Cyclic succinic dehydrogenase activity in rat liver mitochondria

Succinic dehydrogenase activity was assayed in isolated rat liver mitochondria. Rats had been exposed for at least two weeks to a 24 hour feeding-fasting schedule, 5 hours feeding, 19 hours fasting. Enzyme activity was determined at nine specific hours over a 24 hour period. Lowest enzyme activity occured six hours after the feeding cages had been closed. The highest activity, which was 158 percent greater than the lowest activity, occurred during the next feeding period. It is concluded that time of sacrifice is an important consideration when determining succinic dehydrogenase activity.     

17-beta-Hydroxysteroid dehydrogenase in rabbit bone marrow

Because of the general presence of 17-B-hydroxysteroid dehydrogenase (17-B-HSD) in animals and human erythrocytes, it is very likely that this enzyme is also present in the erythrocyte precursor cells in bone marrow. Adult male white New Zealand rabbits were used to demonstrate the existence of the 17-B-HSD in bone marrow cells and to evaluate the biological function of 17-B-HSD in the erythropoietic system in bone marrow. Anemia was artificially induced in these animals in order to stimulate the proliferation of erythropoietic cells. This was accomplished by bleeding or by intra-peritoneal injection of 40 mg/kg of phenylhydrazine. The 17-B-HSD activities were then examined by histochemical and biochemical assays. The results showed a two to three-fold increase of the enzyme activities in both peripheral erythrocytes and bone marrow cells of anemic animals. Our experiments further demonstrate the fine control of erythropoiesis. The enzyme, which favors the conversion of oestradiol to oestrone, is itself boosted by an anemic state. As a result, the inhibitory action of hemopoiesis by oestradiol was relieved.