Isoproterenol toxicity

Dilated cardiomyopathy associated with chronic overuse of an adrenaline inhaler

Endogenous catecholamines in excess are known to cause dilated cardiomyopathy. A patient presented with dilated cardiomyopathy after many years of overusing an adrenaline inhaler. Pathological features and a considerable improvement in myocardial function after withdrawal implicated the exogenous catecholamine excess in the pathogenesis of the cardiomyopathy.

Cardiotoxic effects of the combined use of caffeine and isoproterenol in the minipig

Beta agonists such as isoproterenol are widely used in the treatment of acute asthmatic attacks. It would not be unexpected that some patients receiving isoproterenol might have ingested caffeine as an over-the-counter drug or beverage. This study explores the possible interaction between these two drugs. Anesthetized minipigs were injected with 0.5 mg/kg caffeine iv followed by a 10-min infusion of 1 microgram/kg.min isoproterenol. Heart rate, EKG, respiration, and blood pressure were recorded continuously and the animals were sacrificed at 72 h. The two drugs in combination produced subtle changes in heart rate and blood pressure with significant alteration in the EKG tracing (premature ventricular contractions and extrasystoles). These changes persisted for 8 to 24 h. At autopsy both gross and microscopic lesions were noted in 10 of the 13 minipig hearts receiving the combination of drugs. This was not true of the six minipigs given only caffeine or the eight minipigs receiving only the infusion of isoproterenol. No changes in EKG tracings or pathologies were noted with caffeine and only two of eight animals infused with isoproterenol showed any lesions. Results indicate that doses of caffeine equivalent to that expected from drinking a cup of coffee appear to increase the toxicity of isoproterenol to a point that EKG changes and myocardial pathologies are observed.

Effect of cardiotoxic concentrations of catecholamines on Na+-Ca2+ exchange in cardiac sarcolemmal vesicles

The mechanism by which the administration of large doses of catecholamines produces myocardial necrosis in experimental animals and humans has not yet been ascertained. One of the consequences of such administration is the accumulation of high concentrations of Ca in the heart and it has therefore been suggested that this is the factor that leads to cell injury. The elevated intracellular Ca appears to be due in part to enhanced Ca influx resulting from catecholamine-induced opening of membrane Ca channels and in part to increased membrane permeability caused by membrane damage. It is not clear, however, why the myocardial cells are unable to extrude their extra load of Ca, at least initially, so as to maintain normal Ca concentrations. The effects of high concentrations of epinephrine and isoproterenol on Na+-Ca2+ exchange transport in isolated sarcolemmal vesicles prepared from hearts of Sprague-Dawley rats were determined. It was found that catecholamine concentrations of 10(-4) to 10(-2) M inhibited the exchange in a dose-related manner while choline, in the same concentrations, had no effect. It is therefore possible that cardiotoxic concentrations of catecholamines also interfere with Na+-Ca2+ exchange transport across the myocardial sarcolemma in vivo and thereby inhibit the efflux of intracellular Ca.

Role of calcium and free fatty acids in epinephrine-induced myocardial necrosis

A possible mechanism by which large doses of catecholamines produce myocardial necrosis was investigated. Male Sprague-Dawley rats, 275 to 325 g in weight, were injected once, sc, with 3 mg/kg epinephrine (E) or infused iv for 1 hr with E at a rate of 1.2 or 1.7 micrograms/min, and also injected iv with either 45Ca or [3H]palmitic acid (3H-PA) at the same time as or at various periods of time after E administration but exactly 0.5 or 1 hr before death. Controls were injected with saline solution. Heart/plasma ratios of radioactivity (H/P) were determined. The ratios increased in the case of both 45Ca and [3H]PA within 0.5 hr after E, reached peak values after 18 to 24 hr with 45Ca and 3 to 6 hr with [3H]PA, and remained above values for the controls for at least 72 hr with 45Ca and 48 hr with [3H]PA. The rate of 45Ca influx into heart 20 hr after E administration paralleled the severity of the myocardial damage that had been produced. When 45Ca and E were injected simultaneously, H/P increased progressively with time to 30 times control values, indicating the accumulation and retention of Ca in the heart. Under the same conditions, H/P values with [3H]PA also rose but remained constant at a level two to three times that in controls. Total cardiac free fatty acids (FFA) rose slightly and remained constant at the elevated level. It was not possible to distinguish a given point in time at which the increase in either Ca or FFA influx, initially due to the normal pharmacological effect of E, began to occur as a consequence of damage produced by the latter. It is concluded that high concentrations of catecholamines promote the deposition of Ca and FFA in myocardial cells in various forms, and that the deposition of these substances as soaps in the plasma membranes may cause permeability changes that lead to cell injury.

Myocardial infarction association with the Riley-Day syndrome

The "sudden death" of a 23-year-old Ashkenazy Jew, suffering from "familial dysautonomia" was probably caused by an arrhythmia accompanying a myocardial infarction. Such a report is unique. Diffuse coronary atherosclerosis and direct myocardial "catecholamine cardiomyopathy" seem responsible for the myocardial damage. However, diversion of the endocardial blood flow toward dpicardium and a "coronary steal" phenomenon, both the result of a sudden catecholamine discharge, could aggravate the ischemic injury.

Inhibition of epinephrine-induced myocardial necrosis in rats by administration of single doses of ethanol

The oral administration of single doses (0.5-6.0 g/kg) of ethanol to rats, shortly before injecting them with a large dose (3.0 mg base/kg) of epinephrine subcutaneously, significantly reduced the severity of the myocardial damage produced by the epinephrine. The larger the dose of ethanol, the greater was the protective effect. The results were the same, regardless of the method used to determine the degree of cardiac injury. Experiments employing various agents to determine the mechanisms of ethanol action have tentatively suggested that a platelet de-aggregating or an osmotic effect of alcohol may be involved.