Effects of perfusion pressure on intracellular calcium, energetics, and function in perfused rat hearts.

Effects of perfusion pressure in a range from 50 to 140 cmH2O on intracellular Ca2+ concentration ([Ca2+]i) were evaluated along with cardiac function, energy metabolism, and left ventricular geometry in a concentration of 2 or 4 mM of extracellular Ca2+ ([Ca2+]o) in isovolumic perfused rat hearts. [Ca2+]i was evaluated with a surface fluorometry technique in hearts loaded with indo-1/AM. The systolic and diastolic values and the amplitude (difference between systolic and diastolic values) of indo-1 fluorescence ratio (an index of [Ca2+]i) were linearly related to perfusion pressure. Changes in the fluorescence ratio were harmonious with rapid changes in left ventricular pressure and stabilized within 30-40 s after changes in perfusion pressure. Developed pressure and O2 consumption were closely, linearly correlated with the fluorescence ratio irrespective of [Ca2+]o. Left ventricular end-diastolic wall thickness, measured by 2-dimensional echocardiography, paralleled perfusion pressure and showed a good correlation with the fluorescence ratio. Diastolic myocardial adenosine 3',5'-cyclic monophosphate significantly decreased only at the lowest perfusion pressure. The ln[phosphocreatine]/[Pi] also changed with altered perfusion pressure. In conclusion, perfusion pressure modulates [Ca2+]i, which in turn regulates myocardial contraction and associated O2 utilization.

Comparison of the findings on preoperative dipyridamole perfusion scintigraphy and intraoperative transesophageal echocardiography: implications regarding the identification of myocardium at ischemic risk.

The evidence of myocardium at potential ischemic risk on preoperative dipyridamole perfusion scintigraphy was compared with that of manifest ischemia on intraoperative transesophageal echocardiography in 26 patients at high risk of a coronary event undergoing noncardiac surgery. The clinical outcome was also assessed. Induced intraoperative wall motion abnormalities were more common in patients and myocardial segments with, than in those without, a preoperative reversible perfusion defect (both p less than 0.05). Conversely, a preoperative reversible perfusion defect was more common in patients and segments with, than in those without, a new intraoperative wall motion abnormality (both p less than 0.05). Six patients, five with a reversible scintigraphic defect but only three with a new wall motion abnormality, had a hard perioperative ischemic event. Events occurred more often among patients with, than in those without, a reversible perioperative scintigraphic defect (5 [33%] of 15 vs. 1 [9%] of 11) but this difference did not reach significance (p = 0.14), probably owing to the sample size. Intraoperative wall motion abnormalities were all reversible and did not differentiate between risk groups; these findings were possibly influenced by treatment. These preliminary data support the known relation between reversible scintigraphic defects and perioperative events and identify another manifestation of ischemic risk in the relation between reversible scintigraphic defects and induced intraoperative wall motion abnormalities. The value of intraoperative echocardiography in identifying ischemia and guiding therapy in patients with a reversible scintigraphic abnormality should be further assessed.

Mechanics and energetics of overstretch: the relationship of altered left ventricular volume to the Frank-Starling mechanism and phosphorylation potential.

Isovolumic perfused rat hearts containing an intraventricular balloon were used to assess the effects of incremental balloon volumes on developed pressure, oxygen consumption, coronary flow, phosphorylation potential obtained by P-31 nuclear magnetic resonance, wall thickness obtained by two-dimensional echocardiography, and diastolic wall stress. Three phases in developed pressure were noted: (1) volumes from 0 to 150 microliter resulted in a continuous increase in developed pressure; (2) with volumes from 150 to 250 microliter, developed pressure remained constant whereas developed (systolic) and diastolic wall stress rose sharply; and (3) with volumes from 250 to 400 microliter, developed pressure fell whereas developed (systolic) and diastolic wall stress continued to rise. The ln [(PCr)/(Pi)] was in synchrony with oxygen consumption at 0 and 50 microliter balloon volumes, and then diverged at volumes greater than 100 microliter. Oxygen consumption increased from 0 to 50 microliter, was constant from 50 to 250 microliter balloon volume, and then declined. The ln [(PCr)/(Pi)] fell precipitously at balloon volumes greater than 100 microliter, most likely limited by oxygen consumption. Coronary flow did not change significantly until 250 microliter or more of water was added to the balloon, and then it started to decline. Volumes greater than 100 microliter result in overstretch of myofibers, as observed by the precipitous decline in ln [(PCr)/(Pi)], and the steep increase in diastolic wall stress. With excessive volume loading, the drop in phosphorylation potential, ln [(PCr)/(Pi)], appears to contribute to the decrease in developed pressure.

Improvement in myocardial performance without a decrease in high-energy phosphate metabolites after isoproterenol in Syrian cardiomyopathic hamsters.

