Prostaglandin E1 infusion in unstable angina: Effects on anginal frequency and cardiac function

Control of Ca2+ and metabolic homeostasis by the Na+/Ca2+ exchangers (NCXs) in health and disease

Spatial and temporal control of calcium (Ca²⁺) levels is essential for the background rhythms and responses of living cells to environmental stimuli. Whatever other regulators a given cellular activity may have, localized and wider scale Ca²⁺ events (sparks, transients, and waves) are hierarchical determinants of fundamental processes such as cell contraction, excitability, growth, metabolism and survival. Different cell types express specific channels, pumps and exchangers to efficiently generate and adapt Ca²⁺ patterns to cell requirements. The Na⁺/Ca²⁺ exchangers (NCXs) in particular contribute to Ca²⁺ homeostasis by buffering intracellular Ca²⁺ loads according to the electrochemical gradients of substrate ions - i.e., Ca²⁺ and sodium (Na⁺) - and under a dynamic control of redundant regulatory processes. An interesting feature of NCX emerges from the strict relationship that connects transporter activity with cell metabolism: on the one hand NCX operates under constant control of ATP-dependent regulatory processes, on the other hand the ion fluxes generated through NCX provide mechanistic support for the Na⁺-driven uptake of glutamate and Ca²⁺ influx to fuel mitochondrial respiration. Proof of concept evidence highlights therapeutic potential of preserving a timed and balanced NCX activity in a growing rate of diseases (including excitability, neurodegenerative, and proliferative disorders) because of an improved ability of stressed cells to safely maintain ion gradients and mitochondrial bioenergetics. Here, we will summarize and review recent works that have focused on the pathophysiological roles of NCXs in balancing the two-way relationship between Ca²⁺ signals and metabolism.

Endothelium, fibrinolysis, cardiac risk factors, and prostaglandins: a unified model of atherogenesis

A model of atherogenesis is described in which it is proposed that a state of relative impairment of intravascular fibrinolytic function is the primary defect which makes possible both the initiation and the continued progression of arterial plaques. The key mechanism by which impaired fibrinolysis is atherogenic centers on the unique disruptive effect which fibrin has on the contiguous endothelium of the vascular intimal surface. From this perspective, in areas of spontaneous endothelial injury, impaired fibrinolysis maintains and promotes the gradual enlargement of the area of injury by causing persistently increased intimal permeability and by allowing enhanced fibrin and platelet deposition. This hypothesis thus represents a modification of the response-to-injury hypothesis in which the emphasis has been shifted from the initial endothelial injury to a state of interference with the normal process of healing endothelial injuries. Consistent with this viewpoint, it is noted that all positive risk factors for vascular disease are associated with impairment of fibrinolytic function and, conversely, negative cardiac risk factors enhance fibrinolysis. It is further proposed that one or more prostaglandins, or closely related metabolites, represent the mediators of primary physiologic importance with regard to in vivo regulation of fibrinolysis. By this hypothesis, adequate dietary intake of essential fatty acids, as well as maintenance of unimpaired eicosanoid metabolism, become centrally important in both preventing and reversing arteriosclerosis. This two-tiered model can be used to organize and potentially explain the interrelationship between diverse and apparently divergent sets of epidemiological data which previous models have been unable to accommodate.

A phase I/II study of prostaglandin E1 for the prevention of hepatic venocclusive disease after bone marrow transplantation

We conducted a phase I/II trial of prostaglandin E1 (PGE1) for the prevention of hepatic venocclusive disease (VOD). Twenty-four patients at high risk for VOD received PGE1 at four dose levels ranging from 1.25 to 10 ng/kg/min. Severe toxicity was experienced at all dose levels and was manifested as cutaneous erythema and desquamation, severe pain in dependent extremities, fluid retention and grade 4 oedema, or hypotension. In 12/24 patients, PGE1 administration was stopped prior to day 15 due to severe toxicity attributed to the drug. Three of 12 patients who received PGE1 for the entire course of treatment and 9/12 patients whose PGE1 was stopped prior to day 15 developed severe toxicity which was attributed to PGE1 (P = 0.039). Severe toxicity attributed to PGE1 was not related to either PGE1 concentration or PGE1 clearance. Six of 12 patients whose PGE1 infusion was stopped prior to day 15 and 2/12 patients who received PGE1 for the full course of treatment developed severe VOD (P = 0.19). We conclude that PGE1 causes significant toxicity in patients undergoing marrow transplantation. The ability of PGE1 to prevent severe VOD in patients at high risk remains unproven.

