Phosphate Excretion Rates Research Articles

Combination Oxylanthanum Carbonate and Tenapanor Lowers Urinary Phosphate Excretion in Rats.

This study evaluated the combined effects of oxylanthanum carbonate (OLC), an investigational phosphate binder, and tenapanor, an approved sodium/hydrogen exchanger 3 (NHE3) inhibitor that reduces paracellular phosphate absorption, on urinary phosphate excretion in rats on a high phosphorus diet. Sixty-four male Sprague Dawley rats were randomized into eight groups: vehicle; tenapanor (0.15 mg/kg) only; OLC (0.75%, 1.5%, and 3%) only; and combination OLC (0.75%, 1.5%, and 3%) + tenapanor (0.15 mg/kg). Vehicle and tenapanor were dosed orally twice/day whereas OLC was incorporated into diets. We collected 24-hour urine samples to measure urinary phosphate excretion, a proxy for intestinal phosphate absorption efficiency. Primary analyses compared pooled results in the three OLC dose groups. In the tenapanor 0.15 mg/kg group, mean urinary phosphate excretion from Days 9 to 11 was 8.5 mg/day (12.5%) lower compared to the vehicle group. In the OLC alone groups, mean urinary phosphate excretion (pooled across the 0.75, 1.5, and 3% OLC dose groups) was 12 mg/day (17.7%) lower compared to the vehicle group. Compared to vehicle, urinary phosphate excretion was 28.0 mg/day (41.3%) lower in the combination OLC + tenapanor groups (p=0.016). Bliss model of independence assessing the statistical significance between observed and predicted results indicated that combination OLC + tenapanor was synergistic (p=0.009 for 0.75% OLC + tenapanor and p=0.010 for 1.5% OLC + tenapanor). In summary, we demonstrated sizeable reductions in urinary phosphate excretion in response to OLC monotherapy and the most pronounced reductions in urinary phosphate excretion when using OLC in combination with tenapanor.

Combination Oxylanthanum Carbonate and Tenapanor Lowers Urinary Phosphate Excretion in Rats

Combination Oxylanthanum Carbonate and Tenapanor Lowers Urinary Phosphate Excretion in Rats

Determinants of the serum phosphate concentration in chronic kidney disease.

If Ccr is creatinine clearance and EP and TRP are rates of phosphate excretion and reabsorption, the serum phosphate concentration (Ps) is the sum of EP/Ccr and TRP/Ccr, i.e., the amounts of phosphate excreted and reabsorbed per volume of filtrate. At equilibrium, influx of phosphate into plasma determines EP, and EP/Ccr quantifies the contribution of phosphate influx to Ps. We used data obtained at 688 clinic visits of 387 patients to analyze the evolution of Ps in chronic kidney disease (CKD) stages G1 - 5 (dialysis excluded). EP/Ccr was calculated as (Pu×crs)/cru and TRP/Ccr as Ps-EP/Ccr (where u is urine, s is serum, and cr is creatinine). Means of these parameters were plotted against CKD stages, and correlations among variables were determined with regression analyses. In comparison to values in CKD stages G1 - 2, EP/Ccr rose and TRP/Ccr fell by the same amount in CKD G3a and G3b, and Ps did not change. In stages G4 and G5, EP/Ccr increased sharply, TRP/Ccr fell minimally, and Ps rose significantly. At estimated glomerular filtration rate (eGFR) ≥45 mL/min/1.73m2, TRP/Ccr was the principal determinant of Ps at eGFR < 45 mL/min/1.73m2, contributions of EP/Ccr and TRP/Ccr to Ps were comparable. Taken together, our results show that in CKD stages G4 and G5, the effect of phosphate reabsorption on Ps changes negligibly while that of phosphate influx increases dramatically. Because the tubular response to rising EP/Ccr is limited, maintenance of stable Ps in advanced CKD requires extreme reduction of phosphate influx into plasma. TRP/Ccr may define the lowest attainable Ps.

