Nisoldipine inhibits lipid peroxidation induced by coronary occlusion in pig myocardium.

STUDY OBJECTIVE: The aim was to investigate the effect of the Ca++ channel blocker nisoldipine on the content of lipid peroxidation products in pig myocardium after acute coronary occlusion. DESIGN: Open chest pigs were subjected to the occlusion of the left anterior coronary artery (LAD) with or without nisoldipine. After 30 min ischaemia, myocardial samples were taken from the ischaemic area and from the non-ischaemic posterior wall of the left ventricle for determination of lipid peroxidation products. SUBJECTS: Subjects were farm pigs of either sex. In 10 pigs, the LAD was occluded without drug pretreatment; 11 pigs were infused with nisoldipine (10 micrograms.kg-1) 30 min before the LAD occlusion. Sham operated controls received no drug (n = 7) or nisoldipine (n = 9). MEASUREMENTS AND MAIN RESULTS: Myocardial samples were assayed for the content of lipid peroxidation products: malondialdehyde, conjugated double bonds, and fluorescent end products. Plasma nisoldipine concentration was measured in some experiments. Following the LAD occlusion, the content of lipid peroxidation products increased in both ischaemic and non-ischaemic myocardial regions as compared to the hearts of sham operated pigs. Pretreatment with nisoldipine completely prevented these increases. At a time of the coronary occlusion, plasma nisoldipine concentrations were within the therapeutic range. CONCLUSION: Ca++ antagonist prevents the excessive peroxidation of myocardial membrane lipids which affects the whole myocardium when there is acute local ischaemia. Prevention of myocardial damage in the non-ischaemic region may determine survival of the infarcted heart.

Increased blood level of prostaglandin-like substances during cardiopulmonary bypass in the dog.

Total heart-lung bypass (TBP) for open-heart surgery is often accompanied by a progressive reduction of systemic blood pressure. Since the lung is the main site of elimination of prostaglandins (PGs) from venous blood, TBP may lead to an increase in blood content of vasodilator PGs. TBP was performed in dogs and blood level of prostaglandinlike substances (PLS) was monitored continuously by a bio-assay method. The concentration of PLS increased during TBP to 0.8 ng.cm(-3) blood (in PGE2 equivalents). Restoration of normal circulation led to the disappearance of PLS from the blood. The increase in PLS during TBP was abolished by indomethacin. This was invariably accompanied by elevation of systemic blood pressure. It is suggested that an increased concentration of vasodilator PLS during TBP may contribute to the hypotension observed in total body perfusion.

Evidence for increased lipid peroxidation in the non-ischaemic portion of the heart with coronary occlusion.

Lipid peroxidation products, malondialdehyde (MDA), conjugated double bonds (CDB), and fluorescent end products (RF), were measured in porcine left ventricular myocardium. Myocardial samples were taken 15-20 min after left anterior descending coronary artery (LAD) ligation from ischaemic and non-ischaemic regions. Products of lipid peroxidation were also measured in the left ventricular myocardium of sham operated pigs. Non-ischaemic regions of the hearts with LAD occlusion showed a significantly higher content of lipid peroxidation products than intact hearts of sham operated pigs. The results suggest that enhancement of lipid peroxidation reflecting increased free radical generation may contribute to myocardial damage in the non-ischaemic, apparently "healthy" portion of the heart with acute coronary occlusion.

Muscular work and the release of prostaglandin-like substances.

Experimental evidence for the release of prostaglandin-like substances, mainly of the E type, into the venous outflow from working skeletal muscles in the dog is described. Muscular exercise of the hind-leg produced by sciatic nerve stimulation evoked the release of prostaglandin-like substances detected in femoral venous blood by the bioassay method. This release occurred during and after muscular work, was abolished by indomethacin, and was not present in gallamine-treated dogs. The results suggest that endogenous vasodilator prostaglandins released during and after muscular work may contribute to local hyperaemic response during and, mainly, after muscular activity.

Apparent inosine uptake by the human heart.

