Phosphorus Excretion Rates Research Articles

Improving the efficiency of feed utilization in poultry by selection. 2. Genetic parameters of excretion traits and correlations with anatomy of the gastro-intestinal tract and digestive efficiency

BackgroundPoultry production has been widely criticized for its negative environmental impact related to the quantity of manure produced and to its nitrogen and phosphorus content. In this study, we investigated which traits related to excretion could be used to select chickens for lower environmental pollution.The genetic parameters of several excretion traits were estimated on 630 chickens originating from 2 chicken lines divergently selected on apparent metabolisable energy corrected for zero nitrogen (AMEn) at constant body weight. The quantity of excreta relative to feed consumption (CDUDM), the nitrogen and phosphorus excreted, the nitrogen to phosphorus ratio and the water content of excreta were measured, and the consequences of such selection on performance and gastro-intestinal tract (GIT) characteristics estimated. The genetic correlations between excretion, GIT and performance traits were established.ResultsHeritability estimates were high for CDUDM and the nitrogen excretion rate (0.30 and 0.29, respectively). The other excretion measurements showed low to moderate heritability estimates, ranging from 0.10 for excreta water content to 0.22 for the phosphorus excretion rate. Except for the excreta water content, the CDUDM was highly correlated with the excretion traits, ranging from -0.64 to -1.00. The genetic correlations between AMEn or CDUDM and the GIT characteristics were very similar and showed that a decrease in chicken excretion involves an increase in weight of the upper part of the GIT, and a decrease in the weight of the small intestine.ConclusionIn order to limit the environmental impact of chicken production, AMEn and CDUDM seem to be more suitable criteria to include in selection schemes than feed efficiency traits.

Phosphorus flux by macrobenthic invertebrates in a shallow eutrophic lake Donghu: spatial change

We estimated phosphorus flux mediated by benthic invertebrates from the sediments to the water in a shallow eutrophic lake (lake Donghu, central China) and quantified spatial (littoral and central sites) and specific (among different benthic taxa) differences. The mass-specific excretion rates of phosphorus (soluble reactive phosphorus (SRP, ηmol·mg dry mass –1 ·h –1 ) by benthic invertebrates (abundant taxa) were estimated experimentally and calculated as a final minus of initial nutrient mass divided by dry mass of organisms. Results showed high importance of chironomid larvae as a contributor to the total P flux from sediments to water in shallow lake Donghu. Benthic biomass (from 0.002 to 32.8 g dry mass·m –2 ) distribution and speciescomposition (31taxa)werestudied(October 2009)inthreeregions of lake Donghu (Guozhenghu, Miaohu, Yujiahu) using samples from three depths: the shallow littoral site (0.2–1 m depth), central site with 2 m depth, and central site with more than 3 m depth. The total estimated SRP excretion by benthic invertebrate reaches 36% of the direct SPR flux from sediments to water in this lake. The phosphorus regeneration by benthic animals is the most intensive in the shallow littoral sites (69.5 µmol P·m –2 ·day –1 ) and at least 20 times greater than in central sites (3.4 µmol P·m –2 ·day –1 ) of lake Donghu. The results support notable differences in the SRP excretion rates between taxa and sites. The spatial difference in the SRP flux might be considered as a general feature of lakes with periodical changing oxygen near bottom.

The role of arctic zooplankton in biogeochemical cycles: respiration and excretion of ammonia and phosphate during summer

The study of the structural and functional properties of key components of polar marine ecosystems has received increased attention in order to better understand the ecological consequences of future sea temperature rise and seasonal ice retraction. Owing to this purpose, during the ATOS-Arctic cruise, held in July 2007 in the framework of the 2007–2008 International Polar Year, we studied the respiratory carbon demand of mesozooplankton as well as their contribution to the regeneration of inorganic nitrogen and phosphorus (NH4-N and PO4-P) via excretion. The studied area comprised several stations along a latitudinal gradient in the East Greenland current, plus a network of stations NW of the Svalbard islands. The specific respiratory carbon losses and phosphorus (PO4-P) excretion rates were similar or slightly higher than some reports for Arctic mesozooplankton, but the nitrogen (NH4-N) excretion rates were higher by a factor of 3 when compared with previous data sets. The mesozooplankton respiratory losses were equivalent to 23% of primary production, and at turn zooplankton contributed by excretion to more than 50% of the N and P required by phytoplankton. Although C:N, C:P and N:P metabolic atomic quotients almost coincided with the average Redfield’s stoichiometric ratios, the low C:N values when compared to previous reports suggested a predominance of protein-related metabolic substrates. The potential consequences of changes observed in the C:N, N:P and C:P metabolic ratios of mesozooplankton for Arctic marine ecosystems are discussed.

