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Objective To determine whether lisinopril, an angiotensin converting enzyme (ACE) inhibitor, and bestatin, an aminopeptidase inhibitor with broad specificity, could affect collagen production in control and transforming growth factor (TGF)-beta(1) -treated cardiac fibroblasts. Design and methods Cardiac fibroblasts from passage 2 from normal male adult rats were cultured to confluency, incubated with or without 600 pmol/l TGF-beta(1) for 2 days in serum-free Dulbecco's modified Eagle's medium and then incubated with the test products (lisinopril or bestatin) for 1 day in this medium with added ascorbic acid, beta-aminoproprionitrile and tritiated proline. Soluble collagen was measured in the conditioned medium and non-soluble collagen in the cell layer. ACE activity was measured fluorimetrically with hippuryl-histidyl-leucine as substrate, and DNA with the bisbenzimide dye, Hoechst 33,258. Aminopepticlase activity was estimated by spectrophotometric determination of the liberation of p-nitroaniline from alanine-p-nitroanilide. Results Lisinopril dose-dependently reduced ACE activity in control and TGF-beta(1)-treated cardiac fibroblasts. Bestatin inhibited the basal and TGF-beta(1)-stimulated aminopeptidase activity in a concentration -depe n dent manner. Lisinopril (110 mumol/1) decreased (P < 0.05) the production of soluble and non-soluble collagen in control cardiac fibroblasts. TGF-beta(1) (600 pmol/1) increased (P< 0.05) the production soluble and non-soluble collagen, and this effect was decreased (P < 0.05) by lisinopril. Bestatin (1100 mumol/l) reduced (P < 0.01) the production of soluble collagen in control and TGF-beta(1) -treated cardiac fibroblasts, but did not affect the production of non-soluble collagen in these cells. Conclusions Our data suggest that ACE and aminopepticlases are involved in the basal and TGF-beta(1)-stimulated production of collagen in adult rat cardiac fibroblasts in culture. (C) 2004 Lippincott Williams Wilkins.