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Cardiac fibrosis is one of the hallmarks of a diabetic cardiomyopathy. When activated, cardiac fibroblasts (CFs) increase the production of extracellular matrix proteins. Transforming growth factor (TGF)-β1 is known to mediate cardiac fibrosis through the SMAD pathway. High glucose (HG = 25 mM) cell culture media can activate CFs using TGF-β1. There is a need to identify effective antifibrotic agents. Studies in animals indicate that treatment with (−)-epicatechin (Epi) appears capable of reducing myocardial fibrosis. Epi binds to G-protein coupled estrogen receptor (GPER) and activates downstream pathways. We evaluated the potential of Epi to mitigate the development of a profibrotic phenotype in HG stimulated CFs. CF primary cultures were isolated from young male rats and were exposed for up to 48 h HG media and treated with vehicle or 1 μM Epi. Relevant profibrotic end points were measured by the use of various biochemical assays. HG exposure of CFs increased TGF-β1 protein levels by ∼15%, fibronectin ∼25%, urea levels ∼60%, proline incorporation ∼70%, and total collagen ∼15%. Epi treatment was able to significantly block HG induced increases in TGF-β1, fibronectin, urea, proline, and total collagen protein levels. GPER levels were reduced by HG and restored in CFs treated with Epi an effect associated with the activation (i.e., phosphorylation) of c-Src. Epi treatment also reverted SMAD levels. Altogether, results demonstrate that CFs cultured in HG acquire a profibrotic phenotype, which is blocked by Epi an effect, likely mediated at least, in part, by GPER effects on the SMAD/TGF-β1 pathway. [ABSTRACT FROM AUTHOR]