Altered chondrocytic oxidative metabolism during the restoration of depleted intercellular matrix

The depletion of proteoglycans (PGs), induced by a single intravenous injection of papain, is a useful model for studying the response of chondrocytes in vivo to injury. The present study concentrated on the activity of enzymes related to the synthesis of PGs, either directly, with uridine diphosphoglucose dehydrogenase (UDPGD), or indirectly, through the general oxidative metabolism of the chondrocytes. Most of the enzymes showed diminished activity on day 2; in some, there was little change in activity, whereas in others there was marked increase in activity over the following days. Thus, on day 9 the activities of glucose-6-phosphate dehydrogenase and of glyceraldehyde-3-phosphate dehydrogenase were twice the original (day 0) values, and those of succinate dehydrogenase and of UDPGD were one and a half times greater than the original activities. Such increased enzymatic activity preceded the increase in PG content, which by day 14 reached up to 80% of the initial value. Both the increased activity and the replenishment of the PG content were inhibited when hydrocortisone (10 mg/kg) was injected.