Intestinal Ca and phosphate transport: differential responses to vitamin D3 metabolites.

1977 ◽  
Vol 233 (6) ◽  
pp. E488 ◽  
Author(s):  
M W Walling
Keyword(s):  
Vitamin D ◽  
Phosphate Transport ◽  
Active Metabolites ◽  
Rat Intestine ◽  
Differential Distribution ◽  
Dihydroxyvitamin D3 ◽  
Pi Transport ◽  
Vitamin D3 Metabolites ◽  
Stimulation Of

The transport of Ca and inorganic phosphate (Pi) was studied in the absence of electrochemical gradients across rat intestine in vitro. 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) increased the active absorption of both Ca and Pi in all segments of the small intestine, with changes occurring only in absorptive fluxes, whereas secretory fluxes were unaffected. Active Ca absorption was greatest in the duodenum (greater than jejunum greater than ileum) and active Pi absorption was highest in jejunum (greater than duodenum greater than ileum), in agreement with earlier reports. 24R,25-dihydroxy-vitamin2D3 had similar effects on transport but was less potent. The ratios of Pi absorptive fluxes to Ca absorptive fluxes remained remarkably constant during 80-200% increases in absorption produced by 1,25(OH)2D3, suggesting coupled Ca-Pi transport or coordinate stimulation of Ca and Pi absorptive processes by hormonally active metabolites of vitamin D. The results seem most compatible with a differential distribution of vitamin D-responsive Ca and Pi absorptive cells with a predominance of cells with Ca absorptive sites occurring in duodenum, more Pi absorbing cells in jejunum, and a nearly equal ratio of each type in ileum.

scholarly journals Epimers of Vitamin D: A Review

2020 ◽  
Vol 21 (2) ◽  
pp. 470 ◽  
Author(s):  
Bashar Al-Zohily ◽  
Asma Al-Menhali ◽  
Salah Gariballa ◽  
Afrozul Haq ◽  
Iltaf Shah
Keyword(s):  
Vitamin D ◽  
Biological Activity ◽  
Hydroxyl Group ◽  
Vitamin D Metabolites ◽  
Dihydroxyvitamin D3 ◽  
In Vivo Models ◽  
Vitamin D Receptors ◽  
Potential Factors

In this review, we discuss the sources, formation, metabolism, function, biological activity, and potency of C3-epimers (epimers of vitamin D). We also determine the role of epimerase in vitamin D-binding protein (DBP) and vitamin D receptors (VDR) according to different subcellular localizations. The importance of C3 epimerization and the metabolic pathway of vitamin D at the hydroxyl group have recently been recognized. Here, the hydroxyl group at the C3 position is orientated differently from the alpha to beta orientation in space. However, the details of this epimerization pathway are not yet clearly understood. Even the gene encoding for the enzyme involved in epimerization has not yet been identified. Many published research articles have illustrated the biological activity of C3 epimeric metabolites using an in vitro model, but the studies on in vivo models are substantially inadequate. The metabolic stability of 3-epi-1α,25(OH)2D3 has been demonstrated to be higher than its primary metabolites. 3-epi-1 alpha, 25 dihydroxyvitamin D3 (3-epi-1α,25(OH)2D3) is thought to have fewer calcemic effects than non-epimeric forms of vitamin D. Some researchers have observed a larger proportion of total vitamin D as C3-epimers in infants than in adults. Insufficient levels of vitamin D were found in mothers and their newborns when the epimers were not included in the measurement of vitamin D. Oral supplementation of vitamin D has also been found to potentially cause increased production of epimers in mice but not humans. Moreover, routine vitamin D blood tests for healthy adults will not be significantly affected by epimeric interference using LC–MS/MS assays. Recent genetic models also show that the genetic determinants and the potential factors of C3-epimers differ from those of non-C3-epimers.Most commercial immunoassays techniques can lead to inaccurate vitamin D results due to epimeric interference, especially in infants and pregnant women. It is also known that the LC–MS/MS technique can chromatographically separate epimeric and isobaric interference and detect vitamin D metabolites sensitively and accurately. Unfortunately, many labs around the world do not take into account the interference caused by epimers. In this review, various methods and techniques for the analysis of C3-epimers are also discussed. The authors believe that C3-epimers may have an important role to play in clinical research, and further research is warranted.