Effect of prostaglandin E1 on myocardial contractility in dogs anesthetized with halothane: load-independent and noninvasive assessment using transesophageal echocardiography

The presence of an inotropic action of prostaglandin E1 (PGE1) in vivo is controversial, and there are conflicting results obtained by various indices of myocardial contractility. In this study, a direct effect of PGE1 on contractility was investigated in dogs by use of a load-independent contractile index: left ventricular end-systolic wall stress (LVESWS) versus the velocity of circumferential fiber shortening with rate-corrected (Vcfc) relationship using transesophageal echocardiography (TEE). Hemodynamics, arterial blood gas, and TEE data were obtained before PGE1 infusion (control), and with a 10%, 20%, and 30% decrease in mean arterial pressure (MAP) following intravenous PGE1 administration. PGE1 infusion rates were 0.19 +/- 0.03 at 10%, 0.82 +/- 0.17 at 20%, and 2.32 +/- 0.36 micrograms/kg/min at a 30% decrease in MAP. Pulmonary capillary wedge pressure, systemic vascular resistance index, and left ventricular stroke work index significantly decreased, and heart rate, cardiac index, and stroke volume index were not significantly altered. Analysis of the TEE data showed LVESWS (index of afterload) significantly decreased from 92.0 +/- 11.2 g/cm2 to 72.7 +/- 7.8 at 10%, 59.3 +/- 7.8 at 20%, and 44.6 +/- 6.2 at a 30% decrease in MAP, and Vcfc significantly increased from 0.595 +/- 0.065 circ/sec of control value to 0.670 +/- 0.056 at 10%, 0.824 +/- 0.049 at 20%, and 0.939 +/- 0.070 at a 30% decrease in MAP. In the LVESWS versus Vcfc relationship, no significant difference could be detected between the control state and the 10%, 20%, and 30% decrease in MAP, and no inotropic effect was found.(ABSTRACT TRUNCATED AT 250 WORDS)

ACE inhibitors for the treatment of myocardial ischemia?

Apart from their established use in the treatment of hypertension and heart failure, ACE inhibitors have been suggested to exert anti-ischemic effects. This article reviews the mechanisms of systemic and intracardiac angiotensin formation, as well as its interaction with the bradykinin, the prostaglandin, and the sympathetic nervous system. While high doses of angiotensin can precipitate myocardial ischemia. experimental data on a potential beneficial effect of ACE inhibitors on ischemic myocardial blood flow and function are inconsistent and controversial. Pooling the few available clinical data, several ACE inhibitors may attenuate myocardial ischemia at rest and during exercise. However, a significant fraction of patients does not benefit or even deteriorates. Recent experimental studies suggest a beneficial role of ACE inhibitors in attenuating reperfusion arrhythmias and postinfarction left ventricular remodeling. Unless the mechanisms and determinants of potential anti-ischemic actions of ACE inhibitors can be better defined, their use for treatment of myocardial ischemia cannot be recommended at present.

Unstable angina

Unstable angina can manifest as an array of symptom complexes. In some patients, medical therapy will stabilize the episodes of angina, and only predismissal exercise testing or angiography (or both) will be necessary. At the other end of the spectrum are patients with rest angina or multiple episodes of silent ischemia who are refractory to medical therapy and experience undetected microinfarction. Most of these patients require immediate catheterization and subsequent intervention with intra-aortic balloon pulsation, percutaneous transluminal coronary angioplasty, or coronary artery bypass grafting. An entire spectrum of manifestations exists between these two extremes. One challenge during the 1990s will be better stratification of patients with unstable angina so that safe, efficient, cost-effective treatment strategies can be appropriately applied to all patients.

