Charles F. Chesney

Right ventricular hypertrophy in monocrotaline pyrrole treated rats

Abstract Single, tail-vein injections of 2–4 mg/kg body weight of monocrotaline pyrrole produced an endothelial lesion in the cells lining the capillaries and arterioles of the rat lung. Within 4 weeks, numerous pulmonary vessels became partially or completely occluded by fibrin and platelet thrombi, by enlargement of the endothelium, and by hypertrophy of smooth muscle cells in the tunica media. Impairment of the pulmonary blood flow led to tissue hypoxia which was reflected by an increase in hemoglobin, hematocrit, and erythrocyte count values. In addition, there was a fourfold increase in peak systolic blood pressure within the lumen of the right ventricle. This hypertension was progressive and caused an increase in the workload of the right heart. Right ventricular hypertrophy developed gradually over 2–3 weeks so that by 4 weeks the right side of the heart weighed almost 3 times that of the controls. It is suggested that monocrotaline pyrrole injected animals provide a readily reproducible model for experimental cardiac hypertrophy which mimics the gradual onset of cardiac disease observed clinically in man.

Modifications of pyrrolizidine alkaloid intoxication resulting from altered hepatic microsomal enzymes

Abstract Levels of hepatic microsomal activity are instrumental in determining the toxicity of the pyrrolizidine alkaloid, monocrotaline. Following the stimulation of microsomal enzymes with phenobarbital prior to the administration of monocrotaline, rats gained less weight, developed more severe lung lesions at an earlier time, and died more rapidly than those that received only monocrotaline. However, in rats pretreated with the enzyme inhibitor chloramphenicol, there was an absence of mortality, the growth rate was unaffected and the lesions were less severe than in rats given monocrotaline or in those pretreated with phenobarbital and subsequently given monocrotaline. The acute toxic effects produced by the metabolic pyrroles may be suppressed by the use of inhibiting agents such as chloramphenicol, thereby permitting the development of more chronic lesions such as megalohepatocytosis in monocrotaline-intoxicated animals.

Identification and toxicological effects of dehydroretronecine, a metabolite of monocrotaline.

Summary The major detectable pyrrole metabolite of the pyrrolizidine alkaloid, monocrotaline, present in the liver, blood, and urine of rats, has been identified as dehydroretronecine. The subcutaneous injection of this metabolite into rats produces ulceration and hemorrhage of the stomach wall. Inhibition of hepatic parenchymal cell mitosis in regenerating liver was recorded within 52 hr following its administration and persisted for at least 6 weeks.

Resistance of the guinea pig to pyrrolizidine alkaloid intoxication

Abstract Severe hepatotoxicity following intoxication with pyrrolizidine alkaloids has been observed in most domestic and laboratory animals. The guinea pig has been an unexplained exception to this generalization. Administration of monocrotaline, a pyrrolizidine alkaloid contained in the seed and vegetation of Crotalaria spectabilis , produced no clinical or pathologic alterations in guinea pigs. The in vitro microsomal ability to convert monocrotaline to its N-oxide derivative was present to the same degree in rats and guinea pigs, but the level of dehydrogenation activity in the rat was considerably greater than in the guinea pig. The ability to produce monocrotaline pyrroles in vivo was also much greater in rats than guinea pigs. However, when the pyrrolic metabolites were administered by iv injection into the mesenteric blood supply, both species developed marked hepatic necrosis. Therefore, monocrotaline N-oxides are not converted to toxic metabolites and are not toxic per se. Monocrotaline pyrroles appear to be the only metabolites yet determined which are responsible for the lesions produced by monocrotaline intoxication. The fact that N-oxidase activity, but not dehydrogenase activity, is present in guinea pig hepatic microsomes supports the contention that N-oxides and pyrroles are formed by separate enzymatic pathways during pyrrolizidine poisoning.

