Parenteral iron therapy and phosphorus homeostasis: A review.

Phosphorus has an essential role in cellular and extracellular metabolism; maintenance of normal phosphorus homeostasis is critical. Phosphorus homeostasis can be affected by diet and certain medications; some intravenous iron formulations can induce renal phosphate excretion and hypophosphatemia, likely through increasing serum concentrations of intact fibroblast growth factor 23. Case studies provide insights into two types of hypophosphatemia: acute symptomatic and chronic hypophosphatemia, while considering the role of pre-existing conditions and comorbidities, medications, and intravenous iron. This review examines phosphorus homeostasis and hypophosphatemia, with emphasis on effects of iron deficiency and iron replacement using intravenous iron formulations.

Phosphorus absorption and gene expression levels of related transporters in the small intestine of broilers.

To investigate the P absorption and gene expression levels of related co-transporters, type IIb sodium-dependent phosphate co-transporter (NaPi-IIb), inorganic phosphate transporter 1 (PiT-1) and inorganic phosphate transporter 2 (PiT-2) in the small intestine of broilers, 450 1-d-old Arbor Acres male broilers were randomly allocated to one of three treatments with ten replicate cages of fifteen birds per cage for each treatment in a completely randomised design. Chickens were fed a diet with no added inorganic P (containing 0·06 % non-phytate P (NPP)) or with either 0·21 or 0·44 % NPP for 21 d. Plasma P concentration in the hepatic portal vein, mRNA and protein expression levels of NaPi-IIb, PiT-1 and PiT-2 were determined at 7, 14 and 21 d of age. The results showed that the concentration of P in plasma in the hepatic portal vein increased as dietary NPP increased (P<0·0001). At 14 and 21 d of age, the increase in dietary NPP inhibited (P<0·003) NaPi-IIb mRNA expression level in the duodenum, as well as PiT-1 mRNA and protein expression levels in the ileum, but promoted NaPi-IIb protein expression level (P<0·002) and PiT-2 mRNA and protein expression levels (P<0·04) in the duodenum. These results suggest that NaPi-IIb, PiT-1 and PiT-2 might be important P transporters in the small intestine of broilers. Higher intestinal P absorption may be achieved by up-regulating the protein expression levels of NaPi-IIb and PiT-2 and down-regulating the protein expression of PiT-1.

Short communication: Effect of abomasal inorganic phosphorus infusion on phosphorus absorption in large intestine, milk production, and phosphorus excretion of dairy cattle.

The objective of the study was to evaluate the effect of inorganic phosphorus (Pi) infusion on P absorption in large intestine, milk production, and phosphorus excretion. Four ruminally and ileally cannulated crossbred cows were used in a 4 × 4 Latin square with 21-d periods. Cows were fed a total mixed ration containing 0.21% P, providing 50% of the cows' P requirement. Cobalt-EDTA was used as marker to measure large intestine digesta flow. On d 13 to 21 of each period, each cow was infused daily with 0, 20.1, 40.2, or 60.3 g of Pi into the abomasum and total collection was conducted on d 18 to 21. Ileal samples were collected every 9 h on d 18 to 21. Feed, digesta, and fecal samples were analyzed for total P and Pi using the molybdovanadate yellow method and blue method, respectively. All data were analyzed using PROC GLIMMIX in SAS 9.3 (SAS Institute Inc., Cary, NC) using contrasts to evaluate linear, quadratic, and cubic effects of Pi infusion dose. Dry matter intake, apparent dry matter digestibility, milk yield, and milk total P were unaffected by Pi infusion. Ileal flow and fecal excretion of total P and Pi increased linearly with increasing infused Pi. In the large intestine, net absorption of TP and Pi was increased linearly with increasing infused Pi. The magnitude of absorption from the large intestine was greater than reflected in current models, raising questions that could be evaluated with longer infusion periods or dietary alteration.

Examining the Proportion of Dietary Phosphorus From Plants, Animals, and Food Additives Excreted in Urine.

