title: Rapid nongenomic inhibition of renal 25-hydroxyvitamin D3 1-hydroxylase by 1,25-dihydroxyvitamin D3.
abstract: The physiological role of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] in inhibition of its own formation remains obscure. This study utilizes a kidney slice system to study the effect of physiological concentrations of 1,25(OH)2D3 on 25-hydroxyvitamin D3 1-hydroxylase (1-hydroxylase) formation in vitamin D-replete rats fed a normal-phosphate (NP) or low-phosphate (LP) diet. In vitro, 1-hydroxylase activity was assessed by measuring 1,25(OH)2D3 accumulation at 30 or 60 min after addition of 25-hydroxyvitamin D3 substrate. Degradation of 1,25(OH)2D3 was also assessed over 60 min. Rats fed the LP diet had a threefold increase in 1-hydroxylase activity but the same rate of degradation of 1,25(OH)2D3 as those fed the NP diet. The addition of 50 pM 1,25(OH)2D3 caused a proportional inhibition of 1-hydroxylase in NP and LP rats when added before or 10 min after addition of substrate but not at later time points; 150 pM 1,25(OH)2D3 completely inhibited 1-hydroxylase in the NP but not the LP rats. This inhibitory effect was not reversed by actinomycin D or cycloheximide. These results indicate that physiological concentrations of 1,25(OH)2D3 directly and rapidly modulate 1-hydroxylase activity via a nongenomic mechanism in both LP and NP diet rats.
authors.affiliation: Department of Medicine, University of Western Australia.
authors.forename: I M
authors.initials: IM
authors.lastname: Dick
authors.forename: R
authors.initials: R
authors.lastname: Retallack
authors.forename: R L
authors.initials: RL
authors.lastname: Prince
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000037:antagonists & inhibitors*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002112:Calcifediol / Q000378:metabolism; D002117:Calcitriol / Q000378:metabolism / Q000494:pharmacology*; D002118:Calcium / Q000097:blood; D003513:Cycloheximide / Q000494:pharmacology*; D003609:Dactinomycin / Q000494:pharmacology*; D004032:Diet; D066298:In Vitro Techniques; D007668:Kidney / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D007700:Kinetics; D008297:Male; D010710:Phosphates / Q000097:blood; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors*
chemical_list: D010710:Phosphates; D003609:Dactinomycin; D003513:Cycloheximide; D013250:Steroid Hydroxylases; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium