Calcium and inorganic phosphate secretion of rat ileum in vitro

Peters, J R; Binswanger, U

doi:10.1007/bf01852270

Cited by 9 publications

(6 citation statements)

References 36 publications

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“…The importance of the ileum in intestinal phosphate uptake is unclear: while some studies have reported that the rat ileum has little or no capacity to absorb phosphate (Peters and Binswanger ; Marks et al. ), others have reported that the magnitude of phosphate absorption is similar in the duodenum, jejunum and ileum, perhaps in vivo attributable in part to differences in length (surface area for absorption) and transit time (resident time for absorption) (Cramer ; Kayne et al.…”

Section: Discussionmentioning

confidence: 99%

Experimental and regional variations in Na⁺-dependent and Na⁺-independent phosphate transport along the rat small intestine and colon

et al. 2015

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Despite the importance of extracellular phosphate in many essential biological processes, the mechanisms of phosphate transport across the epithelium of different intestinal segments remain unclear. We have used an in vitro method to investigate phosphate transport at the brush border membrane (BBM) of intact intestinal segments and an in vivo method to study transepithelial phosphate absorption. We have used micromolar phosphate concentrations known to favor NaPi‐IIb‐mediated transport, and millimolar concentrations that are representative of the levels we have measured in luminal contents, to compare the extent of Na+‐dependent and Na+‐independent phosphate transport along the rat duodenum, jejunum, ileum, and proximal and distal colon. Our findings confirm that overall the jejunum is the main site of phosphate absorption; however, at millimolar concentrations, absorption shows ~30% Na+‐dependency, suggesting that transport is unlikely to be mediated exclusively by the Na+‐dependent NaPi‐IIb co‐transporter. In the ileum, studies in vitro confirmed that relatively low levels of phosphate transport occur at the BBM of this segment, although significant Na+‐dependent transport was detected using millimolar levels of phosphate in vivo. Since NaPi‐IIb protein is not detectable at the rat ileal BBM, our data suggest the presence of an as yet unidentified Na+‐dependent uptake pathway in this intestinal segment in vivo. In addition, we have confirmed that the colon has a significant capacity for phosphate absorption. Overall, this study highlights the complexities of intestinal phosphate absorption that can be revealed using different phosphate concentrations and experimental techniques.

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Section: Discussionmentioning

confidence: 99%

Experimental and regional variations in Na⁺-dependent and Na⁺-independent phosphate transport along the rat small intestine and colon

et al. 2015

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“…Our studies have revealed that the ileum of the rat has a very limited capacity to absorb phosphate. Indeed, it has been proposed that the rat ileum is a secretory site for calcium and phosphate, and that this occurs paracellularly (Peters & Binswanger, 1988). The factors controlling paracellular transport of phosphate are unknown, although ileal calcium secretion may be influenced by 1,25-dihydroxyvitamin D 3 (Peters & Binswanger, 1988).…”

Section: Discussionmentioning

confidence: 99%

“…Indeed, it has been proposed that the rat ileum is a secretory site for calcium and phosphate, and that this occurs paracellularly (Peters & Binswanger, 1988). The factors controlling paracellular transport of phosphate are unknown, although ileal calcium secretion may be influenced by 1,25-dihydroxyvitamin D 3 (Peters & Binswanger, 1988). In contrast, the mouse small intestine has the ability to absorb phosphate in all segments examined, with the highest rate occurring in the ileum.…”

Section: Discussionmentioning

confidence: 99%

Intestinal phosphate absorption and the effect of vitamin D: a comparison of rats with mice

Marks¹,

Srai²,

Biber³

et al. 2006

Experimental Physiology

115

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Previously, it was thought that intestinal phosphate transport occurred exclusively in the proximal small intestine of rodents and humans. However, a recent study has demonstrated that the ileum of mice contributes significantly to the absorption of dietary phosphate, but it is not known whether this region is also an important site of phosphate absorption in the rat. In the present study, we have investigated the mRNA and protein levels of the sodiumphosphate cotransporter, NaPi-IIb, in three regions of rat and mouse small intestine, and related its expression levels to the rate of net phosphate absorption, as measured using the in situ intestinal loop technique. 1,25-Dihydroxyvitamin D 3 is an important physiological regulator of intestinal phosphate absorption that increases phosphate transport in both the duodenum and jejunum of the rat. Based on the recently proposed regional profile of phosphate absorption along the mouse small intestine, we have re-evaluated the effects of 1,25-dihydroxyvitamin D 3 using three distinct regions of the mouse and rat small intestine. Our studies have revealed important differences in the intestinal handling of phosphate between mice and rats. In mice, maximal phosphate absorption occurs in the ileum, which is paralleled by the highest expression levels of NaPi-IIb mRNA and protein. In contrast, in rats maximal absorption occurs in the duodenum with very little absorption occurring in the ileum, which is similar to the pattern reported in humans. However, in both rodent species only the jejunum shows an increase in phosphate absorption in response to treatment with 1,25-dihydroxyvitamin D 3 .

