Decrease In Developed Pressure Research Articles

Functional and metabolic remodelling in GLUT4-deficient hearts confers hyper-responsiveness to substrate intervention

Impaired glucose uptake is associated with both cardiac hypertrophy and contractile dysfunction, but whether there are common underlying mechanisms linking these conditions is yet to be determined. Using a ‘gene dose’ Cre-Lox GLUT4-deficient murine model, we examined the effect of suppressed glucose availability on global myocardial gene expression and glycolysis substrate bypass on the function of isolated perfused hearts. Performance of hearts from 22- to 60-week-old male GLUT4 knockout (KO, >95% reduction in GLUT4), GLUT4 knockdown (KD, 85% reduction in cardiac GLUT4) and C57Bl/6 wild-type (WT) controls was measured ex vivo in Langendorff mode perfusion. DNA microarray was used to profile mRNA expression differences between GLUT4-KO and GLUT4-KD hearts. At 22 weeks, GLUT4-KO hearts exhibited cardiac hypertrophy and impaired contractile function ex vivo, characterized by a 40% decrease in developed pressure. At 60 weeks, dysfunction was accentuated in GLUT4-KO hearts and evident in GLUT4-KD hearts. Exogenous pyruvate (5 mM) restored systolic pressure to a level equivalent to WT (GLUT4-KO, 176.8±13.2 mmHg vs. WT, 146.4±9.56 mmHg) in 22-week-old GLUT4-KO hearts but not in 60-week-old GLUT4-KO hearts. In GLUT4-KO, DNA microarray analysis detected downregulation of a number of genes centrally involved in mitochondrial oxidation and upregulation of other genes indicative of a shift to cytosolic β-oxidation of long chain fatty acids. A direct link between cardiomyocyte GLUT4 deficiency, hypertrophy and contractile dysfunction is demonstrated. These data provide mechanistic insight into the myocardial metabolic adaptations associated with short and long-term insulin resistance and indicate a window of opportunity for substrate intervention and functional ‘rescue’.

Gap junction uncoupling protects the heart against ischemia

Background: Many stimuli can successfully protect the heart against ischemia. We investigated whether gap junction uncoupling before ischemia was myoprotective. We also studied the function of the adenosine triphosphate-dependent potassium channel, which has been implicated in the mechanism of pharmacologic preconditioning, with respect to gap junction physiology. Methods: Twenty-eight rabbit hearts were placed on a Langendorff perfusion apparatus. Five were given a 5-minute infusion of 1 mmol/L heptanol (a gap junction uncoupler), 5 were given 10 μmol/L 2,3-butanedione monoxime (an electromechanical uncoupler), and 6 were given no drug. The left anterior descending coronary artery was then occluded for 1 hour and reperfused for 2 hours. Six hearts received 10 μmol/L glybenclamide before heptanol to evaluate the role of the adenosine triphosphate-dependent potassium channel. Six hearts underwent ischemic preconditioning with 2 cycles of 5 minutes of global ischemia and reperfusion. Action-potential duration of the ischemic zone, left ventricular developed pressure, and coronary flow were measured continuously. Infarct size was determined at the end of reperfusion. Results: Heptanol significantly reduced infarct size (from 46% ± 2% to 22% ± 5%, P <.01), an effect that was not prevented by glybenclamide. Butanedione monoxime decreased developed pressure but did not significantly reduce infarct size (46% ± 5% vs 46% ± 2%, P = not significant). There were no differences among groups with regard to developed pressure or action-potential duration. Conclusion: Directly blocking gap junctions preconditions the heart. This protection is not a direct result of a decrease in developed pressure before a prolonged ischemic period nor is it achieved through a mechanism involving the adenosine triphosphate-dependent potassium channel.J Thorac Cardiovasc Surg 2002;124:371-6

FGF-2-induced Negative Inotropism and Cardioprotection are Inhibited by Chelerythrine: Involvement of Sarcolemmal Calcium-independent Protein Kinase C

