Time course of platelet-activating factor (PAF) mediated nitric oxide (NO) release. Cells were stimulated with 1 nM platelet-activating factor for the times indicated in the absence of WEB2170 (open circle) or in the presence of 10 µM WEB2170 added after 15 min of stimulation (solid triangle). The results are expressed as means ± S.E.M. of a typical experiment (triplicate determinations per experiment; 4 similar experiments). Statistical analysis was performed using Student’s unpaired t test. * p < 0.01 and *** p < 0.0001 when compared with basal values of total NO. ** p < 0.001 when compared with the 30 min timepoint when WEB2170 treatment was initiated. After 30 min, basal NO release was 1535 pmol/well and release in the presence of WEB2170 alone was 1595 pmol/well. These values have been subtracted from the test data.