24,25(OH)2D3 affects the calcemic effects of 1,25(OH)2D3 by mechanisms independent of intestinal calcium absorption.
To better define the interaction between 1,25(OH)2D3 and 24,25(OH)2D3 in different states of renal function, the fractional absorption of Ca45 (FCa45) and plasma calcium (PCa) were determined in rats with intact kidneys and in rats with reduced renal mass after 5/6 nephrectomy. The two series of experiments were performed in control animals, and in rats treated with: 1) 1,25(OH)2D3, 54 ng/rat/day, 2) 24,25(OH)2D3 in the same dose, and 3) 1,25 and 24,25(OH)2D3 in the same (and equal) doses. In all animals 1,25(OH)2D3 administration was associated with a significant increase in PCa and in FCa45. In rats with normal renal function, however, 24,25(OH)2D3 enhanced and in rats with reduced renal mass it suppressed the hypercalcemic effect of 1,25(OH)2D3. These variations in PCa were not associated with further alteration in FCa45 which was similar after 1,25(OH)2D3 and after combined 1,25 and 24,25(OH)2D3 in normal rats and in rats with chronic renal failure. FCa45 was found to be of the same magnitude in rats with normal renal function and in rats with reduced renal mass. These results confirm previous findings of normal intestinal absorption of Ca in mild to moderate renal failure. The above data suggest that 24,25(OH)2D3 used in an equivalent dose does not influence the intestinal effects of 1,25(OH)2D3. Therefore, the interaction of 1,25 with 24,25(OH)2D3 in rats with intact kidneys or with reduced renal mass occurs at extra-intestinal sites.
Rubinger
D
D
Nephrology Service, Hadassah University Hospital, Jerusalem, Israel.
Krause
I
I
Alkoby-Gibbs
M
M
Popovtzer
M M
MM
D015650:24,25-Dihydroxyvitamin D 3 / Q000494:pharmacology*; D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000097:blood / Q000378:metabolism*; D007408:Intestinal Absorption; D007668:Kidney / Q000378:metabolism; D008297:Male; D009392:Nephrectomy; D051381:Rats
D015650:24,25-Dihydroxyvitamin D 3; D002117:Calcitriol; D002118:Calcium