title: Renal effect of vitamin D metabolites: evidence for the essential role of the 25(OH) group.
abstract: The effects of 1 alpha (OH)vitamin D3 [1 alpha (OH)D3] and 24,25(OH)2vitamin D3 [24,25(OH)2D3] on the phosphaturic action of parathyroid hormone (PTH) were studied in two groups of parathyroidectomized (PTX) rats. In group 1, PTX PTH-infused rats received intravenous 1 alpha (OH)D3, and in group 2, PTX PTH-infused rats received intravenous 24,25(OH)2D3. PTX PTH-infused rats served as controls. The effects of both vitamin D metabolites on renal PTH-activated adenylate cyclase (AC) were studied in vitro. In group 1, PTH increased fractional excretion of phosphate (CP/CIn) from 0.045 +/- 0.012 (+/- SE) to 0.263 +/- 0.011 (P less than 0.005). 1 alpha (OH)D3 failed to influence this response. In group 2, PTH increased CP/CIn from 0.055 +/- 0.008 to 0.289 +/- 0.027 (P less than 0.005). 24,25(OH)2D3 reduced the PTH-induced rise in CP/CIn from 0.289 +/- 0.027 to 0.192 +/- 0.021 (P less than 0.01) and decreased the urinary excretion of adenosine 3',5'-cyclic monophosphate. In vitro, 24,25(OH)2D3 blunted the PTH-activated AC, whereas 1 alpha (OH)D3 had no effect. These results show that 24,25(OH)D3, similar to two other 25(OH) metabolites of vitamin D-25(OH)vitamin D3 and 1,25(OH)2vitamin D3-suppresses the phosphaturic action of PTH, whereas 1 alpha(OH)D3, which is devoid of a 25(OH) group, lacks this effect. This suggests that a 25(OH) group is a prerequisite for the antiphosphaturic effect of vitamin D, whereas the 1 alpha (OH) group is not essential for this action.
mesh_terms: D015650:24,25-Dihydroxyvitamin D 3; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D004100:Dihydroxycholecalciferols / Q000494:pharmacology*; D005919:Glomerular Filtration Rate / Q000187:drug effects; D006887:Hydroxycholecalciferols / Q000494:pharmacology*; D007444:Inulin; D007668:Kidney / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010280:Parathyroid Glands / Q000502:physiology; D010281:Parathyroid Hormone / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013329:Structure-Activity Relationship
chemical_list: D004100:Dihydroxycholecalciferols; D006887:Hydroxycholecalciferols; D010281:Parathyroid Hormone; D010710:Phosphates; D015650:24,25-Dihydroxyvitamin D 3; D007444:Inulin; D000262:Adenylyl Cyclases; D002118:Calcium; C008088:alfacalcidol