Stable VIP analogue Ro-24-9981 potentiates substance P-induced plasma exudation in hamster cheek pouch.

The purpose of this study was to determine whether vasoactive intestinal peptide (VIP; 300 nM) and a stable cyclic analogue of VIP, Ro-24-9981 (226 nM), modulated neurogenic plasma exudation in the oral cavity in situ and, if so, to determine the mechanisms that mediated these responses. With the use of intravital microscopy, we found that suffusion of substance P induced a significant concentration-dependent formation of fluorescein-isothiocyanate-dextran (mol wt 70 kDa) leaky sites in the hamster cheek pouch (P < 0.05). These effects were significantly and stereospecifically attenuated by NG-nitro-L-arginine methyl ester, an inhibitor of NO synthase, and restored by L-arginine, the substrate for NO synthase (P < 0.05). Topical application of human VIP and Ro-24-9981 had no significant effects of leaky site formation. In addition, human VIP had no significant effects on substance P-induced responses. By contrast, Ro-24-9981 significantly potentiated substance P- and capsaicin-induced leaky site formation (P < 0.05). The effects of Ro-24-9981 on substance P-induced responses were significantly attenuated by NG-nitro-L-arginine methyl ester and restored by L-arginine (P < 0.05). Indomethacin had no significant effects on Ro-24-9981-induced responses. Ro-24-9981 had no significant effects on adenosine- and calcium ionophore A-23187-induced leaky site formation. Collectively, these data suggest that VIP plays no significant role in modulating neurogenic plasma exudation in the oral mucosa. By contrast, Ro-24-9981 amplified this response in a specific receptor-mediated fashion.