[Circadian rhythms in cartilage].

Circadian rhythms in cartilage have been reported repeatedly. However, previous studies used histological analysis or radioisotope-labeled precursors for DNA, collagen and proteoglycan synthesis, and thus it is difficult precisely to evaluate such studies on circadian rhythms in chondrocytes. On the other hand, circadian rhythms in plasma levels of several hormones, which play crucial roles in cartilage metabolism, proved to be significant both in human and animal models. In addition, clock genes--such as Clock, Bmal, Per, Cry and Dec--were identified in suprachiasmatic nucleus (SCN) and some peripheral tissues. These clock genes may be involved in circadian rhythms in cartilage.