In situ localization of transforming growth factor beta 1 in porcine heart: enhanced expression after chronic coronary artery constriction.

We investigated the expression of transforming growth factor beta 1 (TGF-beta 1), a polypeptide differentiation factor probably associated with angiogenic properties in chronically hypoperfused heart tissue. A slowly swelling ameroid constrictor was implanted around the coronary circumflex artery (CX) of young domestic pigs. Two to three weeks after, significant CX stenosis of more than 90% and coronary collateralization could be demonstrated angiographically. The CX dependent experimental myocardial tissue (E) was investigated, with the LAD dependent area of the same pig serving as a control (C). We found significantly enhanced TGF-beta 1 mRNA expression by northern blot hybridization in the experimental myocardium (E) of those pigs with demonstrable coronary collaterals in the absence of a major myocardial infarction. The presence of TGF-beta 1 protein could be demonstrated quantitatively in extracts of the experimental and the control area by immunoblot analysis. By in situ techniques, TGF-beta 1 mRNA and protein could be localized predominantly in cardiac myocytes. We conclude that one adaptive mechanism of the pig heart in chronic coronary artery constriction is the enhanced expression of TGF-beta 1. Cardiac myocytes are a major source of TGF-beta 1. The observed coronary collateralization could be mediated-at least in part-by the angiogenic properties of TGF-beta 1.