Characterization in vitro of H+ secretion and H+:Na+ exchange by an organism normally inhabiting a CO2-rich environment: Hymenolepis diminuta (Cestoda) in the rat intestine

1978 ◽  
Vol 56 (11) ◽  
pp. 2344-2354 ◽  
Author(s):  
R. B. Podesta
Keyword(s):  
Metabolic Pathways ◽  
Intestinal Parasite ◽  
Hymenolepis Diminuta ◽  
Ambient Fluid ◽  
Rat Intestine ◽  
Ion Concentrations ◽  
Intracellular Ion Concentrations ◽  
Metabolic Reactions ◽  
Stimulation Of

H+ and Na+ transport by the intestinal parasite Hymenolepis diminuta were studied in vitro. The flatworms acidified the ambient fluid by secreting H+ and the acidification could not be correlated with organic acid excretion. Ambient CO2-independent H+ secretion was attributed to protons of metabolic origin: dephosphorylation reactions and ionization of organic acids within the tissues. Ambient CO2-dependent H+ secretion was attributed to protons produced as a result of the hydration of CO2 within the tissue and to the stimulation of anaerobic metabolic pathways by CO2 acting as a cosubstrate in energy metabolism. Studies in which Na+ uptake was stimulated by CO2 or glucose and inhibited by ouabain, amiloride, or Na+ replacement suggested a partial direct coupling of Na+ absorption and H+ secretion but the different activation energies and the effect of buffer anions other than HCO3− suggested an indirect interaction. Various interactions were considered, including the effect of CO2 and intracellular ion concentrations on metabolic reactions leading to the supply of protons for H+ secretion and energy for ion transport.

Some species differences in the intrinsic factor stimulation of B12 uptake by small intestine in vitro

1959 ◽  
Vol 197 (4) ◽  
pp. 926-928 ◽  
Author(s):  
T. Hastings Wilson ◽  
Elliott W. Strauss
Keyword(s):  
Small Intestine ◽  
Guinea Pig ◽  
Species Differences ◽  
Intrinsic Factor ◽  
Vitamin B ◽  
Guinea Pig Ileum ◽  
Rat Intestine ◽  
Intrinsic Factors ◽  
Stimulation Of

Sacs of everted small intestine from a variety of animals were incubated in bicarbonate-saline containing vitamin B12 with and without intrinsic factor (IF). B12 uptake by rat intestine was stimulated only by its own intrinsic factor. Guinea pig ileum responded to all intrinsic factors tested (guinea pig, rat, hog, hamster, human being and rabbit). The intestines of hamster and rabbit were intermediate in specificity, responding to some, but not all, of the IF preparations. Species differences occur in both the intestine and intrinsic factor preparations. The guinea pig ileum was suggested as a possible assay for both hog and human IF.

Vitamin D3 and glucose-6-phosphate dehydrogenase in rat duodenal epithelial cells

1989 ◽  
Vol 257 (5) ◽  
pp. G760-G765
Author(s):  
L. B. Nasr ◽  
J. D. Monet ◽  
P. Lucas ◽  
C. A. Bader
Keyword(s):  
Vitamin D ◽  
Intraperitoneal Administration ◽  
Middle Part ◽  
G6pd Activity ◽  
Dihydroxyvitamin D3 ◽  
Rat Duodenum ◽  
High Level ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Stimulation Of

A microdensitometric method was employed to determine enzyme activities in situ in undisrupted tissue rat duodenum. The effect of 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] on glucose-6-phosphate dehydrogenase (G6PD) activity and on the two utilization pathways of synthesized NADPH, H1 (mixed function oxidation) and H2 (biosynthesis), was studied. In normal animals, a crypt-to-villus gradient of G6PD activity and of both NADPH utilization pathways was observed. A high level of NADPH utilization occurred predominantly via the H2 pathway. In vitamin D-deficient rat animals, G6PD activity in the middle part of the villus was approximately 60% lower than in normal animals [10.05 +/- 0.35 vs. 3.95 +/- 0.26 (means +/- SE) A585.min-1.micron-3 X 10(5), P less than 0.001] with reduced NADPH utilization via the H2 pathway (8.39 +/- 0.49 vs. 2.73 +/- 0.43 A585.min-1.micron-3 X 10(5), P less than 0.001) but not the H1 pathway (1.65 +/- 0.17 vs. 1.22 +/- 0.19 A585.min-1.micron-3 X 10(5), P = NS). Intraperitoneal administration of 1,25(OH)2D3 (500 pmol) to vitamin D-deficient animals resulted in increased G6PD activity within 30 min (4.09 +/- 0.38 vs. 5.51 +/- 0.39 A585.min-1.micron-3 X 10(5), P less than 0.05), attaining normal levels within 2 h. The H2 but not the H1 pathway of NADPH utilization increased significantly in response to 1,25(OH)2D3. This increase is essentially located in the basal and middle parts of the villus. Thus 1,25(OH)2D3 may influence biosynthesis in the duodenum via stimulation of G6PD activity and the H2 pathway of NADPH utilization.

