Quadriceps and hamstring muscle activity during cycling as measured with intramuscular electromyography.

PURPOSE: The aim of this study was to describe thigh muscle activation during cycling using intramuscular electromyographic recordings of eight thigh muscles, including the biceps femoris short head (BFS) and the vastus intermedius (Vint). METHODS: Nine experienced cyclists performed an incremental test (start at 170 W and increased by 20 W every 2 min) on a bicycle ergometer either for a maximum of 20 min or to fatigue. Intramuscular electromyography (EMG) of eight muscles and kinematic data of the right lower limb were recorded during the last 20 s in the second workload (190 W). EMG data were normalized to the peak activity occurring during this workload. Statistical significance was assumed at p ≤ 0.05. RESULTS: The vastii showed a greater activation during the 1st quadrant compared to other quadrants. The rectus femoris (RF) showed a similar activation, but with two bursts in the 1st and 4th quadrants in three subjects. This behavior may be explained by the bi-articular function during the cycling movement. Both the BFS and Vint were activated longer than, but in synergy with their respective agonistic superficial muscles. CONCLUSION: Intramuscular EMG was used to verify muscle activation during cycling. The activation pattern of deep muscles (Vint and BFS) could, therefore, be described and compared to that of the more superficial muscles. The complex coordination of quadriceps and hamstring muscles during cycling was described in detail.

High levels of cathepsins B, L and S in human seminal plasma and their association with prostasomes.

Semen is a heterogenous and complex fluid with different functions, some of them well known, others still obscure. The aim of this study was to investigate the presence of cathepsins B, S and L in human seminal plasma and their possible associations with other semen variables. Cathepsin B, L and S concentrations were measured in seminal plasma from 99 men utilising commercial ELISA kits. Seminal plasma cathepsin B was approximately 70 times higher, while the cathepsin L values were approximately 500 times higher and the cathepsin S values approximately 40 times higher in seminal plasma than in a group of serum samples. The study shows that seminal plasma contains high levels of cathepsins B, L and S. All three cathepsins were also bound to the surface of prostasomes.

Prostasomes are mediators of intercellular communication: from basic research to clinical implications.

Prostasomes are nanosized microvesicles secreted by acinar epithelial cells of the prostate gland. Furthermore, they are intracellular microvesicles inside another larger vesicle, a so-called storage vesicle, equivalent to multivesicular bodies of late endosomal origin. Prostasomes are thought to play an important role in intercellular communication by direct interaction primarily between the immobile acinar cells of the prostate gland and the mobile spermatozoa. Prostasomes transfer not only membrane components but also genetic material to spermatozoa. They are rich in various transferable bioactive molecules (e.g., receptors and enzymes) that promote the fertilizing ability of spermatozoa. In this review, the pleiotropic biological effects of prostasomes that are relevant for successful fertilization will be discussed. The ability to synthesize and export prostasomes to the extracellular space is observed not only in normal prostate epithelial cells but also in malignant prostate cells. Release of prostasomes by prostate cancer cells suggests a role in malignant cell growth and proliferation. These findings may provide new therapeutic and diagnostic strategies.

Association of cystatin C with prostasomes in human seminal plasma.

It was recently elucidated that cystatin C, a protein targeted to the classical secretory pathway by its signal peptide sequence, can also be secreted in association with exosomes. Accordingly, we wanted to investigate whether there is a secretory link between cystatin C and prostasomes in human seminal plasma. Cystatin C concentrations in seminal plasma from 50 men including 6 vasectomized men were measured by turbidimetry on an Architect Ci8200. Some of the seminal plasma samples were also analysed utilizing an Epics Profile XL-MCL cytometer. We found high concentrations of cystatin C in seminal plasma. The 2.5-97.5 percentiles, performed by bootstrap estimation, were 25.8 [95% confidence interval (CI): 22.3-29.4] to 77.0 mg/L (95% CI: 71.9-82.1). Cystatin C is present in approximately 50 times higher concentration in seminal plasma compared with blood plasma. There was no clear difference as regards seminal plasma content of cystatin C between vasectomized men and the rest of the group. Immunoblot analysis with chicken anti-cystatin C antibody revealed a firm association of cystatin C with prostasomes. Flow cytometric analysis demonstrated that cystatin C was linked to prostasomes also meaning an at least partial prostasomal membrane surface localization.