Dreissenid phosphorus excretion can sustain C. glomerata growth along a portion of Lake Ontario shoreline

One of the effects of the dreissenid invasion into the Laurentian Great Lakes appears to be a resurgence in the abundance of the nuisance alga Cladophora glomerata which experienced a marked decline following phosphorus abatement in the late 1970s and early 1980s. A subsidy of bioavailable phosphorus excreted by dreissenid mussels could be an important mechanism facilitating the growth of C. glomerata. To assess the importance of phosphorus released by mussels to C. glomerata growth in the nearshore, we conducted a survey of mussel distribution and abundance followed by in situ experiments designed to measure dreissenid phosphorus excretion rates. Average dreissenid mussel abundance in our study area was 3674 individuals/m 2, with an average biomass of 52.2 g of shell free dry mass/m 2. The mussels excreted bioavailable soluble reactive phosphorus at an average rate of 7.02 μg SRP/g shell free dry mass/hour, contributing about 11 t of soluble reactive phosphorus to our study area over the C. glomerata growing season. Dreissenids appear to be an important source of recycled bioavailable phosphorus to the nearshore, supplying more soluble reactive phosphorus to our study area than local watercourses and WWTPs, and more phosphorus than is required to sustain local C. glomerata growth.

FISH DISTRIBUTIONS AND NUTRIENT CYCLING IN STREAMS: CAN FISH CREATE BIOGEOCHEMICAL HOTSPOTS

Rates of biogeochemical processes often vary widely in space and time, and characterizing this variation is critical for understanding ecosystem functioning. In streams, spatial hotspots of nutrient transformations are generally attributed to physical and microbial processes. Here we examine the potential for heterogeneous distributions of fish to generate hotspots of nutrient recycling. We measured nitrogen (N) and phosphorus (P) excretion rates of 47 species of fish in an N-limited Neotropical stream, and we combined these data with population densities in each of 49 stream channel units to estimate unit- and reach-scale nutrient recycling. Species varied widely in rates of N and P excretion as well as excreted N:P ratios (6-176 molar). At the reach scale, fish excretion could meet >75% of ecosystem demand for dissolved inorganic N and turn over the ambient NH4 pool in <0.3 km. Areal N excretion estimates varied 47-fold among channel units, suggesting that fish distributions could influence local N availability. P excretion rates varied 14-fold among units but were low relative to ambient concentrations. Spatial variation in aggregate nutrient excretion by fish reflected the effects of habitat characteristics (depth, water velocity) on community structure (body size, density, species composition), and the preference of large-bodied species for deep runs was particularly important. We conclude that the spatial distribution of fish could indeed create hotspots of nutrient recycling during the dry season in this species-rich tropical stream. The prevalence of patchy distributions of stream fish and invertebrates suggests that hotspots of consumer nutrient recycling may often occur in stream ecosystems.

Factors influencing nitrogen and phosphorus excretion rates of fish in a shallow lake