Although inosine has been used clinically to support the myocardium, no data are available on the fate of exogenous inosine in the human heart. We therefore infused six patients, catheterised for coronary angiography, with inosine (5 mg.kg-1.min-1 intravenously) for 6 minutes. Before infusion, the arterio-venous difference of inosine, hypoxanthine and xanthine across the heart was nil. During infusion, arterial inosine increased substantially, exceeding the coronary sinus concentration by a maximum of 200 (SEM 53) mumol.litre-1, p = 0.02, at the fourth minute. Arterial hypoxanthine and xanthine also increased, while the arterio-venous difference became 16(11) and 10(3) (p = 0.04) mumol.litre-1, respectively. Left ventricular dP/dtmax increased by 22(7)% (p = 0.04) at the end of infusion. Thus, there seemed to be substantial uptake of inosine by the human heart, followed by improvement in haemodynamics.

Evidence for the detrimental effect of adrenaline infused to healthy dogs in doses imitating spontaneous secretion after coronary occlusion.

We have previously shown that acute coronary occlusion in the dog is often accompanied by increased adrenaline release into the blood. In the present study the consequences of this humoral reaction were studied in anaesthetised healthy mongrel dogs subjected to adrenaline infusion administered at a rate relevant to spontaneous release of this amine in coronary occlusion. Adrenaline was infused in a dose of 1.2 microgram.kg-1.min-1 for 4 h. Dogs receiving saline served as the control. Adrenaline administration led to the decrease in insulin/glucose ratio, to a significant fall in serum triiodothyronine and in blood pH. Free fatty acid levels doubled. Histochemically, a diminution in succinic dehydrogenase and ATPase activity in adrenaline-treated hearts was found. A significant fall in the activity of mitochondrial hexokinase in these hearts was detected spectrophotometrically. Electron microscopic study revealed alterations in the mitochondrial structure. These findings indicate that an excess of adrenaline in ammounts similar to that seen in experimental infarction leads to profound metabolic and hormonal disturbances and exerts a detrimental effect upon myocardium.

Effect of adrenaline on cardiac force-interval relationship.

OBJECTIVE: The aim was to test the hypothesis that adrenaline affects the force-interval processes. METHODS: The force-interval processes were studied in eight guinea pig papillary muscles (isometric force) and five anaesthetised dogs with atrioventricular block (maximum rate of rise of left ventricular pressure, LVdP/dtmax). The contractility indices were measured during pacing sequences in which a steady state was interrupted after a variable interval by a premature beat followed by an immediate return to the steady state. RESULTS: The relationship between contractility of the premature beat and the preceding interstimulus interval displays an approximately monoexponential initial rising phase, ie, mechanical restitution. With increasing adrenaline dosage in the isolated preparation there was always a significant increase in the force, and in its rate of rise with interval in some cases. Adrenaline had a variable accelerating effect on the time course of this mechanical restitution in isolated papillary muscles, but no effect in the dog preparation. In the isolated preparation adrenaline also slowed the decay in potentiation of the two beats immediately following the premature contraction. A slope of the relationship between the contractility of the second potentiated beat and that of the first was thus increased. This difference was not apparent in the intact preparation. CONCLUSIONS: The speeding up of mechanical restitution by adrenaline may be interpreted as reflecting the time course of reavailability of contractile activator. The slope of the relationship of contractility to that of the previous beat during the decay of postextrasystolic potentiation may be interpreted as the recirculation fraction of contractile activator; this is increased by adrenaline. However, in addition, adrenaline exerts an inotropic effect by another mechanism.

Effect of supplemental oral L-arginine on exercise capacity in patients with stable angina pectoris.

A randomized, double-blind, placebo-controlled study in patients with clinical symptoms of stable angina pectoris and healed myocardial infarction (n = 22) has shown that oral supplementation with L-arginine (6 g/day for 3 days) increases exercise capacity (tested on a Marquette case 12 treadmill according to the modified Bruce protocol). Results suggest that the inefficient L-arginine/nitric oxide system contributes to limitation of myocardial perfusion and/or peripheral vasodilation during maximum exercise in patients with stable angina pectoris.

Effects of antioxidant vitamins C and E on signal-averaged electrocardiogram in acute myocardial infarction.

