While fluid shear stress is an important cardiovascular factor in vivo, it has generally been ignored in in vitro assays of endothelial cell function. We quantified the influence of shear stress on the production of prostacyclin by confluent monolayers of bovine aortic endothelial cells placed in a lucite flow chamber and exposed to flowing culture medium at constant shear stress at 37 degrees C and pH 7.4. Continuous inverted-phase microscopy (x 300) of the monolayers showed no significant contraction or detachment of cells under these conditions. Step increases in shear stress from zero to 14 dyne/cm2 caused rapid rises in prostacyclin production, from a baseline (n = 4) of 0.17 +/- 0.062 ng/cm2.min (mean +/- SEM) to peak values within 2 minutes, followed by a decline over several minutes. Peak prostacyclin production increased (p less than 0.005) with shear stress, from 0.60 +/- 0.13 ng/cm2.min at 0.9 dyne/cm2 (n = 14) to 2.33 +/- 0.67 ng/cm2.min at 14 dyne/cm2 (n = 10). The time integral of production or total production, however, did not significantly change with shear stress at least for shear stresses above 0.9 dyne/cm2. Once stressed, cell monolayers produced additional prostacyclin in response to stimulation by Na arachidonate or the calcium ionophore A23187, but not to repeat mechanical stimulation. We conclude that endothelial cells produce bursts of prostacyclin in response to suddenly imposed arterial-like shear stress, and that the peak rate, but not the time integral, of this production increases with shear stress.