Localization by autoradiography of tritiated isoproterenol in "infarct-like" lesions of rat myocardium

Diminished hypotensive response to isoproterenol in streptozotocin-diabetic rats

1. The cardiovascular reactivity of streptozotocin-diabetic rats has been evaluated with isoproterenol (ISO), a strong beta-adrenergic agonist able to produce, at large dose, myocardial infarction. 2. In the basal state, diabetic rats presented significantly lower heart rate (P less than 0.001), a decreased systolic (P less than 0.05) and an unaltered diastolic blood pressure compared to non-diabetics. 3. Following ISO stimulation, the chronotropic response was similar in both groups of rats, while the fall in systolic and diastolic pressure was markedly reduced compared to those of non-diabetic rats (P less than 0.001). 4. These results suggest that the vasodilation capacity of diabetic rats is diminished.

The role of prenylamine in the prevention of adriamycin-induced cardiotoxicity. A review of experimental and clinical findings

Experimental and clinical trials to determine the potential of prenylamine in the prevention of adriamycin-related cardiotoxicity are reviewed. In mice given 4 mg/kg body weight adriamycin, the incidence of myocardial damage after 19 days' treatment was lower than in those given adriamycin and placebo. Rabbits were given adriamycin (total dose 10.8 mg/kg body weight), adriamycin plus prenylamine (1.5 mg/kg body weight), and adriamycin plus vitamins A (250 IU) and E (40 mg) for 9-11 weeks. Adriamycin-induced electrocardiogram changes were observed to a lesser extent in animals also receiving prenylamine. Heart homogenates from adriamycin-treated animals showed enhanced hydroperoxide-initiated chemiluminescence which was not affected by the simultaneous administration of prenylamine. The extent of adriamycin-induced myocytolysis and the degree of alterations observed on electron microscopy were markedly reduced by prenylamine. In a double-blind clinical trial with 26 oncological patients, no cardiomyopathy, arrhythmia or adverse reactions were observed in the group given adriamycin plus prenylamine. In those given adriamycin plus placebo, two patients developed congestive cardiopathy and another showed severe supraventricular arrhythmias together with hypotension and dyspnoea. The mechanisms of adriamycin-related cardiotoxicity, the effects of prenylamine and the benefit from combined treatment are discussed.

Amelioration of adriamycin-induced cardiotoxicity in rabbits by prenylamine and vitamins A and E

The cardioprotective potentials of prenylamine (a calcium antagonist) and of a combination of vitamins A and E (a singlet oxygen quencher and a free radical scavenger, respectively) were evaluated in rabbits given chronically large doses of Adriamycin (ADM) (10.8 mg/kg body weight for 9 to 11 weeks). Among ADM-treated rabbits, 8 of 10 showed post-treatment ECG changes; in rabbits treated with ADM and prenylamine, changes were found in a smaller number (5 of 10); and in animals treated with ADM and vitamins A and E, the incidence was only one in six (p less than 0.05). Heart homogenates from ADM-treated rabbits showed an increased hydroperoxide-initiated chemiluminescence (expressed as cpm/mg protein X 10(-3)) of 77 +/- 4 compared to control animals (52 +/- 1) (p less than 0.01). Prenylamine administration did not alter hydroperoxide-initiated chemiluminescence in ADM-treated rabbits, whereas treatment with a combination of vitamins A and E showed a significant decrease in hydroperoxide-initiated chemiluminescence in control (40 +/- 2) and ADM-treated rabbits (42 +/- 1). Microscopically, myocardial fibers had mild to severe hydropic vacuolization of sarcoplasm, which led to progressive myocytolysis. A total of 103 +/- 13 damaged fibers were detected over 700 counted fibers. Myocardial damage was lowered to 47 +/- 16 by administration of prenylamine and to 28 +/- 8 by administration of vitamins A and E. It is suggested that ADM leads to myocardial lipid peroxidation (ameliorated by vitamins A and E) with membrane damage and to an increase in calcium permeability, the latter being counteracted by prenylamine.

A routine method for diagnosis of early myocardial infarction

We compared Barbeito-Lopez Trichrome stain with H-E, the basic fuchsin picric acid and Nitro Blue of Tetrazolium stains. The Barbeito-Lopez Trichrome stain was much more sensitive than the other stains for the diagnosis of early myocardial coagulation necrosis.