Prostaglandin deficiency

Healthy cells from virtually all tissues synthesize a variety of prostaglandins, autacoids which can significantly alter cellular functions. An absolute or relative deficiency of prostaglandins has now been demonstrated in many diseases or clinical conditions. These include 'natural' disorders such as peptic ulcer disease and diabetes mellitus. These also include 'acquired' or iatrogenic conditions such as cyclosporine nephrotoxicity and the gastropathy induced by nonsteroidal anti-inflammatory drugs. We believe that the diversity of the disorders associated with prostaglandin deficiency may be wider and of greater pathogenetic importance than is currently recognized. We propose: 1) that prostaglandin deficiency will be demonstrated in many abnormalities which are now described as of uncertain etiology; and 2) that adverse effects from many commonly prescribed drugs may also be related to an unrecognized and unfavorable alteration in prostaglandin synthesis, disposal, or activity.

Nutrition, the gastrointestinal tract and the Acquired Immune Deficiency Syndrome. Facts and perspectives

Diarrhoea and malnutrition are common findings in patients with the Acquired Immune Deficiency Syndrome (AIDS). In this disease, enteropathy leads to fat and D-xylose malabsorption and chronic non-specific inflammation of the small bowel. Moreover, gastrointestinal infection can induce severe diarrhoea. Depletion in real body cell mass, body fat content, and weight loss have been observed. Nutritional therapy is mandatory when weight loss is 10% or greater. Enteral feeding is not easily achieved. Parenteral feeding including fat as a nonprotein calorie source improves general condition. The use of intravenous fat emulsions has been hypothesized to have several beneficial effects. Fluidisation of human immunodeficiency virus membranes by lipid emulsions through cholesterol extraction could decrease the infectivity of the virus. Long term intravenous nutrition may be more than a treatment for malabsorption and depletion; it may possibly have direct pharmacological effects.

Prostaglandin E1 attenuates postischemic contractile dysfunction after brief coronary occlusion and reperfusion

We have previously demonstrated that administration of the prostacyclin analogue iloprost improved postischemic functional recovery in reversibly injured ischemic-reperfused myocardium. The present study investigated the effects of administering an endogenous vasodilator prostanoid, prostaglandin E1 (PGE1), in the stunned myocardium (15 minutes of coronary artery occlusion and 3 hours of reperfusion) of anesthetized dogs. The percentage of regional myocardial segment shortening (%SS) after administration of PGE1 by two routes, intravenously (1 microgram/kg/min) or intraatrially (0.1 microgram/kg/min), to avoid pulmonary metabolism, 15 minutes before and throughout the period of occlusion, was compared to %SS in a control group treated with saline solution. Nearly equivalent reductions in mean arterial pressure during occlusion compared to pretreatment control (PTC) values were produced by intravenous (33%) or intraatrial (25%) PGE1. There was no difference in transmural myocardial blood flow (radioactive microsphere technique) in the ischemic region between the PGE1-treated and control groups at any time. Although there were no differences in %SS in the nonischemic region between groups throughout the experiment, postischemic recovery of segment function in the ischemic-reperfused area was significantly improved (p less than 0.05) at all times during reperfusion by intravenous PGE1 (%SS of PTC: 30 minutes = 65 +/- 8; 3 hours = 58 +/- 7) or intraatrial PGE1 (%SS of PTC: 30 minutes = 57 +/- 12; 3 hours = 50 +/- 4) compared to the control group (%SS of PTC: 30 minutes = 25 +/- 13; 3 hours = 10 +/- 13). Thus treatment with PGE1 attenuates postischemic contractile dysfunction in the stunned myocardium.2+ both.

Prostacyclin I2 (PGI2) increases left ventricular ejection fraction (LVEF)

In order to evaluate the effect of PGI2 on left ventricular ejection fraction (LVEF) an intravenous infusion in 10 patients (3 males, 7 females; 36 to 63 years) with an impaired LVEF (34.7 +/- 14.8%) was performed. LVEF was determined by means of 99mTc-pertechnetate radionuclide ventriculography. An increase of LVEF to 36.2 +/- 13.5% during administration of PGI2 at a rate of 1 ng/kg/min for 15 min and to 43.8 +/- 15.8% during a rate of 5 ng/kg/min (p less than 0.01) for an additional 15 min was observed. Analyzing the data in more detail in 6 patients, an improvement in LVEF became obvious during the administration of 1 ng/kg/min (108, 109, 116, 118, 121, and 123% of pre-infusion value, respectively). In 5 out of these 6 patients a dose-increment to 5 ng/kg/min further increased LVEF (139, 179, 187, 148, and 128% of pre-infusion value, respectively). In contrast, in the other 4 patients no response of LVEF to PGI2 at a rate of 1 ng/kg/min could be observed. However, in 2 out of these 4 patients LVEF increased during the administration of 5 ng/kg/min (111 and 117% of pre-infusion value). Individual changes in hemodynamic parameters showed no correlation to the improvement seen in LVEF in response to PGI2. It is concluded that PGI2 may exert beneficial effects on LVEF, and might be used in certain clinical conditions, such as before heart transplantation, to achieve a temporary improvement in LVEF.

