Regulation of the Renal Hydroxylases by Other Factors

It is well known that strontium brings about a vitamin D-resistant rickets and markedly reduces intestinal calcium absorption It is now clear that the feeding of strontium represses the renal 25-OH-D3-la-hydroxylase and that the administration of 1,25-(0H)2D3 to strontium-fed animals will restore their ability to absorb calcium Thus at least in part the metabolic basis for strontium-induced rickets has been solved. Recent results suggest that strontium suppresses the 1-hydroxylase by suppressing parathyroid secretion  

The administration of large amounts of ethane-1 -hydroxy-1,1 -diphosphonate (EHDP) has been shown to cause vitamin D-resistant rickets and a markedly repressed intestinal calcium absorption. This has also been shown to be due to a repressed 1,25-(OH)2D3 biosynthesis The repressed intestinal absorption brought by the large amount the EHDP can be completely reversed by the exogenous administration of l,25-(OH)2D3 It is unknown how the EHDP blocks the 1-hydroxylase, but it is not the result of direct inhibition  

Calcium demands are highest during periods of rapid growth, pregnancy and lactation. It is attractive to conader that during these periods increased amounts of 

25-(0H)2D3 are made. Blood levels of 1,25-(OH)2D3 have been reported to be high during these periods It has also been reported that growth hormone and prolactin stimulate the 25-OH-D3-l-hydroxylase These reports remain to 

During egg shell formation in birds, there is great demand for calcium  

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