The kidney is the major organ responsible for the regulation of the composition and volume of the body fluids, which is essential for homeostasis. The glycosaminoglycan hyaluronan (HA), with extreme water-binding capacity, is present in the interstitium of the kidney with a heterogenous distribution. The importance of HA in renal water-handling is unknown and was the focus of the present investigation. Acute water-loading in rats caused the amount of papillary HA to increase and during water deprivation, the amount was reduced. Gerbils, with extreme urine concentrating capacity, have less HA in the renal papilla in normal conditions and responded diametrically different to water-loading (reduction in HA). Renomedullary interstitial cells (RMICs), which are probably the main producers of HA in the renal medulla, were cultured at different media osmolalities to mimic the milieu of the medulla during variations in the water balance. The amount of HA found in the media was decreased at high osmolalities and increased at low osmolalities, thereby strengthening the in vivo results. CD44, an HA-receptor involved in the uptake and degradation of HA, was expressed on RMICs in an osmolality dependent manner. During high media osmolality, the CD44 expression increased and at lower osmolalities, the opposite occurred, probably due to the need for uptake and degradation of HA. Renal ischemia-reperfusion injury causes a cortical accumulation of HA, up-regulation of CD44, and a depression of functional parameters. The time periods of ischemia correlated with the accumulation of HA which, in turn, was inversely correlated to GFR. Hyaluronidase injections in this setting failed to reduce HA levels and significantly improve renal function. In conclusion, the results from the present study suggest an important role for HA and RMICs in renal water-handling and that the intrarenal distribution of HA is altered after ischemia-reperfusion injury, which correlates with renal dysfunction.

Diabetes mellitus (DM) is one of the leading causes of end stage renal failure. An increased susceptibility to renal ischemia/reperfusion (I/R)-injury was found in DM rats. Unilateral renal ischemia for as short as 20 minutes led to an irreversible progressive injury in DM kidneys, whereas the injury in non-DM kidneys was almost reversible. The renal I/R injury was characterized by anuria, infiltration of inflammatory cells, tubular atrophy, dilation of the remaining tubuli and tubulointerstitial fibrosis. Necrotic areas were found in the inner parts of the outer medulla and in the papilla. The renal medulla was the most vulnerable part of the kidney. This was seen both by the extent of fibrosis four and eight weeks after I/R and by the presence of TUNEL-positive (apoptotic) cells 6h after ischemia. Increased accumulation of HA and enhanced CD44 expression was seen after I/R in DM kidneys. Treatment with long acting insulin 7-14 days before I/R, decreased the number of apoptotic cells in the renal medulla and protected renal function and morphology after the insult, while insulin treatment after the injury did not have any protective effect. Short acting insulin given 2-6 hours before I/R partially protected renal function but did not improve the morphological picture. Treatment with the angiotensin II receptor type 1 blocker candesartan, the PAF-antagonist UR-12670, the immunosuppressive agents tacrolimus and cyclosporin A, or prednisolone did not improve the outcome of the renal I/R injury in DM. Injection of cobalt protoporphyrin (CoPP) intraperitoneally in order to induce an over-expression of heme oxygenase-1 (HO-1) resulted in a trend towards a better function in DM kidneys after I/R. However, the induction of HO-1 by intraperitoneal CoPP injection was not achieved in all rats, when examined by western blot. In conclusion, unilateral renal I/R leads to a severe progressive injury in DM kidneys. Insulin treatment before ischemia, but not after, reduces the renal injury in DM rats. Studies using a more reliable administration of CoPP are required to decide if induction of HO-1 protects against renal I/R injury in DM.

