Abstract-Transforming growth factor-␤ (TGF-␤) is a ubiquitous growth-regulating protein with an essential role in tissue repair and formation of extracellular matrix (ECM). To better understand the role of different isoforms of TGF-␤ in the cardiac remodeling process induced by norepinephrine (NE), the expression of TGF-␤1, TGF-␤2, and TGF-␤3 was studied and compared with the expression of collagen. NE (0.1 mg/kg ⅐ h) was intravenously infused in female and male Sprague-Dawley rats for several time periods, and freshly obtained ventricular myocardium after 1 day was dissociated into myocyte and nonmyocyte fractions. Prazosin (0.1 mg/kg ⅐ h) and metoprolol (1 mg/kg ⅐ h) were used to block ␣-and ␤-adrenoceptors, respectively. After NE infusion, the three isoforms of TGF-␤ were differentially induced as far as the magnitude and the time course is concerned. The increased expression of TGF-␤2 started earlier with a maximum after 12 hours and was more pronounced (10-fold elevation) than that of the other two isoforms, with a clear specificity for the left ventricle in female hearts. This specificity was also seen in male rats with 16-fold elevation of TGF-␤2 after 1 day of NE-stimulation. The increase of TGF-␤2 was significant only in the myocyte fraction obtained from female as well as from male hearts. The expression of the mRNA of all TGF-␤ isoforms of collagen type I and type III, and of the matrix metalloproteinase (MMP)-2 and its inhibitor TIMP-2 was reduced predominantly by ␣-adrenoceptor blockade with prazosin. The increase in TGF-␤ isoforms correlated with that of the mRNA expression of collagens, MMP-2 and TIMP-2.

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