Passive heat therapy (repeated hot tub or sauna use) reduces cardiovascular risk, but its effects on the mechanisms underlying improvements in microvasculature function have yet to be studied. We investigated the effects of heat therapy on microvascular function and whether improvements were related to changes in nitric oxide (NO) bioavailability using cutaneous microdialysis. METHODS: Eighteen young, sedentary, otherwise healthy subjects participated in 8 weeks of heat therapy (hot water immersion to maintain rectal temperature ≥38.5°C for 60min per session; N=9) or thermoneutral water immersion (sham; N=9), and participated in experiments before and after the 8-week intervention in which forearm cutaneous hyperemia to 39°C local heating was assessed at three microdialysis sites receiving 1) Lactated Ringer's (Control), 2) Nω-nitro-L-arginine (L-NNA, non-specific NO synthase inhibitor), and 3) Tempol, a superoxide dismutase mimetic. The arm used for microdialysis experiments remained out of the water at all times. Data are mean±S.E. cutaneous vascular conductance (CVC = laser Dopper flux/mean arterial pressure), presented as percent maximal CVC (%CVCmax). RESULTS: Heat therapy increased local heating plateau from 42±6 to 53±6%CVCmax (p<0.001) and increased NO-dependent dilation (difference in plateau between Control and L-NNA sites) from 26±6 to 38±4%CVCmax (p<0.01), while no changes were observed in the sham group. When data were pooled across all subjects at 0wks, Tempol had no effect on the local heating response (p=0.53 vs. Control). There were no changes at the Tempol site across interventions (p=0.58). CONCLUSIONS: Passive heat therapy improves cutaneous microvascular function by improving NO-dependent dilation, which may have clinical implications.
- hot water immersion
- oxidative stress
- laser Doppler flowmetry
- Copyright © 2016, Journal of Applied Physiology