Biomedical subjects

S Schaefer

Publications and source records attributed to S Schaefer.

At least 19 recordsLinked to original sources

PubMed1997

Blockade of K(ATP) channels with glibenclamide does not abolish preconditioning during demand ischemia.

The role of adenosine triphosphate-sensitive potassium channels in the adaptive response to demand ischemia was tested in 22 patients treated with placebo or glibenclamide before sequential exercise testing or atrial pacing. Glibenclamide did not affect the improvement in signs of ischemia in both protocols, indicating that opening of these channels is not a mechanism of this adaptive response in humans.

Adaptation, Physiological↗

PubMed1997

Aldose reductase inhibition protects diabetic and nondiabetic rat hearts from ischemic injury.

Diabetes increases the incidence of cardiovascular disease as well as the complications of myocardial infarction. Studies using animal models of diabetes have demonstrated that the metabolic alterations occurring at the myocyte level may contribute to the severity of ischemic injury in diabetic hearts. Of the several mechanisms being investigated to understand the pathogenesis of diabetic complications, the increased metabolism of glucose via the polyol pathway has received considerable attention. Deviant metabolic regulation due to increased flux through aldose reductase in diabetic hearts may influence the ability of the myocardium to withstand ischemia insult. To determine if aldose reductase inhibition improves tolerance to ischemia, hearts from acute type I diabetic and nondiabetic control rats were isolated and retrograde perfused. Each group was exposed to 1 micromol/l zopolrestat, a specific inhibitor of aldose reductase, for 10 min, followed by 20 min of global ischemia and 60 min of reperfusion in the absence of zopolrestat. Zopolrestat reduced sorbitol levels before ischemia in diabetic hearts. The cytosolic redox state (NADH/NAD+), as measured by lactate-to-pyruvate ratios, was significantly lowered under baseline, ischemic, and reperfusion conditions in diabetic hearts perfused with zopolrestat. In these diabetic hearts, ATP was significantly higher in zopolrestat hearts during ischemia, as were phosphocreatine and left ventricular-developed pressure on reperfusion. Zopolrestat provided similar metabolic and functional benefits in nondiabetic hearts. Creatine kinase release was reduced by approximately 50% in both nondiabetic and diabetic hearts treated with zopolrestat. These data indicate that inhibition of aldose reductase activity preserves high-energy phosphates, maintains a lower cytosolic NADH/NAD+ ratio, and markedly protects both diabetic and nondiabetic hearts during ischemia and reperfusion.

Adenosine Triphosphate↗

PubMed1996

Cardiac aspergillosis presenting as myocardial infarction.

Immunosuppression can allow organisms which are not usually pathogenetic to cause disease. Invasive fungal disease is becoming increasingly prevalent because of the growing numbers of patients who are immunosuppressed. Aspergillus species frequently form large masses of fungal elements, thrombin, and fibrin, within the vasculature. These masses can then embolize, leading to organ infarction. Reported herein is a case of aspergillosis invading the myocardium and causing widespread necrosis and infarction. Although the epicardial coronary arteries were free of disease, the patient ultimately died in cardiogenic shock.

Adult↗

PubMed1996

Quantitative assay of PCR-amplified hepatitis B virus DNA using a peroxidase-labelled DNA probe and enhanced chemiluminescence.

We have developed a sensitive and quantitative assay for hepatitis B virus (HBV) DNA in serum or plasma in which PCR and then microtiter hybridization analysis are used. Assay of HBV DNA in serum or plasma is important for demonstrating viral replication, indicating and monitoring antiviral therapy, determining the infectivities of virus carriers, and ensuring the safety of blood products. Under optimum conditions PCR can amplify one HBV DNA molecule to 10(8) copies, but detection of this amount of DNA still requires hybridization with labelled probes or a nested PCR. We labelled one strand of the PCR product with a biotinylated primer. The double-stranded amplicon was incubated in streptavidin-coated microplate wells. The nonlabelled strand was removed after denaturation of the double-stranded DNA with alkali, and the bound strand was hybridized with a peroxidase-coupled single-stranded probe. The amount of bound peroxidase was measured in a luminometer. Four picograms of amplicon was detectable in this system, whereas conventional ethidium bromide staining requires a 1,000 times higher amplicon concentration. The performance of the new assay was compared with those of nested PCR and a PCR system that uses a digoxigenin label, hybridization to a solid-phase adsorbed probe, and colorimetric detection. The chemiluminescence assay was found to be almost as sensitive as nested PCR and approximately five times more sensitive than the colorimetric test.