Phosphorus bioavailability is an emerging topic of interest in the field of renal nutrition that has important research and clinical implications. Estimates of phosphorus bioavailability, based on digestibility, indicate that bioavailability of phosphorus increases from plants to animals to food additives. In this commentary, we examined the proportion of dietary phosphorus from plants, animals, and food additives excreted in urine from four controlled-feeding studies conducted in healthy adults and patients with chronic kidney disease. As expected, a smaller proportion of phosphorus from plant foods was excreted in urine compared to animal foods. However, contrary to expectations, phosphorus from food additives appeared to be incompletely absorbed. The apparent discrepancy between digestibility of phosphorus additives and the proportion excreted in urine suggests a need for human balance studies to determine the bioavailability of different sources of phosphorus.

Effect of low levels of dietary available phosphorus on phosphorus utilization, bone mineralization, phosphorus transporter mRNA expression and performance in growing pigs.

A study was conducted to examine the effects of different dietary levels of available phosphorus (aP) on P excretion, bone mineralization, performance and the mRNA expression of sodium-dependent P transporters in growing pigs. Sixty-day old growing pigs (n = 54) with an average initial BW of 19.50 ± 1.11 kg were randomly allocated to a control diet (C) containing 0.23% available phosphorus (aP), T1 containing 0.17% aP and T2 containing 0.11% aP. There were 6 pens per treatment with 3 pigs per pen. Body weight and feed intake were measured weekly. At the end of each week, one pig from each pen was housed in a metabolic crate for 24 h to collect fecal and urine samples and then sacrificed to obtain third metacarpal (MC3) bones and jejunal and kidney samples. Bones were scanned by Dual Energy X-ray Absorptiometry (DEXA). Fecal and urine samples were sub-sampled and analyzed for P content. The expression of P transporter mRNA in jejunum and kidney samples was measured using quantitative real-time polymerase chain reaction (qRT-PCR). Data were analyzed using GLM procedure of the Statistical Analysis System (SAS Institute version 9.2). Pigs fed the T2 diet had reduced (P < 0.05) average daily gain (ADG) and gain to feed (G:F) compared to those fed the C diet during week 2. Overall, ADG and G:F were also reduced (P < 0.05) in pigs fed the T2 diet compared to those fed the C and T1 diets. Bone mineral density (BMD) and bone mineral content (BMC) were reduced (P < 0.05) in pigs fed the T2 diet compared to those fed the C diet throughout the experiment. At week 1, jejunal mRNA expression of Na (+)-dependent phosphate transporter 2 (SLC34A2) was increased (P < 0.01) in pigs fed the T2 diet compared to C diet. Renal mRNA expression of Na(+)-dependent phosphate transporter 1 (SLC34A1) and SLC34A3 were increased (P < 0.05) in pigs fed the T2 diet compared to those fed the C diet at week 2 and was accompanied by lower (P < 0.05) urinary P in pigs fed the T2 diet during week 2 and week 3. In conclusion, growing pigs are highly sensitive to low dietary P as shown by reduced ADG, bone mineralization and urinary P level, but moderate reduction in dietary P up to 0.17% aP in the diet has the potential to reduce environmental pollution by reducing P concentration in swine manure and without compromising performance.

The New Nordic Diet: phosphorus content and absorption.