Fibroblast growth factor-2 (FGF-2), administered to the isolated rat heart by perfusion and under constant pressure, is protective against ischemia–reperfusion (I–R). Here we have investigated whether FGF-2 cardioprotection: (a) is dependent on flow modulation; (b) is linked to effects on contractility; (c) is mediated by protein kinase C (PKC); and (d) is linked to PKC and/or mitogen activated protein kinase (MAPK) associated with the sarcolemma. The isolated rat heart was used as a model. Under conditions of constant flow FGF-2 induced significant improvement in recovery of contractile function during I–R. Under constant perfusion pressure, FGF-2 induced a negative inotropic effect (15% decrease in developed pressure). Chelerythrine, a specific PKC inhibitor, prevented both the FGF-2-induced negative inotropic effect before ischemia, and cardioprotection during I–R. FGF-2 induced a chelerythrine-preventable, five-fold increase in sarcolemmal calcium-independent PKC activity. It also increased the association of PKC subtypes -ηand -δwith sarcolemmal membranes, detected by Western blotting, as well as, for PKCδ, by immunolocalization. FGF-2 increased the association of PKCηwith the membrane fraction of adult cardiomyocyte in culture, confirming that it can affect PKC signaling in cardiomyocytes directly and in a manner similar to its effectsin situ. Finally, FGF-2 induced increased active MAPK at sarcolemmal as well as cytosolic sites. Active sarcolemmal MAPK remained elevated when the FGF-2-induced protection was prevented by chelerythrine. In conclusion, we have provided evidence that cardioprotection by FGF-2 is independent of flow modulation. PKC activation mediates both the FGF-2-induced negative inotropic effect before ischemia and the cardioprotective effect assessed during reperfusion, suggesting a cause and effect relationship. Furthermore, FGF-2 cardioprotection is linked to targeting of sarcolemmal sites by calcium-independent PKC.

Left-Ventricular Structural and Functional Remodeling in the Mouse after Myocardial Infarction: Assessment with the Isovolumetrically-contracting Langendorff Heart

The goal of this study was to determine whether the isovolumically-contracting Langendorff heart could be used to assess changes in left-ventricular volume and contractile reserve in the mouse heart after myocardial infarction. Myocardial infarction (40±3% of the left ventricle by weight) was induced in CD-1 mice by ligation of the left-anterior descending coronary artery. Two weeks after infarction there was compensatory hypertrophy of the non-infarcted ventricle as indicated by increases in heart-to-body weight ratio (5.5±0.2v4.9±0.2 mg/g;P<0.05;n=12) and the expression of atrial natriuretic peptide mRNA (4.4±1.4-fold;P<0.001;n=4). Left-ventricular pressure–volume relationships were assessedin vitroin isovolumically-contracting hearts perfused with red cell-supplemented buffer (hematrocrit=40%). Myocardial infarction caused left-ventricular dilation with a rightward-shift of the diastolic pressure–volume relationship. This was associated with reduced left-ventricular contractile function, as evidenced by a decrease in developed pressure over a range of left-ventricular volumes. Thus, it is feasible to use the isovolumically-contracting Langendorff preparation to assess the structural and functional consequences of left-ventricular remodeling in the mouse after a myocardial infarction.

Reperfusion induced arrhythmias following ischaemia in intact rat heart: role of intracellular calcium

The aim was to test the hypothesis that reperfusion induced arrhythmias are associated with major alterations in intracellular calcium ([Ca2+]i) regulation. Intracellular calcium, epicardial electrical potentials, and isovolumetric left ventricular pressure were simultaneously recorded in isolated perfused intact rat hearts during ischaemia (10 min) and reperfusion. [Ca2+]i was measured using the bioluminescent calcium indicator aequorin. Neither ventricular tachycardia nor ventricular fibrillation occurred during ischaemia. However, during the first minute of reperfusion ventricular tachycardia or fibrillation were frequently observed. Cellular calcium was altered by varying the perfusate calcium ([Ca2+]o; 0.5, 1.0, and 3.0 mmol.litre-1). 0% (0/6), 50% (5/10), 91% (10/11), respectively, of hearts showed ventricular tachycardia, ventricular fibrillation, or both upon reperfusion (P < 0.001, 0.5 v 3.0 mmol.litre-1). At all [Ca2+]o values examined, early ischaemia was associated with a rapid decrease in developed pressure and transient increase in the peak calcium transient followed by a gradual decline and subsequent increase in diastolic calcium during late ischaemia. The initiation of ventricular tachycardia/fibrillation upon reperfusion was immediately preceded by large increases in the amplitude of the calcium transient. These increases in systolic calcium were not seen in hearts in which ventricular arrhythmias did not occur. The association between reperfusion induced abrupt increases in peak calcium and the occurrence of ventricular tachycardia or fibrillation suggests that intracellular calcium transients may have a significant role in initiating these ventricular arrhythmias.

