Longitudinal changes in myocardial basic fibroblast growth factor (fgf-2) activity following coronary artery ligation in the dog

Although fibroblast growth factor has been identified in normal and ischemic myocardium, temporal changes in mitogenic activity due to fibroblast growth factors in ischemic tissue have not been well established, nor has correlation been made with the known early increases in coronary collateral flow. This study sought to measure fibroblast growth factor activity in myocardium after coronary ligation. Accordingly the left anterior descending coronary artery of dogs was ligated and coronary collateral flow measured with radioactive microspheres. The heart was arrested after 2 h (four dogs), 1 weeks (four dogs), or 2 weeks (three dogs), or 8 weeks (four dogs). Just before arrest collateral flow was again measured with radioactive microspheres, and the perfusion territory of the ligated vessel was demarcated with an intracoronary of Evans blue. The stained ischemic region was separated into central and peripheral portions. A transmural sample was removed from each portion for quantitation of tissue radioactivity and the rest was used for isolation of fibroblast growth factor and the measurement of mitogenic activity with vascular endothelial cells. To determine which fibroblast growth factor (FGF-1 or FGF-2) was being produced by the myocardium, aliquots of the isolated protein were first treated with specific antibodies to FGF-1 or FGF-2 before being assayed for mitogenicity. Coronary collateral flow did not change between 5 min and 2 h following coronary ligation, but was significantly increased at later time points. The ischemic/normal myocardial basic fibroblast growth factor mitogenic activity ratio in the peripheral ischemic tissue was increased after 2 h of ischemia (1.41 ± 0.34), but the increase was not significant. Increases at 1 and 2 weeks (1.75 ± 0.25 and 2.55 ± 0.49, respectively) were significant. By 8 weeks the mitogenic activity levels in the ischemic tissue had returned to normal (ratio 0.71 ± 0.12). Mitogenic activity was totally abolished in those samples exposed to anti-FGF-2 before being applied to the vascular endothelial cells, but was unaffected by exposure to anti-FGF-1. Therefore, basic fibroblast growth factor (FGF-2) activity increases in ischemic myocardium in the initial weeks after coronary occlusion but returns to normal by eight weeks. This increase parallels the dramatic early increase in coronary collateral development and flow. Hence FGF-2 is one of the active angiogenic factors produced by ischemic myocardium. These observations support, but do not prove, a relationship between coronary collateral development and changes in basic fibroblast growth factor mitogenic activity.