Cutaneous vasoconstrictor response to whole body skin cooling is altered by time of day

Abstract

To test for a diurnal difference in the vasoconstrictor control of the cutaneous circulation, we performed whole body skin cooling (water-perfused suits) at 0600 (AM) and 1600 (PM). After whole body skin temperature (T(sk)) was controlled at 35 degrees C for 10 min, it was progressively lowered to 32 degrees C over 18-20 min. Skin blood flow (SkBF) was monitored by laser-Doppler flowmetry at three control sites and at a site that had been pretreated with bretylium by iontophoresis to block noradrenergic vasoconstriction. After whole body skin cooling, maximal cutaneous vascular conductance (CVC) was measured by locally warming the sites of SkBF measurement to 42 degrees C for 30 min. Before whole body skin cooling, sublingual temperature (T(or)) in the PM was significantly higher than that in the AM (P < 0.05), but CVC, expressed as a percentage of maximal CVC (%CVC(max)), was not statistically different between AM and PM. During whole body skin cooling, %CVC(max) levels at bretylium-treated sites in AM or PM were not significantly reduced from baseline. In the PM, %CVC(max) at control sites fell significantly at T(sk) of 34.3 +/- 0.01 degrees C and lower (P < 0.05). In contrast, in the AM %CVC(max) at control sites was not significantly reduced from baseline until T(sk) reached 32.3 +/- 0.01 degrees C and lower (P < 0.05). Furthermore, the decrease in %CVC(max) in the PM was significantly greater than that in AM at T(sk) of 33.3 +/- 0.01 degrees C and lower (P < 0.05). Integrative analysis of the CVC response with respect to both T(or) and T(sk) showed that the cutaneous vasoconstrictor response was shifted to higher internal temperatures in the PM. These findings suggest that during whole body skin cooling the reflex control of the cutaneous vasoconstrictor system is shifted to a higher internal temperature in the PM. Furthermore, the slope of the relationship between CVC and T(sk) is steeper in the PM compared with that in the AM.

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

“…While it is unknown whether time of day influences vasodilator responses to local skin heating, it has been shown that both reflex vasoconstriction and vasodilatation are modified by time of day (0500 h vs. 1500 h) (Aoki et al, 2001;Aoki et al, 2003). Consequently, the potential exists that differences between the present findings and those of Ciplak et al and Frantz et al may be related to diurnal variations.…”

Assessment of Human Skin Microcirculation and Its Endothelial Function Using Laser Doppler Flowmetry

“…In women, skin vascular reactivity depends on the phase of the menstrual cycle: progesteron resets the treshold for active cutaneous vasodilation (Charkoudian & Johnson, 2000). Furthermore, SkBF and the cutaneous microvascular reactivity are subject to diurnal rhytms (Aoki et al, 2003). Another modulator that resets the threshold for active cutaneous vasodilation is physical exercise (Johnson, 1996;Rowell, 1993) that is covered in more detail elsewhere in the chapter.…”

Modification of internal temperature regulation for cutaneous vasodilation and sweating by bright light exposure at night

“…For each site, cutaneous vascular conductance (CVC) was expressed as a percentage of CVC max (%CVC max ). This method of normalization was followed to reduce the effects of site-to-site differences in the absolute values of CVC and to refer values to the common characteristic of maximal vasodilation (Taylor et al 1984), thereby optimizing the ability to make day-to-day and site-tosite comparisons of responses (Aoki et al 1997a(Aoki et al , 2003.…”