Zonal distribution of fatty acid synthase in liver parenchyma of male and female rats

1. A sensitive radiochemical assay was established to determine the activity of fatty acid synthase in microdissected liver tissue of less than 1 μ dry mass. 2. In female rats, the enzyme activity in perivenous tissue was twice that in periportal liver tissue while it was homogeneously distributed in livers of male animals. The overall activity was higher in female than in male animals. 3. The absolute activity, as well as the perivenous/periportal ratio, was reduced during starvation and in diabetes. They were greatly increased after refeeding to values above those observed in animals during normal feeding. 4. Overectomy or administration of testosterone to female rats resulted in a significant reduction of the zonal heterogeneity. 5. Castration of administration of estradiol to male animals was followed by an increase in the enzyme activity exclusively in the perivenous tissue, resulting in a zonal heterogeneity as observed in female rats.