Bacterial Proteins↗

PubMed1996

Cardiac reflex effects of intracoronary bradykinin in humans.

BACKGROUND: Endogenous production of bradykinin (BK) has been postulated to cause hemodynamic changes and cardiac pain during myocardial ischemia, presumably because of the stimulation of cardiac afferent fibers. METHODS: To test the hypothesis that BK results in cardiac reflex responses and can cause the sensation of angina, 10 patients with and without coronary atherosclerosis had BK injected into their right (RCA) and left (LCA) coronary arteries in graded concentrations up to 10(-5) m. Patients were monitored for hemodynamic changes and the presence and quality of pain. RESULTS: Intracoronary BK 10(-5) m caused a significant reduction in blood pressure in most patients with either injection into the RCA or LCA (RCA: 151 +/- 10/90 +/- 5 mm Hg to 119 +/- 11/70 +/- 6 mm Hg, LCA: 161 +/- 11/88 +/- 6 mm Hg to 118 +/- 10/65 +/- 6 mm Hg) that began 12 to 14 seconds after injection. Injection into the LCA also resulted in a significant increase in heart rate (69 +/- 4 to 81 +/- 7 beats/minute), while injection into the RCA did not. Pain occurred after changes in blood pressure in all but one patient, which was present in 5 of 9 patients with RCA injection and 8 of 9 patients with LCA injection, and was often associated with flushing and nausea. Pain caused by BK was not similar to previous clinical ischemic pain in the patients with coronary atherosclerosis. CONCLUSIONS: The absence of a chronotropic response associated with arterial hypotension following injection of BK into the RCA is consistent with activation of cardiac vagal afferents in the left ventricle. The latency and quality of pain in these patients following injection of BK suggests that, while BK is nociceptive, it likely is not the cause of angina in patients with myocardial ischemia.

Adult↗

PubMed1995

Determination of the origin cleavage and joining domain of geminivirus Rep proteins.

Replication of the single-stranded DNA genome of plant geminiviruses follows a rolling circle mechanism. It strictly depends on a 'rolling circle replication initiator protein', the M(r) 41 kDa viral Rep protein, encoded by the C1 or AC1 genes. Using wheat dwarf virus (WDV) and tomato yellow leaf curl virus (TYLCV) as examples, we show that not only the full-size Rep proteins, but also a putative 30 kDa translation product of WDV open reading frame C1-N as well as an artificially shortened 24 kDa Rep of TYLCV, cleave and join single-stranded origin DNA in vitro. Thus the pivotal origin recognition and processing activities of geminivirus Rep proteins must be mediated by the amino-terminal domain of Rep.

Amino Acid Sequence↗

PubMed1995

Myocardial high-energy phosphate and substrate metabolism in swine with moderate left ventricular hypertrophy.