PURPOSE: High phosphorus content in the diet may have adverse effect on cardiovascular health. We investigated whether the New Nordic Diet (NND), based mainly on local, organic and less processed food and large amounts of fruit, vegetables, wholegrain and fish, versus an Average Danish Diet (ADD) would reduce the phosphorus load due to less phosphorus-containing food additives, animal protein and more plant-based proteins. METHODS: Phosphorus and creatinine were measured in plasma and urine at baseline, week 12 and week 26 in 132 centrally obese subjects with normal renal function as part of a post hoc analysis of data acquired from a 26-week controlled trial. We used the fractional phosphorus excretion as a measurement of phosphorus absorption. RESULTS: Mean baseline fractional phosphorus excretion was 20.9 ± 6.6 % in the NND group (n = 82) and 20.8 ± 5.5 % in the ADD group (n = 50) and was decreased by 2.8 ± 5.1 and 3.1 ± 5.4 %, respectively, (p = 0.6) at week 26. At week 26, the mean change in plasma phosphorus was 0.04 ± 0.12 mmol/L in the NND group and -0.03 ± 0.13 mmol/L in the ADD group (p = 0.001). Mean baseline phosphorus intake was 1950 ± 16 mg/10 MJ in the NND group and 1968 ± 22 mg/10 MJ in the ADD group and decreased less in the NND compared to the ADD (67 ± 36 mg/10 MJ and -266 ± 45 mg/day, respectively, p < 0.298). CONCLUSION: Contrary to expectations, the NND had a high phosphorus intake and did not decrease the fractional phosphorus excretion compared with ADD. Further modifications of the diet are needed in order to make this food concept beneficial regarding phosphorus absorption.

Effect of a mixture of GOS/FOS® on calcium absorption and retention during recovery from protein malnutrition: experimental model in growing rats.

INTRODUCTION: During growth, protein deprivation impairs epiphyseal growth plate (EGP) height, bone volume (BV) and endochondral ossification. During catch-up growth, Ca availability becomes essential to ensure the extra amount needed to achieve optimal peak bone mass and strength. GOS and FOS improve mineral absorption in the colon. PURPOSE: The effect of a mixture of GOS/FOS® 9:1 added to a 0.5 %Ca (NCa) and a 0.3 %Ca (LCa) diets on Ca, P and Mg absorptions and bone mineralization, density and structure using an experimental model of growing rats recovering from early protein malnutrition was investigated. METHODS: To induce protein malnutrition, rats were fed a low protein diet: 4 % (LPD) during 1 week and then were randomly assigned to recovery groups (R) until day 50 (T = 50) as follows: R0.5 %: NCa; RP0.5 %: NCa + 5.3 % GOS/FOS®; R0.3 %: LCa and RP0.3 %: LCa + 5.3 % GOS/FOS®. Control groups received the 0.5 %Ca or 0.3 %Ca diet from weaning until day 40 or 50. RESULTS: Body weight and length increased in C groups throughout the study; both were arrested in all R during LPD consumption and increased immediately after re-feeding. Independently of dietary Ca content, LS counts, ß-glucosidase and Ca, P and Mg absorption increased, whereas cecum pH, ß-glucuronidase, urease and tryptophanase decreased in RP0.5 %: and RP0.3 %: as compared to the other studied groups (p < 0.01). Prebiotic consumption decreased CTX levels and increased femur Ca, Mg and P contents, total skeleton bone mineral content, proximal tibia and spine BMD, BV, EGP height and hypertrophic zone thickness, stiffness and elastic modulus as compared to recovery groups fed the prebiotic-free diets. CONCLUSION: Under the present experimental conditions, GOS/FOS® mixture induced colonic positive effects, which increased Ca, P and Mg absorption. Thus, consuming the prebiotic-containing diet resulted in an extra amount of minerals that improved bone development in growing rats recovering from protein malnutrition.

Reexamining the Phosphorus-Protein Dilemma: Does Phosphorus Restriction Compromise Protein Status?

Dietary phosphorus restriction is recommended to help control hyperphosphatemia in hemodialysis patients, but many high-phosphorus foods are important sources of protein. In this review, we examine whether restricting dietary phosphorus compromises protein status in hemodialysis patients. Although dietary phosphorus and protein are highly correlated, phosphorus intakes can range up to 600 mg/day for a given energy and protein intake level. Furthermore, the collinearity of phosphorus and protein may be biased because the phosphorus burden of food depends on: (1) the presence of phosphate additives, (2) food preparation method, and (3) bioavailability of phosphorus, which are often unaccounted for in nutrition assessments. Ultimately, we argue that clinically relevant reductions in phosphorus intake can be made without limiting protein intake by avoiding phosphate additives in processed foods, using wet cooking methods such as boiling, and if needed, substituting high-phosphorus foods for nutritionally equivalent foods that are lower in bioavailable phosphorus.