Oxidant stress increases heat shock protein 70 mRNA in isolated perfused rat heart.

Ischemia/reperfusion (I/R) and preconditioning of the heart by coronary artery occlusions increase expression of heat shock protein 70 (HSP 70). Because free radicals are generated during I/R, we hypothesized that the oxidant stress might contribute to an increased expression of HSP 70. Isolated rat hearts were perfused with free radical-generating systems such as xanthine/xanthine oxidase (X/XO), irradiated rose bengal (RB) generating singlet oxygen, and H2O2 for 15 min followed by 30 min of recovery period. Significant decrease in developed pressure and coronary flow occurred after perfusion with X/XO, H2O2, and RB. During I/R, the developed pressure and coronary flow were 60 +/- 8 and 80 +/- 5%, respectively, of control, which improved significantly with superoxide dismutase. The expression of HSP 70 mRNA increased over 13-fold in hearts perfused with X/XO, 6- to 7-fold with RB, and over 5-fold with H2O2. With I/R, an over 10-fold increase in HSP 70 mRNA was observed, which decreased significantly in the presence of superoxide dismutase. These results demonstrate that oxidant stress directly increases HSP 70 mRNA in the rat heart. It is concluded that one of the potential mechanisms of expression of HSP 70 by I/R may be oxygen radicals.

Effect of acute edema on left ventricular function and coronary vascular resistance in the isolated rat heart

The impact of acute myocardial edema on coronary flow and left ventricular performance was studied in isolated isovolumic rat hearts. After 15 min of aortic perfusion with Krebs-Henseleit buffer, hearts (10/group) were either removed for determination of water content or perfused for another 90 min. Three groups were perfused at a constant pressure of 60, 100, or 140 mmHg, and two groups were perfused at 60 or 140 mmHg with adenosine added. Compared with the 15-min group, there was a significant increase in water content in all groups except the 60-mmHg group (P < 0.005). There was a direct linear relationship between increases in coronary vascular resistance over time and water content (P < 0.0001). A decrease in developed pressure and peak +dP/dt was observed only in those groups that accumulated water. An inverse linear relationship was found between changes in developed pressure and water content (P = 0.0001). Water content had no effect on end-diastolic pressure below 5 ml/g; above 5 ml/g, a direct linear relationship was evident (P = 0.009). The results suggest that myocardial edema increases vascular resistance and decreases systolic performance. End-diastolic pressure is less influenced by edema than either systolic or coronary vascular function.

Contrasting effects of propionate and propionyl-L-carnitine on energy-linked processes in ischemic hearts

Propionyl-L-carnitine, unlike L-carnitine, is known to improve myocardial function and metabolism altered during the course of ischemia-reperfusion. In this study, the effect of propionyl-L-carnitine has been compared with that of propionate and carnitine on the performance of rat hearts perfused with a glucose-containing medium either under normoxia, ischemia, or postischemic reperfusion. In the postischemic phase, contractile parameters were partially restored both in the control and in the propionate plus carnitine-treated hearts, were markedly impaired by propionate, and were fully recovered by propionyl-L-carnitine. In addition, propionyl-L-carnitine, but not propionate, reduced the functional decay of mitochondria prepared from the ischemic hearts. Even in normoxic conditions propionate, unlike propionyl-L-carnitine, caused a drastic reduction of free CoA and L-carnitine. The concomitant increase in lactate production and decrease in ATP content might be explained by the inhibition of pyruvate dehydrogenase caused by the accumulation of propionyl-CoA. Indeed, when pyruvate was the only oxidizable substrate, propionate induced a gradual decrease in developed pressure, which was largely prevented by L-carnitine. The protective effect of propionyl-L-carnitine may be a consequence of the anaplerotic utilization of propionate in the presence of an optimal amount of ATP and free L-carnitine.

