Notes on the history of experimental cardiology

Due to the numerous chapters discussing the history of this society, substantial aspects of cardiovascular research are covered to a great extent. Therefore it is extraordinarily difficult to find a convincing classification for the field of "Experimental Cardiology". What remains, if physiology, heart surgery, coronary heart disease, diagnostic imaging, heart failure, hypertension, electrophysiology, arteriosclerosis and pathology are presented separately? Therefore I decided to choose different ways of covering the meetings up to the end of World War II and then for the time after 1948. Only some congresses are mentioned. I proceed chronologically, whereby I have indicated relevant or interesting personal, but rather political aspects, that attracted my attention when studying the meeting reports. The selection is certainly personally influenced. Methodological problems (cardiac output, electrocardiogram (ECG), phonocardiography (PCG), RR, etc.) as well as issues of circulatory regulation were in the foreground at the early meetings. The classical history of cardiovascular research of the American Physiological Society of 1964 (5) and a series of works about the history of cardiology (e.g., (1, 2, 6)) published in the last few years outline the most important lines of development. The areas energy supply, energy demand and myocardial metabolism are covered rather incidentally there. I want to focus on these aspects on the basis of the meetings.

Stimulation of nitric oxide synthesis by the aqueous extract of Panax ginseng root in RAW 264.7 cells

1. In this study, we investigated the effect of Panax ginseng root aqueous extracts upon inducible nitric oxide synthesis in RAW 264.7 cells. Panax ginseng root extract has been used in the Asian world for centuries as a traditional herb to enhance physical strength and resistance and is becoming more and more popular in Europe and North America. 2. Incubation of murine macrophages (RAW 264.7 cells) with increasing amounts of aqueous extracts of Panax ginseng (0.05 - 0.8 microg microl(-1)) showed a dose dependent stimulation of inducible nitric oxide synthesis. 3. Polysaccharides isolated from Panax ginseng showed strong stimulation of inducible nitric oxide synthesis, whereas a triterpene-enriched fraction from an aqueous extract of Panax ginseng did not show any stimulation. 4. Inducible nitric oxide synthase protein expression was enhanced in a dose dependent manner as revealed by immunoblotting when cells were incubated with increasing amounts of Panax ginseng extract. This was associated with an incline in inducible nitric oxide synthase mRNA-levels as determined by semiquantitative polymerase chain reaction and electromobility shift assay studies indicated enhanced nuclear factor-kappaB DNA binding activity. 5. As nitric oxide plays an important role in immune function, Panax ginseng treatment could modulate several aspects of host defense mechanisms due to stimulation of the inducible nitric oxide synthase.

Angiogenesis stimulation in explanted hearts from patients pre-treated with intravenous prostaglandin E(1)

BACKGROUND

Prostaglandin E(1) (PGE(1)) is a potent vasodilator and induces angiogenesis in animal tissues. Previous clinical studies demonstrated that PGE(1) improves hemodynamic parameters in patients with heart failure listed for heart transplantation (HTX). Therefore, we designed a retrospective immunohistochemistry study to investigate various markers of angiogenesis using hearts explanted from PGE(1)-treated patients with idiopathic dilated cardiomyopathy (IDCM).

METHODS AND RESULTS

We investigated neovascularization in 18 hearts explanted from patients with IDCM: 9 patients received treatment with chronic infusions of PGE(1) for end-stage heart failure before HTX, whereas the remaining patients with IDCM did not receive PGE(1) and served as controls. We used immunoreactivity against CD34, von Willebrand factor (vWf), vascular endothelial growth factor (VEGF), and MIB-1 (Ki-67) to quantify angiogenesis, and used sirius red staining to determine the degree of fibrosis. Compared with the control group, PGE(1)-treated patients had significantly more CD34-, vWf- and MIB-1-positive cells in the sub-endocardium, myocardium and sub-epicardium (p < 0.01). The degree of fibrosis in the hearts of PGE(1)-treated patients was significantly lower than in control patients (p < 0.05), but we did not see any difference in the percentage of muscle mass. Finally, throughout the ventricles, we found significantly more VEGF-positive capillaries in the PGE(1) group (p < 0.0001).

CONCLUSIONS

The data suggest that PGE(1) could be a potent inducer of angiogenesis and the angiogenic factor VEGF, and could cause reduced fibrosis in the failing human heart.

Oxidized low-density lipoprotein is localized in the ventricles of hearts from patients with coronary heart disease

The present study was designed to investigate whether oxidized low-density lipoprotein is accumulated in the left and right ventricular walls of patients with coronary heart disease (n=10) compared with patients with dilated cardiomyopathy (n=9) or healthy heart donors (controls, n=5). Sections from both ventricles of explanted hearts and coronary arteries of the same patients were analyzed by semiquantitative immunohistochemistry for the presence of oxidized low-density lipoprotein. Oxidized low-density lipoprotein was enriched in the left and right ventricular walls from coronary heart disease patients compared with patients with dilated cardiomyopathy (P=0.0012 for left ventricle and P=0.103 for right ventricle) or controls (P=0.0012 for the left ventricle and P<0.05 for the right ventricle). The accumulation of oxidized low-density lipoprotein was higher in the left than in the right ventricles in all three groups. Positive immunoreactivity for oxidized low-density lipoprotein was mainly identified in the endocardium and the subendocardial areas of the ventricles and co-localized with macrophages. Accumulation of oxidized low-density lipoprotein in the ventricles significantly correlated with the enrichment in the respective coronary arteries, whereas only poor correlations were observed between various hemodynamic parameters and ventricular oxidized low-density lipoprotein accumulation. Ventricular accumulation of oxidized low-density lipoprotein seems to be a generalized pathophysiological process which does not exclusively involve the coronary arteries. Higher oxidative stress in combination with impaired oxygen supply in the endocardium could have favored low-density lipoprotein deposition and oxidation.

