EFFECTS OF LOCAL COOLING ON MICROVASCULAR HEMODYNAMICS AND LEUKOCYTE ADHESION IN THE STRIATED-MUSCLE OF HAMSTERS

Objectives: Cellular metabolism is dependent on the local temperature in tissues. Induced hypothermia has been shown to be protective in a n umber of conditions, especially traumatic, ischemic, burn, and neurolo gical injury. However, the protective mechanisms of cold therapy remai n controversial and the hemodynamic changes in the microcirculation of striated muscles in response to hypothermia have not been studied in detail previously. Methods: In this study, we investigated the microva scular response of local cooling and rewarming in the striated muscle of hamsters by use of the dorsal skinfold preparation and in vivo fluo rescence microscopy. Results: We found that reduction of the surface t emperature to 8 degrees C for 30 minutes caused arteriolar vasoconstri ction with a decrease in diameters by 43 +/- 7% while the venular and capillary diameters remained unchanged, The cooling procedure also mar kedly reduced the functional capillary density and the blood flow velo city and diameters in all vessel types, i.e,, arterioles, venules, and capillaries, Moreover, the percentage of capillaries with no flow inc reased from 0.4 +/- 0.5% to 44 +/- 14% after 10 minutes of cold therap y. However, these hemodynamic changes induced by local hypothermia wer e completely reversed to the precooling values after termination of co oling and 30 min of rewarming. Strikingly, we found no increase in the number of adherent leukocytes and vascular permeability after the coo ling and rewarming period, while, in contrast, additional experiments with warm ischemia (30 minutes) and reperfusion (30 minutes), i.e., re duced microvascular perfusion and reperfusion at normothermia, caused a sustained decrease in local perfusion and a nine-fold increase in ve nular leukocyte adhesion. Conclusions: Taken together, our functional data demonstrate that hypothermia markedly reduces microvascular perfu sion, which is completely restored upon rewarming. The reduced microva scular perfusion during hypothermia did not provoke an inflammatory re sponse, whereas leukocyte recruitment was prominent after reduced perf usion at normothermia, indicating that transient hypothermia has no ad verse effects on microvascular parameters in the striated muscle in vi vo.