In vitro metabolic response of articular cartilage segments to low levels of hydrostatic pressure.

Bovine and human articular cartilage segments exhibit variable alterations in metabolism following in vitro exposure to hydrostatic pressure. A decrease in incorporation of the labeled substrates 35SO4, 3H-glycine and 3H-uridine to values less than 50% of non-pressurized tissue results from exposure to pressures between 75 and 300 psi. A pressure of 375 psi consistently results in a 10-15% increase in cartilage synthetic activity in the presence or absence of 10% fetal calf serum. Dialyzed fetal calf serum increases the metabolic response at 375 psi from 10% to 55%. The recovery phase following exposure to pressure includes a release (rebound) phenomenon whereby a burst of metabolic activity elevates the metabolic rate to normal levels when the tissues are inhibited (75-300 psi) and accelerates the metabolic rate by 60% in tissues whose metabolism was elevated (375 psi). These data suggest that articular cartilage chondrocytes have the capacity to rapidly and differentially transform mechanical signals derived from application of hydrostatic pressure into metabolic events. The direction of the response is apparently dictated by the magnitude of the applied force and presence of dialyzable components in serum. Although the force applied only partially mimics in vivo forces, the observed responses to pressure support the thesis that pressure modulation of metabolic activity in articular cartilage may be an important factor in its maintenance.