Urea-induced inducible nitric oxide synthase inhibition and macrophage proliferation

BACKGROUND

Atherosclerosis is a major cause of morbidity and mortality in chronic renal failure and is associated with the proliferation of macrophages within atherosclerotic lesions.

METHODS

Because the progression of atherosclerosis as a consequence of decreased nitric oxide (NO) synthesis has been described, we investigated the correlation between the inhibition of inducible NO synthase (iNOS) by urea, macrophage proliferation as assayed by cell counting, tritiated-thymidine incorporation and measurement of cell protein, and macrophage apoptosis.

RESULTS

Urea induces a dose-dependent inhibition of inducible NO synthesis in lipopolysaccharide-stimulated mouse macrophages (RAW 264.7) with concomitant macrophage proliferation. Macrophage proliferation as determined by cell counting became statistically significant at 60 mmol/L urea corresponding to a blood urea nitrogen level of 180 mg/100 mL, concentrations seen in uremic patients. iNOS protein expression showed a dose-dependent reduction, as revealed by immunoblotting when cells were incubated with increasing amounts of urea. The decrease of cytosolic DNA fragments in stimulated macrophages incubated with urea shows that the proliferative actions of urea are associated with a decrease of diminished NO-mediated apoptosis.

CONCLUSIONS

These data demonstrate that inhibition of iNOS-dependent NO production caused by urea enhances macrophage proliferation as a consequence of diminished NO-mediated apoptosis. This fact may be important for the development of atherosclerotic lesions during chronic renal failure and is in accordance with recently published studies showing that under conditions with decreased constitutive NOS activity, iNOS might substitute the synthesis of NO. iNOS expression in vascular smooth muscle cells and macrophages is supposed to prevent restenosis following angioplasty or heart transplant vasculopathy. This is supported by the fact that specific inhibition of endogenous iNOS activity with L-N6-(1-iminoethly)-lysine accelerates the progression of vasculopathy in transplantation atherosclerosis.

Regulation of cyclosporin A sensitive mitochondrial permeability transition by the redox state of pyridine nucleotides

The mechanisms involved in the induction of cyclosporine A sensitive mitochondrial swelling by oxidative stress were investigated in isolated guinea pig liver mitochondria. The aim of our study was to investigate, if swelling is inevitably associated with the oxidation of pyridine nucleotides, and if the oxidized pyridine nucleotides have to be hydrolysed for the induction of mitochondrial swelling. Quantitative measurement of oxidized pyridine nucleotides was performed with HPLC. Mitochondrial swelling was recorded by monitoring the decrease in light scattering of the mitochondrial suspension. Reduction and oxidation of pyridine nucleotides were followed by monitoring the changes of the autofluorescence signal of reduced pyridine nucleotides. Qualitative measurement of mitochondrial membrane potential was performed with the fluorescence indicator rhodamine 123. Neither t-butyl hydroperoxide nor the dissipation of the mitochondrial inner membrane potential with FCCP (carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone) induced the opening of the membrane permeability transition pore, unless an extensive oxidation of mitochondrial pyridine nucleotides took place. Mitochondrial swelling induced by our experimental conditions was always sensitive to cyclosporine A and accompanied by a cyclosporine A sensitive release of inner mitochondrial pyridine nucleotides without pyridine nucleotide hydrolysis. Not the cycling of calcium across the mitochondrial inner membrane but the accumulation of calcium inside the mitochondria was a prerequisite for mitochondrial swelling. The mitochondrial membrane permeability transition is neither caused nor accompanied by the hydrolysis of mitochondrial pyridine nucleotides.

Testosterone inhibits expression of inducible nitric oxide synthase in murine macrophages

We investigated the effect of testosterone, the main sexual steroid hormone in men, upon inducible nitric oxide synthesis in murine macrophages. Incubation of murine macrophages (RAW 264.7 cells) stimulated by bacterial lipopolysaccharide (2 microg/ml) with increasing amounts of testosterone (0.1-40 microM) showed a dose dependent inhibition of inducible nitric oxide synthesis. Inducible nitric oxide synthase protein expression was reduced in a dose dependent manner as revealed by immunoblotting when cells were incubated with increasing amounts of testosterone. This was associated with a decline in iNOS mRNA-levels as determined by competitive semiquantitative PCR. As nitric oxide plays an important role in immune defense and atherosclerosis prevention, testosterone-induced iNOS inhibition could lead to an elevated risk of infection as well as to the development of atherosclerotic lesions.

Postischemic cardiac function recovery in the isolated rat heart: effects of adenosine deaminase and nucleoside transport inhibition

BACKGROUND AND AIMS

This study assessed the cardioprotective effects of inhibitors of adenosine metabolism in an isolated perfused rat heart model. Specifically, we studied the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)-adenine and the selective nucleoside transport inhibitor S-(p-nitrobenzyl)-6-thioinosine, in terms of their potential to enhance protection when added to Bretschneider's cardioplegic solution.

