title: Local action of phosphate depletion and insulin-like growth factor 1 on in vitro production of 1,25-dihydroxyvitamin D by cultured mammalian kidney cells.
abstract: The hormonal form of vitamin D, 1,25(OH)2D, is synthesized mostly in proximal renal tubular cells. Experimental and clinical studies suggest that the growth hormone may be involved in growth-related fluctuations of plasma 1,25(OH)2D and in the increase of 1,25(OH)2D induced by in vivo phosphate deprivation, an action possibly mediated by insulin-like growth factor 1 (IGF 1). We tested the effects of phosphate depletion and IGF 1 addition on 1,25(OH)2D3 production in cultured kidney cells: opossum kidney (OK) cells, LLC-PK 1, and rabbit's proximal tubular cells. Confluent cell monolayers were preincubated in various phosphate concentrations, in the presence and absence of IGF 1. Then, 5 nM of [3H]25 (OH)D3 or 2 microM of 25 (OH)D3 were added to the medium and the cells were incubated for a further 120 min. The amount of biosynthesized 1,25(OH)2D3 in lipid extracts was determined after two different straight phase high performance liquid chromatographies. The experiment showed the following: (a) LLC-PK 1 and rabbit's cells expressed a detectable ability to synthesize 1,25(OH)2D3, while OK cells did not. (b) Partial or total phosphate deprivation increased the amount of 1,25(OH)2D3 produced, respectively in LLC-PK 1 and in rabbit's cells. (c) IGF 1 (25 ng/ml) increased 1,25(OH)2D3 production in rabbit's cells, particularly in phosphate-free medium (1.6-fold), and in LLC-PK 1 cells, in partial phosphate depletion (2.75-fold in 1 mM phosphate, P = 0.015, n = 5, and 3.2-fold in 0.5 mM phosphate, P = 0.043, n = 4). Our findings demonstrate a local action of phosphate depletion and of IGF 1 on 1,25-dihydroxyvitamin D3 production.
authors.affiliation: CNRS URA 583, Hôpital Saint Vincent de Paul, Paris, France.
authors.forename: L
authors.initials: L
authors.lastname: Condamine
authors.forename: C
authors.initials: C
authors.lastname: Menaa
authors.forename: F
authors.initials: F
authors.lastname: Vrtovsnik
authors.forename: F
authors.initials: F
authors.lastname: Vztovsnik
authors.forename: G
authors.initials: G
authors.lastname: Friedlander
authors.forename: M
authors.initials: M
authors.lastname: Garabédian
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003470:Culture Media; D004100:Dihydroxycholecalciferols / Q000096:biosynthesis* / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism; D018374:LLC-PK1 Cells; D009893:Opossums; D010710:Phosphates / Q000378:metabolism*; D011817:Rabbits; D013552:Swine
chemical_list: D003470:Culture Media; D004100:Dihydroxycholecalciferols; D010710:Phosphates; D007334:Insulin-Like Growth Factor I