Lead reduces tension development and the myosin ATPase activity of the rat right ventricular myocardium

Lead (Pb2+) poisoning causes hypertension, but little is known regarding its acute effects on cardiac contractility. To evaluate these effects, force was measured in right ventricular strips that were contracting isometrically in 45 male Wistar rats (250-300 g) before and after the addition of increasing concentrations of lead acetate (3, 7, 10, 30, 70, 100, and 300 µM) to the bath. Changes in rate of stimulation (0.1-1.5 Hz), relative potentiation after pauses of 15, 30, and 60 s, effect of Ca2+ concentration (0.62, 1.25, and 2.5 mM), and the effect of isoproterenol (20 ng/mL) were determined before and after the addition of 100 µM Pb2+. Effects on contractile proteins were evaluated after caffeine treatment using tetanic stimulation (10 Hz) and measuring the activity of the myosin ATPase. Pb2+ produced concentration-dependent force reduction, significant at concentrations greater than 30 µM. The force developed in response to increasing rates of stimulation became smaller at 0.5 and 0.8 Hz. Relative potentiation increased after 100 µM Pb2+ treatment. Extracellular Ca2+ increment and isoproterenol administration increased force development but after 100 µM Pb2+ treatment the force was significantly reduced suggesting an effect of the metal on the sarcolemmal Ca2+ influx. Concentration of 100 µM Pb2+ also reduced the peak and plateau force of tetanic contractions and reduced the activity of the myosin ATPase. Results showed that acute Pb2+ administration, although not affecting the sarcoplasmic reticulum activity, produces a concentration-dependent negative inotropic effect and reduces myosin ATPase activity. Results suggest that acute lead administration reduced myocardial contractility by reducing sarcolemmal calcium influx and the myosin ATPase activity. These results also suggest that lead exposure is hazardous and has toxicological consequences affecting cardiac muscle.

Functional expression of kinin B1 and B2 receptors in mouse abdominal aorta

Previous studies have shown that the vascular reactivity of the mouse aorta differs substantially from that of the rat aorta in response to several agonists such as angiotensin II, endothelin-1 and isoproterenol. However, no information is available about the agonists bradykinin (BK) and DesArg9BK (DBK). Our aim was to determine the potential expression of kinin B1 and B2 receptors in the abdominal mouse aorta isolated from C57BL/6 mice. Contraction and relaxation responses to BK and DBK were investigated using isometric recordings. The kinins were unable to induce relaxation but concentration-contraction response curves were obtained by applying increasing concentrations of the agonists BK and DBK. These effects were blocked by the antagonists Icatibant and R-715, respectively. The potency (pD2) calculated from the curves was 7.0 ± 0.1 for BK and 7.3 ± 0.2 for DBK. The efficacy was 51 ± 2 percent for BK and 30 ± 1 percent for DBK when compared to 1 æM norepinephrine. The concentration-dependent responses of BK and DBK were markedly inhibited by the arachidonic acid inhibitor indomethacin (1 æM), suggesting a mediation by the cyclooxygenase pathway. These contractile responses were not potentiated in the presence of the NOS inhibitor L-NAME (1 mM) or endothelium-denuded aorta, indicating that the NO pathway is not involved. We conclude that the mouse aorta constitutively contains B1 and B2 subtypes of kinin receptors and that stimulation with BK and DBK induces contractile effect mediated by endothelium-independent vasoconstrictor prostanoids.

Influências de dietas ricas em ácidos graxos saturados e insaturados sobre o miocárdio de ratos / Influences of rich in saturated and unsaturated fatty acids diets in rat myocardium

OBJETIVOS: O estudo avaliou a influência de dietas ricas em ácidos graxos saturados (AGS) e ácidos graxos insaturados (AGI) sobre a função mecânica, a morfologia e o estresse oxidativo do miocárdio de ratos. MÉTODOS: Ratos Wistar com 60 dias de idade foram alimentados com dieta padrão (n = 8) ou dietas ricas em AGS (n = 8) ou AGI (n = 8) durante 60 dias. A função mecânica foi avaliada em músculo papilar isolado do ventrículo esquerdo (VE) por meio de contrações isométrica e isotônica, em condição basal (1,25 mM de cálcio), após elevação da concentração extracelular de cálcio para 5,2 mM e estimulação beta-adrenérgica com isoproterenol 1,0 µM. Fragmentos do VE foram usados para estudo de estresse oxidativo e microscopias óptica e eletrônica. RESULTADOS: As dietas suplementadas com AGS e AGI não alteraram a função mecânica do músculo cardíaco. Entretanto, ambas provocaram estresse oxidativo, com aumento do hidroperóxido de lipídio e redução da concentração de superóxido dismutase. A dieta AGI diminuiu a expressão da catalase e a AGS reduziu a quantidade de glutationa peroxidase miocárdica. Ambas as dietas promoveram discretas alterações morfológicas visualizadas ultra-estruturalmente, como depósitos lipídicos e lesões das membranas celulares. CONCLUSÃO: Os resultados sugerem que dietas enriquecidas com AGS e AGI não acarretam alteração da função mecânica do músculo cardíaco isolado, mas causam discretas lesões estruturais e estresse oxidativo no miocárdio.

