Adenosine causes transient dilatation of coronary arteries in man

We investigated the effects of i.v. adenosine on coronary blood flow in 10 normal subjects undergoing investigation for chest pain. Coronary flow transiently doubled after greater than or equal to 3.5 mg adenosine without increase in perfusion pressure, systolic load or inotropic state at a constant, paced heart rate. The data provide direct evidence that adenosine dilates coronary arteries in man. The transience of the effect suggests a possible role for adenosine in repeated estimations of coronary flow reserve.

Unstimulated release of endothelium derived relaxing factor is independent of mitochondrial ATP generation

Rabbit aortic strips were used to investigate the effect of mitochondrial inhibitors on basal (unstimulated) endothelium dependent relaxation. Since haemoglobin inhibits and the cyclic GMP phosphodiesterase inhibitor, MB22948, amplifies endothelium dependent relaxation they were used to provide evidence of basal activity of endothelium derived relaxing factor (EDRF). Basal activity was not inhibited by incubation with any of three differently acting inhibitors of mitochondrial ATP generation. The mechanism underlying basal EDRF production may thus differ from that of stimulated EDRF production, which is abolished by these mitochondrial inhibitors.

A phorbol ester inhibits the release of endothelium-derived relaxing factor

The effect of the phorbol ester phorbol-12,13-dibutyrate (PDB), an activator of protein kinase C, on endothelium-dependent relaxation was studied in noradrenaline-constricted isolated aortic ring preparations of the rabbit. Endothelium-dependent relaxation induced by acetylcholine or substance P was inhibited by PDB (greater than or equal to 10(-7) M). Endothelium-dependent relaxation induced by the calcium ionophore A23187 (7.5 X 10(-8) and 10(-7) M) was unaffected by PDB (to 10(-6) M). The mechanical responses to acetylcholine or sodium nitroprusside in endothelium-denuded rings were not altered by PDB (to 10(-6) M). The results suggest a role for protein kinase C in receptor-mediated EDRF release mechanisms.

Endothelium-derived relaxing factor inhibits in vitro platelet aggregation

We studied the effects of endothelium-derived relaxing factor (EDRF), bovine retractor penis muscle inhibitory factor and sodium nitroprusside, three stimulants of guanylate cyclase, on the in vitro aggregation of washed human platelets. Platelet aggregation induced either by collagen or by the thromboxane A2 analogue U46619 was inhibited by all three agents. The anti-aggregatory effect of each agent was inhibited by haemoglobin. The anti-aggregatory effect of EDRF was potentiated by superoxide dismutase. These findings are discussed in relation to a potential role for EDRF in haemostasis.

The incidence and significance of early pericardial effusion after open heart surgery

The presence and severity of postoperative pericardial effusions were studied echocardiographically in 114 consecutive patients (70 males, 44 females; mean age 56 +/- 10 years). An effusion was present in 35 patients at 3-5 days. An effusion was less common when a drainage tube was inserted for 24-36 h in the posterior as well as the anterior mediastinum than when only an anterior drain was used. Patients with effusions differed from those without in having more supraventricular arrhythmias, more wound infections, smaller total blood drainage and longer postoperative hospital stay. Three patients with posterior pericardial effusions developed cardiac tamponade 5-18 days postoperatively. The data show that pericardial effusions are associated with postoperative complications and suggest that effusion formation can be reduced by using posterior as well as anterior chest drains.

Preparation of human saphenous vein for coronary artery bypass grafting impairs its capacity to produce prostacyclin

Prostacyclin production was measured from freshly isolated human saphenous vein and from vein subjected to routine surgical preparation for coronary bypass grafting. Surgical preparation had no effect on spontaneous prostacyclin production but significantly reduced stimulated rates from 16.9(1.1) to 7.1(0.5) pg.min-1 per mg wet weight (n = 27). Stimulated prostacyclin production was not reduced by storage of vein for 2 h at 23 degrees C in blood or saline nor by distension, but it was reduced to 5.0(0.6) pg.min-1 per mg (n = 10) by de-endothelialisation. Reduced prostacyclin production, which might in itself contribute to vein graft occlusion, provides a quantitative biochemical estimate of endothelial integrity.