Acute effects of ethanol on cardiac function and intracellular calcium in perfused rat heart

The aim was to evaluate effects of ethanol on cardiac function and intracellular Ca2+ ([Ca2+]i) in perfused rat hearts. A Langendorff perfused rat heart preparation was used. Changes in [Ca2+]i were evaluated by surface fluorometry in hearts loaded with Indo 1-AM. Clinically relevant concentrations of ethanol (0.2 or 0.4% vol/vol) had no significant haemodynamic effects. High concentrations of ethanol (1, 2, 3, and 4% vol/vol) showed dose dependent decreases in developed pressure and the systolic peak and overall amplitude of the Indo 1 fluorescence transients (identical to [Ca2+]i), that were partially antagonised by high extracellular Ca2+ ([Ca2+]o = 4 mM). The ethanol concentrations that decreased developed pressure by 50% were 1.4 and 2.6% in the low (1.5 mM) and high [Ca2+]o, respectively. Four per cent ethanol decreased the amplitude of Indo 1 fluorescence transients to 54.5(SD 3.1) and 64.6(7.9)% of control values in the low and high [Ca2+]o, respectively. A relationship between the amplitude of Indo 1 fluorescence and developed pressure was fitted to a single sigmoid curve irrespective of [Ca2+]o. During ethanol washout, there was a dose dependent overshoot of the fluorescence ratio. Only high concentrations of ethanol depressed left ventricular function in a dose dependent manner by decreasing the amplitude of [Ca2+]i transients. High [Ca2+]o partially antagonised acute alcoholic cardiac depression by increasing the amplitude of [Ca2+]i transients. [Ca2+]i is a mediator of the acute cardiac effects of ethanol in perfused intact rat hearts.

Improvement in contractile recovery of isolated rat heart after cardioplegic ischaemic arrest with endogenous phosphocreatine: involvement of antiperoxidative effect?

The aim was to attempt to get further insight into the mechanism of the cardioprotective action of phosphocreatine (PCr). Three experimental protocols were used: (1) The effect was examined of exogenous PCr (10 mmol.litre-1) on myocardial oxidative damage produced by H2O2 perfusion (90 mumol.litre-1) of isolated rat heart. (2) Isolated rat hearts were subjected to 35 min cardioplegic ischaemia followed by reperfusion. A control group was studied along with two PCr groups, one corrected for Ca2+ to compensate its binding with PCr (1.4 mmol.litre-1 CaCl2 in St Thomas's Hospital cardioplegic solution), and the other not (1.2 mmol.litre-1). (3) The effect was studied of PCr alone and in combination with the antioxidant tocopherol phosphate (0.1 mumol.litre-1) on contractile and metabolic recovery of isolated rat heart reperfused after 40 min cardioplegic ischaemia. Studies were performed on hearts of 84 male Wistar rats, weighing 250-300 g. (1) Oxidative stress resulted in irreversible contracture and impairment of sarcolemmal integrity revealed by using the transmembrane tracer ionic lanthanum. These effects coincided with the decrease of developed pressure from 116 (SEM 3) to 38(3) mm Hg and rate-pressure product from 498(13) to 165(16) mm Hg.s-1. The Ca2+ binding property of PCr was estimated experimentally and the stability constant of the complex CaPCr was found to be 35.4(0.7) mmol; from this the Ca2+ bound by PCr was calculated to be 14% in the experimental conditions used. Ca2+ concentration in K-H buffer containing PCr was increased to compensate its binding with PCr. PCr prevented H2O2 induced contracture, preserved sarcolemmal integrity, and attenuated H2O2 induced decrease in developed pressure and rate-pressure product [73(6) mm Hg and 340(28) mm H.s-1, respectively, p less than 0.05 compared with control]. (2) PCr reduced the diastolic pressure [29(10) v 68(10) mm Hg in control group at 30 min of reperfusion, p less than 0.05] and enhanced the developed pressure [81(10) v 46(10) mm Hg in controls, p less than 0.05] and rate-pressure product [325(44) v 158(40) mm Hg.s-1 in controls, p less than 0.05]. When CaCl2 was increased to 1.4 mmol.litre-1 the protective effect of PCr was not abolished. (3) PCr resulted in improvement of developed pressure [49(7) v 18(5) mm Hg in controls at 40 min of reperfusion, p less than 0.05] and rate-pressure product [184(27) v 71(20) mm Hg.s-1 in controls, p less than 0.05]. The degree of contractile recovery in the tocopherol group was almost the same as in the PCr group. Combined addition of PCr and tocopherol further increased the developed pressure and rate-pressure product to 72(4) mm Hg and 284(23) mm Hg.s-1, respectively. Similarly, PCr and tocopherol in combination provided substantial inhibition of creatine kinase release into perfusate, at 3.8(0.4) v 10.9(2.5) IU in controls, p less than 0.05. PCr decreases the vulnerability of myocardium to oxidative stress and ischaemic damage. These effects cannot be explained by PCr induced shifts in Ca2+ concentration. Protective effects of PCr and tocopherol are quantitatively additive, most probably due to their different mechanisms of action, and tocopherol may be effective in extending the ability of PCr to stabilise cell membrane structure.

