Histamine-induced secretion of VWF, but not tPA, is affected by inhibition of PLD-mediated PA production. (A,B) Quantification of VWF and tPA secretion after PLD inhibition. HUVECs grown to confluency were treated for 10 minutes in culture medium with n-butanol to inhibit the PLD-mediated generation of PA. Control experiments used culture medium alone (control) or culture medium containing tert-butanol that does not serve as a substrate for PLD. Subsequently, the cells were subjected to histamine stimulation for 20 minutes (A) or 5 minutes (B), respectively, and the acute release of VWF (A) and tPA (B) into the cell culture supernatant was then determined by specific ELISAs. The relative histamine-triggered increase of VWF and tPA secretion exceeding the constitutive level is given in percentage as the mean value plus or minus SEM. The effect on secretion was quantified in sets of independent experiments (number of experiments shown at the base of each column). One-way ANOVA with unpaired Student t test was performed to evaluate statistical significance (*P < .01).