Prostaglandin production by 3T3-L1 cells in culture.

Rapidly growing cultures of 3T3-L1 preadipocytes produce large quantities of prostaglandins when they are either stimulated with the calcium ionophore A23187 or incubated with arachidonic acid. The main prostaglandin produced under all conditions was prostaglandin E2. Prostaglandin production in response to ionophore stimulation or incubation with arachidonic acid decreased markedly, however, as the cultures approached confluence, were maintained in the confluent state, or were stimulated to differentiate. Enrichment of confluent, differentiated cultures with arachidonic acid did not enhance prostaglandin production. Recovery of prostaglandin production occurred when logarithmic growth was reinstituted by reseeding confluent cultures at low cell densities, but sparse cultures maintained in a low-growth phase did not recover the ability to produce large amounts of prostaglandin E2. Therefore, the decline in prostaglandin synthetic capacity appears to be associated with the decrease in growth rate as the cells approach confluence. Media conditioned by confluent cells reduced prostaglandin E2 production when added to rapidly growing cells, suggesting that an inhibitor of prostaglandin synthesis may be formed by the confluent cultures. Nondifferentiating 3T3 fibroblasts, which similarly release mainly prostaglandin E2, also exhibited a decrease in prostaglandin production as the cultures became confluent. The amounts of prostaglandins produced by 3T3 cells in the confluent state were much greater, however, than those produced by confluent or differentiated 3T3-L1 cultures. These findings suggest that the low capacity to produce prostaglandins may be involved in either the induction or maintenance of differentiation in 3T3-L1 cells.