Constant Coronary Pressure Research Articles

Preconditioning with hyperbaric oxygen and calcium and potassium channel modulators in the rat heart

The aim of this study was to establish the effect of combined therapy with hyperbaric oxygen (HBO2) therapy and verapamil, amlodipine or nicorandil on functional recovery and oxidative stress markers after ischemia in the isolated rat heart. The study included 48 rats (Wistar albino, male gender, eight weeks old, body weight 200±50g). All animals were exposed to HBO2 treatment over 14 days. Isolated heart rats were perfused by the Langendorff retrograde method at a constant coronary pressure of 70 cm H2O. After stabilization period the hearts were divided into the following groups: HBO2 group (animals exposed to only HBO2 preconditioning); HBO2 + verapamil; HBO2 + amlodipine; andHBO2 + nicorandil (animals pretreated with HBO2 and appropriate pharmacological agent). Afterward, the hearts in all groups were subjected to 20-minute global ischemia and 30-minute reperfusion. Parameters of heart function were registered, including maximum and minimum rate of pressure development, systolic and diastolic left ventricular pressure, heart rate and coronary flow. Levels of pro-oxidants such as index of lipid peroxidation, measured as thiobarbituric acid-reactive substances, nitrites, levels of superoxide anion radicals and hydrogen peroxide were determined in coronary venous effluent. Changes in cardiac tissue were evaluated by hematoxylin and eosin staining. Obtained results clearly indicate that blockage of calcium channel or the activation of adenosine triphosphate-sensitive potassium (KATP) in combination with HBO2 prevented ischemia/reperfusion-induced cardiac deleterious effects, thus contributing to improvement of functional recovery of the heart. However, future studies are certainly necessary for better understanding the mechanisms through which combination of these two maneuvers of preconditioning triggers cardioprotection.

Positive inotropic effects of carbon monoxide‐releasing molecules (CO‐RMs) in the isolated perfused rat heart

Carbon monoxide (CO) generated by the enzyme haeme oxygenase-1 (HO-1) during the breakdown of haeme is known to mediate a number of biological effects. Here, we investigated whether CO liberated from two water soluble carbon monoxide-releasing molecules (CO-RMs) exerts inotropic effects on the myocardium. Rat isolated hearts perfused either at constant flow or constant pressure were used to test the effect of CO-RMs. CORM-3, a fast CO releaser, produced a direct positive inotropic effect when cumulative doses (3, 10 and 30 microg min(-1)) or a single dose (5 microM) were infused at either constant coronary pressure (CCP) or constant coronary flow (CCF). The inotropic effect mediated by CORM-3 was abolished by blockade of soluble guanylate cyclase or Na(+)/H(+) exchanger, but not by inhibitors of L-type Ca(2+) channels and protein kinase C. CORM-3 also caused a slight reduction in heart rate but did not alter coronary flow. In contrast, the slow CO releaser CORM-A1 produced significant coronary vasodilatation when given at the highest concentration (30 mug min(-1)) but exerted no effect on myocardial contractility or heart rate. A rapid CO release from CORM-3 exerts a direct positive inotropic effect on rat isolated perfused hearts, whereas CO slowly released by CORM-A1 had no effect on myocardial contractility but caused significant coronary vasodilatation. Both cGMP and Na(+)/H(+) exchange appear to be involved in this effect but further work is needed to determine the relative contribution of each pathway in CO-mediated inotropic effect.

Activation of p38 Mitogen-Activated Protein Kinase Contributes to the Early Cardiodepressant Action of Tumor Necrosis Factor

The purpose of this study was to determine whether p38 mitogen-activated protein kinase (p38-MAPK) contributes to tumor necrosis factor-alpha (TNFalpha)-induced contractile depression. Tumor necrosis factor has both beneficial and detrimental consequences that may result from the activation of different downstream pathways. Tumor necrosis factor activates p38-MAPK, a stress-responsive kinase implicated in contractile depression and cardiac injury. In isolated hearts from mice lacking the p38-MAPK activator, MAPK kinase 3 (MKK3), perfused at constant coronary pressure or flow, we measured the left ventricular developed pressure (LVDP) and the relationship between end-diastolic volume and LVDP in the presence and absence of 10 ng/ml TNFalpha. Within 15 min at constant pressure, TNFalpha significantly reduced LVDP and coronary flow in outbred and mkk3(+/+) mice. This early negative inotropic effect was associated with a marked phosphorylation of both p38-MAPK and its indirect substrate, HSP27. In hearts lacking MKK3, TNFalpha failed to activate p38-MAPK or to cause significant contractile dysfunction. The actions of TNFalpha were similarly attenuated in MAPK-activated protein kinase 2 (MK2)-deficient hearts, which have a marked reduction in myocardial p38-MAPK protein content, and by the p38-MAPK catalytic site inhibitor SB203580 (1 micromol/l). Under conditions of constant coronary flow, the p38-MAPK activation and contractile depression induced by TNFalpha, though attenuated, remained sensitive to the absence of MKK3 or the presence of SB203580. The role of p38-MAPK in TNFalpha-induced contractile depression was confirmed in isolated murine cardiac myocytes exposed to SB203580 or lacking MKK3. Tumor necrosis factor activates p38-MAPK in the intact heart and in isolated cardiac myocytes through MKK3. This activation likely contributes to the early cardiodepressant action of TNFalpha.