METHODS

Rat hearts were infused for 5 min with Krebs-Henseleit buffer solution (group 1), Bretschneider's cardioplegic solution (group 2), Bretschneider's cardioplegic solution with the addition of 25 microM erythro-9-(2-hydroxy-3-nonyl)-adenine and 5 microM S-(p-nitrobenzyl)-6-thioinosine (group 3), and Bretschneider's cardioplegic solution with the addtion of 25 microM erythro-9-(2-hydroxy-3-nonyl)-adenine only (group 4). After cardioplegic arrest and 45 min of ischemic storage at 25 degrees C, the functional recovery of the hearts was tested during 15 min of Langendorff reperfusion and then 45 min of working heart reperfusion.

RESULTS

In relation to the cardioprotective effects of Bretschneider's cardioplegic solution alone, we observed an improved recovery of hemodynamic function of the hearts with the addition of both erythro-9-(2-hydroxy-3-nonyl)-adenine and S-(p-nitrobenzyl)-6-thioinosine. However, the myocardial adenosine triphosphate (ATP) concentration remained unchanged. Bradycardia observed under the addition of erythro-9-(2-hydroxy-3-nonyl)-adenine alone was prevented by the addition of S-(p-nitrobenzyl)-6-thioinosine.

CONCLUSION

A combination of both substances may be tested further for cardiac preservation, as it might improve the recovery from ischemia at moderate temperatures.

Inhibition of inducible nitric oxide synthesis by the herbal preparation Padma 28 in macrophage cell line

Padma 28 is a mixture of herbs used in traditional Tibetan medicine with anti-inflammatory activities. We investigated the effects of Padma 28 on nitric oxide (NO) production by the inducible nitric oxide synthase (iNOS) in lipopolysaccharide stimulated mouse macrophages (RAW 264.7). Padma 28 (0-900 microg/mL) induced a concentration dependent inhibition of inducible nitric oxide synthesis. iNOS protein expression showed a concentration dependent reduction as revealed by immunoblotting when cells were incubated with increasing amounts of Padma 28. Padma 28 decreased iNOS mRNA levels as shown by RT-PCR. Aqueous extracts from costi amari radix (costus root, the dried root of Saussurea lappa) and the outer cover of myrobalani fructus (the dried fruit of Terminalia chebula), constituents of the complex herb preparation Padma 28, were found to inhibit inducible nitric oxide synthesis by decreasing iNOS protein and iNOS mRNA levels. The inhibition of inducible nitric oxide synthesis might contribute to the anti-inflammatory activities of Padma 28.

Comparison of the solutions of Bretschneider, St. Thomas' Hospital and the National Institutes of Health for cardioplegic protection during moderate hypothermic arrest

We evaluated three cardioplegic solutions, Bretschneider's cardioplegic solution (HTK), St. Thomas' Hospital solution (STH) and the solution of the National Institutes of Health (NIH), a solution with added nitroglycerin and lidocaine, for their ability to minimize ischemia-reperfusion injury in a working rat heart model. After cardioplegic arrest at 4 degrees C and subsequent 45 min of ischemic storage at 25 degrees C the function recovery of hearts was examined during 1 h of normothermic crystalloid reperfusion using Krebs-Henseleit buffer as perfusion medium. We noted a significantly better preservation of the maximum (+dp/dt(max)) and minimum (-dp/dt(max)) velocity of pressure development and a significantly higher coronary flow with the use of HTK (2,657 mm Hg/s, 2,122 mm Hg/s, 17 ml/min) compared to STH (1,600 mm Hg/s, p < 0.05; 1,591 mm Hg/s, p<0.05; 11 ml/ min, p<0.05), and an intermediate level of preservation of hemodynamic parameters with NIH (2,149 mm Hg/s, 1,766 mm Hg/s, 12 ml/min). Concerning the cardiac output, however, no major difference was found between the HTK (41 ml/min), the STH (34 ml/min) and the NIH group (36 ml/min). The decay of the myocardial energy charge was significantly lower in both the HTK and the NIH group as compared with conservation in STH solution. Lactate was lowest in the HTK group, CK and LDH releases in the effusate remained lowest after HTK and NIH preservation. The data of this study suggest that HTK and NIH most perfectly reduce the impairment of myocardial function and provide better myocardial protection during ischemic arrest at 25 degrees C and superior recovery compared to STH solution.

Inhibition of inducible nitric oxide synthesis by oxidized lipoprotein(a) in a murine macrophage cell line

Increased plasma levels of human lipoprotein(a) (Lp(a)) are highly correlated with the development of atherosclerotic lesions. During our study, we investigated the effects of native and hypochlorite oxidized lipoprotein(a) (ox-Lp(a)) on nitric oxide production by the inducible nitric oxide synthase (iNOS) in lipopolysaccharide/interferon stimulated mouse macrophages (J774A.1). Ox-Lp(a) (0-2 microg/ml) induces a dose dependent inhibition of inducible nitric oxide synthesis. iNOS protein expression showed a dose dependent reduction as revealed by immunoblotting when cells were incubated with increasing amounts of ox-Lp(a). Ox-Lp(a) decreases iNOS mRNA synthesis as shown by reverse transcription-polymerase chain reaction. Ox-Lp(a) induced iNOS inhibition might contribute to the development of atherosclerotic lesions by reducing the anti-atherogenic effects of nitric oxide.

