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

Changes of enzyme activities in the myocardium and skeletal muscle fibres of cardiomyopathic hamsters. A cytophotometrical study

Cytophotometrical measurements of enzyme activities were performed in the myocardium and skeletal muscle fibres from normal and cardiomyopathic hamsters (BIO 8262) during ageing from 12-14 to 120-190 days. Myocardium as well as vastus lateralis muscles of cardiomyopathic hamsters showed changes in enzyme activities. The skeletal muscle fibres were typed into slow-oxidative, fast-oxidative glycolytic and fast-glycolytic to investigate fibre type-related changes in muscles of cardiomyopathic hamsters. The following myopathic changes were mainly found: Myofibrillic ATPase was depressed in the myocardium of both ventricles in all investigated age stages. The ATPase activity of the right ventricle was more decreased than that of the left one. Additionally, a metabolic shift was observed in myocardium and slow-oxidative muscle fibres at the onset of clinical symptoms, which appeared from day 150 to day 190. During the period from 42 up to 190 days of life an increase of oxidative (succinate dehydrogenase) activity was measured in the myocardium of both ventricles and in slow oxidative fibres of vastus lateralis muscle as a proximal muscle. At earlier ages, the fast fibres of myopathic vastus lateralis muscle showed higher glycolytic (glycerol-3-phosphate dehydrogenase) activity than those of normal muscles. However, at the age of 120-190 days the metabolic profile of fast fibres was normalized. In gastrocnemius muscle as a distal muscle no changes of enzyme activities were measured, suggesting the investigated hereditary myopathy effected proximal, but not distal muscles.

Rabbit ventricular myocyte volume changes as a direct result of crystalloid cardioplegia in congestive heart failure induced by aortic regurgitation

OBJECTIVES

We hypothesized that the cell volume of ventricular myocytes isolated from hearts in volume-overload congestive failure would respond differently to hypothermic cardioplegia than would sham-operated cohorts.

METHODS

Adult rabbits underwent either valvotomy and aortic regurgitation-induced heart failure or sham surgery. Congestive failure was confirmed clinically and by means of echocardiography. Cell volumes of isolated myocytes were measured by digital video microscopy. After equilibration in 37 degrees C physiologic solution, cells were suprafused with 9 degrees C standard or low-Cl(-) St Thomas' Hospital solution followed by reperfusion in 37 degrees C physiologic solution.

RESULTS

Exposure to cold St Thomas' Hospital solution for 20 minutes caused sham myocytes to swell by 8% (n = 9); cell volumes fully recovered on normothermic reperfusion. In contrast, congestive failure myocytes (n = 9) maintained their cell volume in cold St Thomas' Hospital solution and during reperfusion. Lowering the [K(+)][Cl(-)] product of St Thomas' Hospital solution by partially replacing Cl(-) with an impermeant anion prevented cellular edema in the sham group (n = 8) but caused a 4% swelling in failure myocytes (n = 10) on reperfusion. Osmotically shrinking the failure cells (n = 9) converted their behavior to that of sham cells.

CONCLUSIONS

In the absence of ischemia, congestive failure myocytes are less sensitive to cardioplegia-induced edema than sham cells. Low-Cl(-) cardioplegia, which prevents edema and protects the normal heart, induced swelling and may be detrimental in myopathic hearts. Differences in volume regulation in failure and sham myocytes may be due to activation of volume-sensitive channels that are turned off by osmotic shrinkage.

Resistance of the failing dystrophic hamster heart to the cardioprotective effects of diltiazem and clentiazem: evidence of coronary vascular dysfunctions