Background: Ischemic stroke ranks as the third major cause of clinical mortality and the leading cause of handicap in adults. Each year, stroke occurs in about 30,000 Swedes. The severity of an acute ischemic stroke depends mainly on the degree and duration of local cerebral blood flow (lCBF) reduction. Prompt reperfusion improves neurological deficits, spontaneous electrical activity, energy metabolism, cerebral protein synthesis (CPS), and tissue repair, among which cell proliferation (neurogenesis, gliosis) and revascularization (angiogenesis) may have important functional and therapeutic implications. Aims of the thesis: (1) To establish the photothrombotic ring stroke(PRS) model with late spontaneous reperfusion in adult mice; (2) To explore angiogenesis and neurogenesis in adult brain after focal cerebral ischemia. Materials and Methods: The PRS model in C57 BL adult mice and the middle cerebral artery suture occlusion (MCAO) model in adult Wistar rats were used. The 5-bromodeoxyuridine (BrdU) was delivered into animal after stroke induction to label DNA duplication. CBF, CPS and adenosine triphosphate (ATP) were measured by laser-Doppler flowmetry (LDF), [14C]–Iodoantipyrine and [3H]-Leucine double tracer autoradiography, and bioluminescence, respectively. Immunocytochemistry / immunofluoresence were performed to detect different proteins. The cell marker colocalization was analyzed by three-dimension (3-D) confocal. The cell counting was performed with a stereological counting system. Results: The PRS model was established in adult mice by irradiating the exposed skull with a 514.5 nm argon laser ring beam (3 mm diameter, 0.21 mm thick) at an intensity of 0.65 W/cm2 for 60s, with concurrent erythrosin B (4.25 mg/kg) intravenous infusion for 15s. The central cortical region within the ring locus was progressively encroached by an annular ring-shaped perfusion deficit, where lCBF LDF declined promptly to 43% of the baseline value at 30 min post irradiation. The lCBF-IAP amounted to 46-17-58 ml/100g/min, where CPS varied from 57-38-112% at 4h-48h-7days post ischemia. ATP declined at 4h, achieved its maximum level at 48h and was markedly reduced at 7 days postischemia. Morphologically, at 4h some neurons in the region at-risk appeared swollen, at 48h the majority were severely swollen, eosinophilic and pyknotic. Tissue morphology became partly restored at 7 days post stroke, when numerous cortical cells were immunolabeled by BrdU or the mitosis-specific marker phosphorylated histone H3 (Phos-H3). Some of these cells were even doubly immunopositive to the neuron-specific marker Neu N and the astrocyte marker GFAP, as analyzed by 3-D confocal. In adult rats exposed to MCAO, widespread BrdU-immunolabeled cells appeared in the cortex, ipsilateral striatum and dentate gyrus of the hippocampus. Some of which were doubleimmunolabeled by the neuron specific markers Map-2, β-tubulin III and Neu N as analyzed by 3-D confocal. As early as 24h postischemia, BrdU-immunopositive endothelial cells were aligned as microvessels, some of which exhibited distinguishable lumens in the ischemic boundary zone, where VEGF-A, B, C proteins and their receptors flt-1, fik-1, flt-4 were overexpressed at 72h after MCAO. Conclusion: PRS model in adult mice elicits a dynamic deterioration and then restoration of local CBF, CPS, ATP and tissue morphology in the spontaneously reperfused cerebral cortex at 7d after stroke, where cortical neurogenesis and gliosis occurred. In adult rats with MCAO, neurogenesis occurred at 30 and 60d in the penumbral cortex and striatum. Angiogenesis occurred as early as 24h, which contributed to the spontaneous reperfusion frequently observed in this setting of acute ischemic stroke.

Reactive oxygen species (ROS) induce oxidative stress and although are primarily recognized for playing a deleterious biological role, they can be beneficial to cell systems. ROS are extremely short-lived and normally tightly regulated by antioxidant defence systems. Cells react to oxidative stress in different ways, which primarily depends on cell type, stress severity, or both. There is a general limitation in extrapolating to humans conclusions drawn from in vitro and animal studies because of important species-specific differences. Therefore, the general aim of this thesis was to study the influence of oxidative stress on human muscle and bone in vivo. In paper I we presented a one-step HPLC method optimized for the simultaneous determination of purine degradation products in small microdialysis samples. The clinical utility of the method was successfully tested in a patient with traumatic brain injury. In paper II we evaluated microdialysis as an in vivo method to characterize the relative kinetics of ROS-related metabolites in human skeletal muscle exposed to ischaemia-reperfusion. Results indicated that microdialysis was feasible and safe to use in monitoring metabolic events during tourniquet-assisted surgery. In paper III we investigated the association between an oxidative stress marker (urinary 8-iso-PGF2α) and bone mineral density (BMD) and whether α-tocopherol modified the association. The main finding was the negative association between 8-iso-PGF2α and BMD and that the association was further dependent on serum α-tocopherol level. In paper IV we performed a randomized controlled trial to evaluate the influence of Q10 supplementation on exercise performance and metabolites of muscular damage. We did not observe any effects on exercise capacity after 8 weeks of Q10 administration. Nor did we find a significant effect on serum markers related to oxidative stress. In conclusion we have studied the influence of oxidative stress on muscle and bone in vivo in humans. The oxidative stress was triggered by four different causes (trauma, ischemia-reperfusion, ageing, and exercise exhaustion).

