To reheat, or to not reheat: that is the question: The efficacy of a local reheating protocol on mechanisms of cutaneous vasodilatation

The aim of this study is to determine the effect of repeated bouts of local skin heating on the roles of nitric oxide synthase (NOS) and sympathetic nerves in cutaneous vasodilatation. In 3 repeated-heating protocols skin blood flux of the forearm and leg was measured using laser-Doppler flowmetry and data are presented as cutaneous vascular conductance (CVC; flux/blood pressure). Local heating was performed from 33 °C (thermoneutral) to 42 °C at 0.5 °C·10 s− 1, allowed to cool passively for ~ 60-min, then reheated at the same rate. In protocol 1, CVC was measured in response to repeated heating. In protocol 2, NOS was inhibited with NG-nitro-l-arginine methyl ester (L-NAME) and in protocol 3, sympathetic nerve blockade was achieved with bretylium tosylate (BT), both infused via intradermal microdialysis. In protocol 1, there were no differences (P > 0.05) in CVC at either the forearm (88 ± 4 vs. 86 ± 4%max) or the leg (97 ± 4 vs. 96 ± 6%max) between heating bouts. In protocol 2, no differences (P > 0.05) in CVC were observed between heating bouts at L-NAME treated sites at either the forearm (55 ± 3 vs. 51 ± 4%max) or the leg (71 ± 3 vs. 70 ± 4%max) . In protocol 3, there were differences (P < 0.001) between BT treated sites when comparing the first and second bouts of heating for both the forearm (75 ± 3 vs. 88 ± 4%max) and the leg (79 ± 3 vs. 97 ± 4%max). The effect of sympathetic blockade on CVC responses to local heating was abolished following repeated bouts of heating. Consequently, it is our suggestion that when examining mechanisms of skin blood flow control, investigators use single bouts of local heating.