Effect of age on development of cor pulmonale in nonhuman primates following pyrrolizidine alkaloid intoxication

Abstract Two groups of Macaca arctoides monkeys, 4 wk and 15 mo of age, were given four injections of the pyrrolizidine alkaloid, monocrotaline, over a 6-mo period. During the terminal month or two of life, the younger monkeys experienced an increase in hemoglobin, hematocrit, red cell mass, and arterial pCO 2 , and a decrease in arterial pO 2 and pH. Increases in right heart and pulmonary artery pressures were suggestive of changes in the pulmonary vasculature. At necropsy, there was bilateral myocardial hypertrophy and right heart dilatation. The lungs were firm and failed to collapse readily when exposed to atmospheric pressure. Microscopically, there was a decided thickening of the pulmonary arterial walls and reduction in, or obliteration of, the luminal dimensions of the vessels. The right ventricular myocardium was edematous, the endocardium fibrotic, and the arterial vessels disrupted. In contrast to the young monkeys, the older animals developed ascites, distended abdominal veins and an increase in portal venous pressure. The livers were firm, small and granular on gross inspection. There was widespread venous occlusion of the hepatic venous system from the centrilobular to the large hepatic veins. Dilated, blood-filled sinuses were obvious in areas closely associated with the occluded vessels. This variation in response of infant and older monkeys is attributed to the difference in the hepatic microsomal enzyme activity and the metabolites produced from the biotransformation of monocrotaline.

Oxidative phosphorylation and respiration by mitochondria from normal, hypertrophied and failing rat hearts.

Abstract The present study was undertaken in order to determine the differences in mitochondrial respiration and oxidative phosphorylation of the myocardium from rats with monocrotaline pyrrole induced pulmonary heart disease. Experimental animals developed right ventricular hypertrophy and heart failure 6 weeks post monocrotaline pyrrole injection. Respiratory function of heart mitochondria in glutamate and succinate substrates was evaluated polarographically. Mitochondrial electron transport and phosphorylating efficiency increased slightly during cardiac hypertrophy, began to decline during impending cardiac failure, and was markedly impaired in congestive heart failure.

Chronic effects of monocrotaline pyrrole on hepatic mitosis and DNA synthesis.

Summary Monocrotaline, a pyrrolizidine alkaloid, and its metabolite, monocrotaline pyrrole, caused a significant suppression of DNA synthesis following partial hepatectomy in rats. Rats receiving mesenteric vein injections of monocrotaline pyrrole prior to partial hepatectomy showed a marked inhibition of liver cell division between 32 and 38 hr following surgery. Both the parent alkaloid and its pyrrole derivative induced megalohepatocytosis in rats 4 wk after their administration. The effect of the pyrrolic metabolite was considerably greater than that of the parent compound, supporting the contention that the consequences of pyrrolizidine alkaloid intoxication are due primarily to in vivo hepatic conversion of the alkaloid to its pyrrole derivative.

Oxidative phosphorylation and respiration by liver mitochondria from polychlorinated biphenyl-intoxicated rats☆

Abstract Respiration and oxidative phosphorylation by intact hepatic mitochondria isolated from rats fed polychlorinated biphenyls (PCBs) were studied polarographically using glutamate and succinate as substrates. High levels of PCBs fed for 3 weeks resulted in an increase in respiration and in ADP/O ratios. However, when PCBs were fed to rats for 20 weeks at 100 ppm, there was no significant difference from control values. Gas Chromatographic determination of PCB levels in mitochondrial fractions revealed 2–3 μg/mg of protein for treated rats in the acute study and about 0·3 μg/mg in the chronic study. Addition of PCBs in vitro to control rat liver mitochondria caused an inhibition of oxidative phosphorylation and respiration at or above a concentration of 50 μg/mg of mitochondrial protein. Since 2,4-dinitrophenol did not initiate uncontrolled respiration in PCB-inhibited rat liver mitochondria, and since inhibition occurred with both substrates, it appears that PCB inhibition in vitro occurs at a site along the respiratory chain.

Ultrastructure of the right ventricle after monocrotaline-induced cor pulmonale in the nonhuman primate (Macaca arctoides).

Abstract The present study is concerned with the ultrastructural changes that occur in the right ventricle of Macaca arctoides monkeys following subcutaneous injection of the pyrrolizidine alkaloid monocrotaline. The monkeys showed right ventricular hypertrophy and congestive heart failure within 7 months following the initial injection of monocrotaline. At sacrifice, all of the monkeys had developed marked dilatation and hypertrophy of the right ventricle. Focal cytolysis involving myocytes, intracellular edema, and fibrosis were observed light microscopically. Ultrastructural changes of the right ventricle included hypertrophy and hyperplasia of the mitochondria, increase in intracellular matrical material, streaming and clumping of the Z-band material, disorganization and degeneration of myofibrils, dilatation of the sacroplasmic reticulum and transverse tubular system, increased number of free and attached ribosomes, and proliferation of intercellular collagen fibers.