Cutaneous sympathetic neural responses to body cooling in type 2 diabetes mellitus.

In humans, sympathetic vasoconstrictor nerves in the skin contribute to resting vascular tone and mediate reflex vasoconstrictor responses to body cooling. Although it is well recognized that type 2 diabetes mellitus (T2DM) is associated with peripheral neurovascular changes, it is unclear to what extent the thermal responsiveness of the cutaneous vasoconstrictor system is altered in individuals with relatively uncomplicated T2DM. We tested the hypothesis that skin sympathetic nerve activity (SSNA) is decreased at baseline and during body cooling in individuals with T2DM compared to healthy controls (C) of similar age and body size. We measured SSNA (microneurography) and skin blood flow (laser-Doppler flowmetry) in the innervated area in 8 T2DM and 12 C subjects at baseline and during 3-4min of rapid whole body cooling via a water-perfused suit. SSNA (total integrated activity) increased, and cutaneous vascular conductance decreased in both groups during body cooling (P<0.01 for both). However, SSNA was not different between groups during either baseline or body cooling conditions (P=NS). The deltas in SSNA between baseline and body cooling were similar between groups: T2DM: 55±27 and C: 57±12 units (P=NS). We conclude that reflex cutaneous sympathetic and vascular responses to rapid whole body cooling are preserved in relatively healthy individuals with T2DM.

Local sensory nerve control of skin blood flow during local warming in type 2 diabetes mellitus.

Cutaneous sensory nerve-mediated vasodilation is an important component of normal microvascular responsiveness to thermal and nonthermal stimuli. Since both neural and microvascular function can be impaired in type 2 diabetes mellitus (T2DM), we tested the hypothesis that local sensory nerve-mediated vasodilation during nonpainful local warming of the skin is less in T2DM compared with healthy controls (C) matched for age and body size. The rapid vasodilation during the first approximately 5 min of this local warming ("initial peak") was previously shown to rely primarily on local sensory nerves. We measured skin blood flow in T2DM and C subjects (n = 7 in each group) at baseline and during 35 min of local warming of the skin to 42 degrees C at two sites on the ventral forearm. One site was pretreated with 4% lidocaine (LIDO) to block local sensory innervation. During local warming, cutaneous vascular conductance (CVC) during the initial peak was not different between groups, either at the untreated site [T2DM 75 +/- 2 vs. C 81 +/- 6% of maximum CVC (%maxCVC); P > 0.05] or at the LIDO site (T2DM 63 +/- 7 vs. C 64 +/- 6%maxCVC; P > 0.05). The difference between untreated and LIDO sites (sensory nerve contribution) was also similar between groups (T2DM 13 +/- 5 vs. C 18 +/- 5%maxCVC; P > 0.05) and was smaller with LIDO than was previously shown with other local anesthetics. Our results suggest that relatively healthy individuals with T2DM do not exhibit impairments in local sensory nerve vasodilation during thermal stimulation compared with controls of similar age and body size.