Ischaemic pre-conditioning means an increased adenosine metabolism with decreased glycolytic flow in ischaemic pig myocardium.

BACKGROUND: Ischaemic pre-conditioning (IP) is a potent protective mechanism for limiting the myocardial damage due to ischaemia. It is not fully known as to how IP protects. The metabolism of adenosine may be an important mechanistic component. We study the role of adenosine turnover together with glycolytic flow in ischaemic myocardium subjected to IP. METHODS: An acute myocardial ischaemia pig model was used, with microdialysis sampling of some metabolites (lactate, adenosine, glucose, glycerol, taurine) of ischaemic myocardium. An IP group was compared with a control group before and during a prolonged ischaemia. ¹4C-labelled adenosine and glucose were infused through microdialysis probes, and lactate, ¹4C-labelled lactate, glucose, taurine and glycerol were analysed in the effluent. The glycogen content in myocardial biopsies was determined. RESULTS: The ¹4C-adenosine metabolism was higher as there was a higher production of ¹4C-lactate in IP animals compared with the controls. The glycolytic flow, measured as myocardial lactate formation, was retarded during prolonged ischaemia in IP animals. Myocardial free glucose and glycogen content decreased during the prolonged ischaemia in both groups, with higher free glucose in the IP group. We confirmed the protective effects of IP with lower myocardial concentrations of markers for cellular damage (glycerol). CONCLUSIONS: This association between increased adenosine turnover and decreased glycolytic flow during prolonged ischaemia in response to IP can possibly be explained by the competitive effect for the metabolites from both glucose and adenosine metabolism for entering glycolysis. We conclude that this study provides support for an energy-metabolic explanation for the protective mechanisms of IP.

Ischaemic preconditioning is related to decreasing levels of extracellular adenosine that may be metabolically useful in the at-risk myocardium: an experimental study in the pig.

AIM: 'Pre-treatment' with short repetitive periods of ischaemia (ischaemic preconditioning) has proved to be a powerful mechanism for modification of the extent of myocardial damage following acute coronary artery occlusion. The exact mechanism of protection induced by ischaemic preconditioning is not known. We herewith put forward a contributing component for protection with preconditioning involving a shift in the adenylate kinase (AK) equilibrium reaction in favour of adenosine triphosphate (ATP) formation. METHODS: A coronary artery was occluded in anaesthetized thoracotomized pigs to induce ischaemic preconditioning as well as a longer period of ischaemia. Microdialysis probes were inserted in ischaemic and control myocardium and were infused with (14)C- adenosine with two different specific activities. (14)C-lactate was identified and measured in the effluent. RESULTS: (14)C-adenosine was taken up by non-preconditioned and preconditioned myocardium during ischaemia. Significantly increased levels of (14)C-lactate were recovered in preconditioned myocardium. (14)C-adenosine with high specific activity resulted in a specific activity of lactate that was 2.7 times higher than that of lactate after administration of (14)C-adenosine with low specific activity. Mass spectrography verified the identity of (14)C-lactate. CONCLUSIONS: Preconditioning up-regulates a new metabolic pathway (starting with 5'-nucleotidase and ending up with lactate) resulting in ATP formation in the micromolar range on top of another effect terminating in a useful shift in the AK equilibrium reaction in favour of ATP generation in the millimolar range. Although the up-regulation of the purine nucleoside phosphorylase pathway is clearly demonstrated, its biological relevance remains to be proved.

Metabolic responses in ischemic myocardium after inhalation of carbon monoxide.

BACKGROUND: To clarify the mechanisms of carbon monoxide (CO) tissue-protective effects, we studied energy metabolism in an animal model of acute coronary occlusion and pre-treatment with CO. METHODS: In anesthetized pigs, a coronary snare and microdialysis probes were placed. CO (carboxyhemoglobin 5%) was inhaled for 200 min in test animals, followed by 40 min of coronary occlusion. Microdialysate was analyzed for lactate and glucose, and myocardial tissue samples were analyzed for adenosine tri-phosphate, adenosine di-phosphate, and adenosine mono-phosphate. RESULTS: Lactate during coronary occlusion was approximately half as high in CO pre-treated animals and glucose levels decreased to a much lesser degree during ischemia. Energy charge was no different between groups. CONCLUSIONS: CO in the low-doses tested in this model results in a more favorable energy metabolic condition in that glycolysis is decreased in spite of maintained energy charge. Further work is warranted to clarify the possible mechanistic role of energy metabolism for CO protection.