Short communication: Comparison of predicted dietary phosphorus balance using bioavailabilities from the NRC (2001) and Virginia Tech model.

The objective of the current work was to use digestion coefficients from the Feng et al. (2015) model (Virginia Tech model) to calculate P bioavailability of common feeds used in dairy production. Compared with the bioavailability calculated by the Virginia Tech model, using the NRC (2001) P absorption coefficient of 0.64 for forages would underestimate the bioavailabilities of alfalfa hay, alfalfa silage, corn silage, grass hay, and mixed mainly legume silage. For concentrates, using the NRC (2001) P absorption coefficient of 0.70 would overestimate the bioavailabilities of corn grain but underestimate bioavailability of high-moisture corn. Two dairy diets were formulated using nutrient values from the NRC (2001): a standard diet that includes minimal by-products, and a by-product diet that has reduced corn and soybean meal which was replaced with corn gluten feed, distillers grains, hominy feed, and wet brewers grains. For each diet, total bioavailable P was calculated using availability values from the NRC (2001) and the Virginia Tech model. Comparison of P balance (the difference between required and bioavailable P) for each diet was made using the 2 sets of bioavailabilities for a reference cow weighing 682 kg, producing 38.6 kg of milk/d (3.5% fat and 3.0% true protein, 100 d in milk), and consuming 23 kg of dry matter/d, yielding an absorbed P requirement of 59.4 g/d. The standard diet supplied 56.69 and 53.52 g of bioavailable P per day using bioavailabilities from the NRC (2001) and Virginia Tech models, respectively, resulting in a P balance of -2.71 and -5.88±0.26 g/d. The by-product diet provided 75.75 and 78.47 g/d of bioavailable P, yielding P balances of 16.35 and 19.07±0.37 g per day, respectively, using the 2 sets of bioavailabilities. Using P bioavailabilities for individual ingredients that were based on the Virginia Tech model resulted in different bioavailable P levels thus resulted in differing dietary P balances in a field setting.

The impact of phosphorus on the immune system and the intestinal microbiota with special focus on the pig.

There is increasing interest in dietary ingredients that are appropriate to support digestive and immune functions, but also maintain a stable microbial ecosystem in the gastrointestinal tract (GIT), particularly in weaned pigs. P is an essential nutrient for both microbes and their host, as it is involved, for example, in bone formation, energy metabolism, cellular signalling and stabilisation of cell membranes. Non-ruminant animals have limited access to phytate, the main storage form of P in plant seeds. The release of P bound to phytate requires phytase activity of plant or microbial origin, resulting in the formation of variable phosphorylated inositol phosphates (InsPs). The present review focuses on interactions between variations in dietary P supply, the immune system of the host, and the intestinal microbial ecosystem. Although results on the interaction between P and the immune system are inconsistent, several studies in different species have shown a positive impact of dietary P and phytase addition on the adaptive immune response. Recent studies with pigs suggest that P supply may influence intestinal microbial composition and activity. Individual InsPs or phosphate may also affect properties of pathogenic micro-organisms, such as metabolism or virulence. In conclusion, P may be considered as part of an integrated approach to support immune functions and maintain a stable microbial ecosystem in the GIT, thereby providing a barrier against potential pathogens. Within this regard, differences in phytate-P content and intrinsic phytase activity of plant feedstuffs, as well as the formation of individual InsPs, have to be taken into account.

The effect of transient, moderate dietary phosphorus deprivation on phosphorus metabolism, muscle content of different phosphorus-containing compounds, and muscle function in dairy cows.

