Effect of hypothermia and HTK on the microcirculation in the rat cremaster muscle after ischaemia

Hypothermia is an important preservation method for tissues and solid organs. The aim of the present study was to assess in rat cremaster muscle the effect of hypothermia, without or with pre-ischaemic HTK (histidine-tryptophan-ketoglutarate-Bretschneider solution) perfusion, on microvascular consequences of 4 or 6 h ischaemia and 2 h of reperfusion. Intravital microscopy was applied to examine capillary perfusion and leucocyte-endothelium interactions. The cremaster muscle was subjected to 4 or 6 h of cold (4 degrees C) or warm (33-34 degrees C) ischaemia and 2 h of reperfusion. Measurements were performed at baseline, prior to HTK perfusion and ischaemia, and at 0, 1 and 2 h after blood flow restoration. Hypothermia completely prevented the 50% reduction in capillary perfusion that was observed previously at start of reperfusion after 4 h warm ischaemia. After 6 h of warm ischaemia, perfusion resumed in only 45 % of capillaries and remained at this low level during reperfusion. In contrast, only a slight decrease (< 10%) in capillary perfusion was observed after 6 h of cold ischaemia. Pre-ischaemic HTK perfusion had no beneficial effect on tissue perfusion. Both hypothermia and HTK attenuated the significant increase in venular leucocyte-vessel wall interactions, which was observed after 4 h of warm ischaemia in a previous study. Combined application of both interventions had no additional effects. After 6 h of warm ischaemia, no increase in leucocyte-vessel wall interactions was observed, possibly due to venular flow reduction. In conclusion, hypothermia preserves capillary perfusion and prevents an increase in leucocyte-vessel wall interactions during reperfusion after muscle tissue ischaemia. Pre-ischaemic perfusion of the vasculature with HTK does not improve the effects of cold storage on tissue perfusion, but attenuates the inflammatory response independently of temperature effect.