Cell growth and the regulation of prostaglandin synthesis

Prostaglandin (PG) synthesis was determined in human embryo lung fibroblasts (HELF) during active, slowed and nongrowing phases. Bradykinin and ascorbic acid were used to induce PG synthesis. The cells were also exposed to arachidonic acid, a PG precursor. During active growth, PGE₂ synthesis in response to stimulation by either bradykinin or ascorbic acid was low. As growth slowed the cellular response changed. During quiescence bradykinin and ascorbic acid stimulated PG production markedly while the conversion of free arachidonic acid to PGE₂ also increased markedly. This change in response by quiescent cells was not due to an increase in cell density. When growing and quiescent cells at the same cell density were compared, the growing cells showed very little response to bradykinin while the quiescent cells were very responsive. The change in response was also not due to any differences in arachidonic acid concentrations in the culture medium during growth and non-growth.