OBJECTIVES: To study the influence of saturated (SFA) and unsaturated fatty acid (UFA) rich diets on mechanical function, morphology and oxidative stress in rat myocardium. METHODS: Male, 60-day-old Wistar rats were fed a control (n=8), a SFA (n=8), or a UFA-rich diet (n=8) for sixty days. Mechanical function was studied in isolated left ventricle papillary muscle under isometric and isotonic contractions, in basal conditions (1.25mM calcium chloride) and after 5.2mM calcium chloride and beta-adrenergic stimuli with 1.0µM isoproterenol. Left ventricle fragments were used to study oxidative stress and morphology under light and electron microscopy. RESULTS: SFA and UFA-rich diets did not change myocardium mechanical function. Both diets caused oxidative stress, with high lipid hydroperoxide and low superoxide-dismutase concentrations. UFA rich diet decreased catalase expression and SFA rich diet decreased the amount of myocardial glutathione-peroxidase. Both diets promoted light ultrastructural injuries such as lipid deposits and cell membrane injuries. CONCLUSION: Results suggest that SFA and UFA rich diets do not alter isolated muscle mechanical function, but promote light myocardial morphological injuries and oxidative stress.

Eucalyptol, an essential oil, reduces contractile activity in rat cardiac muscle

Eucalyptol is an essential oil that relaxes bronchial and vascular smooth muscle although its direct actions on isolated myocardium have not been reported. We investigated a putative negative inotropic effect of the oil on left ventricular papillary muscles from male Wistar rats weighing 250 to 300 g, as well as its effects on isometric force, rate of force development, time parameters, post-rest potentiation, positive inotropic interventions produced by Ca2+ and isoproterenol, and on tetanic tension. The effects of 0.3 mM eucalyptol on myosin ATPase activity were also investigated. Eucalyptol (0.003 to 0.3 mM) reduced isometric tension, the rate of force development and time parameters. The oil reduced the force developed by steady-state contractions (50 percent at 0.3 mM) but did not alter sarcoplasmic reticulum function or post-rest contractions and produced a progressive increase in relative potentiation. Increased extracellular Ca2+ concentration (0.62 to 5 mM) and isoproterenol (20 nM) administration counteracted the negative inotropic effects of the oil. The activity of the contractile machinery evaluated by tetanic force development was reduced by 30 to 50 percent but myosin ATPase activity was not affected by eucalyptol (0.3 mM), supporting the idea of a reduction of sarcolemmal Ca2+ influx. The present results suggest that eucalyptol depresses force development, probably acting as a calcium channel blocker.

Erythropoietin does not affect nitric oxide system in rats with chronic renal failure

We investigated to see whether an altered role of nitric oxide (NO) system is involved in erythropoietin (EPO)-induced hypertension in chronic renal failure (CRF). Male Sprague-Dawley rats were five-sixths nephrectomized to induce CRF. Six weeks after the operation, EPO or vehicle was injected for another 6 weeks. Plasma and urine nitrite/nitrate (NOx) levels were determined. Expression of NO synthase (NOS) proteins in the aortae and kidneys were also determined. In addition, the isometric tension of isolated aorta in response to acetylcholine and nitroprusside was examined. Blood pressure progressively rose in CRF groups, the degree of which was augmented by EPO treatment. Plasma NOx levels did not differ among the groups, while urine NOx levels were lower in CRF groups. Endothelial NOS expression was lower in the kidney and aorta in CRF rats, which was not further affected by EPO-treatment. The inducible NOS expression in the kidney and aorta was not different among the groups. Acetylcholine and sodium nitroprusside caused dose-dependent relaxations of aortic rings, the degree of which was not altered by EPO-treatment. Taken together, EPO-treatment aggravates hypertension in CRF, but altered role of NO system may not be involved.

Effect of aminophylline on muscle fatigue.

The effects of two different concentrations of aminophylline, 50 microM/L and 500 microM/L on muscle fatiguability were tested using frog gastrocnemius-sciatic preparations. Two stimulation protocols, one high energy demand, and the other low energy demand were used to induce muscle fatigue. The indices of fatigue employed were (a) the decrease in peak tetanic contraction, (b) the increase in half-contraction time and (c) the increase in the contraction period in response to a high-energy-demand stimulation protocol of fatigue-induction. At the same time, it prolongs the increase in relaxation50-80 time in response to the same protocol.

Endothelin-1 and carbachol: differences in contractile effects and myosin phosphorylation in lamb tracheal smooth muscle.

