Ambient pulsatile pressure modulates endothelial cell proliferation.

Many studies over the last decade have indicated that circulatory forces such as shear stress and cyclic strain can influence the endothelial cell (EC) phenotype. However, very little is known about the in vitro effects of pressure on EC. To study this, cultured bovine aortic EC were grown in custom designed pressure chambers with carefully regulated CO2/air environment. EC were exposed to either atmospheric, static (135 mmHg) or pulsatile pressure (160/110 mmHg). A pulsed pressure frequency of 60 cycles/min was maintained by computer-controlled solenoid valves, placed in series with pressure lines. EC proliferation was determined both by cell count after trypsin release on days 1,3 and 5 and by 3H-thymidine incorporation. By day 5, a significant decrease in cell number occurred in both pressure groups, confirmed by the thymidine studies. No changes were observed in cell morphology and cell viability as assessed by LDH activity studies. To investigate the mechanism of this effect, EC conditioned media from the three pressure conditions were transferred to non-exposed, control EC. Significant cell growth inhibition was demonstrated in the control EC group treated with conditioned media from EC cultured under pulsatile pressure conditions. This finding suggests that EC exposed to pulsatile pressure secrete an autocrine factor with growth inhibitory properties. This effect was not mediated by the growth factors TGFbeta and IL-1 as shown by Northern blot analysis and antibody-neutralization studies.