ACIDIC AND BASIC FGFS DILATE ARTERIOLES OF SKELETAL-MUSCLE THROUGH A NO-DEPENDENT MECHANISM

Fibroblast growth factor (FGFs) have been known to be potent stimulato rs of vascular endothelial cell proliferation and angiogenesis. Recent experimental evidence indicates that basic FGF (bFGF) is also involve d in modulation of arterial pressure. In this study, we investigated t he effects of acidic FGF (aFGF) and bFGF on muscle microcirculation us ing isolated arterioles and intact cremaster muscles of the rat. In is olated microvessels, aFGF and bFGF (10(-12)-10(-8) M) significantly in creased arteriolar diameter in a dose-dependent and time-dependent-man ner. This effect was abolished during inhibition of nitric oxide synth esis by N-G-monomethyl-L-arginine (L-NMMA, 10(-4) M) but was not affec ted by indomethacin (10(-4) M), an inhibitor of the cyclooxygenase pat hway of arachidonic acid metabolism. The vasodilation induced by FGFs was not observed in endothelium-denuded vessels. Furthermore, we studi ed microvascular hemodynamics in response to the growth factors in the cremaster muscle using intravital microscopy. Both aFGF and bFGF dila ted arterioles of the intact cremaster muscle in a pattern similar to that observed in the isolated arterioles. At a concentration of 10(-10 ) M, aFGF caused a 19% increase in vessel diameter and 56% increase in blood flow. Administration of L-NMMA blocked FGF-induced vasodilation and hyperemia. These results suggest that FGFs modulate blood flow in the skeletal muscle by acting on the endothelium of arterioles. The s ignaling mechanism of FGF-induced vasodilation involves the synthesis of nitric oxide by arteriolar endothelium.