Clearance of the alpha2 macroglobulin-tripsin complex and uptake of trypsin by perfused liver

RESUMO

The uptake and degradation of the alpha2macroglobulin-trypsin (alpha2m-trypsin) complex have been studied using isolated liver cells but not in the liver as a whole. We report the clearance of the complex by the isolated and exsanguinated liver of Wistar male rats, weighing 150-280 g, and compare it with that of the free enzyme. The hepatic clearance of the alpha2m-trypsin complex follows a pattern with a distribution phase followed by an elimination phase, which contrasts with that of trypsin where only the distribution phase is observed. The extraction of trypsin from the perfusate is Ca2+ -independent (156 + 14 pmol/g liver in the presence of 2.5 mM Ca2+, N = 9, versus 140 + 8 pmol/g liver in its absence, N = 7) and is not affected by 100 mM NH4Cl (152 + 7 pmol/g liver, N = 6), 100 U/ml heparin (164 + 14 p/mol/g liver, N = 5), 30 mul/ml carbon particle suspension (150 + 13 pmol/g liver, N = 7) or an acute-phase situation induced by turpentine (125 + 10 pmol/g liver, N = 6) (P>0.05, ANOVA). The hepatic clearance of the alpha2m-trypsin complex is Ca2+ -dependent (1.8 + 0.2 ml/min in the presence of Ca2+, N = 8, versus 0.6 + 0.03 ml/min in its absence, N = 4), affected by NH4Cl (<0.1 ml/min, N = 7), heparin (1.1 + 0.2 ml/min, N = 6) and the acute-phase (0.6 + 0.1 ml/min, N = 6) but bot by the carbon particle suspension (1.8 + 0.2 ml/min, N = 7). These results show that trypsin is not internalized by hepatocytes (no NH4Cl effect) or Kupffer cells (no carbon particle effect) and that the alpha2m-trypsin complex is internalized in a Ca2+ -dependent process by hepatocytes, but not by Kupffer cells, and is affected by an acute-phase reaction.