Capacity of a low calcium diet to induce the renal vitamin D 1a-hydroxylase is decreased in adult rats.
Young animals adapt to a low calcium diet by increasing renal production of 1,25-dihydroxyvitamin D [1,25(OH)2D], the active metabolite of vitamin D. However, the capacity of adult animals to adapt is markedly diminished. With the recent cloning of the cytochrome P450 component (CYP1a) of the renal 1-hydroxylase enzyme complex, it is now possible to determine directly the effect of dietary calcium and maturation on the expression of renal 1-hydroxylase. Using a ribonuclease protection assay, it was found that feeding a low Ca diet markedly increased renal CYP1a mRNA levels in young rats. However, feeding this diet to adult rats produced an increase in CYP1a mRNA that was only 10% that of the young rats. These studies demonstrate that a low calcium diet increases renal 1,25-dihydroxyvitamin D production in young animals but not in adult animals by increasing CYP1a expression. Since the low calcium diet increased plasma parathyroid hormone levels to similar levels in both age groups, this suggests that in the adult there is a renal refractoriness to parathyroid hormone.
Geriatric Research, Education, and Clinical Center, St. Louis VA Medical Center, St. Louis, Missouri, 63125, USA. hjarmbrec@aol.com
H J
HJ
Armbrecht
T L
TL
Hodam
M A
MA
Boltz
V B
VB
Kumar
D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000235:genetics*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D004032:Diet; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D007668:Kidney / Q000201:enzymology*; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D014807:Vitamin D / Q000031:analogs & derivatives / Q000378:metabolism
D010281:Parathyroid Hormone; D012333:RNA, Messenger; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; D003577:Cytochrome P-450 Enzyme System; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002118:Calcium