The hemodynamic basis for the cardiac effects of parathyroid hormone (PTH) and PTH-related protein.

PTH and PTH-related protein (PTHrP) have been regarded to have positive inotropic effects on the heart as well as positive chronotropic and vasodilator effects. However, inotropy due to a direct effect of these peptides has not heretofore been distinguished from an indirect inotropic effect as a result of altered heart rate or coronary flow. The aim of this study was to determine whether PTH and PTHrP have direct inotropic effects in isolated perfused rat hearts. Three groups of hearts were studied; in all groups, hearts contracted isovolumically and were perfused with a constant coronary pressure. In the control group, heart rate, coronary flow, peak pressure (LVPmax), peak rate of rise of LV pressure (dP/dtmax), and peak intracellular calcium (measured by aequorin) all increased with PTH and PTHrP in a dose-dependent manner. When heart rate was fixed by pacing in a second group of rats, PTH and PTHrP increased coronary flow, LVPmax, and dP/dtmax significantly, indicating that inotropic actions were not mediated solely by chronotropic effects. However, when heart rate was fixed by pacing and, additionally, coronary flow was held constant (by maximal prevasodilation with nitroprusside) in a third group of rats, there was no significant effect of either PTH or PTHrP on LVPmax, dP/dtmax, or peak intracellular calcium. To demonstrate the responsiveness of this latter preparation to inotropic stimulation, the beta-adrenergic agonist, isoproterenol, increased LVPmax, dP/dtmax, and peak calcium even when heart rate was fixed and vasodilation was maximal. Thus, PTH and PTHrP are inotropic agents by virtue of their influence on coronary flow and heart rate, but not by any direct effect on contractile elements in the heart.

Coronary Vasoconstrictor Activity of Purified and Modified Human Hemoglobin

Unpurified stroma-free hemoglobin (SFH) from water-lysed human red blood cells, hemoglobin Ao (HbAo), and hemoglobin cross-linked between alpha chains with 3,5-bis-dibromosalicyl-fumarate (HbXLDBBF) were infused into isolated perfused rabbit hearts. Vasoactivity and myocardial performance were determined using an isovolumic Langendorff preparation. With constant coronary flow, infusion of SFH (55 mg/dl) resulted in a 56% increase in aortic pressure as opposed to 29% and 11% increases with HbAo and HbXLDBBF, respectively. Rates of aortic pressure increase were over 6 times greater with SFH than with either HbAo or HbXLDBBF and exhibited concentration dependence only with SFH. Myocardial function remained normal. With constant coronary pressure, coronary flow decreased by 36% with SFH accompanied by a 23% decline in left ventricular developed pressure indicative of ischemia. With HbAo or HbXLDBBF, coronary flow decreased by only 1/3 that with SFH, while developed pressure declined by 4% and 2% with HbAo and HbXLDBBF, respectively. These data suggest that purification of HbAo to a single component can eliminate the dominant of at least two distinct vasoactive factors normally found in SFH. Furthermore, the physiological significance of the vascular response to HbAo is minimal. Preparations of HbXLDBBF accomplish this same result.

Lack of direct coronary vascular effects of Escherichia coli endotoxin in dogs.

This study explored the hypothesis that coronary vascular injury and dysfunction result from intracoronary administration of Escherichia coli endotoxin (0.025 to 0.025 to 0.4 mg/kg) in dogs. Peak hyperemic coronary flow following a 15-sec period of stopped flow and the maximum flow in response to adenosine were used to estimate coronary vascular reserve. The wet-to-dry ratio of myocardial tissue was used to estimate extravascular water content as an indicator of vascular leak due to endothelial injury. Intracoronary saline was used as a control. Peak reactive hyperemia and maximum flow at constant coronary pressure were not different in the animals receiving intracoronary endotoxin (n = 6) and the animals receiving saline (n = 5) during 4 hr following treatment. In addition, wet-to-dry ratios were similar in these two groups. These data fail to support the hypothesis that endotoxin, per se, produces coronary vascular injury of sufficient magnitude to produce myocardial dysfunction.

Screening of inotropic drugs on isolated rat and guinea pig hearts

A technique is described for screening the effects of inotropic drugs on isolated rat or guinea pig hearts perfused at constant coronary pressure and at a frequency of 6 Hz. Their performances, including function curves, were recorded using an intraventricular balloon. Both preparations became either sensitive from initially having been insensitive, or more sensitive from having been slightly sensitive at the outset, to inotropic interventions, provided the external calcium concentration was reduced to 0.25 mM for the rat and 0.50 mM for the guinea pig. The inotropic effect of drugs such as isoproterenol, forskolin, and theophylline was only slightly altered by lowering [Ca] o. Amrinone, sulmazole, and beta agonists such as xamoterol, cicloprolol, pindolol, or RU 42173 almost never caused an inotropic effect at the serum calcium concentration of 2.50 mM, whereas they did provoke a positive response at low [Ca] o. Other compounds such as ouabain, salbutamol, and pimobendan were toxic at high [Ca] o, although at reduced [Ca] o their positive effect on contractility was quite evident.