Although hypothermia and cardioplegic cardiac arrest provide effective protection during cardiac surgery, ischemia of long duration, poor preoperative myocardial function, and ventricular hypertrophy may lead to heterogeneous delivery of cardioplegic solutions, incomplete protection, and impaired postischemic recovery. Calcium antagonists are potent cardioprotective agents, but their efficacy in the presence of cold cardioplegia is still controversial, especially in heart failure, since it is often believed that failing hearts are more sensitive to their negative inotropic and chronotropic actions. However, recent data have demonstrated that the benzothiazepine-like calcium antagonists diltiazem and clentiazem, in selected dose ranges, elicit significant cardioprotection independently of intrinsic cardiodepression, thus lending support to their use in cardioprotective maneuvers involving the failing heart. We therefore evaluated the cardioprotective interaction of diltiazem, clentiazem, and cold cardioplegia in both normal and failing ischemic hearts. Hearts were excised from 200- to 225-day-old cardiomyopathic hamsters (CMHs) of the UM-X7.1 line and age-matched normal healthy controls. Ex vivo perfusion was performed at a constant pressure (140 cmH2O; 1 cmH2O = 98.1 Pa) according to the method of Langendorff. Heart rate, left ventricular developed pressure (LVDP), and coronary flow were monitored throughout the study. Global ischemia was produced for 90 min by shutting down the perfusate flow, followed by reperfusion for 30 min. Normal and failing CMH hearts were either untreated (control) or perfused at the onset of global ischemia with one of the following combinations: cold cardioplegia alone (St. Thomas' Hospital cardioplegic solution, 4 degrees C, infused for 2 min), cold cardioplegia + 10 nM diltiazem, or cold cardioplegia + 10 nM clentiazem. The cardiac and coronary dilator properties of 10 nM diltiazem and 10 nM clentiazem alone were investigated in separate groups of isolated preparations. Failing CMH hearts had lower basal LVDP (42 +/- 2 vs. 77 +/- 2 mmHg (1 mmHg = 133.3 Pa) for normal hearts, p < 0.05), while coronary flow was only slightly reduced (5.6 +/- 0.2 vs. 6.2 +/- 0.2 mL/min for normal hearts). Following 90 min global ischemia, coronary flow was increased in both groups, but the peak hyperemic response declined only in failing CMH hearts (+50 +/- 17 vs. +82 +/- 17% in normal hearts). In normal hearts, LVDP virtually recovered within 5 min of reperfusion but steadily decreased thereafter (-37 +/- 4% at 30 min). In contrast, in failing CMH hearts, LVDP significantly decreased early during reperfusion but improved over time (-19 +/- 7% at 30 min). In normal hearts, the addition of diltiazem or clentiazem to cold cardioplegic solutions resulted in improved postischemic contractile function for the duration of reperfusion (85 +/- 4% vs. only 71 +/- 6% for cardioplegia, p < 0.05). The post-ischemic increase in coronary flow was similar in all groups. In failing CMH hearts, the addition of diltiazem or clentiazem afforded no significant contractile benefit at reperfusion. In nonischemic normal hearts, infusion of diltiazem or clentiazem (10 nM) alone increased coronary flow (+6 +/- 1% for diltiazem and +24 +/- 3% for clentiazem) without significant negative inotropic or chronotropic effects. In nonischemic failing CMH hearts, infusion of diltiazem or clentiazem did not elicit cardiodepression. In contrast their coronary dilator actions reverted to vasoconstriction (diltiazem) or were significantly attenuated (clentiazem). From these experiments we can conclude that, compared with the normal heart, the failing CMH heart adapted differently to global ischemia.

Aqueous shift reagents for high-resolution cation NMR. VI. Titration curves for in vivo 23Na and 1H2O MRS obtained from rat blood

Frequency shift/concentration calibration curves applicable to the use of shift reagents (SRs) for in vivo 23Na MRS studies can be obtained from experiments with whole blood. Here, they are reported for titrations of rat blood with the SRs DyTTHA3- and TmDOTP5-. There are a number of considerations that must be made in order to derive accurate calibration curves from the experimental data. These include the effects of bulk magnetic susceptibility (BMS, since the SRs are paramagnetic), the effects of water flux (since addition of the SR stock solution to blood renders the plasma hyperosmotic), and the consequences of restricted distribution of the SR anion in the erythrocyte suspension. We give in some detail the BMS shift theory that obtains in this case and show also how it applies to excised perfused organ as well as in vivo studies. Also, we report significant effects of adjuvant Ca2+ additions in the TmDOTP5- titrations. These are very important to the successful use of this SR in vivo. Finally, our considerations of BMS lead naturally to an understanding of its manifestations in the shifts of the 1H2O resonance frequencies of cell suspensions and tissues induced by SRs. Since these are being increasingly reported, and often misinterpreted, we devote an experiment and some discussion to this subject. We show that this phenomenon cannot be used to quantitatively discriminate intra- and extracellular 1H2O signals.

