Plasma-kallikrein clearance by the liver of acetaminophen-intoxicated rats.
The liver synthesizes prokallikrein and is the main organ to clear the active enzyme (plasma-kallikrein) from circulation. This clearance, a receptor-mediated endocytosis, is calcium-independent and not affected by the blockade of Kupffer cells. The effects of endothelial cells blockade and of acetaminophen intoxication on the clearance of 10 nM rat plasma-kallikrein (RPK) by the isolated, exsanguinated and perfused rat liver are now reported. Endothelial cells blockade obtained by the addition of large excess (30 uM) of formaldehyde-treated serum albumin to the perfusion fluid does not affect the hepatic clearance of RPK (the half-lives of hepatic uptake were 15.5 +/- 1.0 min in the absence versus 16.5 +/- 1.4 min in the presence of the treated protein, p > 0.05). Some livers were perfused 24 hours after acetaminophen intoxication: 6.6 mmol/kg given i.p. after a 42-hour period of fast. Hepatocyte injury suggested by elevated aminotransferase activity (ALT 10 times control value, AST 30 times control value), acute phase inflammatory response (serum alpha 2-macroglobulin increase) and reduced synthetic function (serum albumin decrease), was confirmed histologically and only zone 3 hepatocytes were necrotic. A 66-hour period of fast does not affect by itself the hepatic clearance of RPK (16.9 +/- 1.3 min of half-life of hepatic uptake) when compared with the control group (15.5 +/- 1.0 min, p > 0.05). On the other hand the RPK clearance by the livers of rats previously intoxicated with acetaminophen was markedly deficient (the half-life of hepatic uptake was 39.2 +/- 3.2 min). These findings suggest that RPK is internalized by hepatocytes, preferentially by those of the perivenular zone of the hepatic acinus.
de Toledo
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CF
Departamento de Medicina, Escola Paulista de Medicina, São Paulo, Brasil.
Borges
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DR
D000082:Acetaminophen / Q000633:toxicity*; D000818:Animals; D001692:Biological Transport; D005215:Fasting; D007610:Kallikreins / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008107:Liver Diseases / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D051381:Rats; D017208:Rats, Wistar / Q000097:blood
D000082:Acetaminophen; D007610:Kallikreins