Tibor Balazs

Mercuric chloride-, gold sodium thiomalate-, and D-penicillamine-induced antinuclear antibodies in mice.

Inducibility of antinuclear antibodies (ANA) by mercuric chloride (HgCl2) was studied in various strains of mice. High response to the treatment was observed in strains A.SW (H-2s), A.CA (H-2f), A.TH (H-2t2), B10.S (H-2s), DBA/1J (H-2q), and P/J (H-2p); strains A.BY (H-2b), B10.M (H-2f), and C3H/HeSnJ (H-2k) showed a low response, while strains A/WySn (H-2a), A/J (H-2a), A.TL (H-2tl), BALB/cJ (H-2d), C57BL/10SnJ (H-2b), B10.A (H-2a), and PL/J (H-2u) did not produce any detectable ANA. Thus, the H-2a haplotype determines resistance to the treatment regardless of the genetic background; the H-2s determines susceptibility, while the H-2b and H-2f are intermediate haplotypes whose effect depends on the interaction with the background genes. Our results with intra-H-2 recombinant strains indicate that the I region of the H-2 complex is the major genetic factor controlling this response. The function of the I region is to control cellular cooperation in the immune response that finally results in production of antibodies specific for a particular antigen. Therefore, we postulated that the I region controls the antibody response to a nuclear antigen released as a result of HgCl2 toxicity in mice. A genetic study of an A.SW X C57BL/10 cross confirmed this observation, showing that resistance to ANA induction by HgCl2 in this strain combination is determined by interaction of a semidominant H-2-linked gene and one or more unlinked genes. The two drugs tested, gold sodium thiomalate and D-penicillamine, also induced ANA in A.SW mice, while other strains tested resisted this treatment.

Development of tissue resistance to toxic effects of chemicals

Abstract Evidence has been presented from both the published literature and the authors own work that after repeated administration of various chemicals which induce degenerative changes, resistance develops in the target tissue to the toxic effects. Such a resistance develops only after an induced lesion, and it is not specific to the inducing agent, but extends to agents causing similar lesions. The resistance lasts during the period of exposure to the noxious agent and for varying times thereafter. It is looked upon as an adaptation mechanism to the adverse environment; thus it is of epidemiological interest. This phenomenon is of significance also in the safety studies of chemicals. The present practice of performing histopathology examinations solely in prolonged dosing studies may overlook what happened in the early stages of the exposure to potentially toxic agents. The resistance is also of clinical interest, since the toxic effect may not manifest in long-term therapy even though the pharmacologic effect does not diminish. The continuing pharmacologic effect implied that the phenomenon is not related to a pharmacokinetic change. Apart from this, its mechanism has not been established.

Acute cardiomyopathy induced by the vasodilating antihypertensive agent minoxidil

Abstract Minoxidil, a vasodilating antihypertensive drug, was given orally in doses of 0.5, 1.0, or 3.0 mg/kg to adult Beagle dogs on 2 consecutive days. Within 2 hr of administration, each of these doses produced hypotension and a marked tachycardia which persisted for as long as 24 hr after the second dose of minoxidil. Necropsies performed 24 hr after the second dose revealed focal, superficial areas of epicardial or endocardial hemorrhage in dogs given each of the three dose levels. Hemorrhage was associated with a mild inflammatory reaction and was not limited to the right atrium. Focal arteritis, characterized by extravasation of blood and by focal accumulation of erythrocytes and fibrin-like material in the walls of small coronary arteries, occurred in three hearts from the 3-mg/kg dose group. Myocardial necrosis was noted in one of eight dogs given the minimal pharmacologic dose of 0.5 mg/kg, and in five of eight dogs in each of the groups given 1 or 3 mg/kg. Necrosis was most frequent in the left ventricular papillary muscles, particularly the posterior one. An ischemic origin of the necrosis is suggested by the localization of the lesions and by the pharmacologic effects of minoxidil.