Hypophosphatemia is a common finding in periparturient and anorectic cattle. Although the clinical relevance of hypophosphatemia in cattle is uncertain, it has been empirically associated with persistent recumbency, specifically in periparturient dairy cows. The objective of the present study was to determine if transient dietary phosphorus (P) deprivation over a course of 5 wk, by feeding an approximately 40% P-deficient ration to lactating dairy cows, would result in altered muscle function or muscle P metabolism severe enough to present a risk for animal health and well-being. In addition, we wanted to determine the association between the plasma phosphate concentration ([Pi]) and muscle tissue P content to assess to what extent intracellular P deprivation of muscle cells could be extrapolated from subnormal plasma [Pi]. Ten healthy multiparous, mid-lactating dairy cows received a ration with a P content of 0.18% over a period of 5 wk. Following the P-deprivation phase, the same ration supplemented with P to obtain a dietary P content of 0.43% was fed for 2 wk. Blood and urine samples were collected regularly and muscle biopsies were obtained repeatedly to determine the P content in muscle tissue. Function of skeletal and heart muscles was evaluated by electrocardiography and electromyography conducted repeatedly throughout the study. Feeding the P-deficient ration resulted in the rapid development of marked hypophosphatemia. The lowest plasma [Pi] were measured after 9 d of P depletion and were, on average, 60% below predepletion values. Plasma [Pi] increased thereafter, despite ongoing dietary P depletion. None of the animals developed clinical signs commonly associated with hypophosphatemia or any other health issues. Urine analysis revealed increasing renal calcium, pyridinoline, and hydroxypyridinoline excretion with ongoing P deprivation. Biochemical muscle tissue analysis showed that dietary P depletion and hypophosphatemia were not associated with a decline in muscle tissue P content. Electromyographic examination revealed increased occurrence of pathological spontaneous activity in striated muscles after 2 wk of dietary P depletion in several cows, which could be suggestive of neuromuscular membrane instability. No effect on heart muscle activity was identified electrocardiographically. These results suggest that counter-regulatory mechanisms were sufficient to maintain normal muscle tissue P content during transient and moderate P deprivation. Muscle function was not grossly affected, although the increased occurrence of pathological spontaneous activity suggests that subclinical neuropathy or myopathy, or both, may have occurred with ongoing P deprivation. The results presented here indicate that plasma [Pi] is unsuitable for assessing muscle tissue P content in cattle.

Effect of dietary phosphorus on intestinal phosphorus absorption in growing Holstein steers.

The effect of dietary P intake on intestinal P absorption was evaluated in growing Holstein steers. Diets varying in P content (0.15, 0.27, 0.36, and 0.45%, DM basis) were fed to 8 steers (174±10kg of BW) fitted with permanent duodenal and ileal cannulas in a replicated 4×4 Latin square with 14-d periods. Ytterbium-labeled corn silage and cobalt-EDTA were used as particulate and liquid phase markers, respectively, to measure digesta flow. Duodenal and ileal samples and spot urine samples were collected every 9 h from d 11 to 14. Total fecal collection was conducted on d 11 to 14 with fecal bags. Blood samples were collected from the coccygeal vessel on d 14. Feed, digesta, and fecal samples were analyzed for total P and inorganic P. Data were analyzed using PROC GLIMMIX in SAS with a model including treatment, square, period, and interaction of treatment and square. Preplanned contrasts were used to evaluate linear and quadratic treatment effects. Results were reported as least squares means. Dry matter intake (mean=4.90kg/d, 2.8% of BW) and apparent DM digestibility (mean=78.1%) were unaffected by treatment. Duodenal and ileal flow of total P increased linearly with increasing P intake (13.4, 18.5, 23.0, and 27.4g/d; 6.80, 7.87, 8.42, and 10.4g/d). Increasing P intake increased the quantity of P absorbed from the small intestine linearly (6.96, 11.1, 14.6, and 17.2g/d), but absorption efficiency was unchanged (mean=59.6%). Phosphorus was absorbed on a net basis from the large intestine, but this was not affected by treatment and was a small proportion of total P absorption. Blood inorganic P increased linearly with increased dietary P (4.36, 6.31, 7.68, and 8.5mg/dL) and salivary P secretion was unchanged (mean=5.79g/d), suggesting that rumen function was prioritized during short-term P deficiency. These data showing an absence of change in absorption efficiency and salivary P secretion in the face of short-term P deficiency may be used to improve published models of P digestion, absorption, and metabolism.

