Regulation of the renal 25 OH D3hydroxylases by vitamin D3metabolites and analogues in primary chick kidney cell cultures

We have previously shown that 1,25 (OH)2D3acts directly on the kidney cells to regulate the activities of the renal hydroxylases (Spanos et al. 1978). The aim of this study was to investigate whether metabolites other than 1,25 (OH)2D3could also produce similar effects. To this end, primary chick kidney cell cultures were used to study the effects of vitamin D3, its metabolites and analogues on the renal hydroxylases.Fig 1. shows the enzyme activities obtained in confluent chick kidney cell monolayers when they were tested for their ability to metabolize 25-OHD3at different time intervals. The 1a–hydroxylase activity increased progressively reaching a maximum at 7.5 h after which it declined slightly and then remained constant for the whole experimental period. In contrast, the 24–hydroxylase activity declined slowly during the first 24 hours and disappeared rapidly following a second replacement of the