Serum antibodies against prostasomal clusterin in prostate cancer patients.

OBJECTIVE: Clusterin is a ubiquitous secretory sulphated glycoprotein present in prostasomes. It is an anti-apoptotic mediator in prostate cancer and is among the most frequently occurring prostasomal proteins immunogenic in prostate cancer patients. The aim of the present study was to investigate the occurrence of anti-clusterin antibodies in the serum of patients with prostate cancer and whether there is a relationship between anti-clusterin antibody titres and other clinico-pathological variables. MATERIAL AND METHODS: Serum samples were collected from 391 consecutive patients with suspected prostate cancer (150 benign prostate and 241 prostate cancer). The patients' serum samples were used in an ELISA where microtitre wells were coated with purified clusterin from serum of a healthy volunteer. Flow cytometric studies of clusterin and prostasomes were performed. RESULTS: Flow cytometric analyses revealed the presence of clusterin on the surface of seminal prostasomes. Anti-clusterin ELISA titres in sera of patients did not differ significantly from those of a control group. A significant "inverse" correlation existed between anti-clusterin ELISA titres and lymph node metastases (p = 0.047), but only 11 out of 161 patients had metastases. These titres correlated significantly with total prostate (p = 0.021) and transitional zone (p = 0.015) volumes of the patients. CONCLUSIONS: The correlation between serum anti-clusterin antibody titres and other clinico-pathological variables was generally weak in prostate cancer patients, although clusterin has been assigned an important role in tumourigenesis and progression of prostate cancer. However, the anti-clusterin antibody titre appeared to be related to prostate volume, correlating to both transitional zone volume and total volume of the prostate.

Inherited, non-spherocytic haemolysis due to deficiency of glucose-6-phosphate dehydrogenase.

The about 400 million individuals worldwide suffering from a hereditary deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD) may experience different degrees of haemolytic anaemia. Haemoglobin is present in very high concentrations in the erythrocyte cytoplasm, at risk of falling out of solution if the internal environment or the haemoglobin itself is changed. G6PD is a crucial enzyme producing reduced glutathione in the erythrocyte cytoplasm for the purpose of protecting haemoglobin against oxidative damage. The presence of unopposed oxidizing agents leading to oxidation of the sulfhydryl bridges between parts of the haemoglobin molecule decrease the solubility of haemoglobin, leading to precipitations called Heinz bodies. The laboratory investigation of G6PD deficiency is commonly done by a quantitative spectrophotometric analysis or by a rapid fluorescent spot test detecting the generation of NADPH from NADP. Genetic tests based on polymerase chain reaction detect specific mutations and may be used for population screening, family studies, or prenatal diagnosis.

Erythropoiesis in the Rps19 disrupted mouse: Analysis of erythropoietin response and biochemical markers for Diamond-Blackfan anemia.

The human ribosomal protein S19 gene (RPS19) is mutated in approximately 20% of patients with Diamond-Blackfan anemia (DBA), a congenital disease with a specific defect in erythropoiesis. The clinical expression of DBA is highly variable, and subclinical phenotypes may be revealed by elevated erythrocyte deaminase (eADA) activity only. In mice, complete loss of Rps19 results in early embryonic lethality whereas Rps19+/- mice are viable and without major abnormalities including the hematopoietic system. We have performed a detailed analysis of the Rps19+/- mice. We estimated the Rps19 levels in hematopoietic tissues and we analyzed erythrocyte deaminase activity and globin isoforms which are used as markers for DBA. The effect of a disrupted Rps19 allele on a different genetic background was investigated as well as the response to erythropoietin (EPO). From our results, we argue that the loss of one Rps19 allele in mice is fully compensated for at the transcriptional level with preservation of erythropoiesis.

Prostasome antigens as targets for sperm agglutinating antibodies demonstrated by 1-D gel electrophoresis and immunoblottings.

