Complex cleanup.

-The effect of exogenous and endogenous prostaglandins on the patterns of growth and differentiation of Friend erythroleukaemia cells (FLC) were studied. During the differentiation process, DMSO stimulated PGE synthesis by an average of 95o%. The addition of a long-acting synthetic analogue of PGE2, 16,16-dimethylPGE2-methyl ester (di-M-PGE2) to the culture medium only slightly and temporarily slowed cell growth, with no appreciable induction of differentiation. However, in the presence of DMSO, the same concentration of di-M-PGE2 produced 73 0 inhibition of cell growth and accelerated and potently stimulated haemoglobin production. The action of both di-M-PGE2 and DMSO on cell proliferation was dependent upon the state of cell growth at the time of the administration of these compounds. FLC cultures treated with DMSO+di-M-PGE2 produced considerable amounts of haemoglobin before even one duplication cycle was completed. Both DMSO and di-M-PGE2 stimulated endogenous PGE biosynthesis, and the biosynthetic effect of these compounds was synergistic. Inhibition of endogenous prostaglandin synthesis by indomethacin completely abolished the effects produced by DMSO+di-M-PGE2 on the growth, and substantially reduced the stimulated differentiation of FLC. These data suggest that an endogenously synthesized prostaglandin plays a significant role in both the inhibition of replication and in the stimulation of differentiation induced by DMSO and di-MPGE2 in Friend erythroleukaemia cells.