CHANGES IN COLLAGEN-METABOLISM IN RESPONSE TO ENDOTHELIN-1 - EVIDENCEFOR FIBROBLAST HETEROGENEITY

Endothelin-1 (Et-1) is a 21-amino acid peptide primarily synthesized b y endothelial cells. It was originally classified as a potent vasocons trictor but recent evidence suggests that it also possesses a wide var iety of non-vascular actions. It stimulates fibroblast and smooth musc le cell proliferation and it has been shown to stimulate fibroblast co llagen metabolism. However, studies on its ability to regulate collage n production remain incomplete, and its effect on post-translational p rocessing of procollagen has not been studied. This report details the effect of Et-l on the rates of procollagen synthesis and degradation in two fibroblast cell lines; human foetal lung (HFL-1) and whole foet al rat fibroblasts (Rat 2). Fibroblast cultures were incubated for 24h r in the presence or absence of Et-l before procollagen metabolism was determined by measuring hydroxyproline. Non-collagen metabolism was a lso determined in these cultures from the uptake of tritiated phenylal anine. Et-l stimulated procollagen synthesis in HFL-1 fibroblasts and reduced :synthesis in Rat 2 cells. The response was dose dependent wit h the greatest effect at 1.10(-6)M Et-1 for both cell types (155 +/- 6 % of control (mean +/- SD, n = 6, P < 0.01) and 61 +/- 4% of control ( n = 4, P < 0.01) for HFL-1 and Rat 2 fibroblasts, respectively). Non-c ollagen protein synthesis was increased to 148 +/- 5% of control (P < 0.05) at 1.10(-6)M Et-1. Non-collagen protein synthesis remained unaff ected in the HFG-1 fibroblast cultures. Procollagen degradation, expre ssed as a proportion of total procollagen synthesis, was decreased in HFL-1 fibroblasts (control, 29 +/- 2%; Et-1, 1.10(-6)M; 21 +/- 2%; P < 0.01), and increased in Rat 2 fibroblasts (control 42 +/- 1%; Et-1, 1 .10(-6)M; 49 +/- 1%; P < 0.01). Blocking of tbe Et(A) receptor for Et- l, using the receptor antagonist- BQ123, abolished the effect of Et-1 on procollagen metabolism in both cell types. These results suggest th at different populations of fibroblasts exhibit heterogeneous response s to Et-1. It is concluded that Et-1 may play an important role in the extent and distribution of fibrosis seen in diseases associated with the overproduction of Et-1.