The effects of forage particle length and exogenous phytase inclusion on phosphorus digestion and absorption in lactating cows.

Accurate estimates of phosphorus (P) availability from feed are needed to allow P requirements to be met with reduced P intake, thus reducing P excretion by livestock. Exogenous phytase supplementation in poultry and swine diets improves bioavailability of P, and limited research suggests that this strategy may have some application in dairy cattle rations. The effects of exogenous phytase and forage particle length on site and extent of P digestion were evaluated with 5 ruminally and ileally cannulated lactating cows (188 ± 35 d in milk). Cows were assigned in a 2 × 2 factorial arrangement of treatments in 2 incomplete Latin squares with four 21-d periods. Diets contained P slightly in excess of National Research Council requirements with all P from feed sources. During the last 4d of each period, total mixed ration, refusals, omasal, ileal, and fecal samples were collected and analyzed for total P, inorganic P (Pi), and phytate (Pp). Total P intake was not influenced by dietary treatments but Pp intake decreased and Pi intake increased with supplemental phytase, suggesting rapid action of the enzyme in the total mixed ration after mixing. Omasal flow of Pi decreased with phytase supplementation, but we observed no effect of diet in ileal flow or small intestinal digestibility of any P fraction. Fecal excretion of total P was slightly higher and Pp excretion was lower for cows receiving diets supplemented with phytase. Milk yield and composition were unaffected by diets. When phytase was added to the mixed ration, dietary Pp was rapidly degraded before intake and total-tract Pp digestion was increased. The lack of effect of phytase supplementation on dietary P utilization was probably because these late-lactation cows had a low P requirement and were fed P-adequate diets.

Proposed biokinetic model for phosphorus.

This paper reviews data related to the biokinetics of phosphorus in the human body and proposes a biokinetic model for systemic phosphorus for use in updated International Commission on Radiological Protection (ICRP) guidance on occupational intake of radionuclides. Compared with the ICRP's current occupational model for systemic phosphorus (Publication 68, 1994), the proposed model provides a more realistic description of the paths of movement of phosphorus in the body and greater consistency with experimental, medical, and environmental data regarding its time-dependent distribution. For acute uptake of (32)P to blood, the proposed model yields roughly a 50% decrease in dose estimates for bone surface and red marrow and a six-fold increase in estimates for liver and kidney compared with the model of Publication 68. For acute uptake of (33)P to blood, the proposed model yields roughly a 50% increase in dose estimates for bone surface and red marrow and a seven-fold increase in estimates for liver and kidney compared with the model of Publication 68.

Contributions to total phosphorus intake: all sources considered.

High serum phosphorus is linked to poor health outcome and mortality in chronic kidney disease (CKD) patients before or after the initiation of dialysis. Dietary intake of phosphorus, a major determinant of serum phosphorus, seems to be systematically underestimated using the available software tools and generalized nutrient content databases. Several sources of dietary phosphorus including the addition of phosphorus ingredients in food processing, and phosphorus content of vitamin and mineral supplements and commonly used over-the-counter or prescription medications are not fully accounted for by the nutrient content databases and software programs in current clinical use or used in large population studies. In this review, we explore the many unknown sources of phosphorus in the food supply to identify all possible contributors to total phosphorus intake of Americans that have escaped inclusion in past intake estimates. Our goal is to help delineate areas for future interventions that will enable tighter control of dietary phosphorus intake, a critical factor to maintaining health and quality of life in CKD and dialysis patients.

Dietary inorganic phosphorus regulates the intestinal peptide transporter PepT1.