Effects of gammalinolenic acid on plasma lipoproteins and apolipoproteins

Nineteen hypercholesterolemic patients (10 without and 9 with hypertriglyceridemia) were given evening primrose oil rich in gammalinolenic acid (GLA, 18: 3n - 6), in a placebo controlled cross-over design, over 16 weeks (8 + 8 weeks), with safflower oil as the placebo. During supplementation with evening primrose oil, dihomogammalinolenic acid (20: 3n - 6) increased in plasma lipids and red blood cells, and in subjects without hypertriglyceridemia there was a significant decrease in low density lipoprotein-cholesterol and plasma apolipoprotein B compared with the levels observed during safflower oil administration. Our results confirmed that evening primrose oil is effective in lowering low density lipoprotein in hypercholesterolemic patients.

Hemodynamic and angiographic effects of prostaglandin E1 in coronary artery disease

The effects of prostaglandin E1 (PGE1) were assessed in 24 patients with coronary artery disease. Quantitative coronary angiography was performed in 15 patients. PGE1 was found to produce dilation of coronary stenoses (6 +/- 12% to intravenous PGE1, difference not significant, 19 +/- 22% to intracoronary PGE1, p less than 0.05), but usually no change in the diameter of angiographically normal segments. In these patients intracoronary nitroglycerin consistently dilated the normal segments not altered with PGE1 and often led to further dilation of the stenoses. In 9 other patients who were undergoing coronary angioplasty, hemodynamics and the time to ischemia induced by coronary occlusion were measured. In both patient groups PGE1 led to decreases in aortic, pulmonary artery and pulmonary arterial wedge pressures and an increase in heart rate (all p less than 0.05). Before coronary occlusion PGE1 produced coronary vasodilation manifested by preservation in coronary sinus flow (130 +/- 41 to 126 +/- 42 ml/min, difference not significant); as aortic pressure declined coronary resistance decreased (0.9 +/- 0.3 to 0.8 +/- 0.3 mm Hg/ml/min, p less than 0.05). During coronary occlusion residual flow to the affected region was usually similar to control occlusions (37 +/- 20 to 36 +/- 25 ml/min, difference not significant) and collateral resistance was decreased (3.2 +/- 2.9 to 2.9 +/- 2.6 mm Hg/ml/min, p less than 0.05). However, time to ischemia usually remained unchanged. PGE1 shows an interesting angiographic and hemodynamic profile in patients with coronary artery disease. Although no obvious clinical benefit was seen, PGE1 was safely administered both intravenously and directly into narrowed coronary arteries.

The role of linoleic acid and its metabolites in the lowering of plasma cholesterol and the prevention of cardiovascular disease

An increase in linoleic acid intake lowers plasma cholesterol and is one of the safest methods for achieving this end. However, the amounts that must be consumed are large. Linoleic acid is metabolized via several routes and it is probable that a metabolite, rather than linoleic acid itself, is responsible for the cholesterol-lowering effect. If that metabolite could be identified, safe, drug-free, cholesterol-lowering might be achieved with much lower doses. Evidence is reviewed which suggests that a long-chain polyunsaturated fatty acid and/or a prostaglandin metabolite may be responsible for the cholesterol-controlling action of linoleic acid. Such metabolites may be effective also in controlling other risk factors for cardiovascular disease, such as elevated blood pressure and enhanced platelet aggregation. Epidemiological studies suggest that low levels of those metabolites, especially dihomogammalinolenic acid and arachidonic acid, are powerful independent risk factors for development of ischaemic heart disease. Further research in this area is urgently needed now that it is broadly accepted that cholesterol-lowering does indeed reduce the risk of cardiovascular disease.