Kinetic changes of ethanolamine base exchange activity and increase of viscosity in sarcolemmal membranes of hamster heart during development of cardiomyopathy

The activity of the phospholipid base exchange enzyme specific for ethanolamine has been measured in cardiac sarcolemmal membrane preparations from Syrian golden and UM-X7.1 cardiomyopathic hamsters. In Syrian golden hamsters, the Km of the enzyme for ethanolamine does not change with age, whereas it almost doubles in membranes from cardiomyopathic animals, from the 30th to the 150th day of age. During the same period, the membrane cholesterol content increases by 68% in cardiomyopathic hamsters, whereas it does not change significantly in the Syrian golden hamster strain. As a consequence, in the adult animal, the cholesterol to phospholipid ratio and the viscosity of sarcolemmal membranes are higher in UM-X7.1 strain than in Syrian golden hamsters. A cause-consequence relationship between the enzymatic changes and the compositional modifications in the sarcolemma occurring in UM-X7.1 hamsters during the development of cardiomyopathy is proposed.

Effects of quinapril, a new angiotensin converting enzyme inhibitor, on left ventricular failure and survival in the cardiomyopathic hamster. Hemodynamic, morphological, and biochemical correlates

The effect of chronic therapy with quinapril on the temporal progression of left ventricular failure and survival was assessed in the CHF 146 cardiomyopathic (CM) hamster, which is an idiopathic model of congestive heart failure. Age-matched Golden Syrian (GS) hamsters served as normal controls. Quinapril was administered in the drinking water at average daily doses of 10.2, 112.4, and 222.4 mg/kg/day. In untreated CM hamsters, in vitro left ventricular performance progressively deteriorated with increasing age beginning at roughly 180 days. This decline in left ventricular performance was accompanied by a decrease in coronary flow and an increase in left ventricular volume. Administration of quinapril from 180 to 300 days of age prevented the decline of in vitro left ventricular contractile performance and coronary flow and also reduced the age-dependent increases in left ventricular volume. The cardioprotective effects of quinapril were observed at doses of 112.4 and 222.4 mg/kg/day but not at 10.2 mg/kg/day. Lung angiotensin converting enzyme activity was significantly inhibited by quinapril in GS and CM hamsters at 240 and 300 days of age at all dose levels. In contrast, significant inhibition of ventricular angiotensin converting enzyme activity was observed consistently at doses of 112.4 and 222.4 mg/kg/day quinapril but not at 10.2 mg/kg/day. In the survival protocol, CM and GS hamsters were treated with vehicle or quinapril (100 mg/kg/day) from 180 to 522 days of age. During the initial 210 days of treatment (from 180 to 390 days of age) 78.3% of the vehicle-treated CM hamsters died compared with 27.7% of quinapril-treated CM hamsters. Quinapril increased the median survival time of CM hamsters by 32.9% (112 days). It is concluded that chronic quinapril therapy exerts a significant cardioprotective effect and also increases survival.

Mechanism for depressed cardiac function in left ventricular volume overload

To assess the effects of left ventricular chamber volume on the mechanism of changes in left ventricular developed pressure we performed phosphorous-31 nuclear magnetic resonance spectroscopy, hydrogen-1 nuclear magnetic resonance spectroscopy with a shift reagent, two-dimensional echocardiography, atomic absorption spectrophotometry, microsphere analysis, and surface fluorometry on isovolumic isolated perfused rat hearts with incremental intraventricular balloon volumes, while left ventricular pressure was concurrently monitored. A three-phasic response of developed pressure was noted: 0 to 100 microliters balloon volumes resulted in an increase in developed pressure, whereas developed pressure remained constant at 250 microliters and fell at 400 microliters. Oxygen consumption and [Ca2+]i transients followed the same pattern as developed pressure and coronary flow. Intraventricular volumes of 250 microliters or greater (a volume overload) caused endocardial ischemia, a greater decrease in extracellular versus intracellular water, thinning of the left ventricular free wall, and an increase in chamber size. Mechanical pressure on the tissue, induced by the volume overload, caused ischemia as further evidenced by (1) a negative effect on developed pressure, (2) a decrease in [Ca2+]i transients, (3) a [Ca2+]i overload, (4) a moderate decrease in the phosphorylation potential, and (5) an increase in the oxidation-reduction state (nicotinamide-adenine dinucleotide). The high intracellular calcium associated with volume overload may have been due to both compression and ischemia, which leads to an increased number of cross-bridges in rigor, a high end-diastolic pressure, and an increase in wall stress.

