In contrast to many differentiated hepatic functions developing after birth, very little is known about in vivo glucocorticoid influences on postnatal expression of fetal liver enzymes, such as GGT. This study showed that cortisol markedly induces liver GGT activity in unweaned rats, but has no effectafter weaning. Enzyme induction was dose- and time-dependent and occurred in parenchymal cells, progressing with time from zone 1 to zone 2 of the liver acinus. Zone-3 hepatocytes were unresponsive even after a 5-day treatment. Lag-times for GGT induction in zones I and 2 of the liver acinus were 1 to 2 days and 2 to 3 days, respectively. From this, a permissive cell change, determined by the hormone administration itself, seems required for the hepatocyte GGT induction by cortisol in pre-weaning rats.

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