BACKGROUND: Although left ventricular hypertrophy (LVH) is frequently associated with impaired coronary vasodilator reserve, it is uncertain whether this leads to myocardial ischemia under physiological conditions. The goal of the present study was to determine whether swine with moderate LVH exhibit metabolic evidence of ischemia when myocardial oxygen requirements are increased. METHODS AND RESULTS: Myocardial metabolism was evaluated in an open-chest anesthetized preparation at baseline and during dobutamine infusion in 13 adolescent pigs with moderate LVH induced by supravalvular aortic banding and 12 age-matched control pigs. Transmural myocardial blood flow was quantified with radioactive microspheres; the ratio of phosphocreatine to ATP (PCr/ATP) in the anterior LV free wall was measured by 31P-nuclear magnetic resonance; and anterior wall lactate release was quantified from the arterial-coronary venous difference in 14C- or 13C-labeled lactate. In a subset of 5 animals from each group, the metabolic fate of exogenous glucose was determined from the transmyocardial difference in 6-14C-glucose and its metabolites 14C-lactate and 14CO2. Coronary reserve, as assessed by the ratio of blood flow during adenosine infusion to baseline blood flow, was significantly lower in the LVH pigs compared with controls (3.5 +/- 0.4 versus 5.5 +/- 0.4 mL/g.min, P < .05); however, transmural myocardial blood flow was similar in both groups of pigs, both at baseline and with dobutamine stimulation, probably reflecting the higher coronary perfusion pressure in the LVH pigs. At baseline, PCr/ATP tended to be lower in the LVH pigs (P = .09) but decreased similarly with dobutamine infusion in both groups. Isotopically measured anterior wall lactate release did not differ between the groups at baseline, nor did the increase in lactate release differ during dobutamine stimulation. The uptake of glucose, lactate, and free fatty acids did not differ between the groups in the basal state. However, during dobutamine stimulation, glucose uptake was greater in the LVH group (0.84 +/- 0.09 mumol/g.min versus 0.59 +/- 0.08 mumol/g.min, P < .05). In a subset of animals, 14C-glucose was used to assess glucose oxidation. These data showed that the LVH animals had a greater rate of glucose oxidation (0.6 +/- 0.10 versus 0.28 +/- 0.08 mumol/g.min, P < .05) and a greater rate of glucose conversion to lactate (0.20 +/- 0.04 versus 0.09 +/- 0.02 mumol/g.min, P < .05) compared with the control pigs. CONCLUSIONS: These results suggest that despite their reduced coronary vasodilator reserve and the absence of a greater rise in myocardial blood flow to compensate for a substantially higher LV double product, pigs with this model of moderate LVH do not exhibit a greater susceptibility to myocardial ischemia during dobutamine stress. However, LVH pigs exhibit significantly greater use of exogenous glucose during dobutamine stress, as evidenced by increases in both glucose oxidation and anaerobic glycolysis.

Adenosine Triphosphate↗

PubMed1995

A low incidence of p53 mutations in pre-malignant lesions of the oral cavity from non-tobacco users.

To determine the incidence of p53 mutations in pre-malignant lesions of the oral cavity from individuals without prior history of tobacco use, we have analyzed the conserved regions of the p53 gene (exons 5-9) in archival oral cavity lesion specimens obtained from patients with varied tobacco use histories, by polymerase chain reaction/single strand conformational polymorphism (PCR/SSCP) and DNA sequencing analysis. Twenty-six lesions were analyzed from 14 patients, with multiple lesions obtained from 8 patients. Six of these patients used tobacco, (3 being cigarette smokers, 1 ex-cigarette smoker, 1 moderate cigar smoker and 1 snuff chewer). The remaining 8 patients had no prior history of tobacco use. Thirteen of the pre-malignant lesions exhibited severe dysplasia, 9 exhibited moderate dysplasia and 4 exhibited mild dysplasia. Four of the 26 lesions exhibited p53 mutations, each being from a tobacco user. None of the 13 lesions from never-tobacco users exhibited p53 mutations. There was a significantly higher p53 mutation incidence in pre-malignant lesions from tobacco users (including ex-smokers) than in non-tobacco users as well as in cigarette smokers plus snuff chewers than in non-tobacco users. Two of the mutations were observed in lesions exhibiting severe dysplasia: 1 in a lesion exhibiting moderate dysplasia and 1 in a lesion exhibiting mild dysplasia. These data suggest that p53 mutation may be a very early event in oral cavity tumor progression and demonstrate that pre-malignant lesions obtained from non-tobacco users do not exhibit p53 mutations.

