Influence of isoproterenol and calcium on cadmium- or lead-induced negative inotropy related to cardiac myofibrillar protein phosphorylations in perfused rat heart

Effects of dietary selenium on lipid peroxidation, mitochondrial function and protein profiles in the heart of the myopathic Syrian golden hamster (BIO 14.6)

Male, weanling myopathic Syrian Golden Hamsters (BIO 14.6 strain) were fed a selenium-adequate diet (controls) or this diet supplemented with 1.0 ppm selenium (treated) for 30 days. Se-treated animals exhibited a 50% reduction in lipid peroxidation in heart homogenates relative to controls and a 61% increase in mitochondrial glycerophosphate acyltransferase activity. Gel electrophoresis revealed no alterations in cardiac protein profiles from treated or control animals. These data suggest that the selenium prevents peroxidative injury and maintains mitochondrial function in the absence of alterations in cardiac proteins.

Carotid sinus reflexes in rats given small doses of lead

The effect of low level lead poisoning on the carotid sinus reflex in rats was studied. The reflex was evoked by carotid artery clamping, in control and lead-poisoned animals. Wistar rats were given lead acetate trihydrate (50 mg/kg) via stomach tube once weekly for 5 weeks; control animals were given equimolar amounts of sodium acetate. Both groups were fed a regular animal food diet. At the end of the 6th week, and under urethane anesthesia, mean arterial blood pressure and heart rate were continuously recorded for both groups, before and after clamping, and after unclamping the left common carotid artery. In other experiments, some animals were pre-treated with dopamine, 0.040 mg/kg; practolol, 3 mg/kg; propranolol, 0.1 mg/kg; or atropine, 0.1 mg/kg. In animals not given drugs, lead produced a less pronounced rise in mean arterial blood pressure after clamping, and a more pronounced decrease in heart rate after unclamping, compared to control animals. Some drugs altered this response pattern. Atropine led to a more pronounced tachycardia in the lead-poisoned rats, whereas practolol led to a more pronounced bradycardia in the lead-poisoned rats. Propranolol pretreatment led to a less pronounced decrease in heart rate for lead-poisoned rats, again as compared to the controls. Atropine and beta-adrenergic receptor blocking agents produced similar carotid sinus reflex responses in control and lead-poisoned animals.

Response of the cardiovascular system to catecholamines in rats given small doses of lead

Experiments were done in order to assess the influence of low level lead poisoning in rats upon the responses of the rat cardiovascular system to perturbation by norepinephrine, epinephrine, and isoproterenol administration. Wistar rats were given lead acetate (50.0 mg/kg) via stomach tube once weekly for 5 weeks. Control rats were given sodium acetate similarly; both groups of rats were on a regular animal food diet during the experiment. At the end of the sixth week 2 types of responses were determined. Under urethane anesthesia, the response of mean arterial pressure and heart rate in control and lead-poisoned animals to various catecholamines was measured. Also the response of perfusion pressure in isolated mesenteric vessels, to catecholamines, was measured for vessels having been obtained from control and lead poisoned animals. Our results indicate that lead-treated rats, as compared to controls, have augmented and prolonged pressor responses to epinephrine and norepinephrine; less pronounced depression of arterial pressure in response to epinephrine and isoproterenol; and more pronounced tachycardia in response to isoproterenol. In the lead-treated rats, more pronounced vasoconstriction was observed in the perfusion studies upon administration of exogenous norepinephrine. Small doses of lead intensified alpha receptor response, diminished beta receptor response in blood vessels, and increased positive chronotropic action of isoproterenol.