Effect of lipid feeding on endothelium dependent relaxation in rabbit aortic preparations

The effect of a cholesterol enriched diet on concentration responses to 5-hydroxytryptamine, ergometrine, and acetylcholine and on endothelium dependent relaxation was investigated in rabbit aortic strip preparations. Sensitivity to ergometrine was slightly reduced after both two and 10 weeks of cholesterol feeding. Sensitivity to 5-hydroxytryptamine was slightly reduced after two but not after 10 weeks of cholesterol feeding. Sensitivity to acetylcholine was not altered at two or 10 weeks in the absence of endothelium, but the endothelium dependent lowering of the constrictor concentration-response was almost abolished after 10 weeks of cholesterol feeding. Likewise the endothelium dependent relaxant response of preconstricted preparations to acetylcholine was almost abolished after 10 weeks of cholesterol feeding. Thus this model of hyperlipidaemia leads after 10 weeks to loss of endothelium dependent relaxation.

Trial of nifedipine for prevention of oesophageal spasm

We have used a placebo controlled trial to investigate the effect of long-term administration of nifedipine in the prevention of symptomatic episodes of oesophageal spasm. Diary card scoring was used to assess symptoms in 8 patients with oesophageal spasm who were each given nifedipine and placebo for at least 6 weeks. No significant differences in symptoms between the nifedipine and placebo treatment periods were seen.

Endothelium-derived relaxing factor alters calcium fluxes in rabbit aorta: a cyclic guanosine monophosphate-mediated effect

1. Measurement of tension and 45Ca influx and efflux were used to study the effects of endothelium-derived relaxing factor (EDRF), sodium nitroprusside and 8-bromo-cyclic guanosine monophosphate (GMP) on contractile responses and calcium movements in aortic ring preparations of the rabbit. 2. EDRF activity, induced by stimulating endothelium-containing rings with acetylcholine, was associated with relaxation of noradrenaline-constricted rings and with a marked reduction of noradrenaline-stimulated increase in calcium influx. Sodium nitroprusside and 8-bromo-cyclic GMP had a similar effect in de-endothelialized preparations. 3. EDRF also inhibited noradrenaline-stimulated calcium efflux. Sodium nitroprusside and 8-bromo-cyclic GMP had a similar effect in de-endothelialized preparations, both in the presence and absence of extracellular calcium. 4. The vascular smooth muscle relaxant effect of EDRF and of nitrovasodilators may be effected by a cyclic GMP-mediated reduction of cytosolic calcium, through both inhibition of calcium influx and reduction of intracellular calcium release.

Differences in basal endothelium-derived relaxing factor activity in different artery types

Mechanical responses and calcium influx were measured in order to compare basal endothelium-derived relaxing factor (EDRF) activity in isolated preparations of rabbit aorta, rat aorta, and dog coronary artery. EDRF activity was characterized by endothelium-dependent mechanical relaxation and reduction of 45Ca influx which could be blocked by EDRF inhibitors. In resting preparations, the mechanical effects of basal EDRF were negligible in all preparations, and a small effect on calcium influx was demonstrated only in rat preparations. In agonist-constricted preparations, basal EDRF activity had only a small mechanical effect in rabbit preparations but markedly depressed constriction in rat and dog preparations; likewise, it had no demonstrable effect on calcium influx in rabbit preparations but had a marked effect in rat and dog preparations. In both resting and agonist-stimulated rabbit preparations, endothelium caused a cyclooxygenase product-dependent increase in calcium influx. Thus, basal EDRF activity has little or no effect in resting preparations and little or no effect in agonist-stimulated rabbit aorta preparations, but a marked effect in agonist-stimulated rat aorta and dog coronary preparations.

Haptoglobin-haemoglobin complex in human plasma inhibits endothelium dependent relaxation: evidence that endothelium derived relaxing factor acts as a local autocoid

Endothelium dependent relaxation of isometrically mounted rabbit aortic strip preparations was rapidly inhibited by human plasma at dilutions down to 1:1000. Gel filtration and ion exchange chromatography were used to demonstrate that this inhibitory activity was present in fractions containing haptoglobin. Purified haptoglobin itself possessed no inhibitory action against endothelium dependent relaxation, but the haptoglobin-haemoglobin complex did, consistent with the documented ability of haemoglobin to inhibit this phenomenon. The concentration of haemoglobin normally bound to haptoglobin is sufficient to account for the inhibitory properties of human plasma. This suggests that endothelium derived relaxing factor exerts no downstream intravascular effect in vivo and thus that its physiological dilator role is that of a local autocoid acting on subjacent smooth muscle.

Influence of endothelium on drug-induced relaxation of the rabbit aorta

The influence of endothelium on relaxation induced by glyceryl trinitrate (GTN) and isoprenaline (I) has been studied in isolated rabbit aortic ring preparations, in the resting state and after constriction with 5-hydroxytryptamine (5HT). In resting preparations relaxant responses to GTN and I were smaller in the presence of endothelium. In preparations constricted with 5HT relaxant responses to GTN and I were conversely greater in the presence of endothelium. These paradoxical findings are discussed in relation to basal release of endothelium derived relaxant factor.