Protection of reoxygenated cardiomyocytes against sarcolemmal fragility: the role of glutathione

This study addressed the question of whether the sarcolemmal fragility of cardiomyocytes after anoxia and subsequent reoxygenation can be altered by modulation of the cellular glutathione state. Isolated ventricular cardiomyocytes (from adult rats) were exposed to 120 min anoxia and subsequently to 30 min reoxygenation. Osmotic stress was generated by reduction of medium osmolarity from 270 to 80 mosmol/l and sarcolemmal fragility assessed by the leakage of lactate dehydrogenase (LDH). Under normoxic conditions 6.7+/-1.0 % of total LDH activity was found extracellularly. Hyposmolar reoxygenation, but not hypoosmolar anoxia, increased LDH release (17.9+/-2.7% of total, P<0.05). Increasing cellular glutathione content by pretreatment with N-acetylcysteine (1 mM) reduced LDH release following hyposmolar reoxygenation (12.3+/-1.9% vs. 18.2+/-2.9% of LDH in medium, P<0.05). Depletion of glutathione content by pretreatment with buthionine sulphoximine (BSO, 200 microM), increased LDH release following osmotic stress already in normoxia (10.5+/-1.8% of LDH in medium; P<0.05 vs. no BSO), and even further after reoxygenation (21.8+/-3. 2%, P<0.05 vs. normoxia). We conclude that the increased sarcolemmal fragility in reoxygenated cardiomyocytes is due to reoxygenation in the presence of reduced antioxidant defence.

Urea induces macrophage proliferation by inhibition of inducible nitric oxide synthesis

BACKGROUND

Atherosclerosis is a major cause of morbidity and mortality in chronic renal failure and is associated with the proliferation of macrophages within atherosclerotic lesions.

METHODS

Because the progression of atherosclerosis as a consequence of decreased nitric oxide synthesis has been described, we investigated the correlation between the inhibition of inducible nitric oxide synthase (iNOS) by urea, macrophage proliferation as assayed by cell counting, tritiated thymidine incorporation and measurement of cell protein, and macrophage apoptosis.

RESULTS

Urea induces a dose-dependent inhibition of inducible nitric oxide synthesis in lipopolysaccharide-stimulated mouse macrophages (RAW 264.7) with concomitant macrophage proliferation. Macrophage proliferation, as determined by cell counting, became statistically significant at 60 mM urea, corresponding to a blood urea nitrogen level of 180 mg/100 ml, concentrations seen in uremic patients. iNOS protein expression showed a dose-dependent reduction, as revealed by immunoblotting when cells were incubated with increasing amounts of urea. The decrease of cytosolic DNA fragments in stimulated macrophages incubated with urea shows that the proliferative actions of urea are associated with a decrease of NO-induced apoptosis.

CONCLUSIONS

Our data demonstrate that the inhibition of iNOS-dependent NO production caused by urea enhances macrophage proliferation as a consequence of diminished NO-mediated apoptosis.

HTK versus UW solution for myocardial protection during moderate hypothermia

The objective of this study was to assess the protective capacity of UW solution in comparison to Bretschneider's (HTK) cardioplegic solution under moderate hypothermic conditions (25 degrees C), as those usually present during intraoperative myocardial protection. Ischemia-induced alterations of cardiac function parameters were analyzed and compared for each solution after 45 min of ischemic storage and 60 min of reperfusion with oxygenated Krebs-Henseleit buffer (KHB), using a rat working-heart model. Compared to nonischemic values, left-ventricular systolic and diastolic pressure, +dp/dtmax and -dp/dtmax were significantly better maintained in the HTK (95 mm Hg, 7 mm Hg, 2,657 mm Hg/s and 2,122 mm Hg/s) than in the UW group (76 mm Hg, p < 0.05, 11 mm Hg, p < 0.05, 1,745 mm Hg/s, p < 0.05 and 1,600 mm Hg/s, p < 0.05). Concerning the myocardial contents of ATP, creatine phosphate and the energy charge, a minor decrease was observed after preservation in HTK compared to UW solution. The results of this study indicate superior myocardial protection with the use of HTK solution for protection of the heart at 25 degrees C compared to UW solution.

Spectrophotometric determination of ascorbic acid and dehydroascorbic acid

We present a method for measuring ascorbic acid in methanol/trichloroacetic acid extracts prepared from human plasma after enzymatic oxidation of ascorbic acid to dehydroascorbic acid by ascorbate oxidase. Samples were assayed by spectrophotometrically monitoring the kinetics of the concentration-dependent absorbance changes of dehydroascorbic acid with phosphate-citrate-methanol buffers. Ascorbic acid was determined as the difference between dehydroascorbic acid and total ascorbic acid content. The detection limit was < 0.5 mumol/L. The calibration curve was linear (r > 0.995) over the range 0-1000 mumol/L. Analytical recovery of ascorbic acid added to plasma was 93-105%. The between-day variance was < 7%. Comparison of the spectrophotometric determination (y) with a chromatographic procedure (x) gave y = 1.02x - 0.653 (Sylx = 3.61) over the range of physiologically relevant concentrations. Total analysis time is < 10 min per sample and allows the simultaneous analysis of multiple samples.

