Evidence for a vasomotor cyclo-oxygenase dependent mechanism of sensitization at the cutaneous level

Neurovascular microcirculatory vasodilation mediated by C-fibers and Transient receptor potential vanilloid-type-1 channels (TRPV 1) is impaired in type 1 diabetes

Microvascular dysfunction may have an early onset in type 1 diabetes (T1D) and can precede major complications. Our objectives were to assess the endothelial-dependent (acetylcholine, ACh; and post-occlusive hyperemia, PORH), non-endothelial-dependent (sodium nitroprusside, SNP) and neurovascular-dependent (local heating, LH and current induced vasodilation, CIV) microcirculatory vasodilation in T1D patients compared with matched control subjects using a laser speckle contrast imager. Seventeen T1D patients - matched with 17 subjects according to age, gender, Body-Mass-Index, and smoking status - underwent macro- and microvascular investigations. The LH early peak assessed the transient receptor potential vanilloid type 1 channels (TRPV1) mediated vasodilation, whereas the plateau assessed the Nitirc-Oxyde (NO) and endothelium-derived hyperpolarizing factor (EDHF) pathways. PORH explored sensory nerves and (EDHF), while CIV assessed sensory nerves (C-fibers) and prostaglandin-mediated vasodilation. Using neurological investigations, we observed that C-fiber and A-delta fiber functions in T1D patients were similar to control subjects. PORH, CIV, LH peak and plateau vasodilations were significantly decreased in T1D patients compared to controls, whereas there was no difference between the two groups for ACh and SNP vasodilations. Neurovascular microcirculatory vasodilations (C-fibers and TRPV 1-mediated vasodilations) are impaired in TD1 patients whereas no abnormalities were found using clinical neurological investigations. Clinicaltrials: No. NCT02538120.

Sensory nerves contribute to cutaneous vasodilator response to cathodal stimulation in healthy rats

Cutaneous current-induced vasodilation (CIV) in response to galvanic current application is an integrative model of neurovascular interaction that relies on capsaicin-sensitive fiber activation. The upstream and downstream mechanisms related to the activation of the capsaicin-sensitive fibers involved in CIV are not elucidated. In particular, the activation of cutaneous transient receptor potential vanilloid type-1 (TRPV1) channels and/or acid-sensing ion channels (ASIC) (activators mechanisms) and the release of calcitonin gene-related peptide (CGRP) and substance P (SP) (effector mechanisms) have been tested. To assess cathodal CIV, we measured cutaneous blood flow using laser Doppler flowmetry for 20min following cathodal current application (240s, 100μA) on the skin of the thigh in anesthetized healthy rats for 20min. CIV was studied in rats treated with capsazepine and amiloride to inhibit TRPV1 and ASIC channels, respectively; CGRP8-37 and SR140333 to antagonize CGRP and neurokinin-1 (NK1) receptors, respectively; compared to their respective controls. Cathodal CIV was attenuated by capsazepine (12±2% vs 54±6%, P<0.001), amiloride (19±8% vs 61±6%, P<0.01), CGRP8-37 (15±6% vs 61±6%, P<0.001) and SR140333 (9±5% vs 54±6%, P<0.001) without changing local acidification. This is the first integrative study performed in healthy rats showing that cutaneous vasodilation in response to cathodal stimulation is initiated by activation of cutaneous TRPV1 and ASIC channels likely through local acidification. The involvement of CGRP and NK1 receptors suggests that cathodal CIV is the result of CGRP and SP released through activated capsaicin-sensitive fibers. Therefore cathodal CIV could be a valuable method to assess sensory neurovascular function in the skin, which would be particularly relevant to evaluate the presence of small nerve fiber disorders and the effectiveness of treatments.