Influence of ischemia on [Ca 2+] i transients following drug therapy in hearts from aortic constricted rats

Intracellular calcium transients were studied prior, during and after 30 min of global ischemia in control and aortic constricted rat hearts, with and without acute treatment with verapamil. Calcium transients [Ca 2+] i continued to occur in verapamil treated animals for 18–20 min following the onset of global ischemia, whereas untreated hearts demonstrated calcium transients for only 3–8 min following global ischemia. Following the onset of global ischemia calcium transients continued to occur even though there was no measurable developed pressure. When calcium transients occurred for shorter periods of time during global ischemia the rise in diastolic calcium was greater and recovery was less. Addition of bradykinin to the perfusate showed that an increase in diastolic [Ca 2+] i was related to a decrease in amplitude of developed [Ca 2+] i transients and a decrease in developed pressure, but not to a change in coronary flow.

Ca2+ transient, Mg2+, and pH measurements in the cardiac cycle by 19F NMR.

19F NMR indicators have been used to measure the free cytosolic cation concentrations ([Mn+]i, where M is the atomic symbol and n is the value of the charge) of Ca2+, H+, and Mg2+ in perfused ferret hearts. The [Ca2+]i transient, cytosolic pH (pHi), and [Mg2+]i have also been followed at 16 phases in the cardiac cycle in hearts paced at 1.25 Hz at 30 degrees C. The initial [Ca2+]i rose rapidly after a 50-ms delay, was maximal at greater than 1.5 microM after 150 ms, and declined thereafter to the initial concentration. In contrast, no significant changes in pHi (pH 7.03 +/- 0.08) or [Mg2+]i (1.2 +/- 0.1 mM) were detected in the cycle. A decrease in developed pressure when the [Ca2+]i indicator (but not the pHi or [Mg2+]i indicator) was loaded into hearts was substantially reversed by the addition of 50 microM ZnCl2 to the perfusion medium. The Zn2+ was taken up into the myoplasm and displaced Ca2+ bound to the indicator, a symmetrically substituted difluoro derivative of 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (5FBAPTA), as evidenced by the appearance of the Zn-5FBAPTA resonance. The decrease in developed pressure caused by 5FBAPTA, therefore, may be due to its Ca2+ buffering effect on the myoplasm. By coloading hearts with the [Ca2+]i and pHi indicators, simultaneous measurement of several [Mn+]i was demonstrated, which should provide a useful addition to the methods available to monitor cardiac function and pharmacology.

31P and 1H magnetic resonance spectroscopy of acute alcohol cardiac depression in rats.

