Surface-active properties of vasoactive intestinal peptide

The purpose of this study was to determine whether human vasoactive intesti nal peptide (VIP) aggregates in aqueous solution and, if so, whether the pe ptide interacts with a biomimetic phospholipid monolayer and increases surf ace pressure. Using a custom-made Teflon trough containing HEPES buffer (pH 7.4) at room temperature and a surface tensiometer, we found that the crit ical micellar concentration (CMC) of VIP is 0.4 mu M. Surface pressure of a dipalmitoylphosphatidylcholine (DPPC) monolayer spread over the HEPES buff er declined significantly over 120 min because of phospholipid decompositio n. However, injection of VIP at concentrations above CMC into the subphase of the monolayer elicited a significant concentration-dependent increase in surface pressure that persisted for 120 min (P < 0.05). Unlike VIP, inject ion of [(8)Arg]-vasopressin at an equimolar concentration only prevented th e time-dependent decline in DPPC monolayer surface pressure. Taken together , these data indicate that human VIP aggregates in aqueous solution and exp resses surface-active properties at physiological concentrations in vitro. We suggest that these attributes could have a role in modulating the bioact ive effects of the peptide in vivo. (C) 2000 Elsevier Science Inc. All righ ts reserved.