Prostacyclin production by confluent and non-confluent human endothelial cells in culture

Prostacyclin (PGI2) production by cultured human umbilical vein endothelial cells was examined by platelet bioassay and by radioimmunoassay of its stable metabolite 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha). Confluent cultures produced PGI2 in a burst of activity approx. 20 min after changing the growth medium. This occurred in either normal, serum-supplemented growth medium or in balanced salt solution. The mechanical action of changing the growth medium did not appear to be responsible for this burst of PGI2 production. PGI2 production by non-confluent cultures decreased as cell density increased towards confluence. Supplementing the growth medium with arachidonic acid did afford some protection against decreased PGI2 production, whilst the use of conditioned media potentiated this effect. Reduction of cell density by passaging confluent cultures further demonstrated the inverse relationship between PGI2 production and cell density. These results are discussed in relation to the control of PGI2 production in cultured endothelial cells.