Spectrophotometric determination of ascorbic acid and dehydroascorbic acid

We present a method for measuring ascorbic acid in methanol/trichloroacetic acid extracts prepared from human plasma after enzymatic oxidation of ascorbic acid to dehydroascorbic acid by ascorbate oxidase. Samples were assayed by spectrophotometrically monitoring the kinetics of the concentration-dependent absorbance changes of dehydroascorbic acid with phosphate-citrate-methanol buffers. Ascorbic acid was determined as the difference between dehydroascorbic acid and total ascorbic acid content. The detection limit was &lt; 0.5 mumol/L. The calibration curve was linear (r &gt; 0.995) over the range 0-1000 mumol/L. Analytical recovery of ascorbic acid added to plasma was 93-105%. The between-day variance was &lt; 7%. Comparison of the spectrophotometric determination (y) with a chromatographic procedure (x) gave y = 1.02x - 0.653 (Sylx = 3.61) over the range of physiologically relevant concentrations. Total analysis time is &lt; 10 min per sample and allows the simultaneous analysis of multiple samples.

Echocardiography for teaching cardiac physiology in practical student courses

We have introduced echocardiography into the physiology courses for medical students to improve their understanding of cardiac physiology. Echocardiography allows a visualization of the events of the cardiac cycle and facilitates the correlation of anatomic structures with their physiological functions. The students record views on the human heart in the long and short axis, they follow wall and value motions, and they interpret the obtained data in correlation with electrocardiography and phonocardiography. Echocardiography offers the opportunity to measure the interval of isovolumetric contraction and isovolumetric relaxation and permits the calculation of parameters assigned to left ventricular contractility. An evaluation showed that medical students consider echocardiography to be the most significant and interesting part of the physiology courses. In conclusion, echocardiography has been shown to be a valuable tool for teaching cardiac physiology.

Small bowel tissue high-energy phosphate regeneration after 7 hr of cold ischemic storage: comparison of University of Wisconsin and Eurocollins solutions

As adenine nucleotide content has been shown to correlate with post-transplant function of livers and hearts, it was the aim of our study to investigate the regeneration of rat small bowel tissue high-energy phosphates after 7 hr of cold storage followed by incubation of everted small bowel sacs in normothermic oxygenated KHB for 1 hr. We compared the University of Wisconsin (UW) and the Eurocollins (EC) solutions. Krebs-Henseleit-bicarbonate buffer (KHB) was used to point out the effect of simple cold ischemic storage. After 7 hr of cold storage only small bowel stored in UW and EC solutions retained the capacity for almost total regeneration of ATP necessary for optimal posttransplant function, whereas in the KHB group we found only minimal regeneration. A similar pattern was found for the energy charge. These data support the superiority of UW and EC solutions over simple cold storage in KHB for preservation of small bowel.

Spectrophotometric determination of dehydroascorbic acid in biological samples

We describe a method for accurately and precisely measuring dehydroascorbic acid in perchloric acid extracts prepared from human plasma, lymphocytes, and mammalian cells. Samples were assayed by spectrophotometrically monitoring the kinetics of the concentration-dependent absorbance changes of dehydroascorbic acid with phosphate-methanol-containing buffers. The lowest detectable dehydroascorbate concentration using this assay is estimated to be below 0.1 mumol/liter. Total analysis time is less than 10 min and allows the simultaneous measurement of numerous samples. The calibration curve is linear (r > 0.995) over the range 0-200 mumol/liter. The dehydroascorbic acid concentrations measured in supplemented samples agree with known concentrations. Interference of ascorbic acid and 2,3-diketogulonic acid with this assay was excluded. The correlation with a highly specific chromatographic procedure gave comparable results over the range of physiologically relevant concentrations. The procedure avoids the most commonly applied method of measuring the native ascorbic acid, then reducing the dehydroascorbic acid, and finally measuring the total ascorbic acid and determining dehydroascorbic acid by the difference. Stabilization of ascorbic acid during assay was achieved by addition of desferrioxamine.

Influence of incubated atracurium on rat liver function

Degradation of atracurium by Hofmann elimination and ester hydrolysis depends mainly on pH and temperature and is said to be independent of liver and kidney function. Consequently atracurium is used widely in patients with liver failure. However, there is evidence that incubation of atracurium at 37 degrees C and pH 8 leads to leakage of LDH from hepatocyte cell cultures. We have tested the hepatotoxic effects of incubated atracurium in an isolated perfused rat liver model. After equilibration, atracurium 2010 mumol ml-1 (preincubated at pH 8 and 37 degrees C for 120 min) was administered over a period of 10 min followed by perfusion of Krebs-Henseleit bicarbonate buffer for 60 min. We found that incubation resulted in considerable degradation of atracurium and formation of laudanosine. Administration of incubated atracurium did not produce either biochemical or morphological damage to liver cells, but caused considerable increase in bile flow. We conclude that administration of preincubated atracurium did not produce impairment of liver cell function. The increase in bile flow could be beneficial if it occurs clinically.

Administration of atracurium during reperfusion of rat livers after 21 h of cold ischaemic storage in different solutions

The pharmacokinetics of atracurium are not altered by impaired hepatic function. The drug is therefore used widely in liver transplant patients. In previous work on the hepatotoxic effects of atracurium in an isolated, perfused rat liver model, we could not detect biochemical (release of lactate dehydrogenase or aspartate aminotransferase) or histological evidence of liver cell damage, except a reduction in hepatic tissue ATP content. In the present study, rat livers were reperfused with Krebs-Henseleit bicarbonate buffer with or without atracurium after 21 h of cold ischaemic storage in University of Wisconsin (UW), Bretschneider's HTK or Euro-Collins solution. UW-protected livers showed a complete restoration of ATP, total adenine nucleotides and energy charge during reperfusion, but the addition of atracurium diminished the regeneration capacity to about 50%. The energy charge (an index for determination of liver viability) was also reduced markedly.

