CORRELATION BETWEEN SYNTHETIC ACTIVITY AND GLYCOSAMINOGLYCAN CONCENTRATION IN EPIPHYSEAL CARTILAGE RAISES QUESTIONS ABOUT THE REGULATORY ROLE OF INTERSTITIAL PH

Current data provide compelling evidence that the pH of the interstiti al fluid of cartilage is an important determinant of the metabolic act ivity of chondrocytes, and this has served as the basis for a mechanis tic proposal whereby chondrocytes could sense mechanical compression. The objective of the current study was to test this hypothesis further by examining biosynthetic activity in cartilage as a function of glyc osaminoglycan content, which is the major determinant of interstitial pH. On the basis of previous data, increased biosynthetic activity wou ld be anticipated to correlate with a decreased glycosaminoglycan cont ent and an elevated interstitial pH. In contrast to our expectations, we found that the biosynthetic activity (monitored by measurement of i ncorporation of sulfate and proline) was positively correlated with th e glycosaminoglycan content of tissue. These results raise doubt as to whether interstitial pH provides a dominant mechanism for controlling the metabolism of chondrocytes.