The enzyme histochemistry of the osteoclasts of normal and “ia” rats

Enzymes involved in oxidative metabolism as well as acid phosphatase were studied histochemically in osteoclasts from newborn normal rats and their littermates who suffered from a generalized defect in bone resorption (the “ia” rat). The osteoclasts of normal rats demonstrated intense activity for DPNH and TPNH diaphorase as well as succinic, malic and lactic dehydrogenase. Isocitric and glutamic dehydrogenase were less than one‐half as active but no less definite. In the “ia” rat the reaction for the diaphorases and dehydrogenases were exactly as observed in the normal. Acid phosphatase was observed in normal osteoclasts as a general cytoplasmic reaction and also in a band of concentrated activity at the junction of the cell and bone. The osteoclasts from “ia” animals had greater acid phosphatase activity (more than twice as reactive) than the normal. However, the “junctional band” was only rarely observed in this anomaly. The junctional band may represent sites into which enzymes such as acid phosphatase are secreted in the resorption process and therefore only associated with active osteoclasts. It is possible that the “ia” rat may successfully form but not secrete the enzyme.