Non invasive in vivo imaging will lead to better understanding of Angiotensin II Type 1 Receptor’s (AT1R) role in disease progression and may guide therapy in cardiovascular patients. Two models were used in this project: 5/6 nephrectomy and transient left anterior descending (LAD) ligation. Rats were scanned with [13N]ammonia and [11C]methyl-candesartan, both of which are Positron Emission Tomography (PET) tracers, at 8 weeks (nephrectomy) and 2 weeks (LAD ligation) after surgery. Western blot analysis was used to corroborate PET data. Nephrectomy: Renal AT1R image analysis displayed a 40% decrease in kidney AT1R in nephrectomized animals compared to sham (p<0.05) which was confirmed with Western blot and biodistribution. LAD ligation: Left Ventricle AT1R Western blot analysis exhibited a 60% increase in 20min ligation (p<0.05) with maintained myocardial blood flow. In conclusion, changes in renal AT1R were successfully imaged using [11C]methyl-candesartan in nephrectomized animals, and 20min LAD ligation/reperfusion is an appropriate model to image an increase in cardiac AT1R following ischemic injury.

Non invasive in vivo imaging will lead to better understanding of Angiotensin II Type 1 Receptor’s (AT1R) role in disease progression and may guide therapy in cardiovascular patients. Two models were used in this project: 5/6 nephrectomy and transient left anterior descending (LAD) ligation. Rats were scanned with [13N]ammonia and [11C]methyl-candesartan, both of which are Positron Emission Tomography (PET) tracers, at 8 weeks (nephrectomy) and 2 weeks (LAD ligation) after surgery. Western blot analysis was used to corroborate PET data. Nephrectomy: Renal AT1R image analysis displayed a 40% decrease in kidney AT1R in nephrectomized animals compared to sham (p<0.05) which was confirmed with Western blot and biodistribution. LAD ligation: Left Ventricle AT1R Western blot analysis exhibited a 60% increase in 20min ligation (p<0.05) with maintained myocardial blood flow. In conclusion, changes in renal AT1R were successfully imaged using [11C]methyl-candesartan in nephrectomized animals, and 20min LAD ligation/reperfusion is an appropriate model to image an increase in cardiac AT1R following ischemic injury.

Η µεταµόσχευση πνεύµονα είναι µια αποδεκτή θεραπευτική λύση για τους ασθενείς µε πνευµονική νόσο τελικού σταδίου. Η πρώιµη δυσλειτουργία του µοσχεύµατος παραµένει µία από της κύριες αιτίες πρώιµης θνητότητας και νοσηρότητας. Το σύνδροµο ισχαιµίας – επαναιµάτωσης είναι ο υπεύθυνος κύριος παθογενετικός µηχανισµός. Η ακριβής αιτιοπαθολογία του συνδρόµου ισχαιµίας – επαναιµάτωσης δεν έχει πλήρως ερευνηθεί. Η πειραµατικές µεταµοσχεύσεις ως τώρα δεν µπόρεσαν να αποµονώσουν την κλινική εικόνα της βλάβης ισχαιµίας – επαναιµάτωσης, όπως είναι η υποξία, η σοβαρή βλάβη της ενδοθηλιακής διαπερατότητας και το γενικευµένο κυψελιδικό οίδηµα. Η ερευνητική µας οµάδα όπως και πολλές άλλες διεθνώς, χρησιµοποίησε ως τώρα το µοντέλο µεταµόσχευσης ενός πνεύµονα από το ένα ζώο σε άλλο. Ο πρώτος στόχος µας ήταν να δηµιουργήσουµε ένα σταθερό και επαναλήψιµο πειραµατικό πρωτόκολλο που θα µπορούσε να αναπαράγει τις τοπικές και συστηµατικές εκδηλώσεις του συνδρόµου ισχαιµίας- επαναιµάτωσης χωρίς όµως τη συµµετοχή της παθολογίας της απόρριψης, διατηρώντας παράλληλα τους λιγότερους χειρουργικούς