Magnetic susceptibility shift selected imaging: MESSI

Paramagnetic compounds are often used to enhance contrast in MRI by virtue of their increase in the kinetics of the relaxation of water 1H magnetization. Here, we demonstrate a method for contrast enhancement which is based on the resonance frequency shifts caused by the bulk magnetic susceptibility (BMS) effects of such compounds. This involves the frequency selective excitation in the absence of field gradients, during the imaging sequence, of a portion of the water 1H resonance which is rendered inhomogeneous by BMS shifts only. The image which results is of that portion of the sample which gives rise to the portion of the spectrum excited. A phantom sample which simulates some aspects of tissue, particularly blood vessels with different orientations in the magnetic field, was prepared. The contrast enhancement exhibited here avoids some of the distortions attendant to the use of paramagnetic reagents. This new approach can, in principle, utilize the natural BMS differences found in all tissue.

Glycolysis in heart failure: a 31P-NMR and surface fluorometry study

Glycolysis is slow in the heart, especially in the cardiomyopathic heart. Glycolysis is partially rate-limited by phosphofructokinase (PFK), an enzyme which is inhibited by calcium (Ca2+)i and hydrogen ions (H+)i and activated by cAMP. (H+)i and (Ca2+)i are augmented in cardiomyopathy. With glucose as the only substrate (NADH)/(NAD) the phosphorylation potential and developed pressure were significantly lower, and concentrations of phosphomonoester sugars and hydrogen ions (H+)i were significantly higher in isolated cardiomyopathic hearts as compared to healthy hamster hearts. Pyruvate lowered diastolic (Ca2+)i in cardiomyopathic hamster hearts. With pyruvate as the substrate (NADH)/(NAD), the phosphorylation potential and developed pressure increased significantly and concentrations of phosphomonoester sugars (PME), (H+)i and diastolic (Ca2+)i decreased significantly in myopathic hamster hearts. The results suggest that late heart failure in the myopathic hamster is associated with calcium and/or hydrogen ion-induced inhibition of glycolysis.

Postischemic recovery of mechanical performance and energy metabolism in the presence of left ventricular hypertrophy. A 31P-MRS study

The present study was undertaken to define the effects of left ventricular hypertrophy on postischemic recovery of myocardial performance and high energy phosphate metabolism. Hemodynamics and 31P-magnetic resonance spectra were monitored simultaneously in the isolated Langendorff-perfused rat heart during 30 minutes of ischemia and 30 minutes of reperfusion. Left ventricular hypertrophy was produced by either suprarenal aortic constriction or chronic thyroxine administration. In chronic pressure overload hypertrophy, minimal coronary resistance was significantly higher (p less than 0.001) and the loss of purine nucleosides in the coronary effluent during early reperfusion significantly larger (p less than 0.001) compared with both normal hearts and thyroxine-induced hypertrophied hearts. Postischemic recovery of the baseline values for left ventricular developed pressure and phosphorylation potential was 43 +/- 4% and 82 +/- 4%, respectively, in chronic pressure overload hypertrophied hearts; 86 +/- 4% and 91 +/- 3%, respectively, in normal hearts (chronic pressure overload hypertrophy versus normal hearts, p less than 0.001 and p less than 0.05); and 100 +/- 4% and 98 +/- 2%, respectively, in thyroxine-induced hypertrophied hearts (normal hearts versus thyroxine-induced hypertrophied hearts, p less than 0.05 and p less than 0.05). Recovery after reperfusion was not related to intracellular pH, ATP, phosphocreatine, or inorganic phosphate levels during ischemia. Also, recovery was not related to developed pressure or oxygen consumption before ischemia. However, recovery was inversely related to coronary resistance and directly related to coronary flow before ischemia. Thus, functional and/or anatomic alterations of the coronary vascular bed and a greater loss of purine nucleosides during reperfusion are likely responsible for the attenuated compensatory response to ischemia and reperfusion in left ventricular hypertrophy induced by chronic pressure overload. On the other hand, the excess muscle mass per se does not seem to alter recovery, since thyroxine-induced myocardial hypertrophied hearts responded at least as well as normal hearts.

