C-25 hydroxylation of vitamin D3 in periportal and perivenous region of hepatic acinus.

Many biotransformation activities have absolute or modulated localization within the hepatic acinus. To investigate the intrahepatic acinar zonation of vitamin D3 (D3) metabolism, hepatic D3 extraction was investigated by antegrade or retrograde perfusion of normal livers and livers bearing selective periportal (PP) or perivenous (PV) destruction; D3 C-25 hydroxylation was studied after selective harvesting of PP or PV hepatocytes by digitonin-collagenase perfusion. Data indicate that hepatic D3 extraction is not regioselective and not perturbed by destruction of the proximal (PP) or distal (PV) part of the acinus, indicating that D3 extraction takes place in the most proximal hepatocytes being perfused. These observations suggest that, in vivo, D3 extraction will take place according to its concentration gradient within the hepatic acinus, thus resulting in a preferential PP extraction of the vitamin. D3 C-25 hydroxylation was higher in PP than in PV hepatocytes in the presence of 1.9 mM Ca2+, with 25-hydroxyvitamin D3 [25(OH)D3] formation of 34.6 +/- 3.9 and 24.4 +/- 1.1 fmol.h-1.(10(6) hepatocytes)-1, respectively (P less than 0.05). Modulators of extracellular [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)] or intracellular Ca2+ (parathyroid hormone, A23187), however, significantly influenced 25(OH)D3 formation with similar decreases in the PP (31%) and PV (26%) areas in the presence of EGTA but with increases in the presence of Ca2+ ionophore A23187 of 189 +/- 16% in PP and of 260 +/- 20% in PV hepatocytes, resulting in similar production in both regions of the acinus.(ABSTRACT TRUNCATED AT 250 WORDS)