Adult↗

PubMed1995

Requirement of glycolytic substrate for metabolic recovery during moderate low flow ischemia.

Low flow ischemia with stable hemodynamic function can result in partial metabolic recovery characterized by an increase in phosphocreatine (PCr). Prior data suggest that glycolytic production of adenosine triphosphate (ATP) may be critical for this recovery and that the ATP produced by oxidative phosphorylation alone may be insufficient. This study tested the hypotheses that, during moderate low flow ischemia, (a) metabolic recovery is dependent on glycolytic production of ATP, and, therefore, (b) a mitochondrial substrate such as pyruvate alone is inadequate to allow metabolic recovery. High energy phosphates, pH, and lactate release were measured during 2 h of moderate low flow ischemia. Hearts were perfused with either a glycolytic plus mitochondrial substrate (glucose, insulin and pyruvate) or a mitochondrial substrate alone (pyruvate). Flow reductions required to reduce PCr by approximately 8% resulted in stable and equal reductions of rate-pressure product in each group. PCr recovered fully during the ischemic period in control hearts with glycolytic substrate, associated with preservation of normal end-diastolic pressure, and increased lactate release during the first hour of ischemia. Reperfusion of these hearts restored hemodynamic function and increased PCr above baseline values. In contrast, the use of pyruvate alone as a substrate resulted in a progressive fall of PCr during ischemia, increased end-diastolic pressure, and no significant increase in lactate release. Reperfusion in these hearts restored hemodynamic function, but did not result in normalization of PCr. Both groups had significant reductions in ATP during ischemia. Recovery of PCr during ongoing moderate low flow ischemia is observed in the presence of mixed glycolytic and mitochondrial substrates (glucose, insulin and pyruvate) but is not observed with pyruvate as a sole mitochondrial substrate. These data support a critical role for glycolytic flux under these conditions, suggesting that ATP generated solely by oxidative phosphorylation is not sufficient to promote metabolic recovery or maintain diastolic function during moderate low flow ischemia.

Adenosine Diphosphate↗

PubMed1995

Effects of glycogen depletion on ischemic injury in isolated rat hearts: insights into preconditioning.

Limitation of myocardial injury and infarction has been demonstrated by interventions such as ischemic preconditioning or the use of pyruvate as a substrate, which reduces glycogen content before, and acidosis during, ischemia. An isolated perfused rat heart model of global ischemia was employed to test the hypothesis that glycogen depletion reduces ischemic injury as measured by creatine kinase release. 31P-nuclear magnetic resonance spectroscopy was used to measure high-energy phosphates (ATP and phosphocreatine), phosphomonoesters (PME), and intracellular pH. Compared with control glucose-perfused hearts with normal glycogen content (1.49 +/- 0.13 mg Glc/g wet wt), glycogen-depleted pyruvate, ischemic preconditioned, and glycogen-depleted glucose hearts all had reduced glycogen content before ischemia (0.62 +/- 0.16, 0.81 +/- 0.10, and 0.67 +/- 0.12 mg Glc/g wet wt, respectively; P = 0.003) and significantly higher pH at the end of ischemia (5.85 +/- 0.02, 6.33 +/- 0.06, 6.24 +/- 0.04, and 6.12 +/- 0.02 in control, glycogen-depleted pyruvate, preconditioned, and glycogen-depleted glucose-perfused hearts, respectively; P < 0.01), although acidification during the initial phase of ischemia was differentially affected by the three interventions. Glycogen-depleted pyruvate and preconditioned hearts had reduced PME accumulation, greater recovery of function and phosphocreatine, and lower creatine kinase release on reperfusion, whereas glycogen-depleted glucose-perfused hearts were similar to control hearts. In summary, glycogen depletion by these three methods limits the fall in pH during global ischemia, although glycogen depletion in the absence of preconditioning does not limit ischemic injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1995

In vitro transformation by hepatitis B virus DNA.