Many immunoinfertile men have sperm agglutinating antibodies that are directed against prostasome-derived antigens, but these antigens have not been defined so far. We selected serum samples with high ELISA titres against prostasomes from a group of immunoinfertile patients with sperm agglutinating antibodies and used the sera for immunoblottings on 1-D SDS-PAGE of prostasomes and sperm cells. The immunoblottings with individual antiprostasome antisera on 1-D SDS-PAGE of prostasomes, revealed three to 10 bands for each serum. Eighty-five per cent of the serum samples contained bands in the 70-75 kDa region and 80% of the samples contained bands in the 50-55 kDa region. Immunoblottings of extracted sperm cells, revealed one to six bands in the molecular weight range 25-82 kDa and two of the samples recognized two bands with molecular weights (50 and 43 kDa) similar to immunoblottings of prostasomes. The prostasomal antigens recognized by the high titre-antisera of immunoinfertile men were generally different from the sperm antigens recognized by the same sera. This suggests that prostasomes offer a new set of antigens available for research on male immunoinfertility and immunocontraception.

Validity of elevated interstitial levels of taurine as a predictor of myocardial ischemic injury.

The microdialysis (MD) technique allows for continuous in vivo monitoring of dynamic changes in the interstitial levels of energy-related metabolites. The release of taurine from the myocyte has been suggested as a marker of ischemic injury. The relationship between (interstitial) taurine release and the degree of myocardial ischemic injury was evaluated following a 40 min long ischemia in a porcine heart-infarct-model. Different protocols of ischemia and reperfusion were used in order to achieve a graded level of myocardial injury. Both interstitial peak levels and the area under curve of taurine obtained during ischemia and reperfusion correlated with the degree of ischemic injury (assessed by developed infarct size estimation). The release of taurine in the myocardium measured by the MD-technique correlated with the degree of ischemic injury during ongoing ischemic insult. Hence, taurine determination in the MD-setting represents a powerful tool to follow the development of myocardial ischemic injury over time.

Rubidium-86 uptake and energy metabolism in suspended human erythrocytes monitored by microdialysis.

We aimed to develop a model for studying membrane leakiness. A microdialysis technique was used to investigate rubidium-86 (86Rb) uptake in suspended human erythrocytes in vitro, with the aim of later applying the technique to in vivo studies. Suspensions were prepared from washed erythrocytes and 86Rb administered directly or via the microdialysis probe. The effects on 86Rb uptake of varying the haematocrit were measured. Erythrocytes were also treated with the K+ ionophore valinomycin or the Na+/K+-ATPase inhibitor ouabain. The effects on 86Rb uptake, microdialysate content of lactate and pyruvate, and erythrocyte content of 2,3-bisphosphoglycerate (2,3-BPG) were measured. Valinomycin dissipates the potassium gradient and activates Na+/K+-ATPase, demonstrated by decreased erythrocyte 86Rb uptake with increasing concentrations of valinomycin. This increased ion pump activity enhanced glycolysis, which was demonstrated by accumulation of pyruvate and lactate due to enhanced consumption of 2,3-BPG. The microdialysis technique is appropriate for in vitro studies of ion fluxes across cellular membranes.

Polyol-pathway-dependent disturbances in renal medullary metabolism in experimental insulin-deficient diabetes mellitus in rats.

AIMS/HYPOTHESIS: The renal medullary region is particularly vulnerable to reduced oxygen concentration because of its low blood perfusion and high basal oxygen consumption. This study investigated renal metabolic changes in relation to the previously observed decreased oxygen tension in streptozotocin-induced diabetic rats. METHODS: Blood perfusion, oxygen tension and consumption, interstitial pH, and glycolytic and purine-based metabolites were determined in the renal cortex and the medulla of non-diabetic and diabetic animals by, respectively, laser Doppler flowmetry, oxygen and pH microelectrodes, and microdialysis. The importance of increased polyol pathway activity for the observed alterations was investigated by daily treatment with the aldose reductase inhibitor AL-1576 throughout the course of diabetes. RESULTS: The diabetes-induced decrease in renal oxygen tension, due to augmented oxygen consumption, did not result in manifest hypoxia in either the cortical or the medullary region, as evaluated by microdialysis measurements of purine-based metabolites. The profound alterations in medullary oxygen metabolism were, however, associated with an increased lactate : pyruvate ratio and a concomitantly decreased pH. Notably, the renal medullary changes in oxygen tension, oxygen consumption, lactate : pyruvate ratio and pH were preventable by inhibition of aldose reductase. CONCLUSIONS/INTERPRETATION: Substantial metabolic changes were observed in the renal medulla in diabetic animals. These disturbances seemed to be mediated by increased polyol pathway activity and could be prevented by inhibition of aldose reductase.

A new test for immunological infertility: an ELISA based on prostasomes.