Hepatotoxicity testing of atracurium and laudanosine in the isolated, perfused rat liver

The pharmacokinetics of atracurium, which is degraded by Hofmann decomposition and ester hydrolysis, is not altered by impaired liver function. Atracurium should, therefore, be ideal for patients with heptic failure, and is now widely used in clinical practice. However, some studies reported considerable hepatotoxicity after atracurium, especially from its breakdown products--for example, leakage of lactate dehydrogenase (LDH) from isolated rat hepatocytes. Therefore, we have studied, in an isolated perfused rat liver model, biochemical and morphological changes after administration of either atracurium or its main metabolite, laudanosine. Despite using extremely high concentrations of these substances, we could not detect, biochemically (release of LDH or aspartate amino-transferase (AST)) or histologically, any signs of liver cell damage.

Small bowel tissue high-energy phosphate alterations during hypothermic storage using different protecting solutions

Since posttransplant function is closely related to energy status after the storage period, the aim of our study was to determine high-energy phosphates in rat small bowels after 21 h of simple ischemic cold storage using different storage solutions. We compared Eurocollins-solution, Bretschneiders-HTK-solution and a modified University of Wisconsin-solution. After flushing the small bowel both intravascularly and intraluminally with the protecting solution, segments of rat small bowel were stored in the same solution at 4 degrees C for 21 h. Determination of high-energy phosphates by high-performance liquid chromatography were done at indicated times. We found that small bowel stored in Eurocollins-solution produced the best graft viability after 21 h of cold storage by maintaining a sufficient level of high-energy phosphates. The high ATP levels were produced by the pronounced anaerobic glycolysis which was facilitated by the high concentration of glucose in the Eurocollins-solution.

Hepatic energy metabolism during hypothermic storage and reperfusion using different protecting solutions

Effects of 5 cold storage solution on hepatic high energy phosphate metabolism and metabolic function were examined using the isolated perfused rat liver. University of Wisconsin (UW), Euro-Collins (EC), and 2 cardioplegic solutions, Bretschneider's HTK and St. Thomas Hospital solution, were studied for their protective capacity. Krebs-Henseleit bicarbonate buffer (KHB) was used to point out the effect of simple hypothermia. Liver ATP, total adenine nucleotides and energy charge losses were significantly lower during 21 h of storage in UW-preserved livers. Also, only UW-protected livers were able to complete regeneration of ATP and total adenine nucleotides after 1 h of reperfusion, whereas EC, HTK, St. Thomas and KHB stored livers only showed minimal regeneration. Concerning metabolic function, UW protected livers liberated significantly less LDH and sGOT as well in the 21-hour storage solution as into the perfusate under reperfusion conditions. This study demonstrates the capability of UW solution in liver preservation by its ability to maintain and restore high energy phosphates.

A new method for studying the incorporation of nonesterified fatty acids into cardiac lipids by using deuterium-labelled palmitate

A new method for measuring the incorporation of exogenous fatty acids into myocardial lipids of working rat hearts using deuterium-labelled palmitate has been developed. After perfusing isolated hearts, the fatty acid composition of triglycerides, diglycerides, monoglycerides, cholesterol esters, and nonesterified fatty acids (NEFA) was measured by a mass fragmentographic method. Hearts perfused only with 5 mM glucose and 1 mM lactate perfusion as basic substrates showed a significant decrease of triglyceride content, while the other lipids were not found to be significantly reduced. The fatty acid composition of all lipids were not affected. An addition of D31-palmitate complexed to albumin at a molar ratio of 5:1, caused a dose-dependent incorporation into triglycerides and diglycerides which suggested saturation kinetics. The tissue content of nonesterified D31-palmitate was found to be linearly related to its concentration in the perfusate. It may be of note that the concentration of the other NEFA was significantly affected neither by a fatty-acid-free perfusion nor by a perfusion with D31-palmitate. A significant incorporation of the supplied fatty acid into cholesterol esters and monoglycerides could not be detected.

An index for estimation of oxygen consumption in rat heart by hemodynamic parameters

To find a suitable index for the estimation of O2 consumption of rat hearts by use of hemodynamic parameters, isolated hearts were perfused under different working conditions. Coronary flow, arteriovenous O2 difference, cardiac output, and ventricular pressure curve were recorded and continuously fed into a computer. O2 consumption and different hemodynamic parameters such as dP/dtmax, maximum ventricular pressure, pressure-time integral, and heart rate were computed on-line. With the use of these data of 64 different steady states, numerous formulas containing hemodynamic parameters were tested with respect to their ability to predict O2 consumption. The best fit of the data was obtained by a linear combination of the products of rate times dP/dtmax and rate times pressure-time integral of one beat (r = 0.993). Indexes containing approximations of wall stress were not found to improve the predictive ability.

Development of ischemia-induced damage in defined mitochondrial subpopulations

Two mitochondrial subpopulations were isolated from guinea-pig heart by density gradient centrifugation. Under control conditions, both contain functionally intact mitochondria in which ischemic damage develops similarly. However, in one subpopulation adenine nucleotide content, adenine nucleotide translocase activity, oxidative phosphorylation and Ca2+ uptake are a quarter lower than in the other one when related to mitochondrial protein mass. Cytochrome contents and uncoupled electron flux are the same. Changes develop most evidently at the very beginning of ischemia for NAD-linked respiration. When ischemia progresses, cytochromes and the translocator protein are gradually lost or inactivated. Thereupon only partial recovery of mitochondrial function can be obtained after 20 min of reperfusion.

