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Vitamin D status and metabolism in an ovine pregnancy model: effect of long-term, high-altitude hypoxia.

ABSTRACT: Vitamin D status increases during healthy mammalian pregnancy, but the molecular determinants remain uncharacterized. The first objective of this study was to determine the effects of pregnancy, and the second objective was to examine the role of chronic hypoxia on vitamin D status and metabolism in an ovine model. We analyzed the plasma levels of cholecalciferol, 25-OH-D, and 1?,25-(OH)2D in nonpregnant ewes, near-term pregnant ewes, and their fetuses exposed to normoxia (low altitude) or hypoxia (high-altitude) for 100 days. Hypoxic sheep had increased circulating levels of 25-OH-D and 1?,25-(OH)2D compared with normoxic sheep. Hypoxia increases in 25-OH-D were associated with increased expression of renal 25-hydroxylases CYP2R1 and CYP2J. Pregnancy did not increase further the plasma levels of 25-OH-D, but it significantly increased those of the active metabolite, 1?,25-(OH)2D, in both normoxic and hypoxic ewes. Increased bioactivation of vitamin D correlated with increased expression of the vitamin D-activating enzyme CYP27b1 and decreased expression of the inactivating enzyme CYP24a1 in maternal kidneys and placentas. Hypoxia increased parathyroid hormone levels and further increased renal CYP27b1. Pregnancy and hypoxia decreased the expression of vitamin D receptor (VDR) in maternal kidney and lung, with opposite effects on placental VDR. We conclude that ovine pregnancy is a model of increased vitamin D status, and long-term hypoxia further improves vitamin D status due to pregnancy- and hypoxia-specific regulation of VDR and metabolic enzymes.

SUBMITTER: Goyal R

PROVIDER: S-EPMC4935137 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Vitamin D status and metabolism in an ovine pregnancy model: effect of long-term, high-altitude hypoxia.

Goyal Ravi R Billings Tara L TL Mansour Trina T Martin Courtney C Baylink David J DJ Longo Lawrence D LD Pearce William J WJ Mata-Greenwood Eugenia E

American journal of physiology. Endocrinology and metabolism 20160503 11

Vitamin D status increases during healthy mammalian pregnancy, but the molecular determinants remain uncharacterized. The first objective of this study was to determine the effects of pregnancy, and the second objective was to examine the role of chronic hypoxia on vitamin D status and metabolism in an ovine model. We analyzed the plasma levels of cholecalciferol, 25-OH-D, and 1α,25-(OH)2D in nonpregnant ewes, near-term pregnant ewes, and their fetuses exposed to normoxia (low altitude) or hypox ...[more]

PMID: 27143557

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Project description:Abstract Objectives Vitamin D may have an adjunctive role in the prevention and treatment of iron deficiency (ID) through its proposed role in the regulation of erythropoiesis and circulating hepcidin concentrations. Observational studies have shown associations between low vitamin D and iron status; however, there are few data from intervention trials. In participants of the Maternal Vitamin D for Infant Growth Trial (MDIG; NCT01924013), among whom the baseline prevalence of vitamin D deficiency was 64%, we examined the effect of prenatal vitamin D supplementation on iron status during pregnancy by testing the effect of vitamin D supplementation on serum ferritin concentrations. Methods In this double-blind, dose-response, randomized trial in Dhaka, Bangladesh, women were recruited at 17–24 weeks’ gestation and randomly assigned to receive a prenatal vitamin D3 dose of 4200, 16,800, 28,000 IU/week or placebo. Serum ferritin was quantified using an electro-chemiluminescence immunoassay. Plasma C-reactive protein (CRP) was analysed by enzyme-linked immunoassay. Linear regression was used to test the hypothesized effect of vitamin D supplementation on serum ferritin (n = 1011 of 1300 enrolled). In a sensitivity analysis, we adjusted for concurrent CRP to correct for inflammation (n = 920). Regression correction was used to generate an inflammation-corrected estimate of the prevalence of ID (n = 920). Results Prevalence of ID (serum ferritin <15 µg/L) was high overall (27% corrected for inflammation; 12% uncorrected). Geometric mean (95% confidence interval) serum ferritin concentrations were lower in each of the vitamin D supplementation groups [43.1 (38.1, 48.7), 44.8 (40.4, 49.7) and 45.1 (41.5, 49.1) µg/L in the 4200, 16,800 and 28,000 IU/week groups, respectively] compared to the placebo group [50.3 µg/L (45.0, 56.2)], although none of the pairwise differences between each vitamin D group and placebo were statistically significant at the P < 0.05 threshold. Adjusting for CRP did not change the inferences. Conclusions In a population with concurrently high prevalence rates of iron and vitamin D deficiency, prenatal vitamin D supplementation did not lead to improvements in iron status by late gestation. The possibility of a negative effect of vitamin D supplementation on iron status should be further explored. Funding Sources The Bill and Melinda Gates Foundation.

Dataset Information

Vitamin D status and metabolism in an ovine pregnancy model: effect of long-term, high-altitude hypoxia.

Publications

Vitamin D status and metabolism in an ovine pregnancy model: effect of long-term, high-altitude hypoxia.

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