Differential enzyme distribution in lobules of livers from young and old mice and rats.

In the livers from young (3–6 month) and old (30 month) C57/BL mice and BN/Bi rats light microscope histochemistry has shown that enzyme activity is not always distributed evenly throughout the lobule. The mitochondrial enzyme succinic dehydro-genase, the plasma membrane enzyme 5’-nucleotidase and the endoplasmic reticulum enzyme glucose-6-phosphatase showed heavier reaction product in the periportal regions of the lobule compared with the centrilobular regions. Alkaline phosphatase showed an altered distribution pattern with age: in young livers this was uniform throughout the lobule while in old livers there was enhanced periportal activity. Electron microscope cytochemistry showed that this was due to increased numbers of bile canaliculi in this region containing reaction product and to the additional presence of reaction product associated with the microvilli lining the space of Disse.