Rat renal 25-hydroxyvitamin D3 1- and 24-hydroxylases: their in vivo regulation

1984 ◽  
Vol 246 (2) ◽  
pp. E168-E173 ◽  
Author(s):  
Y. Tanaka ◽  
H. F. DeLuca
Keyword(s):  
Vitamin D ◽  
Inorganic Phosphorus ◽  
Hydroxylase Activity ◽  
Deficient Diet ◽  
Dihydroxyvitamin D3 ◽  
1,25 Dihydroxyvitamin D3 ◽  
Dietary Phosphorus ◽  
Low Calcium

The effects of thyroparathyroidectomy, parathyroid hormone, 1,25-dihydroxyvitamin D3, dietary calcium, dietary phosphorus, age, and sex on the renal 25-hydroxyvitamin D3 1- and 24-hydroxylases measured in vitro in rats have been studied. Thyroparathyroidectomy of vitamin D-deficient rats abolishes 25-hydroxyvitamin D3 1-hydroxylase activity, and administration of bovine parathyroid extract to the thyroparathyroidectomized rat restores diminished 1-hydroxylase activity. Both suppression and restoration of the enzyme activities require many hours (18-24 h) independent of rapid changes in serum calcium and inorganic phosphorus levels in response to these manipulations. Administration of 1,25-dihydroxyvitamin D3 to vitamin D-deficient rats suppresses 25-hydroxyvitamin D3 1-hydroxylase activity and stimulates 25-hydroxyvitamin D3 24-hydroxylase activity within 48 h. Rats maintained on a low-calcium or a low-phosphorus diet with a daily supplement of 20 IU vitamin D3 show high 25-hydroxyvitamin D3 1-hydroxylase activity and low 24-hydroxylase activity as compared with rats similarly treated but fed a diet containing adequate calcium or adequate phosphorus. When vitamin D-sufficient rats having suppressed renal 25-hydroxyvitamin D3 1-hydroxylase activity are placed on a low-calcium vitamin D-deficient diet for 7 days, the 1-hydroxylase activity is greatly stimulated in 6-wk-old rats but much less so in rats with advancing age.

Stimulation of 24R,25-dihydroxyvitamin D3 synthesis by metabolites of vitamin D3

1983 ◽  
Vol 245 (4) ◽  
pp. E359-E364 ◽  
Author(s):  
G. S. Reddy ◽  
G. Jones ◽  
S. W. Kooh ◽  
D. Fraser ◽  
H. F. DeLuca
Keyword(s):  
Vitamin D ◽  
Vitamin D3 ◽  
The Other ◽  
Hydroxyl Group ◽  
Vitamin D Metabolites ◽  
Structural Requirements ◽  
Dihydroxyvitamin D3 ◽  
Hydroxylated Metabolites ◽  
Perfusion Period ◽  
Stimulation Of

Previously we have shown that the isolated perfused kidney from vitamin D-deficient rats converts [3H]25(OH)D3 into [3H]1 alpha,25(OH)2D3. When certain vitamin D metabolites were added to perfusate the same kidney began to synthesize [3H]24R,25(OH)2D3. In this study we investigated the structural requirements of the vitamin D molecule necessary to stimulate synthesis of [3H]24R,25(OH)2D3 in a 1-hydroxylating kidney. Kidneys were perfused with tracer [3H]25(OH)D3 (450 pM) alone and in the presence of a variety of hydroxylated metabolites and fluorinated analogues of vitamin D3 at concentrations of 450 pM to 25 microM. Tracer [3H]25(OH)D3 alone resulted in synthesis of only [3H]1 alpha,25(OH)2D3 during the 6-h perfusion period. 25-Hydroxylated metabolites [25(OH)D3, 25 nM; 1 alpha,25(OH)2D3, 25 nM; 24R,25(OH)2D3, 25 nM; 24(F)2,25(OH)D3, 50 nM] stimulated [3H]24R,25(OH)2D3 production at 2 h of perfusion. On the other hand, analogues without the 25-hydroxyl group [D3; 1 alpha(OH)D3; 25(F)D3; 1 alpha(OH),25(F)D3; 1 alpha(F)D3; 1 beta(F)D3]; did not stimulate [3H]24R,25(OH)2D3 synthesis. We conclude that the 25-hydroxyl group is an essential determinant of 24-hydroxylation.