Energy metabolism and enzyme release of cultured adult rat heart muscle cells during anoxia

An intact preparation of adult ventricular muscle cells was incubated in substrate-free, pH-constant, anoxic Tyrode solution. The time course of metabolic changes was found to depend on the relation of cell number to incubation volume: the smaller the volume, the faster anoxic damage develops. Energy needs decline rapidly during anoxia. Yet glycolytic energy production remains insufficient, since it also declines. Glycogenolysis stops after degradation of only half the glycogen present initially. Release of cytosolic enzymes (LDH, MDH) starts with the initial decrease in high-energy phosphates and proceeds correlated to the actual ATP content (r = -0.98) during the stage of reversible cell injury. An ATP content of 2 mumol/g wet wt. marks a critical threshold, below which more and more cells become irreversibly damaged. In the cell culture system, the anoxic process develops similarly to that of the oxygen deficient organ, however prolonged as in arrested hearts.

Relation between enzyme release and metabolic changes in reversible anoxic injury of myocardial cells

Cultured adult cardiac myocytes were exposed to anoxia under substrate-free conditions. When compared to the metabolic changes in the oxygen deficient organ, those in the anoxic cell culture proceed in a similar, yet prolonged manner. Release of cytosolic enzymes starts with minor energetic disturbances and proceeds in close correlation to the actual ATP decay. Below 2 mumol ATP/gww, an increasing number of cells becomes irreversibly damaged, but above, 30 min reoxygenation leads to extensive recovery of the whole preparation. The results indicate that leakage of cytosolic enzymes during the early stage of anoxia is due to a gradual protein release from the individual cells, related to reversible membrane alterations.

Ultrastructure of cultured adult myocardial cells during anoxia and reoxygenation

Cultured heart cells from adult rats were exposed to anoxia in a substrate-free Tyrode's solution at constant pH. In this system the metabolic and the morphologic pattern can be investigated simultaneously. Anoxic changes develop gradually above 2 mumol adenosine triphosphate (ATP)/ gww . Morphometry reveals that the morphologic changes are closely related to the energetic state: creatine phosphate (CP) decay is accompanied by the loss of small mitochondrial matrix granules (r = 0.97). The fall of ATP is coincident with sarcomere shortening (r = 0.95) and, below 4 mumol/ gww , with mitochondrial swelling (r = -0.88). The number of lipid droplets correlates with the ATP level during anoxia and reoxygenation (r = -0.92). The early energetic depletion is accompanied by a moderate release of cytosolic enzymes and morphologic changes: the appearance of sarcolemmal microblebs and an increase in subsarcolemmal vesicles. Below an average ATP level of 2 mumol/ gww an increasing number of individual cells fail to recover when reoxygenated . However, that failure is accompanied neither by massive enzyme release nor by ultrastructural damage regarded as typical for the "oxygen paradox."

Absence of reoxygenation damage in isolated heart cells after anoxic injury

Cultured adult cardiac myocytes were exposed to anoxia under substrate-free conditions and then reoxygenated. When comparing the oxygen deficient organ to the anoxic cell culture, we see that metabolic changes in the latter system proceed in a similar, yet prolonged manner, as in arrested hearts. Release of cytosolic enzymes starts with minor energetic disturbances and proceeds closely correlated to the actual ATP level. Below 2 mumol ATP/gww, an increasing number of cells becomes irreversibly damaged, above this level, 30 min reoxygenation leads to extensive recovery of the whole preparation. The results indicate that leakage of cytosolic enzymes during the early stage of anoxia is due to a gradual protein release from the individual cells and is related to reversible membrane alterations. Reoxygenation does not induce changes considered typical of the 'oxygen paradox'. Since mechanical cell-cell interactions are absent in this model, it is suggested that aggravation of tissue damage in heart tissue reoxygenated late is mainly caused by mechanical forces.

Myocardial fatty acid oxidation: evidence for an albumin-receptor-mediated membrane transfer of fatty acids

Using a computer-assisted working rat heart preparation, which allows continuous registration of the respiratory quotient, it was tested which parameters determine fatty acid oxidation in the myocardium. Supplying albumin and palmitate in different concentrations the rate of fatty acid oxidation was measured. The UFA concentrations were calculated using stepwise equilibrium constants. When keeping constant the NEFA/albumin ratio and raising total NEFA concentration, an increase in fatty acid oxidation was found showing a saturation curve. Increasing NEFA at constant albumin concentration, however, results in a linear increase in fatty acid oxidation. Keeping constant the total NEFA concentration elevation of albumin shows an inhibitory effect. These results suggest the existence of a receptor for albumin on heart cell surface, which mediates uptake of albumin-bound NEFA. An additional supply of glucose and lactate does not show any effect on these relations. Acetate and dichloroacetate, an activator of the pyruvate dehydrogenase, are found to be competitive inhibitors of fatty acid oxidation.

Early enzyme release from myocardial cells is not due to irreversible cell damage

It is often assumed that the release of enzymes from oxygen deficient heart tissue is due to the irreversible damage of myocardial cells. However, because of diffusion barriers and inhomogeneity of oxygen-deficient tissue this hypothesis cannot be proven in heart tissue. The question whether enzyme release may already occur during reversible injury is of considerable relevance in clinical medicine: first, because the amount of released enzyme activity has been used to estimate the mass of damaged tissue in cardiac infarction and, second, because the stress of some diagnostic interventions may lead to cardiac enzyme release, which according to the irreversibility hypothesis would indicate the death of cells in a cell constant organ.

