The influence of Vitamin D metabolites on the calcification of cartilage matrix and the C-propeptide of type II collagen (Chondrocalcin)

The influence of vitamin D metabolites (at 1 X 10(-10) M) on the calcification of cartilage matrix (measured by 45Ca2+ uptake) and the C-propeptide of type II collagen (measured by radioimmunoassay) has been studied using organ cultures and chondrocytes isolated from growth plates of vitamin D-deficient and -sufficient 11-day-old rats. Vitamin D-deficient rats had reduced amounts of C-propeptide in their serum and freshly isolated growth plate chondrocytes. In all chondrocytes cultured from vitamin D-deficient animals, the C-propeptide content was maximal at 24 hr whereas calcification continued to increase for up to 72 hr. In organ and chondrocyte cultures of tissue from vitamin D-sufficient rats, both 1,25-dihydroxycholecalciferol (1,25(OH)2D3) and 24,25-dihydroxycholecalciferol (24,25(OH)2D3) were required for maximal stimulation of calcification and maximal increases in C-propeptide content. In these D-replete tissues, 24,25-(OH)2D3 had a less stimulatory effect on both calcification (organ and cell cultures) and C-propeptide (organ cultures only), while 1,25(OH)2D3 alone had no effect in cell cultures but an inhibitory effect in organ cultures. Studies of cells or tissue from growth plates of vitamin D-deficient rats demonstrated that 24,25(OH)2D3 alone produced maximal calcification and maximal increases in the C-propeptide content. 1,25(OH)2D3 generally had an inhibitory effect on both calcification and C-propeptide when used alone. In the presence of 1,25(OH)2D3, the stimulatory effect of 24,25(OH)2D3 was partly abrogated. Maximal stimulation of calcification and increases in C-propeptide by 24,25(OH)2D3 were observed at 1 X 10(-9) M and 1 X 10(-10) M. In none of these studies was there any effect on proteoglycan content.(ABSTRACT TRUNCATED AT 250 WORDS)