HEAT-SHOCK ATTENUATES ENDOTHELIUM-DEPENDENT VASODILATION IN SKELETAL-MUSCLE MICROCIRCULATION

Endothelium-derived relaxing factors (EDRFs) mediate vasodilation of s mall arterioles in skeletal muscle under various (patho)physiological conditions: Escherichia coli sepsis, systemic hypoxia, and topical ace tylcholine (ACH) application. To test if heat shock changes EDRF-depen dent reactivity of arterioles to ACH, we used closed-circuit videomicr oscopy in the in vivo cremaster muscle of rats whose systemic temperat ures had been slowly raised to and maintained at 41 degrees C. We also tested for ACH responses after increasing cremaster muscle temperatur es and maintaining those at 40 degrees C. The experiments showed that EDRF-dependent vasodilation of small arterioles to acetylcholine was s ubstantially attenuated in response to systemic and local heat treatme nt. In two other animal groups, concentration-dependent vasodilation o f small arterioles to sodium-nitroprusside was not as much attenuated in the response to local tissue temperature elevation. This suggests t hat locally elevated tissue or systemically elevated body temperatures can change generation or efficacy of EDRFs in the post-hyperthermia p hase in the skeletal muscle microcirculation.