Enhancement of Cardiotoxic Effects of β-Adrenergic Bronchodilators by Aminophylline in Experimental Animals

To examine the cardiotoxic interaction between beta-adrenergic bronchodilators and theophylline, we tested the effects of isoproterenol or bitolterol alone and in combinations with aminophylline in experimental animals, both electrocardiographically and histologically. The sc LD50 values for isoproterenol in 4- to 5-month-old, 500-600 g (heavy) and 1.5- to 2-month-old, 150-200 g (small) male Sprague-Dawley rats were 0.6 mg/kg and 1300 mg/kg, respectively, and values for bitolterol were 4 mg/kg and greater than 1800 mg/kg, respectively. Results of the electrocardiographic studies in heavy rats, using the calculated LD20 dosage of isoproterenol with or without pretreatment of aminophylline, demonstrated that both mortality and the arrhythmia-inducing effect of isoproterenol were significantly potentiated by aminophylline but only mortality was increased in small rats. Aminophylline also potentiated the electrocardiographic effects of 1/40 of the LD50 dosage of isoproterenol in heavy rats but did not enhance the effects of bitolterol at this dose level. Potentiation of the arrhythmogenic effect of isoproterenol was also observed in rabbits. The severity of the myocardial lesions produced by isoproterenol or bitolterol in heavy rats was significantly enhanced by aminophylline. The heavy rat appears to be a sensitive model for studying the interaction of these classes of drugs.

A comparative study of minoxidil-induced myocardial lesions in beagle dogs and miniature swine.

Minoxidil, a long-acting vasodilating antihypertensive agent, reduces arterial blood pressure by a direct action on arteriolar smooth muscle. The present studies examined the gross anatomic, histologic and ultra-structural myocardial alterations produced by 2 daily doses of minoxidil in beagle dogs (0.5, 1, or 3 mg/kg) and miniature swine (1, 3, or 10 mg/kg). Both myocardial necroses and hemorrhages were observed in dogs and pigs 24 hr after the last dose of minoxidil. In both species, the necroses were most frequent in the left ventricular papillary muscles, particularly the posterior one, but were less severe in swine. An ischemic origin of the necroses was suggested by the location of the lesions and by the pharmacologic effects of minoxidil. Gross epicardial or endocardial hemorrhages involving the atria and, to a lesser extent, the ventricles were observed in both species but were more severe in dogs. The atrial lesions were manifested grossly by diffuse redness and microscopically by interstitial edema, extravasated erythrocytes and infiltration of mononuclear cells. Hemorrhages, occurring on the epicardial surfaces, were often associated with lesions that involved small arteries having 3–6 layers of medial smooth muscle cells and were characterized by endothelial injury, intramural accumulations of erythrocytes and platelets, periadventitial hemorrhage, fibrin deposits and an inflammatory cell reaction. These lesions preferentially involved the right atrium in dogs and the left atrium in pigs. Pretreatment of beagle dogs with pyribenzamine (3 doses of 6 mg/kg every 8 hr), cimetidine (3 doses of 15 mg/kg every 8 hr), or both, had no effect on the incidence or severity of minoxidil-induced hemorrhagic lesions. The hemorrhagic lesions may be caused by overstretching of the vascular walls due to excessive, prolonged vasodilatation.

Reduced arachidonic acid levels in major phospholipids of heart muscle in the diabetic rat.

The fatty acid composition of phospholipids and triglycerides in heart muscle was examined in normal and alloxan-diabetic male Wistar rats. In diabetes the major phospholipids, phosphatidyl choline and phosphatidyl ethanolamine, showed significant changes in fatty acid composition, whereas cardiolipin and phosphatidyl serine + phosphatidyl inositol did not show marked changes in fatty acid profile. In phosphatidyl choline there was a significant diminution in arachidonic acid, 20 : 4(n-6) and palmitic acid, 16 : 0, and a corresponding increase in linoleic acid, 18 : 2(n-6), and stearic acid, 18 : 0. In phosphatidyl ethanolamine the level of 20 : 4(n-6) was significantly reduced. The diabetic heart had normal levels of individual phospholipids, whereas the triglycerides were increased by 90% and contained significantly higher levels of 18 : 2(n-6). The results confirm that diabetes is associated with a diminution in fatty acid desaturation, affecting the fatty acid composition of phosphatidyl choline in particular. These changes may be relevant to development of atherosclerosis and relative resistance to catecholamine-induced cardiac necrosis in diabetes.