Bulk magnetic susceptibility shifts in NMR studies of compartmentalized samples: use of paramagnetic reagents

The bulk magnetic susceptibility (BMS) shift of a nuclear resonance frequency caused by a paramagnetic compound is of importance in vivo NMR, both magnetic resonance spectroscopy and magnetic resonance imaging. However, since it is a rather complicated phenomenon, it has been the source of many misinterpretations in the literature. We have reworked and organized the theory of the BMS shift. This includes accounting for the important effects of local susceptibility. We have conducted experiments on phantom samples in order to illustrate the principles involved. Our phantoms consist of capillaries and coaxial cylinders. They simulate the situations of blood vessels oriented parallel and perpendicular to the magnetic field and the interstitial spaces surrounding them. In most of our experiments, the paramagnetic compound was one of several different hyperfine shift reagents for cation resonances. These were chosen to cover a range of potencies, in both magnitude and sign, of the shifts they produce. However, we also used a reagent which was incapable of inducing a hyperfine shift and thus could cause only a BMS shift. Although we report only 23Na spectra in this paper, the latter samples simulate the cases where one observes the water 1H resonance in experiments employing hyperfine shift reagents for cations. There have been a number of such investigations recently reported in the literature. The principles considered in this paper allow us to offer new interpretations for the results of several experiments published in the last few years.

Effects of perfusion pressure on energy and work of isolated rat hearts

A chemomechanical study of hypertrophied hearts of 6-month-old spontaneously hypertensive rats (SHR) and that of age-matched Wistar-Kyoto (WKY) rats was carried out, analyzing the response of the heart to steady-state changes in coronary perfusion pressure. The ratio of heart (dry)-to-body (wet) weight of WKY rats was 0.37 +/- 0.02 (10(-3] and for SHR was 0.58 +/- 0.03 (10(-3] (p less than 0.01). In the apex-ejecting, isolated, pyruvate-perfused working hearts of WKY rats and SHR, coronary flow was constant when coronary perfusion pressure was set between 140 and 190 cm H2O (range of autoregulation). Coronary flow was perfusion pressure dependent when the coronary perfusion pressure was set below 110 cm H2O for both WKY rats and SHR. Cardiac output, developed pressure, rate of pressure development (dP/dt), and oxygen consumption were constant in the range of autoregulation but decreased in the direction of coronary flow when coronary flow was reduced by a drop in perfusion pressure. Similarly, the phosphorylation potential, phosphocreatine, adenosine triphosphate, and cyclic adenosine monophosphate were constant in the range of autoregulation but decreased directionally with coronary perfusion pressure below 110 cm H2O for both SHR and WKY rats. There was a significantly lower phosphorylation potential in SHR as compared with WKY rats when coronary perfusion pressure was reduced to 80 cm H2O. In the region of autoregulation, coronary flow and oxygen consumption were significantly less in SHR, although developed pressure was significantly greater at both high and low workloads.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Increased left ventricular diastolic stiffness in the early phase of hereditary cardiomyopathy

Isolated hearts from normal and cardiomyopathic hamsters (160 to 180 days of age) were perfused through the aorta and assessed by echocardiographic and 31P-NMR (nuclear magnetic resonance) techniques. A decreased left ventricular systolic pressure in cardiomyopathic hamsters was associated with diminished cardiac size and left ventricular wall thickness. However, the ratio of inner/outer cross-sectional area and estimated left ventricular volume at any given left ventricular weight was significantly higher, indicating relative left ventricular chamber enlargement in cardiomyopathic hamsters. Left ventricular volumes were increased with an intraventricular balloon. Gradual inflation of the balloon resulted in increments of left ventricular systolic and developed stress that rose to the same values in both groups. At this point, the normalized stress-strain relationship was approximately two times steeper for cardiomyopathic hamsters, while at lower strain values the diastolic stress in cardiomyopathic hamsters was less than in controls, possibly due to cardiac dilatation. Almost the same degree of dilatation was induced in control hearts by the acute addition of 1% alcohol, but it was not followed by increased diastolic stiffness. Examination of hearts by 31P-NMR techniques revealed a decreased phosphocreatine/inorganic phosphate (PCr/Pi) ratio in the cardiomyopathic hamsters that progressed further with balloon inflation and was associated with a relative fall in PCr and adenosine triphosphate (ATP) content. Results suggest increased diastolic stiffness in cardiomyopathic hamsters, which was not seen in acute cardiac depression with alcohol. Diastolic volume overload with increased wall stress is probably the major factor contributing to increased diastolic stiffness early in the cardiomyopathy.

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.