AMBIENT PULSATILE PRESSURE MODULATES ENDOTHELIAL-CELL PROLIFERATION

Many studies over the last decade have indicated that circulatory forc es such as shear stress and cyclic strain can influence the endothelia l cell (EC) phenotype. However. very little is known about the in vitr o effects of pressure on EC. To study this, cultured bovine aortic EC were grown in custom designed pressure chambers with carefully regulat ed CO2/air environment. EC were exposed to either atmospheric, static (135 mmHg) or pulsatile pressure (160/110 mmHg). A pulsed pressure fre quency of 60 cycles/min was maintained by computer-controlled solenoid valves, placed in series with pressure lines. EC proliferation was de termined both by cell count after trypsin release on days 1,3 and 5 an d by H-3-thymidine incorporation. By day 5, a significant decrease in cell number occurred in both pressure groups, confirmed by the thymidi ne studies. No changes were observed in cell morphology and cell viabi lity as assessed by LDH activity studies. To investigate the mechanism of this effect, EC conditioned media from the three pressure conditio ns were transferred to non-exposed, control EC. Significant cell growt h inhibition was demonstrated in the control EC group treated with con ditioned media from EC cultured under pulsatile pressure conditions. T his finding suggests that EC exposed to pulsatile pressure secrete an autocrine factor with growth inhibitory properties. This effect was no t mediated by the growth factors TGF beta and IL-1 as shown by Norther n blot analysis and antibody-neutralization studies. (C) 1998 Academic Press Limited.