There is strong epidemiological evidence that the hepatitis B virus (HBV) contributes to the development of hepatocellular carcinoma (HCC). In several immortalized cell lines, an in vitro transforming activity of HBV DNA and expression vectors for the viral protein X (HBx) has now been demonstrated. Furthermore, it appears as if still unknown parts of the HBV genome other than HBx contribute to the transforming activity of HBV DNA in vitro. Only one of several studies found that HBx-transgenic mouse lines develop HCC. A mouse line transgenic for the large surface protein of HBV develops HCC due to concomitant necroinflammatory infection. Growing evidence shows the importance of recombination of integrated viral DNA and cellular DNA for HCC development. A direct transforming potential of one of these viral integrates has been demonstrated. Chemical carcinogens are more effective in HBV-containing cell lines or transgenic mice.

Animals↗

PubMed1995

Ischemic preconditioning stimulates sodium and proton transport in isolated rat hearts.

One or more brief periods of ischemia, termed preconditioning, dramatically limits infarct size and reduces intracellular acidosis during subsequent ischemia, potentially via enhanced sarcolemmal proton efflux mechanisms. To test the hypothesis that preconditioning increases the functional activity of sodium-dependent proton efflux pathways, isolated rat hearts were subjected to 30 min of global ischemia with or without preconditioning. Intracellular sodium (Nai) was assessed using 23Na magnetic resonance spectroscopy, and the activity of the Na-H exchanger and Na-K-2Cl cotransporter was measured by transiently exposing the hearts to an acid load (NH4Cl washout). Creatine kinase release was reduced by greater than 60% in the preconditioned hearts (P < 0.05) and was associated with improved functional recovery on reperfusion. Preconditioning increased Nai by 6.24 +/- 2.04 U, resulting in a significantly higher level of Nai before ischemia than in the control hearts. Nai increased significantly at the onset of ischemia (8.48 +/- 1.21 vs. 2.57 +/- 0.81 U, preconditioned vs. control hearts; P < 0.01). Preconditioning did not reduce Nai accumulation during ischemia, but the decline in Nai during the first 5 min of reperfusion was significantly greater in the preconditioned than in the control hearts (13.48 +/- 1.73 vs. 2.54 +/- 0.41 U; P < 0.001). Exposure of preconditioned hearts to ethylisopropylamiloride or bumetanide in the last reperfusion period limited in the increase in Nai during ischemia and reduced the beneficial effects of preconditioning. After the NH4Cl prepulse, preconditioned hearts acidified significantly more than control hearts and had significantly more rapid recovery of pH (preconditioned, delta pH = 0.35 +/- 0.04 U over 5 min; control, delta pH = 0.15 +/- 0.02 U over 5 min). This rapid pH recovery was not affected by inhibition of the Na-K-2Cl cotransporter but was abolished by inhibition of the Na-H exchanger. These results demonstrate that preconditioning alters the kinetics of Nai accumulation during global ischemia as well as proton transport after NH4Cl washout. These observations are consistent with stimulation of the Na-K-2Cl cotransporter and Na-H exchanger by preconditioning.

Ammonium Chloride↗

PubMed1994

Effects of regional myocardial lidocaine infusion on high energy phosphates.