χειρισµούς στο µόσχευµα. Είναι γνωστό ότι κατά τις πνευµονικές µεταµοσχεύσεις σε πειραµατικά µοντέλα εµφανίζονται αλλαγές στη σύνθεση και λειτουργικότητα του επιφανειοδραστικού παράγοντα και επιπλέον εξαγγείωση πρωτεϊνών του πλάσµατος στην κυψελίδα µε αποτέλεσµα την επιπρόσθετη επιβάρυνση της λειτουργίας του επιφανειοδραστικού παράγοντα. Οι αλλαγές στον επιφανειοδραστικό παράγοντα κατά τις πνευµονικές µεταµοσχεύσεις έχει προταθεί ότι συµµετέχουν σηµαντικά στην παθοφυσιολογία των βλαβών που σχετίζονται µε τη µεταµόσχευση. Έτσι µπορούµε να υποθέσουµε ότι διαδικασίες που θα µπορούσαν να σταθεροποιήσουν το σύστηµα του επιφανειοδραστικού παράγοντα θα οδηγούσαν πιθανότερα σε βελτίωση της λειτουργίας του µοσχεύµατος. Έχει αποδειχτεί ότι ο εξωγενώς χορηγούµενος επιφανειοδραστικός παράγοντας µιµείται τις επιφανειοδραστικές ιδιότητες του ενδογενούς. Ο δεύτερος στόχος της µελέτης µας ήταν να εξετάσουµε αν η εξωγενής χορήγηση επιφανειοδραστικού παράγοντα θα βελτίωνε τις ιδιότητες 103 του µοσχεύµατος αλλά και ποια επίδραση θα είχε η µη χορήγηση ενός ανοσοδιεγερτικού παράγοντα του επιφανειοδραστικού παράγοντα όπως είναι το SP-A επί του συνδρόµου ισχαιµίας επαναιµάτωσης. Χρησιµοποιήσαµε 14 νεαρούς χοίρους µέσου βάρους 27(±3,5) Kg εφαρµόζοντας ένα µοντέλο αυτοµεταµόσχευσης πνεύµονα in situ. Ο πνεύµονας παρασκευάστηκε και εκπλύθηκε µέσω της πνευµονικής αρτηρίας ορθόδροµα χρησιµοποιώντας διάλυµα U Wisconsin. Οι πνευµονικές φλέβες αποκλείστηκαν µετά τη συµβολή τους επί του αριστερού κόλπου και το υγρό συντήρησης παροχετεύτηκε από αντιστόµειο στον αριστερό κόλπο. Το µόσχευµα παρέµεινε σε θερµοκρασία 4-8 0C για διάστηµα 3 ωρών, διατηρώντας την κεντρική θερµοκρασία ανάµεσα 37 και 38.50 C. Ακολούθησε επαναιµάτωση του µοσχεύµατος. Στην οµάδα ελέγχου (Β) χορηγήθηκε ελεύθερος SP-A επιφανειοδραστικός παράγοντας 1.5 ml/Kg µέσω βρογχοσκοπίου, πριν τη θωρακοτοµή. Τα πειραµατόζωα θυσιάστηκαν 3 ώρες µετά την επαναιµάτωση. Μετά από 3 ώρες από την επαναιµάτωση, (οµάδα Α vs. Β) η PVRI ήταν 447.80 dyne.sec-1cm-5m-2 (±66.8) vs. 249.51(p<.001) ενώ το NO(*p<0.05,**p<0.001), η EPO και η πνευµονική ευενδοτότητα (**p<0.002) διατηρήθηκαν στατιστικά σηµαντικά. Η µέση κυψελιδική επιφάνεια ήταν 5280.84 (4991.1) µm2 vs. 3997,89 (3284.70) µm2(p<0.005). Η ιστολογική µελέτη έδειξε µικρότερη διήθηση µικροφάγων και λεµφοκυττάρων στην οµάδα χορήγησης επιφανειοδραστικού παράγοντα στο τέλος της επαναιµάτωσης. Συµπεράσµατα Το νέο αυτό µοντέλο ετερόπλευρης µεταµόσχευσης πνεύµονα αποδείχθηκε αξιόπιστο και αναπαρήγαγε όλη την παθολογία του συνδρόµου ισχαιµίας επαναιµάτωσης, χωρίς την επίδραση των µηχανισµών απόρριψης. Επιπλέον αποδείχτηκε ότι η προθεραπεία του µοσχεύµατος µε εξωγενή επιφανειοδραστικό παράγοντα µειώνει τη βλάβη ισχαιµίας-επαναιµάτωσης διατηρώντας όχι µόνο την πνευµονική ευενδοτότητα αλλά και το δείκτη πνευµονικών αντιστάσεων. Επιπλέον οι συγκεντρώσεις του NO και η 104 105 δραστηριότητα του EPO διατηρήθηκαν καλύτερα, ενώ και η µορφολογία της κυψελίδας φαίνεται να διατηρείται σηµαντικά καλύτερα. / Lung transplantation is a well accepted treatment for patients with end stage pulmonary disease. Early graft dysfunction remains one of the major causes of early morbidity and mortality, with reperfusion injury (RI) being the most responsible mechanism. The exact pathophysiology of RI in lung transplantation has