Prostaglandins and the Zone of Calcified Cartilage in Osteoarthritis.

The zone of calcified cartilage (ZCC) which provides the critical interface between cartilage and bone acts as the growth plate in the developing joint. In osteoarthritis, it has been hypothesized that the ZCC may again function in joint remodeling. This could result in thinning of the cartilage. This report is the first experimental confirmation of this hypothesis. Osteoarthritis was induced using the Hulth procedure in 2.3--2.7-kg rabbits. Approximately 3 weeks after surgery, half of the menisectomy rabbits and half of the nonmenisectomy rabbits were given 20 &mgr;g of misoprostol interarticularly for 5 days per week for 2.5 weeks. In the patellae and tibial plateau, the rate of movement of the tidemark of the ZCC was measured. Medial aspect femoral condyle cartilage was incubated in the presence of [(35)S]sulfate and [(3)H]proline. After menisectomy, rate of movement of the ZCC was dramatically increased and was unchanged by misoprostol. Proteoglycan synthesis was highly elevated in the osteoarthritis-induced knees, and misoprostol suppressed the rate of [(35)S]sulfate but not [(3)H]proline incorporation.