Prostacyclin and PGE1 treatment of pulmonary hypertension

Prostacyclin and PGE1 show promise in treatment of many forms of pulmonary hypertension. Their clinical use can be expected to increase as their pulmonary vasodilating effects become better known. There is as yet no unequivocal reason to choose one agent over the other, but several observations suggest that prostacyclin will eventually be preferred. First, prostacyclin appears to have a shorter half-life (1 to 2 min), which means that any drug-induced adverse effects will disappear more quickly. Although it is commonly said that up to 80% of PGE1 is metabolized with one passage through the lungs, in one study 34% of intravenously administered radiolabeled PGE1 remained in the bloodstream 20 min after administration. Second, prostacyclin causes less severe and less prolonged rebound platelet activation after discontinuation. Third, prostacyclin has been shown to reduce resting pulmonary vascular tone and hypoxic pulmonary vasoconstriction in virtually every published study in every species tested at every stage of development (fetal, newborn, and adult life); results with PGE1, although very impressive, have been less consistent. Nevertheless, there is little doubt that PGE1 is a powerful pulmonary vasodilator in most clinical situations complicated by pulmonary hypertension. Further, PGE1 is available for clinical use, while prostacyclin remains an investigational drug. Thus, it is likely that PGE1 will become the "nitroprusside" of the lesser circuit for intensive care use, a position PGE1 will hold alone at least until prostacyclin becomes available. Chronic infusions of prostacyclin may prove particularly useful in patients with primary pulmonary hypertension awaiting heart-lung transplantation. Eventually, orally available prostacyclin and PGE1 analogs will offer a new therapeutic avenue in many diseases complicated by chronic pulmonary hypertension.

Eicosanoids and myocardial ischaemia

The available data clearly suggest large alterations in myocardial eicosanoid generation during myocardial ischaemia and demonstrate important actions of eicosanoids on myocardial function during ischaemic conditions. These actions include direct effects on the injured myocardium as well as influences on other target cells, such as platelets and leukocytes. Selective modifications of eicosanoid generation, for example by providing exogenous PGI2 or by inhibiting oxygen toxicity are most challenging approaches for the design of new and potentially valuable cardioprotective agents. Antagonism of thromboxane formation and/or action might be of some value in ischaemia but appears to be less important for reperfusion injury. Leukotrienes and other noncyclic fatty acid peroxidation products are another group of potentially deleterious agents and there is a definite need for more selective inhibitors of leukotriene formation and/or action to establish their role in ischaemia.

Calcium antagonists stimulate prostaglandin synthesis by cultured rat cardiac myocytes and prevent the effects of hypoxia

The effect of three calcium antagonists on the synthesis of prostacyclin (PGI2, assayed as 6-Keto-PGF1 alpha) and PGE2 by cultured rat cardiac myocytes and fibroblasts was investigated. In myocytes only, bepridil, diltiazem and verapamil (10(-9) to 10(-7) M) stimulated PGs synthesis by two- to three-fold, dose-dependently. At a concentration of 10(-6) or 10(-5) M the intensity of the stimulation of PGI2 and PGE2 decreased. Cobalt chloride (2 X 10(-3) M) did not change PGs synthesis (pg/mg of protein/30 min; means +/- SE, N = 10; PGE2: 365 +/- 59 and 463 +/- 89 treated vs controls; PGI2: 824 +/- 214 and 799 +/- 143 treated vs controls). After 30 min exposure of myocytes to hypoxic conditions (glucose-free medium and low PO2), the glycogen content was half that of the controls (P less than 0.001), ATP content did not change and PGI2 and PGE2 synthesis increased (X1.5, P less than 0.05). When applied to myocytes 30 min before inducing hypoxia, the three calcium antagonists stimulated PGs synthesis by three- to seven-fold at maximal effect, and bepridil (10(-8) M) or diltiazem (10(-7) M) prevented the hypoxia-induced decrease in glycogen content. With 10(-5) M drug concentration, the effect on PGs was not significant, except for the effect of bepridil on PGI2 (P less than 0.05). It is concluded that therapeutic concentrations of calcium antagonists simultaneously prevent the decrease in myocyte glycogen induced by hypoxia and stimulate PGs synthesis by myocytes.