Postnatal differentiation of sex-specific distribution patterns of G6Pase, G6PDH and ME in the rat liver

The activity of the liver enzymes G6Pase, G6PDH and ME was studied in rats of 2-9 weeks old by histochemical means. In addition, G6PDH and ME activity was quantitatively determined in homogenates. In the 2nd and 3rd week G6Pase is similarly distributed in both sexes: while in the periportal zone high activity is demonstrable, the perivenous zone shows only low activity. After this period a nearly homogeneous distribution pattern becomes evident in all animals. Sex difference occurs after the 6th week: in the livers of male rats the periportal "maximum" is sometimes combined with a second peak in the perivenous area, in females a steep gradient emerges with high activity in the periportal zone and a low one in the perivenous zone. In the first postnatal weeks G6PDH activity is very low in parenchymal cells, but very prominent in Kupffer cells. Around the 5th week there is an increase, predominantly in the perivenous zone of both sexes. While there is again a further decrease demonstrable in male rats, the G6PDH activity of female rats rises to high adult values. This increase seems to be restricted to the perivenous zone. ME can be demonstrated at first in leucocytes. In the course of the 3rd week there is an increase of activity in both sexes: ME is demonstrable in parenchymal cells of the perivenous area and in scattered hepatocytes of the periportal area. In male rats, the perivenous activity is diminished towards the end of the investigation period, in females, however, a high activity remains in the perivenous zone. The data show that in females the activity of NADP dependent enzymes is high in the perivenous zone, so it may be assumed that a lipogenic area is situated around the terminal efferent vessels. Because of the sex difference this area may be hormone-dependent. The lipogenic area is situated opposite to the gluco(neo)genic area which corresponds to the periportal zone.