Evaluation of antiplatelet agents in the prevention of aorto-coronary bypass occlusion

The cumulative occlusion rates of aorto-coronary artery venous bypass grafts average from 16 to 26% per distal anastomosis within 12 months and about 2% per following year. The potential benefit of oral anticoagulants and platelet inhibitor drugs has been tested to prevent graft occlusion and to retard the atherosclerotic process. Oral anticoagulants started on the third postoperative day do not significantly reduce graft occlusion after 6 months. Among the platelet inhibitor drugs, dipyridamole started before surgery, followed by dipyridamole and aspirin soon after surgery, was the drug regimen with the best results. More randomised double-blind clinical trials are highly desirable to confirm these findings and to resolve the question of relative efficacy and safety for the various drugs reported to have shown benefit when used in combination.

Production of endothelium derived relaxant factor is dependent on oxidative phosphorylation and extracellular calcium

The production (synthesis or release or both) of endothelium derived relaxant factor was studied in rabbit aortic strip preparations and an aortic-coronary artery bioassay system. Production of endothelium derived relaxant factor was rapidly inhibited by agents that inhibit mitochondrial electron transport or F1-ATPase, or which uncouple oxidative phosphorylation, but was only slowly impaired by inhibition of glycolysis. It was dependent also on the presence of extracellular calcium with a rapid on-off response time. This study shows that production of endothelium derived relaxant factor appears to be dependent on both oxidative phosphorylation and extracellular calcium.

Acute haemodynamic effects of nifedipine at rest and during maximal exercise in patients with chronic cor pulmonale

The pulmonary hypertension of cor pulmonale can be reversed by sustained correction of hypoxia but continuous oxygen treatment poses problems in clinical practice. Alternative methods of relieving pulmonary vasoconstriction have therefore been explored. Eight patients with chronic cor pulmonale (five of them men) were studied to measure the haemodynamic effects of the calcium antagonist nifedipine, both at rest and on maximal, symptom limited exercise. The mean duration of exercise was unchanged by nifedipine (7.8 (SD 3.3) compared with 7.3(3.1) min). Cardiac output rose from 5.2(1.5) l min-1 to 8.6(3.3) 1 min-1 on exercise. Nifedipine increased resting cardiac output by 26%, but did not influence maximal exercise output. It did not significantly alter resting mean pulmonary artery pressure but reduced the level during exercise from 67(15) to 52(11) mm Hg. Nifedipine lowered resting pulmonary vascular resistance (PVR) by 32% and exercise PVR by 28%. It reduced supine mean systemic arterial pressure by 17%, standing pressure by 22%, and pressure at the maximal exercise level by 20%. Nifedipine lowered supine systemic vascular resistance (SVR) by 35%, standing SVR by 28%, and exercise SVR by 20%. Haemodynamic changes were achieved without adverse symptoms, alteration in arterial PO2, or impairment of calculated oxygen delivery. Nifedipine therefore reduced both pulmonary and systemic vasomotor tone at rest and during exercise. It did not alter exercise tolerance, which is probably limited by underlying respiratory disease. It seems possible therefore that nifedipine could delay the development of cor pulmonale, although this hypothesis remains to be tested.

Patterns of use and incidence of smokeless tobacco consumption in school-age children

A sample of 5,392 students were surveyed using a 42-item, multiple-choice questionnaire from a population of 19,040 Texas school-age children. The geographic distribution was 70% urban and 30% rural, with a representative sampling of the various racial and ethnic groups within Texas. The results of the survey indicated that 486 (9%) of the students regularly used smokeless tobacco, 810 (15%) regularly smoked cigarettes, and 4,096 (76%) used no tobacco products. Further, 77% perceived cigarette smoking as very harmful, while only 40% perceived smokeless tobacco as very harmful. Age of initiating use indicated that 55% of smokeless tobacco users started before the age of 13 years, whereas only 36% of cigarette smokers began that early.

Evidence that cyclic guanosine monophosphate (cGMP) mediates endothelium-dependent relaxation

The mechanism of action of endothelium-derived relaxant factor (EDRF) was studied using aortic strip preparations of the rabbit and a bioassay system of a rabbit coronary artery perfused in series with an intact aorta. Methylene blue (an inhibitor of guanylate cyclase) inhibited, and 2-O-propoxyphenyl-8-azapurine-6-one (MB22948, an inhibitor of cGMP phosphodiesterase) potentiated the vascular effects of EDRF whether these were due to its basal or to stimulated release. Infusion of these agents at different sites in the bioassay indicated that they act pharmacologically at the smooth muscle level and not on release of EDRF or by chemical interaction with EDRF. The data are consistent with the hypothesis that EDRF-induced relaxation is mediated by elevation of smooth muscle cGMP levels.

