— Heart rate reduction (HRR) improves left ventricular (LV) filling, increases myocardial O ₂ supply, and reduces myocardial O ₂ consumption, which are all beneficial in congestive heart failure (CHF). However, the long-term effects of HRR on cardiac function and remodeling are unknown. Methods and Results— We assessed, in rats with CHF, the effects of long-term HRR induced by the selective I _f current inhibitor ivabradine (as food admix for 90 days starting 7 days after coronary artery ligation). To assess intrinsic modifications of LV tissue induced by long-term HRR, all parameters were reassessed 3 days after interruption of treatment. Ivabradine decreased heart rate over the 90-day treatment period (−18% versus untreated at 10 mg · kg ⁻¹ · d ⁻¹ ), without modifying blood pressure, LV end-diastolic pressure, or dP/dt _max/min . Ivabradine significantly reduced LV end-systolic but not end-diastolic diameter, which resulted in preserved cardiac output due to increased stroke volume. In the Langendorff preparation, ivabradine shifted LV systolic but not end-diastolic pressure-volume relations to the left. Ivabradine decreased LV collagen density and increased LV capillary density without modifying LV weight. Three days after interruption of treatment, the effects of ivabradine on LV geometry, shortening, and stroke volume persisted despite normalization of heart rate. Conclusions— In rats with CHF, long-term HRR induced by the selective I _f inhibitor ivabradine improves LV function and increases stroke volume, preserving cardiac output despite the HRR. The improvement of cardiac function is related not only to the HRR per se but also to modifications in the extracellular matrix and/or function of myocytes as a consequence of long-term HRR.

Sodium sensitivity is usually studied in terms of change of blood pressure (BP) but the specific effects on conduit arteries have not been addressed. In genetic models of hypertension, chronically increased sodium diet is associated with aortic hypertrophy and development of extracellular matrix independent of BP. These alterations, often associated with increased stiffness and secretory properties of vascular smooth muscle, are reversed by lowering sodium intake and/or giving diuretics, independently of BP changes. The arterial changes are chronically modulated by hormonal counterregulatory mechanisms since, when sodium intake is high, bradykinin blockade produces more carotid hypertrophy, and when sodium intake is normal, less aortic collagen accumulates because of AT(1)-receptor blockade. In longitudinal studies on hypertensive subjects, increased sodium intake not only increases BP but also decreases brachial artery diameter, implying pressure-independent mechanisms acting on the arterial wall. The antihypertensive effect of diuretics is associated with little change of arterial geometry and stiffness, probably resulting from marked angiotensin-induced increase of arterial stiffness. This latter effect is blocked by converting-enzyme inhibition. All these arterial changes may be genetically modulated since in salt-sensitive hypertensives, increased sodium intake is associated with decreased arterial distensibility, and in some hypertensive subjects, a polymorphism of the AT(1)-receptor gene has been described in association with increased aortic stiffness and is reversed by converting-enzyme inhibition independent of BP. In genetic models of human and rat hypertension, increased sodium intake is associated with specific alterations of the structure and function of conduit arteries involving extracellular matrix, but independent of BP and atherosclerosis.

Microparticles (MPs) are small fragments generated from the plasma membrane after cell stimulation. Among the candidate proteins harbored by MPs, we recently showed that sonic hedgehog (Shh) is present in MPs generated from activated/apoptotic human T lymphocytes [Martinez et al., Blood (2006) vol. 108, 3012–3020]. We show here that Shh carried by MPs induces nitric oxide (NO) release from endothe‐lial cells, triggers changes in the expression and phos‐phorylation of enzymes related to the NO pathway, and decreases production of reactive oxygen species. When PI3‐kinase and ERK signaling were specifically inhibited, the effects of MPs were reversed. In vivo injection of MPs in mice was also able to improve endothelial function by increasing NO release, and it reversed endothelial dysfunction after ischemia/reperfusion. Silencing the effects of Shh with cyclopamine, a specific inhibitor of Shh, or siRNA, an inhibitor of the Shh receptor Patched, strongly reduced production of NO elicited by MPs. Taken together, we propose that the biological message carried by MPs harboring Shh may represent a new therapeutic approach against endothe‐lial dysfunction during acute severe endothelial injury.—Agouni A., Mostefai, H. A., Porro, C., Carusio, N., Favre, J., Richard, V., Henrion, D., Martinez, M. C., Andriantsitohaina R. Sonic hedgehog carried by micro‐particles corrects endothelial injury through nitric oxide release. FASEB J. 21, 2735–2741 (2007)