not been fully evaluated and understood. Experimental transplantation after cold storage has been so far unable to duplicate the complete clinical picture of RI, such as, hypoxia, severe impairment of endothelial permeability, and frank alveolar oedema. We, among others, in our previous experimental work with pigs, had being using a single lung transplantation model. Our first aim has been to create a steady and reproducible experimental protocol that could demonstrate several parameters associated with the mechanisms of reperfusion injury, including impaired gas exchange, elevated pulmonary vascular resistant, local and systemic aspects of the reperfusion syndrome, but without the interference of the pathology concerning acute graft rejection, and with the minimal possible surgical manipulation of the graft. Animal studies have shown that lung transplantation is followed by changes to both synthesis and activity of surfactant. Surfactant alterations have been suggested to contribute significantly to the pathophysiology of transplantation-associated lung injuries. Therefore, procedures that stabilize the pulmonary surfactant system may prove to be crucial for optimal lung preservation. It has been demonstrated that exogenous surfactant mimics the surface-tension-lowering properties of natural lung surfactant. The second purpose of our study was to evaluate whether differences exist in lung preservation after pre-treatment (prior to graft retrieval) of donor lung with surfactant. We postulated that surfactant would lead to an enhanced preservation of the organ. Therefore, we used Surfactant, Beractant which is a natural bovine lung extract containing phospholipids, neutral lipids, fatty acids, and surfactantassociated proteins SP-B and SP-C to which colfosceril palmitate, palmitic acid, and tripalmiting are added in order to standardise the suspension. It should be noted that it does not contain SP-A. Furthermore, we assessed the effect of surfactant pretreatment to lung haemodynamics, respiratory parameters, serum and BALF nitric oxide and EPO levels and the microscopic morphology of the alveolar. Methods: Fourteen young female white pigs, mean weight 27(±3.5) Kg were used in a newly developed autotransplantation model with in-situ cold ischemia. The hilum was dissected free and the pericardium opened. University of Wisconsin solution was used for lung preservation flushed in an antegrade fashion through the left pulmonary artery. Pulmonary veins were clamped proximal to their origin at the left atrium and vent was created just distally to the clamp. The left main bronchus was clamped with the lung left semi-inflated. Interlobar fissure tissue temperature was monitored and maintained at 4-8 0C, while core temperature was kept between 37 and 38.50 C. After 3 hours of cold ischaemia clamps were removed and the lung was reperfused. In the study group (B, n=6) free-SP-A surfactant 1.5 ml/Kg, was administrated into the left main bronchus via flexible bronchoscopy, prior to thoracotomy. Animals were sacrificed after 3 hours of graft reperfusion. Results: At the end of reperfusion, (Control vs. study group) PVRI was 447.80 dyn.sec-1cm-5m-2 (±66.8) vs. 249.51(p<.001) and lung compliance was 14.83 ml/cm H2O (SD 1.78) vs. 18.91 (SD 0.73) (**p<0.002) were adequately preserved. Serum eosinophil peroxidase (EPO) activity persentence change was 18.6 +/- 5.6 vs. 116+/-52 p=0.001. In contrast, EPO activity in BALF was 180 +/- 21 vs 73+/-8, p=0.01. Finally, NO concentration in BALF was 0.75 μM =+/- 0. 