Drug metabolism by periportal and perivenous rat hepatocytes: Comparison of phase I and phase II reactions and their inducibility during culture

Abstract

Hepatocytes were aseptically isolated from either the periportal ( pp; zone 1) or the perivenous (pv; zone 3) region by digitonin-collagenase perfusion and cultured on type I collagen for 4 to 9 days. In freshly isolated cells the pp : pv activity ratios of the acinar marker enzymes γ-glutamyltranspeptidase (γ-GT), alanine aminotransferase (ALAT) and glutamate dehydrogenase (GLDH) were 2.8, 1.6 and 0.76, respectively. During culture ALAT and GLDH activities gradually declined, but the pp-pv difference was retained for at least 4 days. In contrast, the difference in the γ-GT activity was rapidly lost, due to its fast initial activation in pv cells. The initial 7-ethoxycoumarin O-deethylase (ECDE) activity was higher in pv cells; this difference was retained for several days of culture and was increased by induction in vitro with either phenobarbital (PB) or β-naphthoflavone (βNF). Although the basal UDP-glucuronyltransferase (UDPGT) activity with either p-nitrophenol ( pNP) or hydroxybiphenyl (HBP) as substrate did not differ significantly, the in-vitro PB- or βNF-induced activity was higher in pv cells. Both glucuronidation and sulfation of methylumbelliferone tended to be higher in pv cells. Glutathione S-transferase was initially significantly higher in pv cells and this difference was augmented after in vitro induction by PB or βNF. After six days in culture all the observed pp-pv differences had disappeared. These results suggest that hepatocytes isolated from the perivenous region seem to maintain their initially higher capacity for phase I and phase II drug reactions during culture and also respond more strongly than periportal cells to in vitro induction.