The effect of chronic treatment with trandolapril on cyclic AMP-and cyclic GMP-dependent relaxations in aortic segments of rats with chronic heart failure

Ramipril improves nitric oxide availability in hypertensive rats with failing hearts after myocardial infarction

A markedly decreased aortic nitric oxide (NO) availability, probably due to impaired endothelial nitric oxide synthase activity with enhanced O2- and peroxynitrite production, seems to be attributable to endothelial dysfunction in spontaneously hypertensive rats (SHR) with severe congestive heart failure (CHF). In this study, we investigated the chronic effect of the angiotensin-converting enzyme inhibitor, ramipril (RA) and the loop diuretic, frusemide (FU), as well as the combination of both on endothelial NO, O2- and peroxynitrite production in aortae from SHR with failing hearts after myocardial infarction (MI).

Heart failure was induced by permanent occlusion of the left coronary artery. SHR were randomised to receive either placebo, RA, (1 mg/kg/day), FU (4 mg/kg/day) or RA+FU (1 and 4 mg/kg/day, respectively). Treatments were started two weeks following MI and continued for six weeks. Reduced aortic and coronary flow indices in the working heart, which can be considered as markers for endothelial function, were significantly normalised and improved, respectively, by RA, FU or RA+FU-treatment. Similarly, all three treatment regimens significantly enhanced the reduced calcium ionophore (CaI)-induced NO-release (assessed by a NO-sensitive microsensor) from aortic endothelial cells of placebo- treated animals with CHF. Concomitantly, the increased CaI-stimulated O 2production (assessed by an electrochemical sensor) in aortic endothelial cells of placebo-treated animals with CHF was significantly reduced by RA and RA+FUtreatment. Treatment with RA and RA+FU also attenuated the dramatic increase in endothelial peroxynitrite concentration (chemiluminescence method), which was observed in placebo-treated rats with CHF. FU did not counteract improved haemo- and cardiodynamic parameters by RA.

Thus, RA and FU act synergistically to enhance bioavailability of endothelium-derived NO, and this may contribute to the clinical usefulness of the combination of these drugs in treatment of heart failure.

The effects of DBcAMP on the expression of eNOS, iNOS and TGF-beta in rat heart tissue

Dibutryl (DB) adenosine 3',5'-cyclic monophosphate (cAMP) is an important modulator of physiological functions. To determine the protective effects of DBcAMP on heart tissue, we evaluated changes in immunoreactivity of endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and transforming growth factor-beta (TGF-beta) in left cervical vagotomized rats treated with DBcAMP. Male rats were divided into four groups. In Group 1, animals were subjected to a left cervical vagotomy. Group 2 received a 1 ml bolus injection of 15 ml/kg DBcAMP in addition to the left vagotomy. DBcAMP alone was given to Group 3 and Group 4 was the control group. For each animal, mean arterial pressure (MAP) and heart rate (HR) were measured. For indirect immunohistochemistry, anti-eNOS, anti-iNOS, and anti-TGF-beta primary antibodies were used. In Group 1, MAP and HR values decreased slightly. In Groups 2 and 3, DBcAMP induced a statistically significant drop in HR and MAP. In Group 1, strong eNOS, iNOS, and TGF-beta immunoreactivities were observed. Immunostaining intensities decreased in Groups 2 and 3. The results of the study reported here suggest that increased immunoreactivities of eNOS, iNOS, and TGF-beta might contribute to the effects on the heart tissue after left vagotomy and imply that DBcAMP acts on heart tissue via nitric oxide.