Summary 1. Fish excretion can be an important source of nutrients in aquatic ecosystems. Nitrogen (N) and phosphorus (P) excretion rates are influenced by many factors, including fish diet, fish growth rate and fish size. However, the relative influence of these and other factors on community‐level excretion rates of fish is unknown.2. We used bioenergetics modeling to estimate excretion rates of eight fish species in a shallow, Minnesota (U.S.A.) lake over four months in both 2004 and 2005. Excretion rates of each species were summed for community‐level N and P excretion rates, as well as the N : P ratio of excretion. We then used a model‐selection approach to assess ability of independent variables to predict excretion rates, and to identify the most parsimonious model for predicting N : P excretion ratios and P and N excretion rates at the community scale. Predictive models were comprised of the independent variables water temperature and average fish density, fish size, fish growth rate, nutrient content of fish and nutrient content of fish diets at the community scale.3. Fish density and nutrient content of fish diets (either N or P) were the most parsimonious models for predicting both N and P excretion rates, and explained 96% and 92% of the variance in N and P excretion, respectively. Moreover, fish density and nutrient models had 1400‐fold more support for predicting N and 21‐fold more support for predicting P excretion relative to models based on fish density only. Water temperature, fish size, fish growth rates and nutrient content of fish showed little influence on excretion rates, and none of our independent variables showed a strong relationship with N : P ratios of excretion.4. Past work has focused on the importance of fish density as a driver of fish excretion rates on a volumetric basis. However, our results indicate that volumetric excretion rates at the community scale will also change substantially in response to changes in relative abundance of fish prey or shifts in relative dominance of planktivores, benthivores, or piscivores. Changes in community‐scale excretion rates will have subsequent influences on algal abundance, water clarity, and other ecosystem characteristics.

Fecal Phytate Excretion Varies with Dietary Phytate and Age in Women

Objective: Information on the excretion of dietary phytate in humans under different conditions is limited. The purpose of this study was to investigate fecal excretion of dietary phytate and phosphorus in a group of young and elderly women consuming high and low phytate diets.Methods: Fifteen young and fourteen elderly women were fed two experimental diets, high phytate and low phytate, for 10 days each with a washout period of 10 days between the two diet periods. Duplicate diet samples from two different menus and complete fecal samples were collected for 5 days during each diet period and analyzed for phytate and phosphorus contents. Mean daily excretions and percentages of dietary intakes of phytate and phosphorus were calculated.Results: Dietary phytate level does impact phytate excretion, but the effect was observed only in young subjects. Fecal phytate excretion of young subjects during the high phytate diet (313mg/d) was significantly higher than during the low phytate diet (176mg/d), however, that of elderly subjects did not vary with dietary phytate levels. Phosphorus excretion, net absorption, and apparent absorption rate were affected by dietary phytate level but not by the age of the subjects.Conclusions: Results of this study indicate that phytate degradation in the gastrointestinal tract is substantial and more variable in young women than in elderly women. The high capacity of phytate degradation in elderly subjects may be related to long-term phytate intake but needs further clarification. Both beneficial and adverse health effects of phytate need to be studied considering the long-term phytate intake and age of subjects as well as dietary phytate levels.

Zooplankton phosphorus excretion in Swarzędzkie Lake (Western Poland) and its influence on phytoplankton

Abstract Zooplankton phosphorus excretion was studied in Swarzędzkie Lake in 2000-2002. Phosphorus excretion rates were high from spring through autumn, but low in winter. The highest value, 203.7 μgP 1-1 d-1 (vertical profile mean), was recorded in June 2000. The mean rate was 26.6 μgP 1-1 d-1 and was 10 times greater for rotifers than for both cladocerans and copepods. In most months, the calculated phosphorus excretion rate was greater than the sum of tributary external phosphorus loading and internal bottom sediment loading. Nevertheless, the influence of the zooplankton phosphorus excretion rate on yearly phytoplankton abundance, biomass and chlorophyll a was not statistically significant. Yearly variance in phytoplankton variables was best explained by a canonical variable composed of internal loading and zooplankton phosphorus excretion (total redundancy 32.8%).

Role of the polychaete Neanthes succinea in phosphorus regeneration from sediments in the Salton Sea, California