06 vs. 0.91 +/- 0.15 p< 0,05 and serum NO were adequately preserved (*p<0.05,**p<0.001). The mean alveoli surface area estimated by computerized morphometry were 5280.84 (4991.1) μm2 vs. 3997,89 (3284.70) μm2(p<0.005). Histology revealed less macrophage and lymphocyte accumulation in the study group at the end of reperfusion. Conclusions: This new model of unilateral lung auto transplantation with a cold storage of the graft, proved to be very reliable in reproducing all aspects of ischemia/reperfusion injury, and we, therefore, propose its use in experimental studies dealing with this yet to be fully clarified clinical entity. Moreover it has demonstrated that pre-treatment of the donor lung with a surfactant agent reduced the ischemia and reperfusion injury by means of maintaining lung compliance and resulting in less respiratory and haemodynamic disturbances. Also, alveoli surface area, alveoli morphology, EPO and NO concentration were better preserved. These data supports the hypothesis that donor lung pretreatment with surfuctant has a beneficial effect on graft properties. Further studies are required before discussing potential benefits in clinical practice.

PKCe plays a very important role in mediating the protection against myocardial ischemia and reperfusion injury induced by ischemic preconditioning (IPC) and pharmacologic preconditioning (PPC). The redistribution of PKCe was assessed by subcellular fractionation and western blotting in the Langendorff-perfused rabbit heart. Either 5min ischemia or 5min administration of adenosine A1 and/or A3 agonists, bradykinin, angiotensin II, and d1-opioid agonists resulted in PKCe redistribution from the cytosol to the mitochondria. This effect of IPC on PKCe redistribution was visible up to at least 30min of reperfusion, while that of PPC was lost by 10min of drug washout, indicative of the transient nature of PKCe redistribution. PKCe redistribution to mitochondria by IPC was also visualized using immunogold electron microscopy. Thus, IPC and PPC caused PKCe redistribution from the cytosol to the mitochondria, which was longer-lasting in IPC than in PPC.

PKCe plays a very important role in mediating the protection against myocardial ischemia and reperfusion injury induced by ischemic preconditioning (IPC) and pharmacologic preconditioning (PPC). The redistribution of PKCe was assessed by subcellular fractionation and western blotting in the Langendorff-perfused rabbit heart. Either 5min ischemia or 5min administration of adenosine A1 and/or A3 agonists, bradykinin, angiotensin II, and d1-opioid agonists resulted in PKCe redistribution from the cytosol to the mitochondria. This effect of IPC on PKCe redistribution was visible up to at least 30min of reperfusion, while that of PPC was lost by 10min of drug washout, indicative of the transient nature of PKCe redistribution. PKCe redistribution to mitochondria by IPC was also visualized using immunogold electron microscopy. Thus, IPC and PPC caused PKCe redistribution from the cytosol to the mitochondria, which was longer-lasting in IPC than in PPC.