High energy phosphates [phosphocreatine (PCr) and adenosine triphosphate (ATP)] are maintained in the heart under conditions of altered myocardial contractility and under certain conditions of maintained in the heart under conditions of altered myocardial contractility and under certain conditions of myocardial ischemia (such as hibernating myocardium). However, the metabolic consequences of reduced regional contractility have not been investigated. This study was designed to test the hypotheses that (1) under conditions of normal blood flow, reduction in regional contractility does not result in changes in PCr or ATP and (2) under conditions of reduced blood flow, reduction in regional contractility prevents the expected decline in high energy phosphates usually seen in regional ischemia. An in situ open chest swine preparation was used in which regional contractility was reduced with the administration of intracoronary lidocaine. High energy phosphates were measured using phosphorus-31 magnetic resonance spectroscopy (NMR) under conditions of normal flow and reduced flow. Intracoronary lidocaine infusion in 9 animals did not change blood flow from basal levels, but significantly reduced regional segment shortening from 0.16 +/- 0.02 to 0.02 +/- 0.01. The ratio of PCr/ATP did not change with lidocaine infusion (control: 1.53 +/- 0.09; lidocaine: 1.59 +/- 0.11), but oxygen content in the anterior interventricular vein increased from 8.25 +/- 0.69 to 9.83 +/- 0.91 ml/O2/100 ml blood in parallel studies (P = 0.04). While the lidocaine infusion was maintained, subsequent coronary stenosis significantly reduced subendocardial blood flow from 0.91 +/- 0.06 to 0.41 +/- 0.06 ml/min/g without significantly altering high energy phosphates (PCr/ATP = 1.51 +/- 0.15). In contrast to the 29% decline in PCr previously seen with regional ischemia, PCr was unchanged with this degree of flow reduction in the presence of lidocaine. Thus, PCr and ATP are unchanged under conditions of reduced contractility, consistent with equilibrium of energy synthesis and utilization. In addition, factors which reduce myocardial contractility, either pharmacologically or endogenously, protect against the metabolic consequences of reduced flow by reducing MVO2.

Adenosine Triphosphate↗

PubMed1994

Balloon mitral valvulotomy as a bridge to valve replacement.

Balloon mitral valvulotomy is used in treating mitral stenosis. We stabilized a near-moribund patient who had combined aortic and mitral valve stenoses with this technique on an emergency basis. Following valvulotomy, mitral valve area increased from 1.1 to 2.2 cm2, pulmonary capillary wedge pressure decreased from 31 to 21 mmHg, and cardiac index increased from 1.9 to 2.8 L/min/m2. When the patient's condition improved, we replaced the aortic and mitral valves with St. Jude Medical bileaflet prostheses. Balloon mitral valvulotomy has not been previously described as a "bridge" to operation. The patient in this report was at extremely high risk with cardiopulmonary and hepatorenal failure, and is the first where valvulotomy was used as temporary rather than definitive management. It should be considered only in cases without calcified, fibrotic valves and where the operative risk is considered prohibitive.

Adult↗

PubMed1993

Identification of the initiation sequence for viral-strand DNA synthesis of wheat dwarf virus.

The intergenic region of the circular single-stranded DNA genome of geminiviruses contains a sequence potentially able to fold into a stem-loop structure. This sequence has been reported to be involved in viral replication by serving as the origin for rolling-circle replication. However, in wheat dwarf virus (WDV) a deletion of 128 bp, removing this sequence, surprisingly does not prevent de novo viral DNA synthesis, but instead abrogates the processing of replicative intermediates into monomeric genomes. This deletion mutant permitted us to study the initiation of viral-strand DNA synthesis independently from its termination and also to identify the sequence within which rolling-circle DNA replication of WDV begins. We have mapped the initiation site of replication to a pentanucleotide, TACCC, a sequence that occurs twice in the large intergenic region of WDV: it is found in the right half of the stem-loop sequence and again 170 bases upstream where it is part of a 15 nucleotide sequence highly homologous to the right half of the stem-loop sequence. Here we show that viral-strand DNA synthesis efficiently initiates at both sequences.

Base Sequence↗

PubMed1993

Plasma catecholamine concentrations during abdominal aortic aneurysm surgery: the link to perioperative myocardial ischemia.