The Salton Sea currently suffers from several well-documented water quality problems associated with high nutrient loading. However, the importance of phosphorus regeneration from sediments has not been established. Sediment phosphorus regeneration rates may be affected by benthic macroinvertebrate activity (e.g. bioturbation and excretion). The polychaete Neanthes succinea (Frey and Leuckart) is the dominant benthic macroinvertebrate in the Salton Sea. It is widely distributed during periods of mixing (winter and spring), and inhabits only shallow water areas following development of anoxia in summer. The contribution of N. succinea to sediment phosphorus regeneration was investigated using laboratory incubations of cores under lake temperatures and dissolved oxygen concentrations typical of the Salton Sea. Regeneration rates of soluble reactive phosphorus (SRP) were lowest (−0.23–1.03 mg P m−2 day−1) under saturated oxygen conditions, and highest (1.23–4.67 mg P m−2 day−1) under reduced oxygen levels. N. succinea most likely stimulated phosphorus regeneration under reduced oxygen levels via increased burrow ventilation rates. Phosphorus excretion rates by N. succinea were 60–70% more rapid under reduced oxygen levels than under saturated or hypoxic conditions. SRP accounted for 71–80% of the dissolved phosphorus excreted under all conditions. Whole-lake SRP regeneration rates predicted from N. succinea biomass densities are highest in early spring, when the lake is mixing frequently and mid-lake phytoplankton populations are maximal. Thus, any additional phosphorus regenerated from the sediments at that time has potential for contributing to the overall production of the lake.

Stoichiometry of nutrient excretion by fish: interspecific variation in a hypereutrophic lake

This study investigates how nutrient cycling rates and ratios vary among fish species, with a particular focus on comparing an ecologically dominant detritivore (gizzard shad) to other fishes in a productive lake. We also examined how nutrient cycling rates are mediated by body size (as predicted by allometry theory), and how variation in nutrient cycling is related to body and food nutrient contents (according to predictions of ecological stoichiometry). As predicted by allometry, per capita nitrogen and phosphorus excretion rates increased and mass‐specific excretion rates decreased, with increasing mass. Body phosphorus content was correlated with body mass only in one species, bluegill. Contrary to stoichiometric predictions, there was no relationship between body P and mass‐normalized P excretion rate, or between body N:P and excreted N:P, when all individuals of all species were considered.However, at the species level, we observed some support for a body nutrient content effect on excretion as predicted by stoichiometry theory. For example, gizzard shad had lower body P (high body N:P) and also excreted P at higher rates (lower N:P) than bluegill, which had high body P (lower body N:P). We applied the Sterner (1990) homeostatic stoichiometry model to the two most common species in the study – gizzard shad and bluegill and found that food N:P had a greater effect than consumer body N:P on excreted N:P. This indicates that, in terms of variation among these species, nutrient excretion may be more of a function of food nutrient content than the nutrient content of the consumer. These results suggest that stoichiometry can provide a framework for variation among species in nutrient cycling and for evaluating the ecosystem consequences of biodiversity loss.

The direct contribution of fish to lake phosphorus cycles

Abstract – Published data are synthesised to assess the direct contribution of fish to the recycling of phosphorus across a lake productivity gradient. Phosphorus excretion rates by fish assemblages are more or less directly proportional to fish biomass, despite changes in mean body mass, species composition and diet with increasing lake productivity. Piecewise linear regression of published data shows for the first time that lacustrine fish biomass increases with total phosphorus (TP) concentration in the water column up to around 140 μg·TP·l−1 but levels off above that value, suggesting that fish contribute less to nutrient recycling as lake productivity increases. The results confirm previous findings that water column nutrient recycling by fish is much less important than by plankton and that fish are important nutrient stores in lakes. The contribution of fish to nutrient recycling is small because of their low turnover rates relative to other taxa.

Can feeding of fish on terrestrial insects subsidize the nutrient pool of lakes?

We estimated consumption and excretion rates of terrestrial-borne phosphorus by a population of the insectfeeding fish species bleak (Alburnus alburnus) in a 0.12-km 2 mesotrophic lake of the German lowlands. Fish abundance, growth rates, and diet composition were determined, and consumption and nutrient metabolism were calculated by a bioenergetics model. Mean bleak abundance was about 77,000 ind. km 22 . About 84% of bleak consumption consisted of terrestrial insects. Annual consumption of lake-external phosphorus (P) by bleak was 432 g, representing ;2.1% of the lake internal P-pool. Annual excretion of terrestrial-derived phosphorus by bleak was equivalent to ;11% of the mean epilimnetic SRP concentration. A substantial subsidy of lake nutrient pools by insectivorous fish is more likely in lakes ,0.03 km 2 owing to the increasing perimeter-to-area ratio between donor and recipient habitats. Terrestrial nutrient subsidy by fish feeding may be important only in small oligotrophic lakes in forested areas.

