On the mechanism of induction of DNA synthesis in cultured arterial smooth muscle cells by leukotrienes. Possible role of prostaglandin endoperoxide synthase products and platelet-derived growth factor.

The induction of DNA replication in rat aortic smooth muscle cells (SMCs) by leukotrienes (LTs) was studied in order to elucidate the mechanisms of action in further detail. The effect of LTB4 was blocked by the prostaglandin (PG) synthesis inhibitor indomethacin and the effects of LTC4 and LTD4 were blocked by the cysteinyl-containing leukotriene receptor antagonists FPL 55712 and ICI 198615. These observations suggest that LTB4 and the cysteinyl-containing leukotrienes act via distinct receptors and point to a role for prostaglandin endoperoxide synthase products in bringing about the effect of LTB4. Radioimmunological determinations and analyses of [3H]arachidonic acid metabolism showed that the SMCs were able to synthesize PGI2 (measured as the stable metabolite 6-keto-PGF1 alpha), PGE2, PGF2 alpha and 15(S)hydroxy-eicosatetraenoic acid (15(S)HETE). Moreover, picomolar concentrations of arachidonic acid, PGI2, PGE2, PGF2 alpha and 15(S)HETE induced DNA replication in the SMCs under serum-free conditions, whereas linoleic acid, 6-keto-PGF1 alpha and 5(S)HETE were inactive in this respect. Analysis of conditioned media for mitogenic activity (with or without antibodies against platelet-derived growth factor, PDGF) and for the presence of material competing with radioiodinated PDGF for binding to specific cell surface receptors indicated that LTB4 stimulated release of PDGF or a PDGF-like molecule from the cells. These findings suggest that the growth-promoting effect of LTB4 is mediated via a prostaglandin endoperoxide synthase product and/or PDGF produced by the cells themselves.