Verapamil prevents isoproterenol-induced cardiac failure in the rat

Virgin, male Sprague-Dawley rats were used to study the production of cardiac failure by a single subcutaneous injection of 85 mg/kg dl-isoproterenol (ISO) and the possible preservation of cardiac function by a pre-treatment of 50 mg/kg verapamil (VER) 5 min prior to 85 mg/kg ISO. At 24 hrs after drug injections cardiac function was assessed in anesthetized, open-chest rats by the measurement of cardiac output and by a volume loading of the heart with a 2 min, 15.3 ml/min jugular vein infusion of Tyrode's solution. Peak cardiac index and peak stroke index were depressed by ISO. VER completely prevented these signs of ISO-induced cardiac failure. A second group of rats was sacrificed 24 hrs after ISO and VER-ISO and their left ventricular calcium contents were determined. ISO caused a significant increase in left ventricular calcium content. VER attenuated the ISO-induced increase in myocardial calcium content, but did not prevent it. This data raises questions as to whether VER's property as a transarcolemmal calcium flux inhibitor was the mechanism of preservation of cardiac function following ISO administration. It is possible that VER may have preserved cardiac function by altering ISO-induced hemodynamic changes in the rat.

Occurrence and significance of coagulative myocytolysis in the specialized conduction system: clinicopathologic observations

In 5 of 18 selected human hearts (15 from patients with early myocardial infarction and severe coronary arterial obstruction), coagulative myocytolysis (myofibrillar degeneration with contraction bands) was demonstrated in the specialized conduction tissue. Its morphologic peculiarities, apparently inherent in the number and arrangement of the affected myofibrils in each type of specific myocell, are described. In nine cases the ordinary cardiac muscle was also involved; in all hearts concomitant changes were present. The debated toxic catecholamine and anoxic aspects of coagulative myocytolysis are briefly reviewed in light of the finding that specialized tissue seems to withstand myocytolytic damage (or any ischemic-anoxic injury) better than ordinary myocardium. This may also explain why coagulative myocytolysis is observed less frequently and evidently in specific rather than in ordinary myocells. Clinicopathologic comparisons focused on arrhythmias, although hampered by inadequacies in routine electrocardiographic documentation, suggest that coagulative myocytolysis of the conduction system may be relevant to life-threatening disturbances in impulse formation and conduction. These data, with their bearing on important current problems in cardiologic emergencies, deserve better morphopathophysiologic assessment.

Isoproterenol-induced 45ca uptake into myocardium of rats

Myocardial lesions induced by isoproterenol (ISP) are similar to those of human "coagulative mycocytolysis" or "myofibrillar degeneration". The localization of tritiated ISP in the damaged myocardium of rats has been recently described. Since H3-ISP was noted in "grooves" along the sarcolemma of ischemic and necrotic fibers, an action on the membrane with exaggerated calcium inflow was suggested. For this reason, the quantity of 45Ca in rats treated with ISP was studied. Thirty rats were given 5 mu Ci of 45Ca. Twenty (Group B) of them were also given ISP 10 mg/kg. Animals were killed at 1 h after the injections. The hearts were sectioned transversally and autoradiography was performed. Serial sections were examined to localize the 45Ca, and its topographic distribution. In Group A (injected only with 45Ca) the myocardium showed + of 45Ca (600 dots in a field x 400) inside the fibers. In Group B (injected also with ISP) 45Ca was deposited +++ (more than 1,200 dots) and related to extensive myocytolysis. These findings confirm that the crucial point in the ISP-induced lesions is the increase of calcium inflow, and if the pathogenesis of human myocytolysis is related to catecholamine effects pharmacological measures may be adopted to prevent these myocardial lesions.

Prenylamine. Autoradiographic and neuropathological studies on myocardial mechanisms of action

Myocardial localization of prenylamine (PNL), a well known antianginal drug, was studied by means of an autoradiographic technique to detect microscopical distribution of tritiated PNL (3H-PLN). Forty Wistar rats received 35 muCi/kg b. w. 3H-PNL i. p., the animals being killed 30 min after injection. Heart slices, 1 mm thick, were processed for both autoradiographic and conventional histological techniques. 3H-PNL was observed, mainly, as striae along sarcolemma; sarcolemmal/intramyocardial 3H-PNL distribution ratio was 6 : 1. Preferential membrane deposition of 3H-PNL is probably related to the calcium transport inhibiting action of the drug, previously described.