To determine the effect of isoproterenol on cardiac energetics and function in an animal preparation of cardiomyopathy, we studied Langendorff perfused hearts from Syrian cardiomyopathic hamsters. High-energy phosphate metabolites (phosphocreatine [PCr], ATP, inorganic phosphate [Pi]) and intracellular pH (pHi) were measured by 31P nuclear magnetic resonance spectroscopy and correlated with left ventricular developed pressure, coronary flow, and O2 consumption before and during a 10(-6)M infusion of isoproterenol. Total intracellular calcium was also determined by atomic absorption spectroscopy with the use of potassium ethylenediamine tetra-acetate cobaltate as a marker for extracellular space. In cardiomyopathic hamsters, isoproterenol infusion increased mean developed pressure by 300% (p less than .005 compared with control; n = 5), O2 consumption eightfold (p less than .0005), and PCr by 40% (p less than .05). PCr/Pi ratio, which is analogous to phosphorylation potential, improved 100% (p = .05). In normal hamsters, isoproterenol infusion resulted in an 83% increase in developed pressure (p less than .001) and a 25% increase in O2 consumption (NS). However, mean PCr and PCr/Pi decreased by 30% and 50%, respectively (p less than .05 for both), during isoproterenol infusion. pHi decreased in normal animals (p less than .01), but tended to improve in diseased animals (NS) during isoproterenol infusion. Freeze-clamp measurements of phosphate metabolites correlated well with the nuclear magnetic resonance data. Intracellular calcium increased from 0.0102 +/- 0.002 to 0.144 +/- 0.030 mumol/ml heart water in normal hamsters during isoproterenol infusion. Cardiomyopathic hamsters had a markedly elevated baseline calcium content of 60.82 +/- 5.85 mumol/ml heart water due to the presence of dystrophic calcification.(ABSTRACT TRUNCATED AT 250 WORDS)

Substrate regulation of the nucleotide pool during regional ischaemia and reperfusion in an isolated rat heart preparation: a phosphorus-31 magnetic resonance spectroscopy analysis.

Isolated rat heart preparations were studied to characterise the alterations in high energy phosphates that occur during reversible regional ischaemia and to determine whether pyruvate, as the sole exogenous energy substrate, would attenuate the ischaemia induced depletion of the nucleotide pool when compared with glucose. Using phosphorus-31 magnetic resonance spectroscopy baseline concentrations of adenosine triphosphate, phosphocreatine, inorganic phosphate, and intracellular pH were compared with values during 30 min of left coronary artery occlusion followed by 30 min of reperfusion. These variables were related to changes in developed pressure, coronary flow, and oxygen consumption. In addition, the total nucleotide pool was evaluated by biochemical analysis of myocardial tissue extracts and coronary effluent. The ischaemic region was characterised by a dye staining technique and cross sectional echocardiographic measurements of regional myocardial wall thinning. In both glucose and pyruvate perfused groups, coronary flow and oxygen consumption decreased to 50-60% of control within 1 min of ischaemia and returned to baseline values with reflow. Developed pressure decreased to 50(9) and 74(8)% (mean(SEM] of control after 30 min of ischaemia in glucose and pyruvate perfused groups respectively. Reperfusion resulted in complete recovery of developed pressure in hearts perfused with pyruvate but not in the glucose group. Glucose perfused hearts had a greater decrease in intracellular pH during ischaemia (7.07(0.01) to 6.36(0.1] than pyruvate perfused hearts (7.06(0.02) to 6.83(0.04]. Reperfusion resulted in a rapid return to baseline intracellular pH in both groups. During ischaemia, adenosine triphosphate values decreased to a greater degree in glucose than in pyruvate perfused hearts (57(4) and 79(5)% of baseline respectively). Thirty minutes of reperfusion did not significantly improve adenosine triphosphate concentrations in either group. Phosphocreatine concentrations decreased to 52(7) and 75(6)% of baseline in glucose and pyruvate perfused groups respectively after the ischaemic period. Reperfusion resulted in normalisation of phosphocreatine values in the pyruvate but not in the glucose perfused group. Biochemical analysis of myocardial tissue extracts confirmed the spectroscopy data and showed that pyruvate inhibits the efflux of adenine nucleotide derivatives. Tissue concentrations of adenosine monophosphate were three times greater and adenosine 50% less after 30 min of ischaemia in the pyruvate perfused group.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemomechanics of altered perfusion pressure in rat hearts.

In an apex-ejecting isolated perfused working rat heart, as well as isovolumic preparations of rat hearts, perfusion pressure was studied independent of afterload. A decrease in perfusion pressure caused an immediate decrease in developed pressure (10s). There was a significant increase in free Pi and the phosphorylation potential after 20-30 min of perfusion at a reduced coronary flow induced by a reduction in perfusion pressure. Developed pressure decreased prior to the phosphorylation potential and inorganic phosphate; however, the phosphorylation set a limit to maximum work performance. At a perfusion pressure of 140 cm H2O and an afterload of 140 cm H2O, work imposed on the heart was maximum; there was no further increase in work.