Ecological responses to simulated benthic‐derived nutrient subsidies mediated by omnivorous fish

Summary1. Fish can play an important role in coupling benthic and pelagic habitats by consuming benthic prey and providing essential nutrients to algae in dissolved form. However, little is known about the factors affecting the magnitude of this nutrient subsidy.2. Using laboratory and mesocosm experiments we evaluated how varying ingestion rates of bluegill sunfish (Lepomis macrochirus) affects fish excretion rates of both nitrogen (N) and phosphorus (P). During the 10‐week mesocosm experiment, we also evaluated how varying ingestion rates may affect plankton community dynamics, and nutrient flux between pelagic and benthic habitats. Lastly, bioenergetic/mass balance models were used to examine the nutrient stoichiometry of fish body composition and excretion products.3. Under laboratory conditions, both N and P excretion rates increased with increased ingestion of benthic prey surrogates (earthworms). This effect was more pronounced for N than P. Furthermore, under the more realistic conditions of the mesocosm experiment ingestion rate had no significant effect on P excretion rate.4. Increased fish ingestion rate in the mesocosm experiment increased total algal biomass and the flux of nutrients from the water column to sediments. Effects of variable ingestion were much stronger on periphyton biomass and algal sedimentation rates than on phytoplankton or zooplankton biomass or composition.5. Fish body nutrient composition was greatly affected by ingestion rate. N content increased and P content decreased with ingestion rate. As a result, the N : P ratio of fish bodies also increased with ingestion rate. The N : P ratio of nutrients excreted by fish also increased with ingestion rate, counter to predictions of stoichiometric theory, which predicts that excreted N : P ratio is negatively correlated to body N : P. However, this finding can be explained by relaxing the assumption of constant nutrient assimilation rates, and our mass balance data suggest that assimilation rates vary indeed with ingestion rate.6. Our study provides experimental evidence that translocation of benthic‐derived nutrients by fish can affect the flux of nutrients among habitats, while also suggesting that stoichiometry models need to better incorporate how variable ingestion rates affect nutrient assimilation and excretion rates.

Seasonal variation in metabolism of cultured Pacific oyster, Crassostrea gigas, in Sanggou Bay, China

Rates of respiration and excretion of the Pacific oyster, Crassostrea gigas, were measured seasonally from June 2002 to July 2003 under ambient conditions of food, water temperature, pH, and salinity in Sanggou Bay, an important mariculture coast in north China. The aim of this study is to obtain fundamental data for further establishing an energy budget model and assessing the carrying capacity for cultivation of C. gigas in north China. Oysters were collected monthly or bimonthly from the integrated culture areas of bivalve and kelp in the bay. Oxygen consumption and ammonium and phosphorus excretion rates were measured, and ratios of O/N and N/P were calculated. One-way ANOVA was applied to determine differences among these parameters that act as a function of seasonal variation. All the physiological parameters yielded highly significant variations with season ( P < 0.01). The rate of respiration varied seasonally, with the highest oxygen consumption rate in July and the lowest rate in January, ranging from 0.07 to 2.13 mg O 2 h − 1 g − 1dry tissue weight (DW). Maximum and minimum ammonium excretion rates were recorded in August and January, respectively, ranging from 0.51 to 5.40 μmol NH 4–N h − 1g − 1 DW. Rates of phosphorus excretion varied from 0.11 (in January) to 0.64 (in July) μmol PO 4–P h − 1g − 1 DW. The O/N and N/P ratios changed from 9.2 (in January) to 59.8 (in July) and from 4.6 (in January) to 10.9 (in August), respectively. For each season, the allometric relationship between the physiological response (e.g., rate of oxygen consumption, ammonium and phosphorus excretion) and DW of the animal was estimated using the formula: Y = a × DW b .