Experimental studies indicate that oxygen-free radicals contribute to ischemic myocardial damage and affect electric properties of cellular membranes. We hypothesize that an association exists between an oxygen-free radical-induced component of myocardial ischemic injury and altered electric function that underlies the genesis of ventricular late potentials in the course of myocardial infarction. If so, antioxidant vitamins C and E may prevent alterations in the signal-averaged electrocardiogram (SAECG). To test this hypothesis, we investigated the effect of supplementation with vitamins C and E on the indices of the SAECG in patients with acute myocardial infarction (AMI). Sixty-one patients with AMI were randomized to receive conventional treatment and vitamins C and E, each 600 mg/day, orally for 14 days (supplemented group, n = 33) or conventional treatment only (control group, n = 28). SAECG was recorded on days 1 or 2 and between days 9 and 13 (mean 10). Serum ascorbic acid, tocopherol, plasma lipid peroxides, and oxygen-free radical production by isolated leukocytes were measured on days 1 or 2 and between days 12 and 14. In the control group, SAECG showed an increase in mean QRS and low-amplitude ( < 40 microV) signal durations, from 99 +/- 10 to 111 +/- 13 ms (p < 0.001) and from 31 +/- 8 to 38 +/- 10 ms (p < 0.001), respectively, and a decrease in the root-mean-square voltage of the last 40 ms of the QRS complex, from 36 +/- 25 to 21 +/- 11 microV (p < 0.002). In vitamin-supplemented patients, all these indices remained unchanged. Oxygen-free radical production by isolated leukocytes was decreased compared with that in controls (p < 0.02). Supplementation was confirmed by elevation of serum ascorbic acid and tocopherol. Results support the hypothesis that in patients with AMI, oxygen-free radical-induced cellular damage contributes to alterations in electric function of the heart as seen on the SAECG.

Effect of early captopril treatment on blood adrenaline levels in acute myocardial infarction (the substudy of ISIS-4). International Study of Infarct Survival-4.

Of patients with acute myocardial infarction eligible for the International Study of Infarct Survival-4, randomized to captopril (n = 30) or placebo (n = 33), the captopril group had a significant decrease in blood adrenaline on day 3 compared with baseline values. Results suggest that suppression of sympathetic activity contributes to the beneficial effects of treatment with angiotensin-converting enzyme inhibitors in the early phase of acute myocardial infarction.

NG-monomethyl-L-arginine increases platelet deposition on damaged endothelium in vivo. A scanning electron microscopic study.

There is increasing evidence that nitric oxide (NO) synthetized in vascular endothelium and in platelets by NO synthase influences vascular tone, down regulates platelet function and platelet-vessel wall interaction both in vitro and in vivo. We investigated the effect of a NO synthase inhibitor, NG-mono-methyl-L-arginine (L-NMMA, 100 mg/kg iv) on platelet-endothelial cell interaction in rabbit arteries ex vivo using scanning electron microscope (SEM). The effect of L-NMMA was examined on intact endothelium and on that damaged by arterial constriction. The infusion of L-NMMA increased systemic blood pressure and decreased carotid blood flow, however, it did not change the appearance of an intact endothelium and did not result in platelet activation on intact endothelial cells. In contrast, SEM of endothelial areas damaged by constriction showed extensive platelet adhesion and aggregation on subendothelium. These morphological changes were not detected in control animals with intact or damaged by arterial constriction endothelium. These results show that under physiological conditions, the inhibition of NO synthase alone does not result in platelet activation in vivo. However, when combined with endothelial injury it may lead to platelet activation and thrombosis.

Platelet adhesion is related to heart rhythm disturbances in the acute phase of myocardial infarction.

This study examines the relationship between platelet adhesion, aggregation and the occurrence of heart rhythm disturbances in 43 consecutive patients (mean age 58) admitted to a coronary care unit with acute myocardial infarction. Blood for platelet studies was taken prior to institution of any medication and heart rhythm was monitored (Holter) for 24 h after admission. The control group consisted of 22 healthy subjects (mean age 55 yr). Platelet adhesion to collagen was measured in EDTA-platelet rich plasma by recording the changes in light transmission in an optical aggregometer. Platelet aggregation was measured by the Born method. Platelet adhesion was increased in the group of patients with acute myocardial infarction as compared to controls and was significantly higher in the patients with complex ventricular arrhythmias (Lown 3-4b, n = 18) than in the patients with stable rhythm. Platelet aggregation in the patients with acute myocardial infarction did not differ significantly from the controls and was not related to heart rhythm disturbances. The causal relationship of increased platelet adhesiveness to collagen and heart rhythm disturbances in acute myocardial infarction remains to be established.

