Fig. 8. Comparison of the shear-stress-induced increase in cyclic GMP in endothelial cells from wild-type and PECAM-1^–/– mice. Endothelial cells were incubated with IBMX (50 µmol l^–1) and either maintained under static conditions or exposed to shear stress (12 dynes cm^–2) for up to 60 minutes. Intracellular cyclic GMP levels were determined by radioimmunoassay and the bar graph summarizes data obtained in three independent experiments (each performed in duplicate); ^*P<0.05, ^**P<0.01, ^***P<0.001 versus static conditions.