Prostanoids contribute to cutaneous active vasodilation in humans

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Abstract
The specific mechanisms by which skin blood flow increases in response to a rise in core body temperature via cutaneous active vasodilation are poorly understood. The primary purpose of this study was to determine whether the cyclooxygenase (COX) pathway contributes to active vasodilation during whole body heat stress ( protocol 1; n = 9). A secondary goal was to verify that the COX pathway does not contribute to the cutaneous hyperemic response during local heating ( protocol 2; n = 4). For both protocols, four microdialysis fibers were placed in forearm skin. Sites were randomly assigned and perfused with 1) Ringer solution (control site); 2) ketorolac (KETO), a COX-1/COX-2 pathway inhibitor; 3) NG-nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor; and 4) a combination of KETO and l-NAME. During the first protocol, active vasodilation was induced using whole body heating with water-perfused suits. The second protocol used local heaters to induce a local hyperemic response. Red blood cell flux (RBC flux) was indexed at all sites using laser-Doppler flowmetry, and cutaneous vascular conductance (CVC; RBC flux/mean arterial pressure) was normalized to maximal vasodilation at each site. During whole body heating, CVC values at sites perfused with KETO (43 ± 9% CVCmax), l-NAME (35 ± 9% CVCmax), and combined KETO/l-NAME (22 ± 8% CVCmax) were significantly decreased with respect to the control site (59 ± 7% CVCmax) ( P < 0.05). Additionally, CVC at the combined KETO/l-NAME site was significantly decreased compared with sites infused with KETO or l-NAME alone ( P < 0.05). In the second protocol, the hyperemic response to local heating did not differ between the control site and KETO site or between the l-NAME and KETO/l-NAME site. These data suggest that prostanoids contribute to active vasodilation, but do not play a role during local thermal hyperemia.