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1 Department of Physiology, University of Texas Health Science Center, San Antonio, Texas, United States
* To whom correspondence should be addressed. E-mail: johnson{at}uthscsa.edu.
Previous work showed that local cooling (LC) attenuates the vasoconstrictor response to whole body cooling (WBC). We tested the extent to which this attenuation was due to the decreased baseline skin blood flow following LC. In 8 subjects skin blood flow was assessed by laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was expressed as LDF divided by blood pressure. Subjects were dressed in water-perfused suits to control WBC. Four forearm sites were prepared with microdialysis fibers, local heating/cooling probe holders and laser-Doppler probes. Three sites were local cooled from 34 to 28 °C, reducing CVC to 45.9±3.9, 42±3.9 and 44.5±4.8 %baseline (P
0.05 vs. baseline; P
0.05 among sites). At two sites CVC was restored to pre-cooling baseline levels with sodium nitroprusside (SNP) or isoproterenol (ISO), increasing CVC to 106.4±12.4 and 98.9±10.1 %baseline, respectively (P
0.05 vs pre-cooling). Whole body skin temperature, apart from the area of blood flow measurement, was reduced from 34 to 31 °C. Relative to the original baseline, CVC decreased (P
0.05) by 44.9±2.8 % (control), 11.3±2.4 % (LC only), 29±3.7 % (SNP), and 45.8±8.7 % (ISO). The reductions at LC only and SNP sites were less than at control or ISO sites (P
0.05); the responses at those latter sites were not different (P
0.05), suggesting that baseline change with LC is important in the attenuation of reflex vasoconstrictor responses to WBC.
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