The selective action of papain on calcification sites

Abstract

Young rats were injected intraperitoneally with a solution of crude papain for 7 days, some being examined at daily intervals. After 7 days, the remainder were allowed to live for 16 more days, some being examined at 3 day intervals. The cartilages of the tibial, fibular and skull base epiphyses and of the mandibular and upper tibial condyles were examined histologically. It was found that the epiphyseal growth cartilages were severely affected, the cartilages becoming narrow, the cells disoriented and losing their characteristic shape, bone formation stopping and the cartilage in some cases being sealed off with bone. The changes were most extreme in the tibia and skull base, and little recovery was seen over the experimental period. In contrast, the fibular cartilage made an almost complete recovery. The articular cartilages of the mandible and tibia were virtually unaffected architecturally, though in common with all cartilage they lost their metachromasia, which returned when the injections were stopped. It is postulated that high metabolic activity plus pressure or stress are contributing factors towards sensitivity to the enzyme. Endosteal bone formation and tooth formation were unaffected by papain. Sudan black stains calcifying sites, but does not do so by staining mucopolysaccharides. It is concluded that these substances play no direct part in the calcification mechanism. Under the experimental conditions described, the action of excess vitamin A upon bone formation bears no resemblance to that of papain as has been claimed by others.