HEPATOCYTE GROWTH-FACTOR, BLOOD CLEARANCE, ORGAN UPTAKE, AND BILIARY-EXCRETION IN NORMAL AND PARTIALLY HEPATECTOMIZED RATS

BACKGROUND: Hepatocyte growth factor (HGF) (also known as scatter factor (SF)) is a heterodimeric protein that is the most potent known complete mitogen for hepatocytes in culture. HGF is a mitogen for many epithelial cells including hepatocytes, kidney tubular epithelial cells, mammary epithelial cells, keratinocytes, etc. The protein encoded by the proto-oncogene c-met is the high affinity receptor for HGF. HGF concentration in the plasma dramatically increases after partial hepatectomy and in fulminant hepatic failure. This study describes the pharmacokinetics of HGF in the rat. EXPERIMENTAL DESIGN: Human recombinant HGF (a gift from Genentech) was radioiodinated and shown to retain biologic activity and structure. Approximately 74 ng of [I-125]HGF was injected into the penile vein of male Fisher rats 5 minutes after a complete bile fistula and jugular venous catheterization were performed for blood and bile sampling. Half of the rats were subjected to 70% partial hepatectomy. RESULTS: The percentage of injected radioactivity present in the liver of control rats was 29.5% +/- 0.5% at 15 minutes and decreased to 8.6% +/- 1.0% at 120 minutes; the kidneys had 6.2% +/- 0.2% at 15 minutes, decreasing to 1.48% +/- 0.3% at 120 minutes. All the other organs examined had less than 1% of the injected radioactivity. The remaining radioactivity was present in low affinity sites in blood, bone, muscle, and skin. In control rats, radioactivity appeared in the bile within 3 minutes, reached a peak between 40 to 50 minutes, and tapered thereafter for a total 2-hour collection of 2.3% +/- 0.5%. In the partially hepatectomized rats, the HGF blood clearance was decreased (partial hepatectomy = 0.27 +/- 0.03 ml/minute; control = 0.53 +/- 0.06 ml/minute, p < 0.006), and the terminal half-life prolonged (partial hepatectomy = 124 +/- 11 minutes; control = 83 +/- 10 minutes, p < 0.03). The initial half-life for HGF, as extrapolated from the chart, was estimated at 3.8 minutes in control rats. CONCLUSIONS: Liver is the principle organ for initial uptake of [I-125]HGF; disappearance from the blood suggests multicompartment kinetics with a rapid phase and a slower phase; only a portion of the hepatic uptake appears in the bile; and partial hepatectomy decreases the blood clearance of [I-125]HGF. These results are correlated with previous findings bearing on the role of HGF elevation after partial hepatectomy as a stimulus for transfer of hepatocytes from G0 to G1 early in liver regeneration after partial hepatectomy.