Cardiac disease continues to be the leading cause of morbidity and mortality following peripheral vascular surgical procedures. Although the mechanism of sudden myocardial infarction remains elusive, many possibilities exist. The role of catecholamines is intriguing in view of the evidence that beta-adrenergic blockers reduce cardiac morbidity and mortality in vascular surgical patients. To ascertain whether the plasma catecholamine levels rise significantly during abdominal aortic aneurysm repair, serial determinations of plasma epinephrine and norepinephrine levels were performed in 18 patients. Epinephrine levels rose significantly from preoperative baseline values both during the operation and postoperatively, and norepinephrine levels rose significantly at 24 hours postoperatively. Although only one patient studied developed a myocardial infarction, the finding that patients undergoing aortic surgery uniformly experienced abnormally high serum catecholamine levels supports other evidence that perioperative myocardial ischemic events have a hormonal component.

Aortic Aneurysm, Abdominal↗

PubMed1993

The conserved nonanucleotide motif of the geminivirus stem-loop sequence promotes replicational release of virus molecules from redundant copies.

Recombinant plasmids containing head-to-tail copies of different coat-protein replacement genomes of wheat dwarf virus (WDV) were used to study the mechanism leading to the release of replicating unit-length molecules in suspension culture cells of Triticum monococcum. For plasmids bearing two complete genomes, the viral unit bracketed by the two large intergenic regions (LIR) becomes preferentially released. Addition of a third copy of the LIR on the inoculum plasmid is necessary for release of both WDV genomes with the same efficiency. Using plasmids containing a single viral genome flanked by two different hybrid LIRs, we show that the sequence TAATATTA, which is part of the conserved geminivirus nonanucleotide motif of the potential hairpin structure, is the region of the LIR within which the release of unit-length molecules occurs. Moreover, the data suggest that this release results primarily from rolling-circle replication, also in situations where intramolecular homologous recombination is simultaneously possible.

Base Sequence↗

PubMed1993

Myocardial adaptation during acute hibernation: mechanisms of phosphocreatine recovery.

OBJECTIVES: Acute hibernation, defined as a prolonged period of moderately reduced oxygen supply and stable haemodynamic function, results in metabolic adaptation characterised primarily by an increase in phosphocreatine. The mechanism of this increase in phosphocreatine is unknown, but has been postulated to result from either an increase in adenosine triphosphate (ATP) production or a decrease in ATP utilisation under conditions of constant myocardial oxygen consumption (MVO2). These experiments were performed to test the hypotheses that (1) acute hibernation could be modelled in an isolated perfused rat heart exhibiting metabolic adaptation; and (2) recovery of phosphocreatine could be explained by alterations in relative creatine kinase flux during hibernation. METHODS: Nuclear magnetic resonance techniques were used in an isolated, perfused rat heart model of acute hibernation to determine the changes in metabolites and creatine kinase kinetics. A flow reduction from 12.5 to 5.4 ml.min-1 was employed for two hours, followed by reperfusion. RESULTS: Reduction of flow resulted in a stable 44% reduction in rate-pressure product. Phosphocreatine had a significant decrease of 9% within the first 15 minutes of ischaemia, but recovered to control values by the end of ischaemia. ATP and [ADP], although unchanged in the early phase of ischaemia, were progressively reduced during the later phase of ischaemia. Intracellular pH fell from 6.99(0.04) to 6.92(0.03) after 15 minutes of ischaemia with little recovery. Saturation transfer measurements showed stability of the forward flux in the creatine kinase reaction during ischaemia, but a progressive reduction in the calculated reverse flux. CONCLUSIONS: These data show that acute hibernation can be modelled in an isolated perfused heart, exhibiting recovery of phosphocreatine despite progressive reductions in ATP. Metabolic changes during acute hibernation have a phasic response characterised by an early ischaemic phase and a later adaptive phase. There is a time related change in measured creatine kinase flux, consistent with a differential change in either ATP production via an increase in MB creatine kinase isoenzyme or a shift in the activity of mitochondrial v cytosolic creatine kinase, a reduction in ATP utilisation via increased efficiency of ATP utilisation at the myofibril, or a changing contribution of glycolytically produced ATP.

Adenosine Diphosphate↗