Encapsulation of VIP into liposomes restores vasorelaxation in hypertension in situ.

The purpose of this study was to determine whether vasoactive intestinal peptide (VIP) elicits vasodilation in the in situ peripheral microcirculation of hamsters with spontaneous hypertension and whether encapsulation of VIP into liposomes modulates this response. Using intravital microscopy, we found that suffusion of VIP (0.05 and 0.1 nmol) alone over cheek pouch resistance arterioles of normotensive hamsters elicited significant vasodilation that was potentiated and prolonged by encapsulation of the peptide into liposomes (P < 0.05). By contrast, VIP (0.5 and 0.1 nmol) had no significant effects on arteriolar diameter in hamsters with spontaneous hypertension. However, encapsulation of VIP into liposomes restored its vasorelaxant effects in hypertensive animals, although the duration of vasodilation was significantly shorter in comparison with controls (P < 0.05). Empty liposomes had no significant effects on arteriolar diameter in either group. These data indicate that VIP-induced vasodilation in the peripheral microcirculation in situ is impaired in essential hypertension and that encapsulation of VIP into liposomes restores, in part, this response.