Neonatal transient renal failure with renal medullary hyperechogenicity: clinical and laboratory features

Sonographic findings of renal medullary hyperechogenicity have been observed in the neonate in association with severe perinatal renal injury, kidney malformations or nephrocalcinosis, and, rarely, in newborn infants with transient renal failure. The aim of the study was to describe the entity of neonatal transient renal failure with renal medullary hyperechogenicity (NTRFMH). We studied nine term neonates, born between August 1999 and February 2004 in our institution (0.1% of the live born infants), who developed transient renal dysfunction after birth, and in whom renal sonograms showed bilateral medullary hyperechogenicity. Seven of the infants (78%) had anuria until 30-45 hours of age, and two (22%) had oliguria. Peak serum creatinine levels ranged between 0.61 and 1.62 mg/dL (mean: 1.09+/-0.27 mg/dL) at 2-3 days of life. Additional findings included proteinuria in nine infants (100%), uric acid crystalluria in seven (78%), hyperuricemia in four (44%), and hypertension in one (11%). Hyperuricosuria was demonstrated in one out of the seven patients in whom this parameter was determined. Urinary excretion rates of calcium, phosphorus and oxalic acid were normal, as were urinary levels of amino acids and organic acids. Full clinical recovery accompanied by normalization of all laboratory parameters was observed in all infants by 4-6 days of life. Subsequent follow-up showed normal renal function, no urinary abnormalities, and normal renal sonograms in all infants. Our summary of the nine infants with NTRFMH reported on here and a review of 19 cases of this condition reported in the literature reveal a not-so-rare entity of unclear etiology, but excellent prognosis. Physicians caring for neonates should be aware of this benign and transient condition.

Almost total replacement of fish meal by plant protein sources in the diet of a marine teleost, the European seabass, Dicentrarchus labrax

Five practical diets in which the supply of protein from fish meal was decreased gradually from 100% to about 2% and replaced by plant protein sources were formulated. European seabass weighing about 190 g were fed these diets for 12 weeks at a water temperature of 22 °C. Feed was dispensed using automatic self-feeders and voluntary feed intake (VFI) was closely monitored. We did not find any significant difference among diets in the apparent digestibility coefficients (ADC) of dry matter (80–82%), protein (94–96%), energy (88–92%) or phosphorus (49–58%). Replacement of fish meal by plant protein ingredients did not influence VFI. All groups had very good growth rates (DGI above 1.3%/day) and there were no significant differences in growth rate, feed efficiency or in daily nitrogen gains among groups. There was, however, a slight increase in fat deposition in fish fed diets with plant protein sources. Ammonia nitrogen and soluble phosphorus excretion rates were measured. Nitrogen and phosphorus balance studies indicated that fish meal replacement by plant ingredients led to a slight increase in nitrogen losses (from 83 to 103 g N/kg weight gain) but led to a significant reduction in total phosphorus losses (from 13 to 5 g P/kg weight gain). These results combined with the remarkable acceptability of diets containing high levels of plant protein ingredients with identical growth performances of European seabass show clearly that dietary fish meal levels can be considerably reduced without any adverse consequence in terms of somatic growth or nitrogen utilisation.

Zooplanktivory and Nutrient Regeneration by Invertebrate (Mysis relicta) and Vertebrate (Oncorhynchus nerka) Planktivores: Implications for Trophic Interactions in Oligotrophic Lakes

We investigated zooplanktivory and nutrient regeneration by the opossum shrimp Mysis relicta and kokanee Oncorhynchus nerka to assess the relative roles of these planktivores in oligotrophic food webs. Using bioenergetic models and clearance rate estimates, we quantified phosphorus (P) excretion rates and consumption of cladoceran prey by Mysis and kokanees in Lake Pend Oreille, Idaho, from 1995 to 1996. Consumption of cladoceran prey by Mysis was 186 kg·ha−1·year−1, whereas consumption by kokanees was less than one quarter as much, at 45 kg·ha−1·year−1. Similarly, Mysis excreted approximately 0.250 kg P·ha−1·year−1 during nighttime migrations into the upper water column, whereas P excretion by kokanees was less than one third as much, at approximately 0.070 kg P·ha−1·year−1. On a volumetric basis, nocturnal excretion by Mysis ranged from 0.002 to 0.007 μg P·L−1·d−1 and accounted for less than 1% of the soluble reactive P typically measured in the upper water column of the lake. Hence, nutrient recycling by Mysis may be limited in the upper water column because of the nocturnal feeding habitats that constrain Mysis to deeper strata for much of the day. In spring and autumn months, low abundance of cladoceran prey coincided with high seasonal energy requirements of the Mysis population that were linked to timing of annual Mysis brood release and abundance of age-0 Mysis. Predation by Mysis accounted for 5–70% of daily cladoceran standing stock, supporting the notion that seasonal availability of cladocerans may be regulated by Mysis predation. In lakes where Mysis experience little predation mortality, they likely play a dominant role in food web interactions (e.g., trophic cascades) relative to planktivorous fishes. Biotic mechanisms, such as successful predator-avoidance behavior, omnivorous feeding habits, and seasonal variation in Mysis biomass, enhance the ability of Mysis to influence food web interactions from an intermediate trophic level.