Antisperm antibodies (ASA) are present in patients with immunological infertility, but the antigens are poorly characterized. Prostasomes adhere to sperm cells and are recognized as antigens for ASA. This investigation aimed to study the prevalence of antiprostasome antibodies in ASA-classified sera. We studied the reactivity of ASA-positive sera from 116 immunoinfertile patients. Ninety-seven per cent (113 of 116) of the patients' sera contained IgG antibodies against seminal prostasomes. Accordingly, prostasomes are one of the major targets for ASA. An enzyme-linked immunosorbent assay based on prostasomes is simpler to perform than ASA tests presently in use. It is also easier to achieve reproducible and standardized results.

Mediated exodus of L-dopa from human epidermal Langerhans cells.

L-3,4-dihydroxyphenylalanine (L-dopa) is not metabolized within human epidermal Langerhans cells (LC); yet they can take up substantial amounts of this amino acid which subsequently can be released into the extracellular space. We recently reported that human epidermal energy metabolism is predominantly anaerobic and that the influx mechanism is a unidirectional L-dopa/proton counter-transport system and now we describe conditions for the mediated transport of L-dopa out of the LC. It is demonstrated that certain amino acids and one dipeptide can effectively trigger the efflux of L-dopa taken up by the LC.Thus, alpha-methyl-dopa (alpha-m-dopa), D-dopa and the dipeptide, met-ala at the outside of the plasma membrane stimulated the efflux of L-dopa from L-dopa loaded LC. Similar effects were achieved by a variety of other amino acids in the extracellular fluid while some other amino acids were inactive. The time required for 50% D-methionine-induced exodus of L-dopa from L-dopa loaded LC was in the range of 5-7 min and a complete exodus of L-dopa was attained at about 20 min of incubation. This dislocation of L-dopa to the extracellular fluid is interpreted as an expression of trans-stimulation. In the case of alpha-m-dopa, D-dopa and met-ala, which admittedly were not able to penetrate the plasma membrane of LC, the concept of trans-stimulation was given a new purport, since none of them were able to participate in an exchange reaction. Finally, it could be concluded that L-dopa escaped by a route different from the one responsible for L-dopa uptake in LC.Thus, while the influx of L-dopa supports extrusion of protons deriving from anaerobic glycolysis in the LC, L-dopa efflux can provide the cells with useful amino acids in an energy-saving way, altogether a remarkable biological process. From this follows that L-dopa has a biological function of its own, besides being a precursor in the catecholamine and pigment syntheses.

The Janus-faced nature of prostasomes: their pluripotency favours the normal reproductive process and malignant prostate growth.

Prostasomes are submicron secretory granules synthesized, stored and secreted by the epithelial cells of the human prostate gland. They are membrane-surrounded also in their extracellular appearance and the membrane architecture is composite. They are believed to be life-giving and act as protectors of the spermatozoa in the lower and upper female genital tract on their way to the ovum. Hence, the prostasomes are immunosuppressive and inhibitory of complement activation. Further, they promote sperm's forward motility and have antioxidant and antibacterial capacities. The prostasomes with their many composite abilities seem to turn against the host cell after the age of 50 y being conducive to the transition of the normal prostate epithelial cell into a neoplastic cell and therewith lay the foundations of the very high prevalence of prostate cancer of men of more than 50 y of age.

Inhibition of the L-dopa transport system in human epidermal Langerhans cells by omeprazole and its analogues.

L-3,4-dihydroxyphenylalanine (L-dopa) transport into human Langerhans cells (LC) occurs by a saturable mediation. This plasma membrane agency is, due to its characteristics, distinguishable from systems transporting other neutral, cationic and anionic amino acids into other cells and serves to catalyze the flow of L-dopa, only, into LC. The uphill operation of this L-dopa transport system is believed to occur by down-gradient countermigration of H(+). Due to the uniqueness of the L-dopa transport system, the widely used analogue inhibition approach was not applicable. Instead we studied omeprazole and its analogues in our search for suitable inhibitory candidates. Omeprazole and most of its analogues were indeed inhibitory in the concentration range 1-100 micromol/L. Conspicuously, the compounds with strongest polarity were least inhibitory. The inhibitory pattern displayed by omeprazole and the other analogues on L-dopa uptake in LC corresponded to some extent to what has been observed previously for purified H(+),K(+)-ATPase from tubulovesicles of the stomach. No effects of the inhibitors were registered on energy charge and lactate production of epidermal biopsies, nor were any gross alterations of ultrastructure of LC noticed.