BACKGROUND: Both organic and inorganic phosphorus (Pi) are present in regularly consumed foods, such as meats, eggs, and dairy products. Pi is often included in foods as an additive (as hidden phosphorus). The intestinal peptide transporter PepT1 mediates protein absorption, which is disturbed in renal insufficiency. Our aim was to determine the effects of dietary Pi content on the peptide transport activity and expression of PepT1. METHODS: The following animal models were used: (1) 7-week-old male Wistar rats; and (2) rats that underwent 3/4 nephrectomy to induce chronic kidney disease (CKD). The rats were fed a normal-protein (20%) diet containing low (0.02%), normal (0.6%), or high (1.2%) Pi levels. They were also fed diets containing varying amounts of protein and either low or normal Pi levels as follows: (1) low Pi/normal protein, (2) low Pi/high (50%) protein, (3) normal Pi/normal protein, and (4) normal Pi/high protein. RESULTS: Intestinal peptide transport activity and PepT1 expression levels were significantly higher in the CKD rats than in sham-operated control ones. Compared with the normal-protein diet, the high-protein diet increased PepT1 expression in the CKD rats. Intestinal dipeptide transport activity and PepT1 protein levels did not increase in the rats fed the low-Pi/high-protein diet. In contrast, intestinal dipeptide transport activity and PepT1 protein expression were markedly increased in the rats fed the normal-Pi/high-protein diet. CONCLUSION: Dietary Pi levels regulate intestinal peptide transport activity through PepT1.

Meta-analysis of factors that affect the utilization efficiency of phosphorus in lactating dairy cows.

A meta-analysis investigation based on literature data was conducted to estimate the effect size of nutritional and animal factors on phosphorus (P) excretion in feces and concentrations of P in milk. Two data sets were created for statistical analysis: One to derive prediction equations for P in feces (25 studies; 130 treatments) and another for P in milk (19 studies; 94 treatments). Prediction equations were derived using mixed model regression analysis with a random effect for study, and equations were evaluated based on values for Bayesian information criterion (BIC), root mean square prediction error (RMSPE), and concordance correlation coefficient (CCC) statistics. In terms of RMSPE and CCC values, fecal P excretion was best predicted by P intake, where P in feces (g/d)=-3.8(±3.45) + 0.64(±0.038) × P intake (g/d) (RMSPE: 18.3%, CCC: 0.869). However, significant effects of crude protein [g/kg of dry matter (DM)], neutral detergent fiber (g/kg of DM), and milk yield (kg/d) on fecal P excretion were also found. Despite a lack of improvement in terms of RMSPE and CCC values, these parameters may still explain part of the variation in fecal P excretion. For milk P, expressed as a fraction of P intake, the following equation had the highest CCC and the lowest RMSPE value: P in milk as a fraction of P intake (g/g)=0.42(±0.065) + 0.23(±0.018) × feed efficiency (i.e., fat- and protein-corrected milk yield/dry matter intake) - 0.11(±0.0199) × P in feed (g/kg of DM) (RMSPE: 19.7%; CCC: 0.761). Equations derived to predict fecal P as a fraction of P intake (g/g) or milk P content (g/kg) could not adequately explain the observed variation and did not perform well in terms of RMSPE and CCC values. Examination of the residuals showed that P balance was a seemingly confounding factor in some of the models. The results presented here can be used to estimate P in feces and milk based on commonly measured dietary and milk variables, but could also be used to guide development of mechanistic models on P metabolism in lactating dairy cattle. Factors to consider in future research and modeling efforts regarding efficiency of P use include the effects of dietary neutral detergent fiber, crude protein, starch, variation in P content of milk, and effects of P resorption from bone and body tissues during early lactation.

Effect of abomasal ferrous lactate infusion on phosphorus absorption in lactating dairy cows.

