“…Zonal differences in hepatocellular proliferation were already reported in rats and mice for several compounds such as Wy-14,643, which stimulates cell proliferation predominantly in zone 1 (Eacho et al, 1991;Marsman et al, 1988;Wada et al, 1992), ethinyl-estradiol in zone 2 (Mayol et al, 1992;Stephan, 2001), and phenobarbital in zone 3 (Kolaja et al, 1996;Schulte-Hermann et al, 1986). In livers of control rats, cell proliferation is highest in the periportal area and decreases towards the draining vein (Geisler et al, 1994;Heuser, 2000;Stephan, 2001;Werlich et al, 1998;Zaijcek et al, 1985). Since mice, as rodents, are phylogenetically closely related to rats, tremendous differences are not assumed; both species, however, vary to some degree in liver morphology and sometimes show significant differences in compound-related effects.…”