Metabolic damage to human saphenous vein during preparation for coronary artery bypass grafting

Segments of saphenous vein from patients undergoing coronary artery by-pass graft surgery were frozen in liquid nitrogen immediately on dissection (control), after stripping of the adventitia and side branch ligation (manipulation), after distention with blood (distention), or at completion of the last proximal anastomosis (prepared vein). Vein was stored during the operation in patient's heparinised arterial blood at room temperature. Frozen vein was extracted with perchloric acid. ATP, ADP, and AMP, adenosine, inosine and hypoxanthine concentrations were measured by high pressure liquid chromatography. Prepared vein had ca 50% lower ATP concentrations and ATP/ADP ratio than control vein, higher concentrations of inosine and hypoxanthine and lower concentrations of AMP and adenosine. ATP concentration and ATP/ADP ratio did not correlate with the time elapsed between dissection and freezing of the prepared vein. The characteristic changes seen in prepared vein were not seen when control vein was simply stored in arterial blood at 23 degrees C, in normal saline at 23 degrees C or 4 degrees C, in Krebs-Ringer bicarbonate buffer at 37 degrees C or at St Thomas's Hospital cardioplegic solution at 4 degrees C. Distention with unlimited pressure did not distension at less than 300 mmHg gave rise to the same changes in ATP concentration and ATP/ADP ratio as in the prepared vein. These results show that vein suffered metabolic changes during preparation for bypass grafting and suggest that uncontrolled distention may contribute to these changes. Such biochemical measurements provide a quantitative estimate of tissue damage and allow objective comparison of different preparative techniques.

Myocardial reoxygenation damage: can it be circumvented?

We investigated whether reoxygenation damage could be prevented by interventions directed towards reducing calcium influx only during the reoxygenation period. We measured reoxygenation contracture and recovery of contractile performance, using isolated papillary muscle preparations from cat and rabbit, pretreated with ouabain so as to exaggerate the phenomenon of reoxygenation contracture. Reoxygenation contracture was abolished and contractile recovery achieved by lowering extracellular calcium during early reoxygenation and then gradually replacing it. Gradual reoxygenation only postponed contracture and contractile failure. The slow channel blocker, diltiazem, but not verapamil or lidoflazine--in similarly negative inotropic concentrations of 10(-4) mol X litre-1, 10(-4) mol X litre-1 and 2 X 10(-5) mol X litre-1 respectively--reduced early reoxygenation contracture, as did Mg2+ (30 mmol X litre-1), Mn2+ (8 mmol X litre-1), or metabolic acidosis (pH 6.5), without in any case allowing contractile recovery. These observations indicate that reoxygenation damage is not an irrevocable consequence of the preceding hypoxic insult. They imply that calcium entry during early reoxygenation contributes both to contracture and contractile failure, that this occurs through paths other than the slow calcium channel, and that diltiazem may have properties additional to those of blocking the slow calcium channel.

The adrenochrome pathway: the major route for adrenalin catabolism by polymorphonuclear leucocytes

Oxygen radical production by polymorphonuclear leucocytes stimulated the oxidation of adrenalin through the adrenochrome pathway. This was detected either spectrophotometrically at 480 nm or separated by hplc and detected radiochemically. The oxidation was detectable within 5 min and continued for at least 4 h. Over the adrenalin concentration range 0.3 microM to 10 mM more than 80% of the oxidation that occurred was through the adrenochrome pathway, the remainder being through the amine oxidase, catechol methyl transferase pathway. Medium isolated after stimulation of the polymorphonuclear leucocytes was also able to oxidise adrenalin to adrenochrome. The results provide a cellular mechanism for the formation of adrenochrome and the other metabolites on this pathway of adrenalin metabolism, in inflammatory conditions where polymorphonuclear leucocyte infiltration occurs.

Frequency-dependent depression of myocardial contractility by slow calcium channel blocking drugs

The negative inotropic effects of two dihydropyridine and two non-dihydropyridine calcium slow channel blocking drugs were studied using ferret isolated papillary muscle preparations contracting both isotonically and isometrically. The degree of inotropic depression was found to be dependent on the frequency of stimulation for all four agents. Frequency dependence of inotropic effect was of the order: nifedipine less than felodipine less than diltiazem less than verapamil.