DEHYDROGENASES IN DEVELOPING BONE IN THE RAT

Sections of mandibles from seventy-five 5-day old rats were studied histochemically for malic, isocitric, α-glycerophosphate, glutamic, lactic, 6-phosphogluconic, glucose-6-phosphate, d(—)- β-hydroxybutyric and succinic dehydrogenases and TPN- and DPN-diaphorases. All the enzymes studied (except TPN-glutamic dehydrogenase) were found in osteocytes, osteoblasts and osteoclasts. The results suggest that all bone cells possess fully functional citric acid cycles, pentose cycles, and the capacity to metabolize fatty acids and carbohydrates. Osteoclasts generally exhibited greater enzymatic activity than either osteoblasts or osteocytes indicating a strong broad metabolic capacity. The demonstration of isocitric dehydrogenase in osteoclasts tends to discredit Walker's theory of bone resorption (18).