Preserved reflex cutaneous vasodilation in cystic fibrosis does not include an enhanced nitric oxide-dependent mechanism

In humans, vasoactive intestinal peptide (VIP) may play a role in reflex cutaneous vasodilation during body heating. We tested the hypothesis that the nitric oxide (NO)-dependent contribution to active vasodilation is enhanced in the skin of subjects with cystic fibrosis (CF), compensating for sparse levels of VIP. In 2 parallel protocols, microdialysis fibers were placed in the skin of 11 subjects with CF and 12 controls. Lactated Ringer was perfused at one microdialysis site and N^G-nitro-L-arginine methyl ester (2.7 mg/ml) was perfused at a second microdialysis site. Skin blood flow was monitored over each site with laser-Doppler flowmetry. In protocol 1, local skin temperature was increased 0.5°C every 5 s to 42°C, and then it maintained at 42°C for ∼45 min. In protocol 2, subjects wore a tube-lined suit perfused with water at 50°C, sufficient to increase oral temperature (T _or) 0.8°C. Cutaneous vascular conductance (CVC) was calculated (flux/mean arterial pressure) and scaled as percent maximal CVC (sodium nitroprusside; 8.3 mg/ml). Vasodilation to local heating was similar between groups. The change (Δ%CVC_max) in CVC with NO synthase inhibition on the peak (9 ± 3 vs. 12 ± 5%CVC_max; P = 0.6) and the plateau (45 ± 3 vs. 35 ± 5%CVC_max; P = 0.1) phase of the skin blood flow response to local heating was similar in CF subjects and controls, respectively. Reflex cutaneous vasodilation increased CVC in CF subjects (58±4%CVC_max) and controls (53 ± 4%CVC_max; P = 0.37) and NO synthase inhibition attenuated CVC in subjects with CF (37 ± 6%CVC_max) and controls (35 ± 5%CVC_max; P = 0.8) to a similar degree. Thus the preservation of cutaneous active vasodilation in subjects with CF is not associated with an enhanced NO-dependent vasodilation.