Hodges GJ, Kosiba WA, Zhao K, Johnson JM
The involvement of heating rate and vasoconstrictor nerves in the cutaneous vasodilator response to skin warming. [JOURNAL ARTICLE]
Am J Physiol Heart Circ Physiol 2008 Nov 14.
Slow local skin heating (LH) causes vasodilator responses, some of which are dependent on sympathetic nerve function. It is not known, however, how the rate of LH affects either the sympathetic or the nonadrenergic components of the responses to LH and whether the adrenergic effects of LH depend on tonic sympathetic activity or if LH stimulates transmitter release. In Part 1, cutaneous vascular conductance (CVC) responses to slow and fast LH (+0.1 and +2 degrees C min(-1)) from 34 to 40 degrees C were compared both at control sites and at sites pretreated with bretylium (BT; blocks transmitter release from adrenergic terminals). We confirmed, as previously found, the axon reflex (AR) response to slow LH to be blocked by BT (P<0.05). Pretreatment with BT reduced the AR with fast LH. BT inhibited the peak vasodilation achieved with both rates of LH (P<0.05). Longer term LH was associated with a slow fall in CVC, the classical 'die-away' phenomenon, at untreated sites (P<0.05) but not at BT pretreated sites. Thus, the LH stimulated AR is only partially dependent on intact sympathetic function and the 'die-away' phenomenon is dependent on such function. In Part 2, we tested whether the conditions in Part 1 (whole body and local skin temperatures of 34 degrees C) completely suppressed sympathetic nerve activity. Infusion of BT by microdialysis did not change CVC (P>0.05), suggesting the absence of tonic activity in those conditions and therefore that the adrenergic components of the responses in Part 1 are via stimulation of transmitter release by LH. Key words: Bretylium, norepinephrine release, local control of blood flow, axon reflex.
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