Estimation of phosphorus requirements of sows based on 24-h urinary phosphorus excretion during gestation and lactation

Phosphorus requirements of reproducing sows were estimated using 24-h urinary P excretion. Thirty-six multiparous sows were fed one of six maize–soybean meal-based diets with total P ranging from 0·40 to 0·80 % in 0·08 % increments with a constant Ca:total P ratio (1·25:1). Diets were fed from day 7·5 ± 1 after breeding until the end of lactation (day 26 ± 1). Urine samples were collected in mid and late gestation (days 77·1 ± 2 and 112·4 ± 1) and early and late lactation (days 4·5 ± 1 and 18·2 ± 1). Phosphorus requirements were estimated using linear and nonlinear regression models. Based on a single 24-h urinary P excretion, estimated daily dietary total P requirements in mid and late gestation were 10·3 g (6·0 g standardised total tract digestible P, STTD P), and estimates for early and late lactation were 31·1 g (16·6 g STTD P) and 40·3 g (22·1 g STTD P), respectively. Plasma P and Ca concentrations were maintained within normal ranges at the estimated levels of P requirements. No differences among treatments were observed for plasma parathyroid hormone (P ≥ 0·06) and bone formation marker (P ≥ 0·16). In lactation, bone resorption marker decreased (P ≤ 0·001) as sows consumed more P. Among the analysed variables, urinary P was the most sensitive response to changes in dietary P intake. Urinary P excretion offers a practical method to estimate P requirements in sows. Our recommended daily total P requirements are 10·3 g for gestation and 35·7 g for lactation.

Combination treatment with tenapanor and sevelamer synergistically reduces urinary phosphorus excretion in rats

The majority of patients with chronic kidney disease (CKD) receiving dialysis do not reach target serum phosphorus concentrations, despite treatment with phosphate binders. Tenapanor is a non-binder, sodium/hydrogen exchanger isoform 3 (NHE3) inhibitor that reduces paracellular intestinal phosphate absorption. This pre-clinical study evaluated the effect of tenapanor and varying doses of sevelamer carbonate on urinary phosphorus excretion, a direct reflection of intestinal phosphate absorption. We measured 24-hour urinary phosphorus excretion in male rats assigned to groups dosed orally with vehicle or tenapanor (0.3 mg/kg/day) and provided a diet containing varying amounts of sevelamer (0-3% w/w). We also evaluated the effect of the addition of tenapanor or vehicle on 24-hour urinary phosphorus excretion to rats on a stable dose of sevelamer (1.5% w/w). When administered together, tenapanor and sevelamer decreased urinary phosphorus excretion significantly more than either tenapanor or sevelamer alone across all sevelamer dose levels. The Bliss statistical model of independence indicated that the combination was synergistic. A stable sevelamer dose (1.5% w/w) reduced mean (±standard error of the mean) urinary phosphorus excretion by 42±3% compared with vehicle; together, tenapanor and sevelamer reduced residual urinary phosphorus excretion by an additional 37±6% (P < 0.05). While both tenapanor and sevelamer reduce intestinal phosphate absorption individually, administration of tenapanor and sevelamer together results in more pronounced reductions in intestinal phosphate absorption than if either agent is administered alone. Further evaluation of combination tenapanor plus phosphate binder treatment in patients receiving dialysis with hyperphosphatemia is warranted.

274 Determination of phosphorus requirement of lactating sows based on 24-hour urinary phosphorus excretion

The objective was to determine phosphorus (P) requirement of lactating sows using 24-hour urinary P excretion as the response criteria. The underlying assumption was that urinary P remains low and constant until the requirements are met then increases as P consumption increases. Thirty-six crossbred PIC Camborough sows (parity 3 to 7) were randomly assigned to 1 of 6 corn-soybean-meal diets with increasing dietary total P (tP) levels (0.40, 0.48, 0.56, 0.64, 0.72, and 0.80%) and a constant calcium (Ca) to tP ratio (1.25:1). Diets were fed from breeding until the end of lactation. Urine and blood samples were collected on days 4 and 18 of lactation and analyzed for P and Ca concentrations. Data were analyzed using MIXED and NLIN procedures of SAS. Phosphorus requirements were estimated using a broken-line regression model. Plasma Ca (ranging from 12.1 to 10.3 mg/dL) was not affected by dietary treatments, and was maintained within the normal physiological range on day 4 and 18 of lactation. Plasma P (ranging from 2.9 to 6.4 mg/dL) linearly increased (P &lt; 0.05) with increasing dietary tP levels on day 4 and 18 of lactation. Only sows fed the 0.40% tP diet failed to maintain plasma P concentrations within the normal physiological range. Clinical signs of P and Ca deficiencies were not observed. Differences in sow and litter performance among treatments were not detected. A nonlinear response of urinary P excretion to dietary P intake was observed. Based on a broken-line linear model fit to 24-hour urinary P excretion, minimum tP requirements of sows at day 4 and 18 of lactation were 0.47 and 0.54%, respectively. In conclusion, 24-hour urine P excretion provided sensitive criteria for estimates of tP requirements in lactating sows. Efforts to adjust heteroscedasticity for animals fed dietary P above the estimated requirement need further evaluation.

