Local action of exogenous growth hormone and insulin-like growth factor-I on dihydroxyvitamin D production in LLC-PK1 cells.
Previous in vivo studies have shown that growth hormone (GH) affects vitamin D and mineral metabolism. Insulin-like growth factor-I (IGF-I) was recently reported to be a regulator of renal 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) production, suggesting that it mediates the effects of GH on vitamin D metabolism. However, there is no direct evidence to support this. The present study was designed to investigate the in vitro effects of GH and IGF-I on the renal production of 1,25-(OH)2D3 and 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3) in a pig kidney cell line, LLC-PK1. Confluent cells were preincubated in serum-free medium with hormone (GH or IGF-I) or vehicle, and then incubated with 25-[3H]OHD3. The levels of 1,25-[3H](OH)2D3 and 24,25-[3H](OH)2D3 produced were determined after lipid extraction and HPLC purification. Production of 1,25-(OH)2D3 and 24,25-(OH)2D3 was increased after both IGF-I and GH preincubation in a dose-dependent manner. Significant increases were found after preincubation with 13 nmol/l IGF-I (1,25-(OH)2D3, 1.8-fold: 24,25-(OH)2D3, 1.5-fold)or 0.9 or 9 nmol/lGH (1,25-(OH)2D3, 1.3-fold and 1.5-fold; 24.25-(OH)2D3, 1.4-fold and 1.5-fold respectively). Furthermore, the effect of 9 nmol/l GH on 1.25-(OH)2D3 and 24,25-(OH)2D3 production was blocked in the presence of IGF-I receptor monoclonal antibody. These results confirm that IGF-I acts on renal tubules, resulting in induction of 1,25-(OH)2D3 and 24,25-(OH)2D3 production, and the findings suggest that GH stimulates 1.25-(OH)2D3 and 24,2 5-(OH)2D3 production by increasing local IGF-I production in the kidney.
Wei
S
S
Department of Pediatrics, Okayama University Medical School, Japan.
Tanaka
H
H
Seino
Y
Y
D015650:24,25-Dihydroxyvitamin D 3 / Q000096:biosynthesis*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D002117:Calcitriol / Q000096:biosynthesis*; D002851:Chromatography, High Pressure Liquid; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D013006:Growth Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000494:pharmacology*; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D018374:LLC-PK1 Cells; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors; D013552:Swine
D000911:Antibodies, Monoclonal; D003470:Culture Media; D015650:24,25-Dihydroxyvitamin D 3; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D017526:Receptor, IGF Type 1; D002117:Calcitriol