Imbalance of plasma membrane ion leak and pump relationship as a new aetiological basis of certain disease states.

The basis for life is the ability of the cell to maintain ion gradients across biological membranes. Such gradients are created by specific membrane-bound ion pumps [adenosine triphosphatases (ATPases)]. According to physicochemical rules passive forces equilibrate (dissipate) ion gradients. The cholesterol/phospholipid ratio of the membrane and the degree of saturation of phospholipid fatty acids are important factors for membrane molecular order and herewith a determinant of the degree of non-specific membrane leakiness. Other operative principles, i.e. specific ion channels can be opened and closed according to mechanisms that are specific to the cell. Certain compounds called ionophores can be integrated in the plasma membrane and permit specific inorganic ions to pass. Irrespective of which mechanism ions leak across the plasma membrane the homeostasis may be kept by increasing ion pumping (ATPase activity) in an attempt to restore the physiological ion gradient. The energy source for this work seems to be glycolytically derived ATP formation. Thus an increase in ion pumping is reflected by increased ATP hydrolysis and rate of glycolysis. This can be measured as an accumulation of breakdown products of ATP and end-products of anaerobic glycolysis (lactate). In certain disease entities, the balance between ATP formation and ion pumping may be disordered resulting in a decrease in inter alia (i.a.) cellular energy charge, and an increase in lactate formation and catabolites of adenylates. Cardiac syndrome X is proposed to be due to an excessive leakage of potassium ions, leading to electrocardiographic (ECG) changes, abnormal Tl-scintigraphy of the heart and anginal pain (induced by adenosine). Cocksackie B3 infections, a common agent in myocarditis might also induce an ionophore-like effect. Moreover, Alzheimer's disease is characterized by the formation of extracellular amyloid deposits in the brain of patients. Perturbation of cellular membranes by the amyloid peptide during the development of Alzheimer's disease is one of several mechanisms proposed to account for the toxicity of this peptide on neuronal membranes. We have studied the effects of the peptide and fragments thereof on 45Ca2+-uptake in human erythrocytes and the energetic consequences. Treatment of erythrocytes with the beta 1-40 peptide, results in qualitatively similar nucleotide pattern and decrease of energy charge as the treatment with Ca2+-ionophore A23187. Finally, in recent studies we have revealed and published in this journal that a rare condition, Tarui's disease or glycogenosis type VII, primarily associated with a defect M-subunit of phosphofructokinase, demonstrates as a cophenomenon an increased leak of Ca2+ into erythrocytes.

Validity of the microdialysis technique for experimental in vivo studies of myocardial energy metabolism.

OBJECTIVES: The validity of the microdialysis technique for experimental in vivo studies of myocardial energy metabolism is not known. To address this question interstitial levels of energy-related metabolites (lactate, adenosine, inosine and hypoxanthine) obtained by the microdialysis technique were compared with corresponding metabolites from myocardial biopsies at given intervals in a porcine heart model using different protocols of ischaemia and reperfusion. METHODS: In an open chest porcine heart model, interstitial levels of energy-related metabolites were monitored using the microdialysis technique. All animals (n = 23) were subjected to 120-min pretreatment followed by 40 min of regional ischaemia and 120 min of reperfusion. Tissue biopsies were obtained in the beginning, middle and at the end of the 40-min ischaemic period and at the end of the reperfusion period. Pretreatment consisted of either rest (group 1, n = 7), or rest for 90 min and one ischaemia/reperfusion (10 + 20 min) cycle (group 2, n = 9), or four ischaemia/reperfusion cycles (10 + 20 min each) (group 3, n = 7). RESULTS: Interstitial levels of energy-related metabolites monitored by the microdialysis technique correlated with tissue biopsy levels of lactate (r = 0.90, P < 0.001), adenosine (r = 0.89, P < 0.001), inosine (r = 0.88, P < 0.001) and hypoxanthine (r = 0.91, P < 0.001), respectively, which were obtained by tissue biopsies at given time intervals. These significant correlations were valid regardless of the functional state of the myocardium. CONCLUSION: We observed significant correlations between microdialysis probe levels and tissue biopsy levels of energy-related metabolites in both ischaemic and non-ischaemic tissue. These data assess the validity of the microdialysis technique (in the current setting) for studying dynamic changes of myocardial energy metabolism.