Effect of adrenochrome on adenine nucleotides and mitochondrial oxidative phosphorylation in rat heart.

Effects of adrenochrome, an oxidation product of epinephrine, on myocardial energy production were investigated by studying changes in adenine nucleotide content and mitochondrial oxidative phosphorylation activities in the isolated rat heart. Perfusion of the heart with 50 mg/L adrenochrome induced a marked decline in contractile force within 5 min and this was associated with a rapid decline in the myocardial ATP/AMP ratio. A significant decrease in ATP and ATP/ADP ratio as well as a significant increase in ADP and AMP content was observed at 10 min of perfusion with adrenochrome. Furthermore, mitochondrial oxidative phosphorylation activities were unchanged except that an increase in state 4 respiration and a decrease in RCI value were seen in the heart perfused with adrenochrome for 10 min. Autoradiography of the sections from hearts perfused with 14C-adrenochrome revealed the localization of a significant amount of radioactivity on mitochondria. Adrenochrome at concentrations of 20 mg/L or higher was found to inhibit the oxidative phosphorylation activities of heart mitochondria under in vitro conditions. The depressant effects of adrenochrome on mitochondrial oxidative phosphorylation were additive to those seen with calcium. These data suggest that adrenochrome in the presence of excess calcium in the myocardial cell may impair the process of energy production in mitochondria and this may result in contractile failure of hearts exposed to this cardiotoxic metabolite of epinephrine.

Modification of adrenochrome-induced cardiac contractile failure and cell damage by changes in cation concentrations.

Adrenochrome has been shown to produce cardiac necrosis as well as failure in the isolated rat hearts. These effects of adrenochrome were influenced by alterations in the Ca2+, Na+, K+, and Mg2+ concentrations of the perfusion medium. Increasing the Ca2+ or K+ concentration or decreasing the Na+ concentration of the adrenochrome-containing perfusion medium partially maintained contractile force but increased the severity of ultrastructural damage. Reducing the K+ concentration of the medium did not alter the failure of contractile force development but increased the severity of ultrastructural damage due to adrenochrome. Reducing the Ca2+ or increasing the Mg2+ concentration of the perfusion medium completely prevented myocardial necrosis due to adrenochrome. Omission of Mg2+ from the perfusion medium neither altered the time course of contractile failure nor effected the severity of necrosis due to adrenochrome. These results for the most part parallel the influence of similar ionic interventions on the severity of necrosis produced by excessive amount of catecholamines.

Effects of adrenochrome on calcium accumulating and adenosine triphosphatase activities of the rat heart microsomes.

The influence of adrenochrome (1-100 microgram/ml or 5.6 x 10(-6)-5.4 x 10(-4) M) on microsomal calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent adenosine triphosphatase (ATPase) activities was studied in vitro. Adrenochrome decreased microsomal calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent ATPase activities. The inhibitory effect of adrenochrome on microsomal calcium uptake activity of the isolated membrane was independent of pH (6.0-8.0), calcium concentrations (10-200 muM), protein concentration (0.02-0.10 mg/ml), temperature (25-37 degrees C) and incubation time (2-30 min). Kinetic study of calcium uptake activity in different concentrations of ATP showed that the inhibition was of a mixed type. Perfusion of hearts with adrenochrome resulted in marked depression in contractile force and the microsomal fraction obtained from these hearts showed depressed calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent ATPase activities. The depression in microsomal The influence of adrenochrome (1-100 microgram/ml or 5.6 x 10(-6)-an irreversible nature. It is proposed that cardiodepressant action of adrenochrome may partly be explained on the basis of its inhibitory effect on the calcium transporting ability of the sarcoplasmic reticulum.

Protection against adrenochrome-induced myocardial damage by various pharmacological interventions.

Perfusion of the isolated rat heart with Krebs-Henseleit solution containing adrenochrome (25 or 50 mg/l), and oxidation product of catechalmines, resulted in contractile failure and myocardial necrosis. Various pharmacological agents known to protect the myocardium against catecholamine-induced necrosis were also found to be effective against adrenochrome-induced changes in the ultrastructure of the isolated perfused rat heart. The alpha-receptor-blocking drugs tolazoline and Dibenamine (dibenzylchlorethamine), and the adrenergic neurone-blocking agents guanethidine and bretylium did not alter the development of contractile failure and necrosis due to adrenochrome. The beta-receptor-blocking compounds propranolol and practolol effectively protected the heart from adrenochrome-induced necrotic damage, and partially prevented contractile failure. The hydrazine-type monoamine oxidase inhibitor iproniazid completely prevented ultrastructural damage and partially maintained contractile-force development in adrenochrome perfused hearts. The non-hydrazine-type monoamine oxidase inhibitor tranylcypromine partially protected the isolated rat heart against adrenochrome necrosis, but disruption of mitochondrial structure was still seen. Tranylcypromine did not significantly improve contractile force development during adrenochrome perfusion. The calcium antagonist D-600 reduced the severity of adrenochrome-induced ultrastructural damage. These results provide strong support for the view that catecholamine-induced cardiotoxicity is mediated through the formation of adrenochrome.

Effects of lanthanum on the heart sarcolemmal ATPase and calcium binding activities.

Effects of lanthanum on Ca2+-ATPase, Mg2+-ATPase, Na+-K+-ATPase, and calcium binding activities were studied in rat heart sarcolemma. Ten to 100 micrometers lanthanum depressed significantly the Ca2+-ATPase activity and 50--200 micrometers lanthanum inhibited the calcium binding activity. Lineweaver-Burk plots of the Ca2+-ATPase activity showed that the inhibition by lanthanum was competitive with calcium concentration. Neither Mg2+-ATPase nor Na+-K+-ATPase activities were affected by lanthanum when the assay medium contained 1 mM EDTA; however, in the absence of EDTA, these enzyme activities were significantly decreased by 10--100 micrometers lanthanum. Rat hearts perfused with HEPES buffer containing 0.5 mM lanthanum showed electron-dense deposits restricted to the outer cell surface and the sarcolemma obtained from these hearts also had the deposits, indicating that the membrane fraction isolated by the hypotonic shock--LiBr treatment method is of sarcolemmal origin. The Ca2+-ATPase activity of the sarcolemma isolated from lanthanum-perfused hearts, unlike the Mg2+-ATPase, Na+-K+-ATPase, and calcium binding activities, was significantly less than the control value. From these observations it is suggested that lanthanum may influence calcium movement across the sarcolemma by affecting sarcolemmal ATPase and calcium binding activities.