Increased activity of circulating polymorphonuclear leukocytes in acute myocardial infarction.

Acute myocardial infarction results in an increased sensitivity of circulating polymorphonuclear leukocytes to ex vivo aggregation. This increase was prevented by pretreatment of leukocytes with BW755, but not with aspirin, suggesting that the activation of blood leukocytes in infarction is due to a stimulation of cellular lipoxygenase.

Effects of oral L-arginine supplementation on exercise-induced QT dispersion and exercise tolerance in stable angina pectoris.

We assessed the effects of L-arginine (an endogenous precursor of nitric oxide) on the magnitude of exercise-induced QT dispersion in patients with coronary artery disease. The study had a randomized double-blind cross-over design. Twenty-five patients with stable coronary artery disease underwent two separate exercise tests: after oral administration of L-arginine (6 g/24 h for 3 days) or placebo. Indications for cessation of exercise included: pulse limit, exhaustion, chest pain, ST segment depression >2 mm. We found that arginine significantly increased exercise duration from 604+/-146 to 647+/-159 s (P<0.03). However, it had no effect on the sum of exercise-induced ST segment depressions (1.9+/-2.3 and 2.4+/-3.3 on and off arginine, respectively, NS). Exercise shortened QT interval to a similar extent in patients treated with placebo or arginine. QT dispersion changed during exercise from 55+/-21 to 60+/-19 ms (NS) and from 60+/-21 to 53+/-17 ms (NS), respectively. We conclude that, in patients with coronary artery disease, oral supplementation of L-arginine does not affect exercise-induced changes in QT interval duration, QT dispersion or the magnitude of ST segment depression. However, it significantly increases exercise tolerance, most likely due to improved peripheral vasomotion. These results may be of clinical and therapeutic importance.

Positive and negative outcomes of L-arginine therapy in cardiovascular diseases.

The author reviews controlled clinical investigation on the effectiveness of L-arginine in cardiovascular diseases. Positive results were observed in hyperlipidemic subjects and in patients with a critical stage of the peripheral arterial occlusive disease. Patients with stable ischemic heart disease responded to L-arginine to some extent, while results of L-arginine therapy in congestive heart failure are inconsistent. Null effects if L-arginine has been documented in essential hypertension.

Effect of magnesium on myocardial damage induced by epinephrine. Ultrastructural and cytochemical study.

Magnesium ion is involved in energy metabolism, transport of ions and control of intracellular Ca2+. Catecholamines, intensify cellular Mg2+ depletion and the detrimental effects of catecholamine excess and Mg2+ deficiency are mutually enhancing in the myocardium. To investigate whether Mg2+ supplementation protects the myocardium against damage induced by catecholamines, we examined the ultrastructure and the ultracytochemical localization of Ca2+ in the myocardium of rabbits infused with epinephrine (1 microgram/kg/min intravenously for 2 hours), in rabbits infused simultaneously with epinephrine and MgSO4 (50 mg/kg, intravenously) and in saline-infused controls. Qualitative evaluation showed that Mg2+ supplementation attenuated the mitochondrial alterations induced by epinephrine and decreased intracellular and endothelial swelling. Ultracytochemistry with oxalate-pyroantimonate showed a shift in the localization of Ca2+ from the vicinity of the sarcolemma in the controls into the mitochondria in epinephrine-treated hearts. Mg2+ supplementation had no effect on the changes in Ca2+ localization induced by epinephrine or on the intensity of the cytochemical reaction. In conclusion, Mg2+ supplementation reduces the ultrastructural features of myocardial damage induced by epinephrine without an effect upon changes in intracellular distribution of Ca2+ induced by epinephrine, as shown cytochemically.