Role of sensory nerves in the rapid cutaneous vasodilator response to local heating in young and older endurance-trained and untrained men

Abstract

The ability to increase skin blood flow (SkBF) rapidly in response to local heating is diminished with advanced age; however, the mechanisms are unclear. The primary aim of this study was to investigate the role of sensory nerves in this age-related change. A secondary aim was to investigate the effect of aerobic fitness on sensory nerve-mediated vasodilatation in young and aged skin. We measured SkBF (using laser Doppler flowmetry) in young and older endurancetrained and untrained men (n = 7 in each group) at baseline and during 35 min of local skin heating to 42• C at two sites on the ventral forearm. One site was pretreated with topical anaesthetic cream to block local sensory nerve function. Cutaneous vascular conductance (CVC) was calculated as SkBF divided by mean arterial pressure and normalized to maximal values (CVC max ) achieved during local heating to 44• C. At the untreated site, the rapid vasodilatation during the first ∼5 min of local heating (initial peak) was lower in the older untrained group (68 ± 3%CVC max ) compared with all other groups (young trained, 76 ± 4%CVC max ; young untrained, 75 ± 5%CVC max ; and older trained, 81 ± 3%CVC max ; P < 0.05). Sensory nerve blockade abolished these differences among the groups (P > 0.05). The contribution of sensory nerve-mediated vasodilatation was lower in the older untrained group compared with all other groups (P < 0.05). Our results suggest that the age-related decline in the rapid vasodilator response to local heating in human skin is explained by diminished sensory nerve-mediated vasodilatation. These findings also indicate that this age-related change can be prevented through participation in regular aerobic exercise.

Sensory and sympathetic nerve contributions to the cutaneous vasodilator response from a noxious heat stimulus

“…4). The plateau phase differed significantly between the untreated control sites (86 ± 4%CVC max ) and the BT-treated sites (78 ± 3%CVC max ) during heating As previously shown, there was a reduced initial peak with EMLA during heating at 42 • C and no difference in the plateau phase (Minson et al 2001;Tew et al 2011a). During conditions of rapid local heating to 44 • C at both untreated and EMLA-treated sites there was no initial peak.…”

“…The EMLA cream was applied to an area of 8 cm 2 under an occlusive dressing and left for a minimum of 2 h (Johnson et al 2005;Hodges et al 2007;Tew et al 2011a). The area was tested for sensory loss both before the study began and at its completion by pin-prick and pinching of the skin (Hodges et al 2007;Tew et al 2011a).…”

“…There is a transient initial peak followed by a nadir, which is succeeded by a prolonged plateau phase. Current data suggest that the initial peak and nadir of the vasodilator response are mediated by an axon reflex (Minson et al 2001;Tew et al 2011a). Additionally, the initial peak has been shown to have nitric oxide and noradrenergic sympathetic nerve components (Minson et al 2001;Houghton et al 2006;Hodges et al 2008Hodges et al , 2009bTew et al 2011b).…”

The contribution of sensory nerves to cutaneous vasodilatation of the forearm and leg to local skin heating

“…It was determined through a priori power analysis that seven participants would be required with an α of 0.05 and β of 0.90, with standard deviations and expected required mean differences established through our laboratory's previous work utilizing cutaneous sensory nerve blockage and local skin heating (Tew et al 2011a;Carter and Hodges 2011) (nQuery Advisor, v. 3).…”

“…The initial vasodilatory response, at least in the forearm, is thought to be primarily mediated by both sympathetic and sensory nerves (Minson et al 2001(Minson et al , 2002Tew et al 2011a;Carter and Hodges 2011), with transient receptor potential vanilloid (TRPV) type 1 ion channels (Wong and Fieger 2010) located on sensory afferent nerves. Additionally, these studies have reported that sensory nerves do not appear to be involved in the secondary sustained vasodilatation during prolonged local skin heating.…”