Beneficial effects of verapamil during metabolic acidosis in isolated perfused rat hearts.

Metabolic acidosis was produced in two groups of isolated, glucose-perfused beating rat hearts. The first group (control) was untreated whereas the second group was pretreated for 48 h by the addition of verapamil (1.2 g/L) to the drinking water. Untreated hearts all developed asystole during a 30 min perfusion with an acidotic substrate (pH = 6.8) or during subsequent reequilibration with physiologic substrate (pH = 7.4). Prior to asystole, all untreated hearts showed evidence of severe mechanical and biochemical deterioration evaluated by 31 P NMR spectroscopy. In contrast, hearts of treated rats showed less mechanical and metabolic deterioration, and all recovered during reequilibration. The mechanism of protection of verapamil against the effects of metabolic acidosis is unclear but appears to be related to preserved mitochondrial function by the drug and not to a reduced demand for energy.

Hydrodynamics in the heart modulates work.

The hydrostatic pressure (perfusion pressure) of the isovolumic isolated perfused rat heart regulated the hydrodynamics (water movement) of the myocardium. An abrupt (10 s) decrease in hydrostatic pressure caused an immediate decrease in oxygen consumption, left ventricular developed pressure, and wall thickness. Wall thickness was determined by two-dimensional echocardiography. When the perfusion pressure was again returned to the control values (140 cm H2O) oxygen consumption, developed pressure, and wall thickness returned to control values within 10-30 s. An abrupt decrease in perfusion pressure also caused an immediate decrease in both extracellular and intracellular water in the heart as determined by H-1 NMR (nuclear magnetic resonance) with the shift reagent Dy(TTHA)3- (Dysprosium triethylene tetramine-hexaacetate). Similar findings were obtained using K(CoEDTA) (potassium cobalt ethylenediaminetetraacetate) utilized as an extracellular marker. With a decrease in intracellular water in the heart, there was a concurrent decrease in intracellular calcium.

Factors influencing myocardial response to metabolic acidosis in isolated rat hearts.

We assessed the effects of metabolic acidosis in Langendorff rat hearts to identify factors influencing myocardial response to metabolic acidosis. Intracellular pH (pHi), beta-ATP, phosphocreatine, and inorganic phosphate (Pi) content were measured by 31P nuclear magnetic resonance spectroscopy along with simultaneous measurements of coronary flow and developed pressure during 30 min of perfusion at pH = 6.8, followed by 15 min of reequilibration at pH = 7.4. Under high work-load conditions, pHi, high-energy phosphates, coronary flow, and developed pressure were severely reduced during metabolic acidosis. Each of these hearts exhibited a progressive decline in developed pressure and stopped beating during reequilibration. Lowering work load prevented severe biochemical or mechanical deterioration, allowing complete recovery during reequilibration. In the presence of high work load, factors found to improve myocardial tolerance to metabolic acidosis included maintaining base-line or higher levels of coronary flow with vasodilators or substitution of pyruvate for glucose as the energy-producing substrate. Raising perfusate osmolality did not prevent severe decreases in coronary flow and developed pressure during acidosis, but did allow a dramatic recovery during reequilibration. Recovery of biochemical and mechanical performance after 30 min of metabolic acidosis was directly related to 1) ln[ATP]/[ADP]f[Pi] greater than or equal to 4.1, where [ADP]f is the concentration of free ADP; 2) pHi greater than 6.40; and 3) ATP level greater than or equal to 75% of control.

Effects of altered coronary perfusion pressure on function and metabolism of normal and cardiomyopathic hamster hearts.

The effects of a sudden decrease in coronary perfusion pressure from 140 to 0 cmH2O for a 10-second interval were analyzed in normal and cardiomyopathic hamster hearts to determine whether cardiomyopathy would affect the relationship between altered coronary perfusion pressure and left ventricular geometry, wall thickness, myocardial hydrodynamics, and hemodynamics. In normal hamsters, an acute reduction in coronary perfusion pressure resulted in a decrease in left ventricular short axis epicardial cross-sectional area, base to apex length, diastolic wall thickness, myocardial water content and developed pressure. In cardiomyopathic hamsters all results induced by lowering the hydrostatic pressure of the perfusing medium were the same except that diastolic wall thickness failed to decline, indicating a decrease in intramyocardial elasticity in dilated cardiomyopathy. In parallel studies, hearts were freeze clamped at end-diastole and high energy phosphates and energy metabolites analyzed. In both normal and cardiomyopathic hamsters no significant changes were observed in ATP, PCr, or Pi levels at 10 s following the decrease in perfusion pressure. However, during the abrupt decrease in coronary perfusion pressure adenosine increased and cAMP decreased in both groups of animals. The erectile effect of altered coronary perfusion pressure is partially attenuated in the cardiomyopathic hamster in which no change in diastolic wall thickness occurs during an abrupt change in the hydrodynamics of the heart.