Department of Pathology, The University of Michigan Medical School, Ann Arbor, Michigan 48109 Received August 3, 1987; Revised Manuscript Received December 11, 1987 abstract: Arachidonate metabolites are potent biological mediators affectingmultiple cellular functions. Although prostaglandins of the E series, which are products of the cyclooxygenase pathway, have been known as inhibitors or down-regulators of fibroblast proliferation and collagen synthesis, the more recently discovered products of the 5-lipoxygenase pathway have not been as extensively investigated with regard to fibroblast function. In this study, a sulfidopeptide product of the lipoxygenase pathway, leukotriene C4 (LTC4), was examined for its ability to modulate rat lung fibroblast collagen synthesis and proliferation in vitro. The data revealed the ability of LTC4 and to a lesser extent leukotriene D4 (LTD4) to stimulate collagen synthesis in a dose-dependent (10_! 1-10-8 M) manner without affecting cellular proliferation as determined by radiolabeled thymidine incorporation; 1 nM LTC4 caused an 85%(p< 0.02) increase above untreated controls in [3H] proline incorporation into collagenous protein in the media, which was blocked by the putative leukotriene receptor antagonist FPL55712 (10 mM) and inhibited by cycloheximide and actinomycin D. This LTC4 stimulatory effect was slightly more specific for collagen synthesis vs noncollagenous protein synthesis but was not accompanied with any change in the collagen type composition. Binding of [3H] LTC4 to these cells was specific, reversible, and saturable, with a Afd of 1.8±0.95 nM. Under equilibrium conditions, there was an estimated 2.39 X 104 receptors per cell. This binding was also inhibited by 10 jitM FPL55712. Competitive binding studies show specificity of this binding for LTC4 relative to LTD4 and FPL55712. Furthermore, no significant conversion of LTC4 to LTD4 or leukotriene E4 was noted during the binding studies. These results indicate the presence of specific LTC4 receptors on these cells which may mediate the cellular effects on protein and collagensynthesis.

T_Jnderstanding how arachidonate metabolites affect fi-broblast growth and function is critical for uncovering the mechanism by which these substances initiate, maintain, and/or down-regulate the fibrogenic response in fibrotic dis-eases. Recent studies have demonstrated the inhibitory effects of prostaglandin E2 (PGE2)‘on fibroblast growth and collagen