Calcium-dependent effects of cadmium on energy metabolism and function of perfused rat heart

Postequilibrated isolated rat hearts were perfused for 60 min with a standard supporting electrolyte buffer containing one of the following calcium concentrations: 0.9, 1.8, 3.5, or 5.0 mM, either with or without added cadmium. Doses of cadmium which proved to be minimally (0.03 microM Cd)--and maximally (3.0 microM Cd)--effective at 0.9 mM Ca were studied at all other calcium concentrations. A dose-dependent positive inotropy that persisted throughout the 60-min perfusion period was induced by the graded increases in the perfusate calcium concentration throughout the range from 0.9 to 5.0 mM. Atrioventricular node conductivity was prolonged significantly in hearts perfused with 0.9 mM Ca as compared to hearts perfused with higher calcium concentrations. Increasing the perfusate calcium concentration caused a dose-dependent increase in heart glycerol 3-phosphorylcholine (GPC) content. The other measured phosphatic metabolites of the heart were not altered significantly by varying the perfusate calcium level. In contrast, cadmium (3.0 microM Cd) induced extensive functional and metabolic aberrations which varied in magnitude as an inverse function of the perfusate calcium concentration. Contractile tension, rate of tension development (dT/dt), heart rate, coronary flow rate, and atrioventricular node conductivity were decreased significantly in response to cadmium perfusion. Moreover, these hearts characteristically had significantly elevated low energy phosphate (inosine monophosphate and inorganic phosphate) and decreased high energy phosphate (ATP, PCr) levels relative to their respective calcium controls. Furthermore, various phosphorylated intermediates of glycolysis (glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate), as well as glycerol 3-phosphate, and uridine diphosphoglucose accumulated significantly in hearts perfused with cadmium at certain calcium concentrations below 5.0 mM. The calcium-activated increase in heart GPC was inhibited completely by 3 microM cadmium. At the minimally effective dose of cadmium (0.03 microM), demonstrable changes were apparent only at the lowest perfusate calcium concentration examined (0.9 mM). These findings are consistent with the hypothesis that cadmium interferes with calcium-activated and calcium-mediated physiologic and biochemical processes of the mammalian heart. The primary mechanistic basis for the action of cadmium appears to be linked to a competition with calcium for membrane and possibly intracellular binding and activation sites.

Cardiac physiologic and tissue metabolic changes following chronic low-level cadmium and cadmium plus lead ingestion in the rat

Female Long-Evans hooded rats received Schroeder's rye-based diet and 0 or 1 microgram/ml cadmium, or cadmium plus lead in mineral fortified drinking water from weaning to 18 months. The heavy metal-fed rats were normal with respect to control, including growth rates and final body weights. Rats receiving added cadmium and cadmium plus lead in the diet were characterized by a persistent hypertension which was evident after 2 months. Cardiac conduction system excitability was depressed preferentially in cadmium-(atrioventricular nodal region) and cadmium plus lead-(His-Purkinje system) fed rats. Although heart rates were comparable to control, myocardial contractile activity (peak active tension and dT/dt) was significantly decreased in intact perfused heart preparations from both heavy metal-treated groups. In conjunction with the observed physiologic changes, various tissue-specific metabolic alterations were detected in heart, kidney, and liver. Generally, prolonged heavy-metal ingestion at these levels resulted in impaired energy metabolism (e.g., decreased ATP, PCr; increased Pj, ADP concentrations) and altered essential mineral composition (e.g., calcium, magnesium, zinc, and to a lesser extent, sodium and potassium; copper levels were unaffected) that varied in severity according to the tissue. The addition of lead to the cadmium diet had little additive effect on the cardiovascular system; however, renal and hepatic tissues did exhibit apparent additive effects further suggesting that cadmium and lead actions and interactions may be tissue dependent. These experimental findings and the biologic inferences derived are consonant with the hypothesis that chronic, life-long cadmium exposure approximating environmental levels may have significant adverse effects on mammalian systems, that include effects on cardiovascular tissues.

Cardiovascular actions of cadmium at environmental exposure levels

A low intake of dietary cadmium induces specific dose-dependent functional and biochemical changes in the cardiovascular tissues of rats. Maximum changes occur when the cadmium intake is 10 to 20 micrograms per kilogram of body weight per day. The changes reflect the accumulation of "critical" concentrations of cadmium in the cardiovascular tissues. The biologic activity of cadmium is demonstrated for intakes that approach those of the average American adult exposed to the usual environmental concentrations of the element but not to industrial concentrations. The sensitivity of the cardiovascular system to low doses of cadmium could not be anticipated by extrapolation from data on exposure to high concentrations of cadmium. The data support the hypothesis that ingested or inhaled environmental cadmium may contribute to essential hypertension in humans.