Acyl-carnitine effects on isolated cardiac mitochondria and erythrocytes

The effects of various long-chain acyl-carnitines (AC) on mitochondrial functions and red cell membrane stability were studied. Lower concentrations slightly stimulate respiration-dependent functions such as phosphorylation rate and Ca++ uptake velocity, whereas higher concentrations inhibit these functions with concomitant depression of the ATP/O ratio. The order of effectiveness among the AC is very similar for different mitochondrial functions. The differences among AC in their actions on red cell stability in hypotonic media and their differences in influence on mitochondrial functions exhibit less resemblance. The relative order of erythrolytic concentrations of AC follows the order of their critical micellar concentrations. Model calculations indicate that the concentrations of AC found in ischemic hearts are below those which exhibit inhibitory effects in vitro. Ultrastructural changes in mitochondria incubated with AC are different from those found in ischemic tissue. From this, it seems questionable whether the elevated AC levels in ischemic hearts are indeed as important for the development of membrane damage as is often supposed.

Kinetic analysis of myocardial fatty acid oxidation suggesting an albumin receptor mediated uptake process

The relationship between extracellular albumin and non-esterified fatty acid (NEFA) concentrations and the rate of fatty acid oxidation was studied. The data were obtained from tests performed on a working rat heart. When NEFA concentration was increased the rate of fatty acid oxidation showed a saturation curve at a constant NEFA/albumin ratio. Keeping constant the albumin concentration, a rise in NEFA concentration resulted in a linear increase of fatty acid oxidation. No correlation, however, was found between fatty acid oxidation and the unbound fraction of fatty acids. These results suggest an albumin receptor mediated NEFA uptake. With this assumption the following rate law of the NEFA uptake was derived: UPT = UPT0 X [FA]/(Km + [ALB] ) where [FA] and [ALB] are the total NEFA- and albumin concentrations, UPT0 and Km are constants. The rates of oxidation computed with this equation show a very good congruence to the values obtained experimentally. The validity of the rate law is confirmed by the fact that it is shown to be in agreement to the results of other investigators.

Temperature dependence of nifedipine action

Recently, the use of calcium antagonists has been proposed as a new cardioplegic principle. At high doses (e.g. 10(-6)M nifedipine [3]) these drugs can be used for induction of reversible cardiac arrest. Apart from their effect on coronary flow, calcium antagonists seem to be beneficial to ischemic tissue because of their negative inotropic effect at high doses [6, 9]. Ionic cardioplegic solutions are commonly used in an advantageous combination with hypothermia. In the case of calcium antagonists, there is an indication that the specific cardioprotective effect is lessened at low temperatures [3]. Nifedipine is known to reduce contraction force without abolishing the generation of action potentials even at excessive doses [2]. To quantify the suppressing effect of nifedipine on the generation of contractions, we determined the maximal possible contraction frequency (Fm) under electrical stimulation at different temperatures. In isolated myocardial cells, Fm can be determined from the cell contour movements even with an almost complete force reduction and therefore it represents a measure for effective contractile refractoriness.

Morphological dedifferentiation of adult cardiac myocytes in coculture with hepatocytes

When adult heart cells are plated on a dish covered with a monolayer of hepatocytes gradual morphological changes are observed. While during the first day the myofibrils are still organized in rod-like shape, later the cells become flat and spread on top of underlying hepatocytes. After two days most cells have a flat, polygonal appearance with spread myofibrillar bundles. At this stage they start spontaneous rhythmic contractions which are characteristic for embryonic myocytes, but not for isolated adult ventricular cells. In this culture myocytes form specific contact structures to adjacent myocytes as well as to hepatocytes. These results demonstrate the phenotypical plasticity of adult heart muscle cells which are believed to be terminally differentiated.

Anoxic injury of adult cardiac myocytes

Cultured adult cardiocytes were exposed to anoxia. The initial decrease of high-energy phosphates was accompanied by a moderate release of cytosolic enzymes and morphological changes: the appearance of sarcolemmal 'microblebs' (approximately 1 micron in diameter) and an increase of subsarcolemmal vesicles. At ATP levels above 2 mumol/gww, metabolic and morphological alterations were reversible. Probably the sarcolemmal changes are causally related to the loss of macromolecules from reversibly injured cells. At ATP levels below 2 mumol/gww, an increasing number of cells become irreversibly hypercontracted. In these cells cytoplasmic masses are protruded into large 'macroblebs' (10-30 micron in diameter), however sarcolemmal continuity is preserved. Thus, enzyme release, irreversible contracture and cytolysis do not occur simultaneously in anoxic isolated cardiocytes.

Temperature dependence of verapamil action

Ca2+-tolerant ventricular myocytes from adult rats were electrically stimulated. The maximal contraction frequency (fm) was determined at different temperatures. In drug-free Tyrode solution, fm follows the Arrhenius equation from 7 to 39.5 degrees C. However, verapamil introduces a discontinuity around 27 degrees C into the Arrhenius plot of fm. Above this transition temperature the calcium antagonist lowers fm more pronouncedly than below. Below, a tenfold higher concentration is needed for the same relative effect as at 37 degrees C. It is argued that this finding might be important in cardiac surgery when calcium antagonists are used for cardioplegia at deep hypothermia.