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“…1 Rapid changes in transcellular distribution are effected primarily by systemic acid-base equilibrium and hormones such as insulin and catecholamines. 2 1,25(OH) 2 D stimulates intestinal PO4 absorption, 4 while parathyroid hormone (PTH) and osteocytederived fibroblast growth factor-23 (FGF-23) are the best-characterized phosphaturic factors.…”

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confidence: 99%

The Human Response to Acute Enteral and Parenteral Phosphate Loads

Scanni

vonRotz

Jehle

et al. 2014

Journal of the American Society of Nephrology

107

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The human response to acute phosphate (PO4) loading is poorly characterized, and it is unknown whether an intestinal phosphate sensor mechanism exists. Here, we characterized the human mineral and endocrine response to parenteral and duodenal acute phosphate loads. Healthy human participants underwent 36 hours of intravenous (IV; 1.15 [low dose] and 2.30 [high dose] mmol of PO4/kg per 24 hours) or duodenal (1.53 mmol of PO4/kg per 24 hours) neutral sodium PO4 loading. Control experiments used equimolar NaCl loads. Maximum PO4 urinary excretory responses occurred between 12 and 24 hours and were similar for low-dose IV and duodenal infusion. Hyperphosphatemic responses were also temporally and quantitatively similar for low-dose IV and duodenal PO4 infusion. Fractional renal PO4 clearance increased approximately 6-fold (high-dose IV group) and 4-fold (low-dose IV and duodenal groups), and significant reductions in plasma PO4 concentrations relative to peak values occurred by 36 hours, despite persistent PO4 loading. After cessation of loading, frank hypophosphatemia occurred. The earliest phosphaturic response occurred after plasma PO4 and parathyroid hormone concentrations increased. Plasma fibroblast growth factor-23 concentration increased after the onset of phosphaturia, followed by a decrease in plasma 1,25(OH)2D levels; a-Klotho levels did not change. Contrary to results in rodents, we found no evidence for intestinal-specific phosphaturic control mechanisms in humans. Complete urinary phosphate recovery in the IV loading groups provides evidence against any important extrarenal response to acute PO4 loads. Plasma phosphate (PO4) concentration is regulated within narrow limits and is the result of intestinal absorption, influx into and efflux from bone, renal excretion, and modest intestinal secretion. 1 Rapid changes in transcellular distribution are effected primarily by systemic acid-base equilibrium and hormones such as insulin and catecholamines. 2 1,25(OH) 2 D stimulates intestinal PO4 absorption, 4 while parathyroid hormone (PTH) and osteocytederived fibroblast growth factor-23 (FGF-23) are the best-characterized phosphaturic factors. Both inhibit proximal tubular sodium-dependent PO4 reabsorption (via Na/PO4 cotransport, NaPi2a and NaPi2c). 5,6 In addition, a-Klotho is a renal transmembrane and secreted protein that functions as an FGF-23 coreceptor and is phosphaturic independently of However, the relative roles of other phosphaturic agents, such as secreted frizzled related protein (sFRP-4), matrix extracellular phosphoglycoprotein, and FGF-8 are not yet defined in humans.1,25(OH) 2 D, PTH, and FGF-23 regulate PO4 metabolism within a complex system of positive and negative feedback mechanisms (for review, see Bergwitz and Jüppner 8 ). Increases in plasma PO4 concentration stimulate PTH secretion, while proximal tubule 1a-hydroxylase and, therefore,

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Calcium and inorganic phosphate secretion of rat ileum in vitro

Cited by 9 publications

References 36 publications

Experimental and regional variations in Na⁺-dependent and Na⁺-independent phosphate transport along the rat small intestine and colon

Experimental and regional variations in Na⁺-dependent and Na⁺-independent phosphate transport along the rat small intestine and colon

Intestinal phosphate absorption and the effect of vitamin D: a comparison of rats with mice

The Human Response to Acute Enteral and Parenteral Phosphate Loads

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Calcium and inorganic phosphate secretion of rat ileum in vitro

Cited by 9 publications

References 36 publications

Experimental and regional variations in Na+-dependent and Na+-independent phosphate transport along the rat small intestine and colon

Experimental and regional variations in Na+-dependent and Na+-independent phosphate transport along the rat small intestine and colon

Intestinal phosphate absorption and the effect of vitamin D: a comparison of rats with mice

The Human Response to Acute Enteral and Parenteral Phosphate Loads

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Experimental and regional variations in Na⁺-dependent and Na⁺-independent phosphate transport along the rat small intestine and colon

Experimental and regional variations in Na⁺-dependent and Na⁺-independent phosphate transport along the rat small intestine and colon