Cardiac depression in the isolated rat heart perfused with 4% ethanol was correlated with intracellular phosphate energetics and tissue water distributions. Energy metabolites were assessed using 31P magnetic resonance spectroscopy (MRS) and correlated to the mitochondrial redox state using epicardial surface fluorometry. Changes in myocardial water compartmentation were measured by using 1H NMR spectroscopy with an extracellular chemical-shift reagent (DyTTHA) and correlated to results of 2D echocardiography (2DE). During alcohol perfusion there was a significant decrease in developed pressure and in coronary flow. No change was seen in ATP, PCr, pHi, Pi, or NADH. After withdrawal of alcohol from the perfusate cardiac function reverted to control values without a depletion of energy levels. During alcohol perfusion 1H MRS showed a marked redistribution of water from the intra- to the extracellular space, corresponding to a 35% left ventricular wall thinning confirmed by 2DE. The results indicate that acute alcohol cardiac depression is related to a dehydration of myocardial cells, but is not associated with intracellular acidosis or energy depletion.

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 μl resulted in a continuous increase in developed pressure; (2) with volumes from 150 to 250 μl, developed pressure remained constant whereas developed (systolic) and diastolic wall stress rose sharply; and (3) with volumes from 250 to 400 μl, developed pressure fell whereas developed (systolic) and diastolic wall stress continued to rise. The in [ (PCr) (Pi) ] was in synchrony with oxygen consumption at 0 and 50 μl balloon volumes, and then diverged at volumes greater than 100 μl. Oxygen consumption increased from 0 to 50 μl, was constant from 50 to 250 μl balloon volume, and then declined. The in [ (PCr) (Pi) ] fell precipitously at balloon volumes greater than 100 μl, most likely limited by oxygen consumption. Coronary flow did not change significantly until 250 μl or more of water was added to the balloon, and then it started to decline. Volumes greater than 100 μl result in overstretch of myofibers, as observed by the precipitous decline in in [ (PCr) (Pi) ], and the steep increase in diastolic wall stress. With excessive volume loading, the drop in phosphorylation potential, in [ (PCr) (Pi) ], appears to contribute to the decrease in developed pressure.

Reversibility of acute alcohol cardiac depression: 31P NMR in hamsters.

Isolated hamster hearts were perfused with 2% ethanol for 30 min and then reequilibrated with control medium. One group of hamsters was pretreated with verapamil. Another group received diltiazem. Myocardial verapamil levels were 9.5 +/- 0.7 mg/g dry wt; diltiazem levels were 22 +/- 7 mg/g dry wt. Energy metabolites were assessed by using 31P NMR standardized with high-pressure liquid chromatography of freeze-clamped tissue. Intracellular calcium was measured by atomic absorption spectrophotometry, marking the extracellular space with K(CoEDTA). After 30 min of perfusion, untreated hamster hearts showed a 74% decrease in developed pressure, a marked increase in end-diastolic pressure, a decrease of ATP from 9.8 to 8.8 mmol, and an increase of Pi from 6.7 to 9.8 mmol, but no change of phosphocreatine (PCr) or intracellular pH (pHi). Verapamil pretreatment partially prevented cardiac depression during alcohol perfusion. Whereas diltiazem had no protective effect. After reequilibration, developed pressure and oxygen consumption significantly exceeded control values. ATP decreased to 8 mmol; pHi, PCr, and Pi showed no significant change. Verapamil-pretreated hearts showed better performance than untreated hearts without change in PCr and Pi, whereas ATP dropped slightly to 8.7 mmol. Thus, functional cardiac depression resulting from acute alcohol exposure is reversible. Increased intracellular calcium levels during alcohol exposure normalized after the removal of alcohol. There was no major change in high-energy phosphates during alcohol exposure or after the removal of alcohol. Verapamil protects the heart from functional depression during alcohol exposure without affecting energy resources.

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.

The contribution of intracellular acidosis to the decline of developed pressure in ferret hearts exposed to cyanide.