Endothelin-1 is a new potent vasoconstrictor peptide produced by the endothelial cells. The contractile effects of endothelin-1 (ET-1) were compared with those of cabachol in lamb tracheal smooth muscle. Equimolar concentrations (10(-6)M) of endothelin 1 and carbachol elicit rapidly rising isometric tension which is maintained indefinitely in a steady state when fibres are stimulated with carbachol. Fibre strips exposed to ET-1 cannot maintain peak isometric force beyond 15-20 min and instead these exhibit a decline in tension towards near relaxed state. In addition to an early transient relaxation, ET-1 stimulation results in a 20,000 Da myosin light chain phosphorylation pattern different from that of carbachol stimulation.

Caffeine effects on heart muscle energetics: species differences

The effects of caffeine (1mM) on energy expenditure and mechanical parameters in rat and toad perfused heart ventricles were examined at various stimulation frequencies. While in rat muscles caffeine significantly depressed developed tension and maximal rates of contraction and relaxation at all frequencies tested, in toad ventricle a slight positive inotropic effect was observed. Even though caffeine did not alter total contraction time in both preparations, in the rat ventricle the last part of relaxation was prolonged. In rat ventricle in the presence of caffeine, the ratios between active heat production per beat and either developed tension or tension time integral increased at all frequencies tested (+303 +/- 47 microJ.mN-1 x g-1 and +1.21 +/- 0.13 mJ.mN-1 x s-1 x g-1 respectively) indicating a decrease in contractile economy. In toad ventricle no changes on these ratios were observed. The fact that only in rat ventricle caffeine decreased muscle economy suggests that caffeine affects a system that is active in rat ventricle but it is not operative in toad ventricle. This gives support to the hypothesis that if in rat ventricle SR-Ca pump (1 ATP hydrolyzed/2 Ca transported) is inhibited by caffeine cytosolic Ca would have to be removed by alternative mechanisms such as Na-Ca exchanger or sarcolemmal Ca pump both with a higher rate of ATP hydrolysis (1 ATP hydrolyzed/Ca transported) with the consequent decrease in muscle economy. Resting heat production was increased by caffeine in both preparations and the magnitude of the increment (+3.0 +/- 0.6 mW.g-1 and +0.75 +/- 0.21 mW.g-1 for rat and toad ventricle respectively) also correlates with the different degree of SR activity in both species

Comparaçäo do cronotropismo negativo da nitrendipina, nifedipina e verapamil no átrio direito isolado de ratos normotensos e com hipertensäo renovascular / Nitrendipine, nifedipine and verapamil: a comparison of the negative chronotropic effects using the isolated right atria from no rmote n sive and re nova s cular hypertensive rats.

Estudar o efeito cronotrópico negativo de nitrendipina, nifedipina e verapamil no átrio direito isolado de ratos normotensos e com hipertensäo renovascular. A hipertensäo foi produzida pela implantaçäo de anel de prata na artéria renal esquerda e nefrectomia direita. Os animais foram estudados 15 dias após a cirurgia, quando a PA média (medida diretamente, no animal acordado, através de cânula intravascular) do grupo hipertenso (154 ñ 4 mm Hg) era maior que a do grupo controle (109 ñ 2 mmHg). A freqüência atrial "in vitro" foi determinada a partir dos registros das contraçöes isométricas. Atrios diferentes foram usados para se obter as curvas dose-resposta (0,01 micronM - 100 micronM) de cada droga. A freqüência atrial "in vitro" foi idêntica nos normotensos (243 ñ 7 bpm) e hipertensos (245 ñ 5 bpm). A sensibilidade às drogas testadas também foi a mesma, em ambos os grupos. A concentraçäo de droga necessária para reduzir 50% da freqüência sinusal foi cerca de 2 micronM para o verapamil, 4 micronM para a nitrendipina e 20 micronM para a nifedipina. A hipertensäo näo altera a sensibilidade do marca-passo sinusal aos bloqueadores de canal de cálcio. O efeito cronotrópico negativo da nitrendipina é intermediário entre o do verapamil e o da nifedipina

Effects of ketamine on contractile responses in vascular smooth muscle

This study was designed to determine the effects of ketamine on contractions induced by norepinephrine (NE), K+ or histamine (Hist) and on agonist-induced calcium mobilization, in rabbit thoracic aorta with or without endothelium. Contractile responses to NE, K+ or Hist were markedly attenuated by prior exposure to ketamine. Subsequent addition of ketamine to the rabbit aorta undergoing an isometric contraction induced by NE, K+ or Hist also decreased the contractile responses in a calcium ion concentration-dependent manner. Preincubation with ketamine produced a concentration-dependent inhibition of contractile responses elicited by the addition of calcium ion (1.6 mM) to a Ca(++)-free depolarizing solution. However, the phasic contraction produced by NE with 2mM lanthanum pretreatment, which is release of intracellular calcium, was also inhibited by ketamine. Moreover, the tonic contraction produced by NE after depletion of the agonist-releasable pool of intracellular calcium, which is thought to be due to calcium influx, was depressed by ketamine. These data suggest that ketamine relaxes NE-contracted rings of rabbit thoracic aorta by decreasing calcium entry and by producing an extracellular calcium-independent relaxant effect.