Immunoreactive fibroblast growth factor (FGF) in rat tissues: molecular weight forms and the effects of...

Rat tissues were extracted at neutral pH with dilute (0.15 M) ammonium sulfate and examined for presence of fibroblast growth factor immunoreactivity (ir-FGF). Ir-FGF was found in substantial amounts in all the tissues but higher amounts were found in liver and kidney. Gel filtration column chromatography showed the presence of three molecular weight peaks of ir-FGF, one associated with the void volume (the major form in kidney extract), another with an apparent molecular weight of 150-180,000 Da (the major form in serum) and a third one of 70,000 Da (the major form in the other tissues examined: pituitary, brain, liver, spleen and thymus). No immunoreactivity coeluted with authentic FGF purified from bovine pituitary glands, suggesting that FGF is present in neutral extracts in association with binding molecules and/or precursors. Hypophysectomy had no major effect on ir-FGF in the tissues, but increased its amount in serum. The results establish a wide distribution of FGF in several embryologically, morphologically and developmentally distinct tissues and indicate that the pituitary is not the major source of FGF immunoreactivity, although it can be involved in the regulation of plasma levels.