1. The concentrations of phosphorus-containing metabolites were measured using 31P nuclear magnetic resonance (n.m.r.) in Langendorff-perfused ferret hearts. The hearts were stimulated at a constant rate and developed pressure was measured. 2. The inhibition of oxidative phosphorylation with cyanide (2 mM) decreased developed pressure. This was accompanied by an intracellular acidosis, a fall in the concentration of phosphocreatine ([PCr]) and a rise in that of inorganic phosphate ([Pi]). 3. The effects of cyanide on developed pressure were compared with those of simply decreasing the intracellular pH (pHi) (by elevating CO2) to match the change produced by cyanide. The change of pHi alone resulted in about 33% of the decrease of force produced by cyanide. 4. The relationship between developed pressure and pHi was investigated by altering CO2. It could be described by an equation of the form:log developed pressure = a + b pHi where a and b were independent of pHi. The addition of cyanide decreased a but had no significant effect on b. In other words a given change of pHi had the same fractional effect on pressure in the absence as in the presence of cyanide. 5. In another series of experiments, after cyanide had been added, pHi was returned to control levels by decreasing CO2. This increased developed pressure. Nevertheless the pressure was still considerably less than in control. Furthermore, if the acidosis was abolished by decreasing CO2 at the same time as cyanide was added developed pressure still decreased. 6. We conclude that most of the decrease of developed pressure produced by cyanide is not produced by intracellular acidosis and may result from increased [Pi].

Negative Inotropic Effects of Furosemide in the Isolated Rabbit Heart

Furosemide is an effective diuretic that initiates a rapid diuresis and peripheral vasodilatation through renal adenylate cyclase inhibition and prostaglandin synthesis. Recently, it has been shown to be associated with activation of the neurohumoral vasoconstrictor mechanism and a further compromise of left ventricular function in patients with heart failure. The present study was performed to investigate the direct effects of furosemide on myocardial performance in the isolated perfused rabbit heart. Furosemide (10(-3) M) caused a significant decrease in developed pressure as well as a similar fall in coronary perfusion pressure. Furosemide also decreased myocardial contractility when the coronary perfusion pressure was kept constant. The change in developed pressure but not the decrease in coronary perfusion pressure could be blocked by treatment with indomethacin. Furosemide did not antagonize rabbit cardiac membrane adenylate cyclase. Therefore, furosemide has a direct inhibitory effect on cardiac contractility that is related to prostaglandin synthesis.

Verapamil preserves adenine nucleotide pool in cardiomyopathic Syrian hamster.

There is a decrease in total adenine nucleotides, cyclic AMP (cAMP), ATP/total ADP, and phosphocreatine (PCr)/creatine (Cr) both in situ and in the perfused heart in the heart failure stage of the cardiomyopathic Syrian hamster. There were decreases in developed pressure, dP/dt, and O2 consumption associated with the decrease in total adenine nucleotides and cAMP. Cardiomyopathic Syrian hamsters (180-240 days old) with congestive heart failure were given water with the calcium entry blocker, verapamil, as an additive 2 mo before death. In the cardiomyopathic group given verapamil the adenine nucleotides, cAMP, and high-energy phosphates were preserved and cardiac performance was not significantly different from that of the verapamil-treated healthy hamsters at the time of death. Pretreatment of cardiomyopathic animals with verapamil (6.6 mg verapamil/ml water consumed by drinking) resulted in significantly higher ATP/total ADP and PCr/Cr compared with nontreated cardiomyopathic hamsters. This is the first report demonstrating that a calcium entry blocker may improve cardiac performance and preserve total adenine nucleotides during the heart failure stage of the cardiomyopathic hamster.

Verapamil, propranolol, and hydralazine protect against the acute cardiac depression induced by adriamycin.

The apex ejecting isolated rat heart perfused with media containing 3 X 10(-5) mol . litre-1 adriamycin for 40 min demonstrated the following changes in contraction patterns: (a) a ten-fold increase in end-diastolic pressure; (b) a 45% decrease in developed pressure; (c) a 17% decrease in coronary flow; (d) a 27% increase in time to peak pressure; (e) a 26% increase in time for pressure to fall 50% during relaxation; and (f) a 65% decrease in maximum (+) and (-) dP/dt. In rats pretreated 1 h before death, verapamil, propranolol, and hydralazine significantly attenuated the cardiac depression produced by adriamycin. The combinations of verapamil and hydralazine, or propranolol and hydralazine were especially efficacious. Particularly striking was the protection afforded against an increase in diastolic pressure. Digoxin pretreatment afforded no protection. It is postulated that the acute depressive effects of adriamycin may be related to calcium overload.