The cardiotoxic effects of pressurized aerosol isoproterenol in the dog

Abstract A pressurized aerosol isoproterenol sulfate was administered through a face mask or through an endotracheal tube to conscious beagle dogs. Tachycardia was elicited by both methods of dosing; however, depression of the ST segment of the EKG and arrhythmia was elicited only by the latter technique. Twenty to 80 sprays given endotracheally at the rate of 5 sprays per minute during inhalation on 2 consecutive days caused EKG changes and focal myocardial necrosis of dose-related severity. The left and right ventricular papillary muscles were the primary sites of the lesion. The presence of induced myocardial necrosis or ACTH pretreatment did not sensitize the heart to isoproterenol. Endotracheal dosing with such a product appears to be a suitable route for the detection of adverse cardiac effects in the dog.

Study of the mechanism of hydralazine-induced myocardial necrosis in the rat

Abstract Hydralazine, 25 mg/kg ip given on 2 consecutive days, causes myocardial necrosis in rats. Propranolol, 10 mg/kg sc twice daily, or verapamil, 10 mg/kg sc twice daily, protected against this effect. Hydralazine alone caused marked tachycardia, but bradycardia occurred when hydralazine and propranolol were given in combination. Verapamil caused a mild tachycardia which was increased further by hydralazine. Pretreatment with dihydrotachysterol, 1 mg/kg po for 3 days, aggravated the hydralazine-induced lesion. 45 Ca measurements indicated increased calcium concentration in the heart 6 hr after hydralazine administration. The data suggest that the lesion is induced by the pharmacological effects of hydralazine and that hypoxia and increased intracellular calcium play a role in the development of necrosis.

Determinants of resistance to the cardiotoxicity of isoproterenol in rats

Induction of myocardial necrosis by isoproterenol produces resistance to the necrogenic effects of subsequent doses of the drug. A series of experiments were performed to further define the determinants of resistance. Myocardial necrosis was induced in male Sprague-Dawley rats by sc injection of isoproterenol at 50 micrograms/kg daily for 10 consecutive days or as a single dose at 50, 5, or 0.5 micrograms/kg. These preconditioning doses were followed, at various times, by a challenge dose of 50 micrograms/kg. The rats were killed 48 hr after the challenge dose, and their hearts were analyzed morphometrically to determine the amount of acute necrosis and scarring. The amount of scar tissue was a reflection of necrosis caused by the preconditioning dose whereas acute necrosis reflected response to the challenge dose. Resistance occurred and lasted longer than 19 to 20 weeks after both single or multiple isoproterenol injections of 50 micrograms/kg, but it was not observed 5 days after administration of a single preconditioning dose. Isoproterenol at 0.5 micrograms/kg produced only very minimal or no myocardial necrosis and did not produce resistance. The resistance was not dependent on the size of the area of necrosis produced during the preconditioning period, showing that it was not due to destruction of all vulnerable muscle by the preconditioning dose(s). The preexistence of lesions, however, was necessary for the development of resistance. It is concluded that development of resistance to the necrogenic effects of isoproterenol reflects an adaptive alteration in the myocardium which survives after a necrogenic dose.

Correlation of human hepatotoxicants with hepatic damage in animals

Substances that cause liver damage in humans were identified through a literature search conducted on Toxline and Medline. Using the same search strategy, species other than man were selected, in whom hepatic injury could be attributed to exposure to the identified substances. A total of 38 substances were identified as producing liver damage, manifested by either clinical chemistry or histopathology. The substances included 24 drugs, 9 industrial chemicals, 3 environmental agents, 1 pesticide, and ethanol. Twelve of the 36 compounds have been toxicologically evaluated in man, rodent, and non-rodent. Histopathologic liver damage was reported in all three species for 11 of these compounds. Only carbencillin produced histopathologic damage in man but not in either the rodent or non-rodent. Where clinical chemistry changes were reported for all three species categories, only eight substances induced similar reactions in all three species. Only with two substances did man and rodent react similarly (both positive), while the non-rodent was negative. The two substances were polychlorinated biphenyl (PCB) and tetrachlorethane. In the majority of the cases in which either or both histopathologic or clinical chemistry changes were reported for man or for the rodent or non-rodent, the changes that occurred were qualitatively similar. The rodent was as sensitive a predictor for hepatic effects as the non-rodent. Although it is impossible to predict how liver damage observed in a laboratory animal is correlated with human liver damage, hepatotoxicity in the rodent must be considered as indicative of potential hepatic damage in man.