The objective of this study was to evaluate the effect of ferrous lactate infusion on postruminal P absorption in lactating dairy cows. Four ruminally cannulated lactating cows were used in a 4×4 Latin square design with 14 d per period. Cows were fed a basal diet containing 0.39% P, providing 100% of the calculated P requirement. On d 8 to 14 of each period, each cow was infused with 0, 200, 500, or 1,250mg of Fe/d in the form of ferrous lactate solution (ferrous lactate in 1L of double-distilled water) into the abomasum. Infusate was formulated to approximate 0, 2, 5, or 12.5mg of Fe/L in drinking water with 100L of water intake/d. Total fecal collection was conducted in the last 4 d of each period to measure nutrient digestion and excretion. Dry matter intake, milk yield, and milk composition were not affected by treatment. Digestibility of DM, NDF, and nitrogen decreased linearly with increasing ferrous lactate infusion. Infusion of ferrous lactate did not affect intake and digestibility of total P, inorganic P, or phytate P. In lactating cows, P absorption was not negatively influenced by abomasally infused ferrous lactate up to 1,250mg of Fe/d.

Relationship of urine dopamine with phosphorus homeostasis in humans: the heart and soul study.

BACKGROUND: Urine dopamine (DA) is produced in the proximal tubule and has been found to increase in response to dietary phosphorus intake, and to contribute to greater urinary phosphorus excretion in animal models. Whether urine DA is associated with phosphorus homeostasis in humans is uncertain. METHODS: This was a cross-sectional study of 884 outpatients. DA was measured from 24-hour urine collections. We examined cross-sectional associations between urine DA and serum phosphorus, 24-hour urine phosphorus (as an indicator of dietary phosphorus absorption), fractional excretion of phosphorus (FEphos), fibroblast growth factor (FGF)-23, and parathyroid hormone (PTH). Models were adjusted for age, sex, race, eGFR, albuminuria, hypertension, heart failure, tobacco use, body mass index, and diuretic use. RESULTS: Mean age was 66.6 ± 11 years and mean eGFR was 71 ± 21.3 ml/min/1.73 m(2). The mean urine DA was 193 ± 86 µg/day, mean serum phosphorus was 3.6 ± 0.6 mg/dl, mean daily urine phosphorus excretion was 671 ± 312 mg/day, and mean FEphos was 17 ± 9%. In adjusted models, each standard deviation higher DA was associated with 78.4 mg/day higher urine phosphorus and 0.9% lower FEphos (p < 0.05 for both). There was no statistically significant association between urine DA, serum phosphorus, FGF-23 or PTH in adjusted models. CONCLUSIONS: Higher dietary phosphorus absorption is associated with higher urine DA in humans, consistent with animal models. However, higher urine DA is not associated with FGF-23 or PTH, suggesting that known mechanisms of renal tubular handling of phosphorus may not be involved in the renal dopamine-phosphorus regulatory pathway in humans.

Lanthanum carbonate reduces urine phosphorus excretion: evidence of high-capacity phosphate binding.

The effectiveness of phosphate binders can be assessed by evaluating urinary phosphorus excretion in healthy volunteers, which indicates the ability of the phosphate binder to reduce gastrointestinal phosphate absorption. Healthy volunteers were enrolled into one of five separate randomized trials; four were open label and one double blind. Following a screening period of ≤28 days, participants received differing tablets containing lanthanum carbonate [LC, 3000 mg/day of elemental lanthanum (in one study other doses were also used)]. Participants received a standardized phosphate diet and remained in the relevant study center throughout the duration of each treatment period. The end point in all studies was the reduction in urinary phosphorus excretion. Reductions in mean 24-h urinary phosphorus excretion in volunteers receiving a lanthanum dose of 3000 mg/day were between 236 and 468 mg/day over the five separate studies. These data in healthy volunteers can be used to estimate the amount of reduction of dietary phosphate absorption by LC. The reduction in 24-h urinary phosphorus excretion per tablet was compared with published data on other phosphate binders. Although there are limitations, evidence suggests that LC is a very effective phosphate binder in terms of binding per tablet.