Antagonistic reaction of the periportal and perivenous zone in the rat liver after castration and estrogen treatment. Histochemical and biochemical studies on G6PDH and malic enzyme activity.

G6PDH and ME activity was determined biochemically in homogenates and demonstrated histochemically in cryostat sections of rat liver. Control animals were sham-operated, the male and female rats of the experimental groups were castrated. After castration groups of rats were treated with daily doses of 3 or 6 micrograms/estradiol benzoate for 21 days. The results show that in the controls there is a sex-dependent distribution pattern of the two enzymes; in males the rather low activity is mainly located in the periportal area, in females the higher activity is demonstrable in the perivenous area. After castration G6PDH activity (and to a lesser extent ME activity) increases, mainly in the periportal zone. Estrogen treatment results in the high activity of both enzymes, which are exclusively located in the perivenous zone. In the periportal zone no G6PDH or ME activity is demonstrable histochemically. This zone-typical effect of estrogen is interpreted in terms of the concept of Metabolic Zonation, according to which it is supposed that the NADPH generating enzymes in the perivenous area have a lipogenic function whereas the periportal activity contributes to bile acid production.