Prevention and reversal of ouabain-induced cardiotoxicity by naloxone in the guinea-pig

The effects of pre- and post-treatment with naloxone on the cardiotoxicity of ouabain in the guinea-pig were studied. After pretreatment with naloxone, the dose of ouabain required to induce ventricular arrhythmias and cardiac arrest were significantly increased, in a dose-dependent manner, compared with the control, indicating a protective effect of naloxone against digitalis intoxication. Administration of naloxone at the onset of cardiac arrhythmias induced by a lethal dose of ouabain restored the cardiac rhythm and consequently saved life in seven out of eight animals, indicating an antiarrhythmic effect of naloxone in digitalis-intoxicated guinea-pigs. The protective and antiarrhythmic effects of naloxone against digitalis intoxication have clinical implications.

Contact dermatitis due to madecassol

Madecassol is an extract of Centella asiatica, a member of the Umbelliferae family. It contains madecassic acid, asiatic acid and asiaticoside. It has been used as a wound healing agent and for the prevention of cicatrization. We report contact dermatitis due to Madecassol and a control study with its individual ingredients.

A cardiac antiarrhythmic screening test using the isolated ischaemic perfused rat heart preparation

Ventricular fibrillation was induced by myocardial ischaemia and reperfusion in the isolated perfused rat heart. The dose-response effectiveness for the prototype antiarrhythmic drugs, propranolol, quinidine and lidocaine in converting the induced ventricular fibrillation to sinus rhythm was determined. The test is easy to perform and does not require skillful surgical procedure and long time for observation. In addition, no arrhythmogenic drugs are used and the amount of substance needed for the test is very small. It is suggested that this simple test be used as a cardiac antiarrhythmic screening test for antiarrhythmic drugs.

Cardiac antiarrhythmic evaluation of naloxone with or without propranolol using a modified chloroform-hypoxia screening test in the rat

The effects of naloxone and propranolol on cardiac arrhythmias and durations from respiratory arrest to ventricular asystole and cardiac standstill were studied in unanaesthetized young rats induced to suffer respiratory arrest and exhibit ventricular fibrillation (VF) by a modified chloroform hypoxia technique. Both naloxone and propranolol reduced the incidence of VF dose dependently, indicating that they have antiarrhythmic effects. Addition of naloxone to propranolol shifted the dose-response curve of propranolol to the left significantly, indicating an additive effect of the two drugs in their antiarrhythmic activity. Both naloxone and propranolol prolonged the duration from respiratory arrest to ventricular asystole. However, joint administration of both did not further prolong this duration indicating an absence of additive effects. Naloxone prolonged the duration from respiratory arrest to cardiac standstill, indicating that naloxone prolonged the survival time. In contrast, propranolol did not produce the same effect. That naloxone both produced antiarrhythmic effect and prolonged the survival time whereas propranolol only corrected cardiac arrhythmias suggests that the antiarrhythmic effect of naloxone may not result in prolongation of survival time and that different mechanisms may be involved in the antiarrhythmic effect.

Naloxone blocks the cardiac effects of myocardial ischaemia and reperfusion in the rat isolated heart

The effects of naloxone on contractility and cardiac rhythm were studied in the rat isolated perfused heart during myocardial ischaemia and reperfusion. Pretreatment of the rat isolated perfused heart with naloxone abolished the reduction in left ventricular pressures and attenuated greatly the arrhythmias due to myocardial ischaemia and reperfusion. Administration of naloxone into the fibrillating rat isolated heart induced by myocardial ischaemia and reperfusion also attenuated the arrhythmias in a dose-dependent manner. The results indicate a possible involvement of the endogenous opioid peptides in the cardiac effects due to myocardial ischaemia and reperfusion. The antiarrhythmic effect of naloxone has great clinical implications.

Naloxone reduces release of creatine kinase in the isolated ischemic rat heart

The effects of naloxone, propranolol, or both on the release of creatine kinase (CK) from the isolated ischemic rat heart were studied. Naloxone at concentrations of 1.1 and 3.6 mmole liter-1 in the perfusate at a rate of 1-2 ml min-1 reduced the release of CK from the isolated ischemic rat heart during myocardial ischemia in a dose-dependent manner. Propranolol at a concentration of 7 mumole liter-1 in the perfusate also reduced the release of CK. Addition of naloxone (1.1 mmole liter-1) to propranolol further reduced the release of CK. The effect of the joint administration of the two drugs seemed to be additive.

Effects of beta-endorphin on the contraction and electrical activity of the isolated perfused rat heart

beta-Endorphin at pharmacological doses reduced both the left ventricular systolic and diastolic pressures of the isolated rat heart. The reduction in the diastolic ventricular pressure was does dependent. Beta-Endorphin also altered the electrical activities of the isolated heart, disturbing the normal electrocardiogram pattern. The degree of disturbance was also dose dependent. Naloxone itself did not produce any effect. However it antagonized the depressant effects and completely abolished the effect of beta-endorphin on the electrical activity of the heart, indicating that beta-endorphin acts via the naloxone sensitive receptors. The results suggest a possible regulatory role of intracardiac endogenous opioid peptides in the cardiac functions.