Objective: Shear stress results in both, an elevated eNOS mRNA in endothelial cells (EC) and release of FGF-2 into the supernatant. We investigated whether, in turn, FGF-2 has regulatory effects on expression and activity of eNOS. Methods: EC from porcine aorta were subjected to shear stress (16dyn/cm²) and subsequently eNOS expression was quantified using RT-PCR technology. The half-life (t1/2) of eNOS mRNA was estimated using actinomycin D (act D) incubations. Additionally cellular NO production was quantified as nitrite using the Griess' reaction. Results: After 6h shear stress, PAEC showed an nearly 2-fold increase of cellular eNOS mRNA. However, simultaneously the stability of the mRNA was reduced from t1/2 > 24h to approx. 6h. This reduction could be mimicked in static culture treating EC with FGF-2 (5ng/ml), the t1/2 of the eNOS mRNA was again reduced to 6h (n=7). Since the RT-PCR measurements of cellular eNOS mRNA reflects the balance of RNA synthesis and degradation shear stress experiments were repeated with simultaneous inhibition of protein synthesis (cycloheximide) and resulted in a much higher transcription ranging at 8-fold above static control. Similar observations were obtained for the eNOS activity. FGF-2 strongly inhibited the NO production seen as an only transient increase of nitrite in shear conditioned medium within the first 4h. However, when the FGF-2 receptor was blocked by an inhibiting peptide the shear induced NO formation steadily increased even after 6h. Conclusion: Shear stress stimulates EC to release FGF-2, which in turn modulates eNOS gene expression by down-regulating eNOS mRNA t1/2 and additionally inhibits the eNOS activity. These processes are might serve as an negative feed back mechanism to prevent an overshooting in shear stress induced vessel dilatation and blood pressure drop.