Direct visualization of leukocyte/endothelial cell interaction during extracorporeal circulation (ECC) in a new animal model

Abstract

The clinical complications of extracorporeal circulation (ECC) have been linked to a systemic activation of cellular and humoral components and to a dysregulation of the microcirculatory compartment. Since to date only in vitro methods exist for evaluation, we developed an animal model to study the effects of ECC on the microcirculation. To establish the model, we assessed whether these effects are dependent on the duration of ECC. Intravital fluorescence microscopy was used on the dorsal skinfold chamber preparation in chronically instrumented, awake Syrian golden hamsters. ECC was realized using a micro-rollerpump and a silicon tube shunting blood between the carotid artery and the jugular vein. ECC was performed in three groups for various times (2, 10 and 20 min) after application of heparin at 300 IU/kg body wt. In hamsters, the application of high-dose heparin releases endothelial bound superoxide dismutase (SOD), a natural scavenger of oxygen-derived free radicals. Protocol II assigned two groups receiving heparin at different doses of 50 and 2000 IU/kg body wt. ECC for 2 min served as control to exclude effects from hemodilution and resulted in a minimal induction of leukocyte/endothelial cell interaction. Isovolemic ECC for 20 min resulted in an increase in rolling (from 11 +/- 3 to 38 +/- 20%, mean +/- S.D., P < 0.05) and adherent leukocytes (from 19 +/- 16 to 215 +/- 145 cells/mm2, mean +/- S.D., P < 0.05) in postcapillary venules. Microhemodynamic parameters and functional capillary density were not significantly affected. Arterial blood pressure and heart rate were stable. Heparin at 2000 IU/kg inhibited post-ECC leukocyte adhesion following ECC, whereas 50 IU/kg showed no protective effects. Leukocyte/endothelial cell interaction, induced by blood contact with synthetic surfaces, was directly visualized in vivo. The number of adherent leukocytes was dependent on the duration of ECC. The application of high-dose heparin followed by release of SOD almost prevented leukocyte activation, suggesting a formation of oxygen free radicals during ECC. The new application of the hamster model may allow to study the underlying pathomechanisms and to develop therapeutic/prophylactic strategies to avert problems associated with ECC.