Cytochrome p450 2C inhibition reduces post-ischemic vascular dysfunction

Cytochrome p450 (CYP) inhibitors provide protection against myocardial infarction following both global and focal cardiac ischemia and reperfusion (I/R). We hypothesized that sulfaphenazole, an inhibitor of CYP2C6 and 9, also attenuates post-ischemic endothelial dysfunction by reducing CYP-mediated superoxide generation (which scavenges nitric oxide (NO)), thereby restoring NO bioavailability and vascular tone. Rat hearts were perfused in the Langendorff mode for 20 min in the presence, or absence, of sulfaphenazole and then subjected to 30 min global no-flow ischemia followed by 15 min reperfusion. Septal coronary resistance arteries were isolated and mounted on glass cannulae for measurements of luminal diameter. Preconstricted arteries were exposed to acetylcholine to elicit endothelium-dependent, NO-mediated vasodilation. Acetylcholine caused near maximal dilation in control tissues not subjected to I/R. Following I/R, endothelium-dependent vasodilation was reduced. Pretreatment with sulfaphenazole restored endothelial sensitivity to acetylcholine. Vasoresponsiveness to endothelium-independent vasodilators, sodium nitroprusside and isoproterenol, were also reduced following I/R. However, sensitivity to endothelium-independent vasodilators was not restored by pretreatment with sulfaphenazole. I/R-induced superoxide production was assessed by dihydroethidium staining of flash frozen hearts. Sulfaphenazole treatment significantly reduced superoxide production in arterial walls following I/R injury. We conclude that sulfaphenazole restores post-ischemic endothelium-dependent, NO-mediated vasodilation by reducing superoxide production, suggesting that CYP2C9 plays a key role in post-ischemic vascular dysfunction.

Effect of PDE5 inhibition on coronary hemodynamics in pacing-induced heart failure

Inhibition of phosphodiesterase type 5 (PDE5) can relax systemic and coronary vessels by causing accumulation of cGMP. Both the endothelial dysfunction with decreased nitric oxide production and increased natriuretic peptide levels in congestive heart failure (CHF) have the potential to alter cGMP production, thereby influencing the response to PDE5 inhibition. Consequently, this study examined the effects of PDE5 inhibition with sildenafil in dogs with CHF produced by rapid ventricular pacing. CHF resulted in decreases of left ventricular (LV) systolic pressure, coronary blood flow, and the maximal first time derivative of LV pressure (LV dP/dt(max)) at rest and during treadmill exercise compared with normal, whereas resting LV end-diastolic pressure increased from 10 +/- 1.4 to 23 +/- 1.4 mmHg. Sildenafil (2 and 10 mg/kg per os) caused a 5- to 6-mmHg decrease of aortic pressure (P < 0.05), with no change of heart rate, LV systolic pressure, or LV dP/dt(max). Sildenafil caused no change in coronary flow or myocardial oxygen consumption in animals with CHF at rest or during exercise. In contrast to findings in normal animals, sildenafil did not augment endothelium-dependent coronary vasodilation in response to acetylcholine in animals with CHF. Furthermore, Western blotting showed decreased PDE5 protein expression in myocardium from failing hearts. These findings demonstrate that PDE5 contributes little to regulation of coronary hemodynamics in CHF.

Decreased nitric oxide availability in normotensive and hypertensive rats with failing hearts after myocardial infarction

Endothelial NO synthase, being deficient in arginine and/or tetrahydrobiopterin, produces in addition to NO a significant concentration of superoxide (O2)(-)). We investigated whether such an imbalance between O2(-) and NO production is present in dysfunctional aortas of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) with failing hearts after myocardial infarction. Heart failure was induced by permanent occlusion of the left coronary artery, resulting in a large infarction of the free left ventricular wall. Eight weeks after myocardial infarction, when WKY and SHR had compensated heart failure and congestive heart failure, respectively, calcium ionophore-induced NO release (assessed by a NO-sensitive microsensor) from aortic endothelial cells was significantly reduced from 478+/-48 to 216+/-16 nmol/L and 693+/-131 to 257+/-53 nmol/L in WKY and SHR, respectively. Concomitantly, significant increases in calcium ionophore-stimulated O2(-) production (assessed by an electrochemical sensor) could be observed in aortic endothelial cells from infarcted WKY rats (22+/-3.2 versus sham, 10.1+/-1.2 nmol/L) and SHR (102+/-8 versus sham, 67+/-5 nmol/L). A dramatic increase in endothelial peroxynitrite concentration (chemiluminescence method) from 35+/-4 to 90+/-3 nmol/L for WKY and from 60+/-5 to 170+/-10 nmol/L for SHR also was detected. Thus, the markedly decreased NO availability probably caused by impaired endothelial NO synthase activity with enhanced O2(-) and peroxynitrite production appears to be attributable to endothelial dysfunction in normotensive rats with chronic heart failure and especially in hypertensive rats with severe congestive heart failure.