Introduction : La prévention de la mort de cellules cardiaques contractiles suite à un épisode d'infarctus du myocarde représente le plus grand défi dans la récupération de la fonction cardiaque. On a démontré à maintes reprises que l'ocytocine (OT), l'hormone bien connue pour ses rôles dans le comportement social et reproductif et couramment utilisée dans l’induction de l’accouchement, diminue la taille de l'infarctus et améliore la récupération fonctionnelle du myocarde blessé. Les mécanismes de cette protection ne sont pas totalement compris. Objectif : Étudier les effets d'un traitement avec de l'ocytocine sur des cardiomyocytes isolés en utilisant un modèle in vitro qui simule les conditions d'un infarctus du myocarde. Méthodes : La lignée cellulaire myoblastique H9c2 a été utilisée comme modèle de cardiomyocyte. Pour simuler le dommage d'ischémie-reperfusion (IR), les cellules ont été placées dans un tampon ischémique et incubées dans une chambre anoxique pendant 2 heures. La reperfusion a été accomplie par la restauration du milieu de culture régulier dans des conditions normales d'oxygène. L'OT a été administrée en présence ou en absence d'inhibiteurs de kinases connues pour être impliquées dans la cardioprotection. La mortalité cellulaire a été évaluée par TUNEL et l'activité mitochondriale par la production de formazan pendant 1 à 4 heures de reperfusion. La microscopie confocale a servie pour localiser les structures cellulaires. Résultats : Le modèle expérimental de l'IR dans les cellules H9c2 a été caractérisé par une diminution dans la production de formazan (aux alentours de 50 à 70 % du groupe témoin, p < 0.001) et par l'augmentation du nombre de noyaux TUNEL-positif (11.7 ± 4.5% contre 1.3 ± 0.7% pour le contrôle). L'addition de l'OT (10-7 a 10-9 M) au commencement de la reperfusion a inversé les effets de l'IR jusqu'aux niveaux du contrôle (p < 0.001). L'effet protecteur de l'OT a été abrogé par : i) un antagoniste de l'OT ; ii) le knockdown de l'expression du récepteur à l'OT induit par le siRNA ; iii) la wortmannin, l'inhibiteur de phosphatidylinositol 3-kinases ; iv) KT5823, l'inhibiteur de la protéine kinase dépendante du cGMP (PKG); v) l'ODQ, un inhibiteur du guanylate cyclase (GC) soluble, et A71915, un antagoniste du GC membranaire. L'analyse confocale des cellules traitées avec OT a révélé la translocation du récepteur à l'OT et la forme phosphorylée de l'Akt (Thr 308, p-Akt) dans le noyau et dans les mitochondries. Conclusions : L'OT protège directement la viabilité des cardiomyocytes, lorsqu'elle est administrée au début de la reperfusion, par le déclenchement de la signalisation du PI3K, la phosphorylation de l'Akt et son trafic cellulaire. La cytoprotection médiée par l'OT implique la production de cGMP par les deux formes de GC. / Introduction: The prevention of the death of contractile cardiac cells following an episode of myocardial infarction represents the largest challenge in the recovery of myocardial function. Oxytocin, the hormone best known for its roles in reproduction and social behaviour and used commonly for the induction of parturition, has been repeatedly demonstrated to decrease the infarct size and to ameliorate the functional recovery of the injured myocardium. The mechanisms for this protection are incompletely understood. Objective: To study the effects of oxytocin treatment on isolated cardiomyocytes using an in vitro model simulating the conditions of a myocardial infarction. Methods: The cardiomyoblastic cell line H9c2 was used as a model of cardiomyocyte. For IR injury, the cells were placed in ischemic buffer and incubated in an anoxic chamber for 2 hours. Reperfusion was achieved by restoring cell media under normoxic conditions. OT was administered in the presence or absence of enzyme inhibitors. Cell death was evaluated by TUNEL and mitochondrial activity by formazan production during 1-4 hours of reperfusion. Confocal microscopy served for localization of cell structures. Results. The experimental model of IR in H9c2 cells was characterized by decreased formazan production (at the range of 50-70% of normoxic control, p < 0.001) and by the increased number of TUNEL-positive nuclei (11.7±4.5 vs. 1.3±0.7% in normoxic control). The addition of OT (10-7 to 10-9 M) at the onset of reperfusion reversed the effects of IR to the control levels (p < 0.001). The protective effect of OT was abrogated by: i) an OT antagonist, OTA and siRNA-mediated OT receptor knockout; ii) the phosphatidylinositol 3-kinases inhibitor wortmannin; iii) the cGMP-dependent protein kinase (PKG) inhibitor, KT5823. Soluble guanylate cyclase (GC) inhibitor ODQ and particulate GC antagonist A71915 only partially blocked the protective effects of OT. Confocal analysis of OT-treated cells revealed translocation of OT receptor and the phosphorylated form of Akt (Thr 308, p-Akt) into the nucleus and mitochondria. Conclusions: OT directly protects cardiomyocyte viability if administered at the onset of reperfusion by triggering signaling of Pi3K, Akt phosphorylation and its cellular trafficking. OT-mediated cytoprotection involves cGMP production by both forms of GC.