title: 24,25(OH)2D3 enhances the calcemic effect of 1,25(OH)2D3.
abstract: The effect of 24,25(OH)2D3 on 1,25(OH)2D3-induced hypercalcemia was studied in normal rats. Serum (S) levels and urinary excretion of Ca2+ (UCaV) were measured in (a) control rats, (b) rats receiving a daily sc injection of 54 ng 1,25(OH)2D3, (c) rats receiving 24,25(OH)2D3 in the same dose and same manner, and (d) rats receiving 1,25(OH)2D3 + 24,25(OH)2D3. The animals were housed in metabolic cages and 24-hr urine specimens were collected. After 24 hr SCa2+ increased similarly with 1,25(OH)2D3 and with 1,25(OH)2D3 + 24,25(OH)2D3, while 24,25(OH)2D3 alone did not change SCa2+. UCaV after 24 hr increased significantly less (P less than 0.025) with 1,25(OH)2D3 + 24,25(OH)2D3 than with 1,25(OH)2D3 alone. After 5 days of 1,25(OH)2D3, SCa2+ rose from 5.1 +/- 0.15 to 6.29 +/- 0.08 whereas 1,25(OH)2D3 + 24,25(OH)2D3 effected a greater increase in SCa2+ up to 6.63 +/- 0.09 (P less than 0.01). 24,25(OH)2D3 alone did not change SCa2+. UCaV after 5 days of treatment rose similarly with 1,25(OH)2D3 and with 1,25(OH)2D3 + 24,25(OH)2D3. After 10 days of 1,25(OH)2D3 SCa2+ was 6.17 +/- 0.15 meq/liter while with the combination SCa2+ rose to 6.74 +/- 0.2 (P less than 0.025). 24,25(OH)2D3 alone did not change SCa2+. These results show that (a) 24,25(OH)2D3 alone does not alter SCa2+ in normal rats, (b) combined administration of 1,25(OH)2D3 + 24,25(OH)2D3 enhances the hypercalcemic response to 1,25(OH)2D3 without a parallel increase in UCaV, and (c) it is suggested that the effect of 24,25(OH)2D3 on serum Ca2+ level, at least partly, may result from its hypocalciuric effect.
mesh_terms: D015650:24,25-Dihydroxyvitamin D 3; D000818:Animals; D001842:Bone and Bones / Q000187:drug effects; D002117:Calcitriol / Q000633:toxicity*; D002118:Calcium / Q000097:blood / Q000652:urine; D004100:Dihydroxycholecalciferols / Q000378:metabolism / Q000494:pharmacology*; D004357:Drug Synergism; D006934:Hypercalcemia / Q000139:chemically induced* / Q000378:metabolism; D007684:Kidney Tubules / Q000187:drug effects; D008297:Male; D010710:Phosphates / Q000652:urine; D051381:Rats; D013997:Time Factors
chemical_list: D004100:Dihydroxycholecalciferols; D010710:Phosphates; D015650:24,25-Dihydroxyvitamin D 3; D002117:Calcitriol; D002118:Calcium