Effects of 1,25(OH)2D3 on enterocyte basolateral membrane Ca transport in rats

1989 ◽  
Vol 256 (3) ◽  
pp. G613-G617 ◽  
Author(s):  
M. J. Favus ◽  
V. Tembe ◽  
K. A. Ambrosic ◽  
H. N. Nellans
Keyword(s):  
Vitamin D ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Cellular Transport ◽  
Dihydroxyvitamin D3 ◽  
Ca Transport ◽  
Intracellular Ca ◽  
Net Flux ◽  
Energy Dependent

One, twenty-five dihydroxyvitamin D3 [1,25(OH)2D3], commonly known as calcitriol, stimulates intestinal Ca absorption through increased activity of a cellular transport process. To determine whether transcellular Ca transport involves energy-dependent Ca efflux across enterocyte plasma membrane in vitamin D-sufficient rats, in vitro bidirectional Ca fluxes were measured under short-circuited conditions across proximal duodenum from rats fed diets adequate in vitamin D and containing a normal Ca diet (NCD), a low Ca diet (LCD), or fed NCD and injected with 50 ng of 1,25(OH)2D3 daily for 4 days before study. LCD or 1,25(OH)2D3 increased Ca net flux [Jnet, mucosal-to-serosal flux minus the serosal-to-mucosal flux] by increasing Ca mucosal-to-serosal flux (Jm----s) (mean +/- SE, NCD vs. LCD vs. 1,25(OH)2D3, 16 +/- 4 vs. 179 +/- 18 vs. 82 +/- 21 nmol.cm-2. h-1, P less than 0.0001). Initial ATP-dependent Ca uptake rates by duodenal basolateral membrane vesicles (BLMV) was greater in vesicles from rats fed NCD compared with LCD and not different from NCD injected with 1,25(OH)2D3. These studies suggest that in vitamin D-replete animals, 1,25(OH)2D3 increases epithelial Ca Jm----s by mechanisms that do not involve ATP-dependent BLM Ca efflux. ATP-dependent Ca exit from the cell under these conditions may play a role in intracellular Ca homeostasis rather than Ca absorption.

Fluoride selectively stimulates Na-dependent phosphate transport in osteoblast-like cells

1991 ◽  
Vol 260 (6) ◽  
pp. E833-E838 ◽  
Author(s):  
T. Selz ◽  
J. Caverzasio ◽  
J. P. Bonjour
Keyword(s):  
Fetal Calf Serum ◽  
Serum Insulin ◽  
Calf Serum ◽  
Phosphate Transport ◽  
Maximal Response ◽  
Factor I ◽  
Pi Transport ◽  
Alanine Transport ◽  
Umr 106 ◽  
Stimulation Of

The influence of fluoride (F) on the transport of Pi was investigated in the osteoblast-like cell line UMR-106. Exposure of cells to F induced a dose-related stimulation of the Na-coupled Pi transport. Pi transport was significantly increased 6 h after 1 mM F incubation, with maximal response observed at 24 h (F 38.0 +/- 2.3, vehicle 19.8 +/- 1.2 pmol.micrograms DNA-1.4 min-1; P less than 0.001). Na-dependent alanine transport was not changed by F. The selective effect of F on Pi transport was not associated with changes in adenosine 3',5'-cyclic monophosphate, cell proliferation, or alkaline phosphatase activity. However, it was completely blunted by inhibiting translational processes with cycloheximide. Furthermore, F enhanced the stimulatory effect on Pi transport of various mitogens such as fetal calf serum, insulin, and insulin-like growth factor I. In conclusion, F can selectively enhance the activity of the Pi transport system present in the plasma membrane of UMR 106 osteoblast-like cells by a mechanism that probably involves newly synthetized proteins.

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