Vitamin D and Cartilage. I.In VitroMetabolism of 25-Hydroxycholecalciferol by Cartilage*

Abstract

In the present work, the capacity of cartilage to metabolize 25-hydroxycholecalciferol was investigated. Cartilage preparations from growth plate, articular surface, rib, scapula, and ear were isolated from 3-week-old normal rabbits and chickens. Each tissue was separately incubated with tritiated 25-hydroxycholecalciferol (, x 10(-9) M) for 1-24 h. Incubations of kidney and muscle were performed simultaneously for comparison. Similarly, cultured chondrocytes isolated from rabbit growth plate and articular cartilage were incubated for 1 or 20 h in medium free of fetal calf serum. After methanol-chloroform extraction of tissues, cells, and their respective media, chloroform phases were chromatographed on Sephadex LH-20 columns. The results show that kidney and cartilage are able to convert 25-hydroxycholecalciferol into a derivative which migrates in the 24,25-dihydroxycholecalciferol region. Cartilage tissue previously boiled is unable to metabolize 25-hydroxycholecalciferol. The conversion of 25-hydroxycholecalciferol occurs with all types of cartilage and is also observed in incubations of cultured chondrocytes. In the latter, the polar 25-hydroxycholecalciferol derivative is detected as early as 1 h after addition of 25-hydroxycholecalciferol. Two findings suggest that the polar derivative of 25-hydroxycholecalciferol produced by cartilage is 24,25-dihydroxycholecalciferol: 1) the cartilage derivative and 24,25-dihydroxycholecalciferol (synthetic and biosynthetic) comigrate during Sephadex LH-20 and high liquid pressure chromatography; and 2) both the cartilage derivative and 24,25-dihydroxycholecalciferol are sensitive to periodate treatment.

Vitamin D Metabolism in Preterm Infants

“…Together with parathyroid hormone (PTH), it mediates bone resorp tion, but whether it also influences bone accretion is still controversial [8]. In condi tions of euparathyroidism, normocalcemia, and normophosphatemia, renal la-hydroxy lase activity decreases and another enzyme, renal 25-hydroxyvitamin-D-24-hydroxylase, becomes predominantly active, yielding 24,25-dihydroxyvitamin D. It has been sug gested that this metabolite, as present in rat epiphyseal cartilage, may play, however, a role in endochondral bone formation [9], The prevailing hypothesis is, that it repre sents the initiation of the degradation path way for l,25-(OH)2D. It will thus not be fur ther discussed in this paper [10],…”

Enhancement of 24,25-Dihydroxyvitamin D Levels in Patients Treated with Continuous Ambulatory Peritoneal Dialysis

“…The kidney is probably the major site of production of 24,25(OH)2D, [3], but extrarenal sites also exist, notably gut [4] and cartilage [5], Generation of this metabolite in all these sites is dependent on the 24-hydroxylase enzyme system. The renal 24-hydroxylase seems to be mainly stimulated by plasma levels of l,25(OH)2D, or normal serum calcium levels, but suppressed by raised levels of parathyroid hormone (PTH) or serum calcium [6].…”

Impaired 24,25-Dihydroxyvitamin D Production in Anephric Human and Pig

“…Another important aspect of this study is whether anephrics of any species have the ability to produce 24,25-(OH)2D in extrarenal tissues such as the intestine (15) or bone (16). Taylor (10) (Figs.…”