Effect of RenaGel, a non-absorbable, cross-linked, polymeric phosphate binder, on urinary phosphorus excretion in rats.

Normalization of serum phosphorus is critical in the treatment of End Stage Renal Failure patients. Aluminum or calcium based phosphate binders, while efficacious, are associated with potential adverse side effects and toxicities. We have developed RenaGel, a novel, non-absorbed hydrogel which binds dietary phosphate leading to increased fecal excretion, decreased absorption and decreased serum phosphorus levels. In this paper, we present results from both in vitro and in vivo studies in which we examined the efficacy of this novel phosphate binder. In vitro, RenaGel was suspended in the test solution, and the mixture was stirred for 1 hour at room temperature. The solid was then filtered off, and the residual liquid analyzed for phosphate. In vivo, RenaGel was mixed in rodent feed at different concentrations and fed to normal rats for up to 4 days. Urine was collected and analysed for phosphate content. In vitro binding studies demonstrate that RenaGel has an extremely high phosphate binding capacity. At an estimated physiological concentration of 5 mM phosphate, RenaGel binds 2.6 mmole phosphate/g of phosphate binder. The in vivo binding study shows that RenaGel mixed into the diet decreased urinary phosphorus excretion in a dose dependent manner. RenaGel particles with a 23 microns mean diameter are more efficacious than the larger ones. In conclusion, the above studies indicate that RenaGel is a potent phosphate binder. RenaGel contains no calcium or aluminum and offers an alternative to existing phosphate binder treatments.

Effect of L-cysteine on some urinary risk factors in experimental hyperoxaluric rats.

To study the effect of L-cysteine on urinary risk factors in hyperoxaluric urolithiasis in rats. Twenty-four rats were divided into four groups of six rats each; those in Group I served as controls, those in Group II had hyperoxaluria induced using sodium glycollate, those in Group III were given cysteine alone and those in Group IV were given sodium glycollate and cysteine. Samples of 24 h urine were collected and analysed to determine the content of calcium, oxalate, phosphorus and magnesium, and the organic acids, glycollic, glyoxylic and citric acid. Hyperoxaluric rats treated with cysteine had significantly lower excretion rates of calcium, oxalate, phosphorus, glycollic and glyoxylic acid than the glycollate fed rats. When cysteine was given, the excretion of urinary citric acid and magnesium were also increased. Cysteine may be a useful agent in preventing oxalate urolithiasis.

P-release from DOP by phosphatase activity in comparison to P excretion by zooplankton. Studies in hardwater lakes of different trophic level

Hydrolysis of natural dissolved organic phosphorus (DOP) in three hardwater lakes of different trophic level was calculated from kinetic data of phosphatase activity (PA) in different size fractions. DOP as well as kinetics of PA were determined every fortnight in depth profiles during the year 1990. 60% of DOP was assumed to be suitable substrate for phosphatases. The rate of hydrolysis increased markedly with higher trophic level. Average hydrolysis rate of DOP in polytrophic lake Thaler See was 3.26 nM P min−1 (6 µg P-PO4 l−1 h−1). In oligotrophic Lake Herrensee, dissolved phosphatases were responsible for more than half of the total hydrolysis. In the other two lakes, bacterial and algal surface PA dominated hydrolysis in changing parts depending on kinetics and DOP concentration. The regeneration rate of phosphate by PA was compared to phosphorus (P) excretion rate of zooplankton. Excretion was calculated from zooplankton data and excretion equations from the literature. In oligotrophic Lake Herrensee, excretion by zooplankton recycled in average 18% of the phosphate amount which was hydrolysed from DOP by PA. With higher trophic level, relevance of P excretion from zooplankton decreased drastically.