Familial hypophosphatemic rickets caused by a PHEX gene mutation accompanied by a NPR2 missense mutation

BackgroundFamilial hypophosphatemic rickets, which is usually acknowledged as X-linked hypophosphatemic rickets (XLH), is a rare hereditary disease. XLH caused by mutations in the PHEX gene often manifests as growth retardation, skeletal deformities, osteodynia and dental dysplasia. NPR2 mutations are reported to cause disproportionate short stature. Our study was designed to identify the gene mutations of three patients in one family.Case descriptionA 40-year-old Chinese male visited the hospital for continuous osteodynia and presented with bilateral leg bowing, absent teeth and a progressive limp. The age of onset was approximately 2 years old. His 63-year-old mother and 42-year-old brother both shared identical symptoms with him. The laboratory tests were consistent with XLH, which showed decreased levels of blood phosphorus and 1,25-dihydroxyvitamin D3 as well as increased urinary phosphorus excretion. Mutation analysis revealed that the proband as well as his mother and his brother all had a PHEX mutation in exon 14 (c.1543C > T), and the proband also had a NPR2 mutation in exon 21 (c.3058C > T).ConclusionsWe report the familial hypophosphatemic rickets of three patients in a Chinese family caused by a PHEX gene mutation in exon 14 (c.1543C > T), which had never been reported in Chinese patients. We first report an XLH case together with a NPR2 mutation that had never been reported before.

The Percentage of Dietary Phosphorus Excreted in the Urine Varies by Dietary Pattern in a Randomized Feeding Study in Adults

ABSTRACTBackgroundUrinary phosphorus excretion has been proposed as a recovery biomarker of dietary phosphorus intake. However, it is unclear whether phosphorus excretion is constant across a range of dietary and nondietary factors.ObjectiveWe assessed whether percentage urinary phosphorus excretion is constant across 3 dietary patterns in the Dietary Approaches to Stop Hypertension (DASH) trial.MethodsDASH is a completed feeding study of 459 prehypertensive and stage 1 hypertensive adults (52% male, 56% black). After a 3-wk run-in on a typical American (control) diet, participants were randomly assigned to the control diet, a diet rich in fruits and vegetables (FV diet), or a diet rich in fruits, vegetables, and low-fat dairy with reduced saturated fat and cholesterol (DASH diet) for 8 wk. We estimated the percentage phosphorus excretion as urinary phosphorus excretion (from 24 h urine) divided by phosphorus intake (from analyzed food composites). Differences between group means for all 3 diets were compared by ANOVA followed by pairwise comparisons with Tukey's honest significant difference test.ResultsAt the end of the intervention, the mean phosphorus intake was 1176 mg/d (95% CI: 1119, 1233 mg/d), 1408 mg/d (1352, 1464 mg/d), and 2051 mg/d (1994, 2107 mg/d) in the control, FV, and DASH diet, respectively (P < 0.001, all comparisons). The mean phosphorus excretion was 734 mg/d (682, 787 mg/d), 705 mg/d (654, 756 mg/d), and 872 mg/d (820, 923 mg/d) in the control, FV, and DASH diet, respectively (P = 0.74 control vs. FV, P < 0.001 all other comparisons). The mean percentage phosphorus excretion was 63% (60%, 67%), 51% (48%, 54%), and 43% (39%, 46%) in the control, FV, and DASH diet, respectively (P < 0.001, all comparisons).ConclusionsThese findings in prehypertensive and stage 1 hypertensive adults strongly suggest that urinary phosphorus excretion should not be used as a recovery biomarker for dietary phosphorus intake, given the wide range of urinary phosphorus excretion across dietary patterns. This trial is registered at clinicaltrials.gov as NCT0000054.