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Vasoactive intestinal peptide fragment VIP_10–28 and active vasodilation in human skin

¹Department of Human Physiology, and ²Institute of Neuroscience, University of Oregon, Eugene, Oregon

Submitted 2 May 2005 ; accepted in final form 9 August 2005

A recent study reported the vasoactive intestinal peptide (VIP) fragment VIP_10–28 inhibited the rise in skin blood flow during heat stress. Our laboratory has reported that the nitric oxide (NO) pathway and histamine receptor-1 (H1)-receptor activation is common to both exogenous VIP-mediated dilation and active vasodilation (AVD). The present study aimed to further examine the specific role for VIP in AVD by using VIP_10–28 to antagonize VIP-mediated dilation in the presence of NO synthase (NOS) inhibition and an H1 antagonist. Study 1 (n = 12) examined whether VIP_10–28 antagonizes vasodilation to exogenous VIP via inhibition of NO-dependent mechanisms. Study 2 (n = 6) investigated AVD in skin sites receiving VIP_10–28 alone and in combination with NOS inhibition. Study 3 (n = 6) examined AVD in sites receiving VIP_10–28 alone and combined VIP_10–28 and H1 antagonism. Due to differences in our findings and those previously published, study 4 (n = 6) investigated whether an increase in baseline skin blood flow could result in a diminished rise in AVD. Red blood cell flux was measured using laser Doppler flowmetry, and cutaneous vascular conductance (flux/mean arterial pressure) was normalized to maximal vasodilation (28 mM sodium nitroprusside). VIP_10–28 augmented vasodilation to exogenous VIP (P < 0.05 vs. control) and hyperthermia (P < 0.05 vs. control). NOS inhibition had no effect on the augmented dilation during exogenous VIP or hyperthermia (P > 0.05). Similarly, H1-receptor antagonists had no effect on the augmented dilation during hyperthermia (P > 0.05 vs. VIP_10–28). In study 4, percentage of maximal cutaneous vascular conductance was attenuated when baseline skin blood flow was elevated before whole body heating. Our results suggest that VIP_10–28 may be an unsuitable antagonist for examining a role for VIP-mediated dilation in human skin.

histamine receptor-1; cutaneous vascular conductance

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