MINERAL METABOLISM ADAPTATION IN LIVING KIDNEY DONORS: PROSPECTIVE OBSERVATIONAL STUDY

Purpose: The aim of this study is to investigate whether uninephrectomy for kidney donation cause change of bone and mineral metabolism and also investigate factors associated with it in prospective kidney donors after uninephrectomy. Methods: Serum and urine creatinine, calcium, phosphorus, and serum intact parathyroid hormone (iPTH), 25(OH) vitamin D and FGF-23 values were obtained pre-donation and postoperatively in 68 donors. Renal fraction excretion rate of phosphate (FEpi) was calculated with 24-hour urine collection. Pre- and post-donation GFR was measured by DTPA scan in all donors. Results: After donor nephrectomy (median 7 months, 4-18months), MDRD eGFR declined (91.4 to 62.2 ml/min/1.73m2) and remnant kidney’s GFR measured by DTPA scan increased (55.1 to 71.3 ml/min), significantly. (both p<0.001) Post-donation serum iPTH increment was marked (43.0 Vs 60.1 pg/ml, p<0.001), whereas 25(OH) vitamin D level change was not significant (25.7 to 25.0 ng/ml, p=0.573). After donation, serum Ca was changed from 9.15 to 9.16 (p=0.856), serum phosphate changed from 3.6 to 3.4 (p=0.005). Renal fraction excretion rate of phosphate (FEpi) was increased after donation. (14.6 to 20.3, p<0.01) In comparison to pre-donation, FGF23 levels are no significantly changed (1094pg/ml vs 1169pg/ml, p=0.766). Conclusions: From after kidney donation, living kidney donor develop secondary hyperparathyroidism related to a decreased serum phaosphate, increased renal fraction excretion of phosphate. FGF23 levels do not rise in living kidney donors. Mineral metabolism adaptation to decreased eGFR in donors might differ from those in CKD patients maybe due to remnant intact nephrons.

Renal Phosphate Handling in Antiretroviral-naive HIV-Infected Patients.

Human immunodeficiency virus (HIV) infection impairs renal function, thereby affecting renal phosphate metabolism. We prospectively estimated the prevalence of phosphate abnormalities (mild, moderate to life-threatening hypophosphataemia, and hyperphosphataemia) before initiating antiretroviral therapy (ART). A cross-sectional analysis was performed on 170 consecutive newly diagnosed ARTnaive, HIV-infected patients attending our HIV/AIDS clinics over a period of one year. Fifty (50) screened HIV-negative blood donors were used for comparison (controls). Blood and urine were collected simultaneously for phosphate and creatinine assay to estimate fractional phosphate excretion (FEPi %) and glomerular filtration rate (eGFR). eGFR showed significant difference between patients' and controls' medians (47.89ml/ min/1.73m2 versus 60ml/min/1.73m2, p <0.001); which denotes a moderate chronic kidney disease in the patients. Of the 170 patients, 78 (45.9%) had normal plasma phosphate (0.6-1.4 mmol/L); 85 (50%) had hyperphosphataemia. Grades 1, 2 and 3 hypophosphataemia was observed in 3 (1.8%), 3 (1.8%), and 1(0.5%) patient(s) respectively. None had grade 4 hypophosphataemia. Overall, the patients had significantly higher median of plasma phosphate than the controls, 1.4 mmol/L (IQR: 1.0 - 2.2) versus 1.1 mmol/L (IQR: 0.3 - 1.6), p <0.001, implying hyperphosphataemia in the patients; significantly lower median urine phosphate than the controls, 1.5 mmol/L (IQR: 0.7 -2.1) versus 8.4 mmol/L (IQR: 3.4 - 16), p <0.001), justifying the hyperphosphataemia is from phosphate retention; but a non-significantly lower median FEPi% than the controls, 0.96% (IQR: 0.3 -2.2) versus 1.4% (IQR: 1.2 -1.6), p > 0.05. Predictors of FEPi% were age (Odds ratio, OR 0.9, p = 0.009); weight (OR 2.0, p < 0.001); CD4+ cells count predicted urine phosphate among males (p = 0.029). HIV infection likely induces renal insufficiency with reduced renal phosphate clearance. Thus, hyperphosphataemia is highly prevalent, and there is mild to moderate hypophosphataemia but its life-threatening form (grade 4) is rare among ART-naive HIV patients.

Mediation of the relationship between proteinuria and serum phosphate: Insight from the KNOW-CKD study.

Proteinuria and hyperphosphatemia are risk factors for cardiovascular disease in patients with chronic kidney disease (CKD). Although the interaction between proteinuria and the serum phosphate level is well established, the mechanistic link between the two, particularly the extent to which this interaction is mediated by phosphate-regulating factors, remains poorly understood. In this study, we examined the association between proteinuria and the serum phosphate level, as well as potential mediators, including circulating fibroblast growth factor (FGF23)/klotho, the 24-h urinary phosphate excretion rate to glomerular filtration rate ratio (EP/GFR), and the 24-h tubular phosphate reabsorption rate to GFR ratio (TRP/GFR). The analyses were performed with data from 1793 patients in whom 24-h urine protein and phosphate, serum phosphate, FGF23, and klotho levels were measured simultaneously, obtained from the KoreaN cohort study for Outcome in patients With Chronic Kidney Disease (KNOW-CKD). Multivariable linear regression and mediation analyses were performed. Total, direct, and indirect effects were also estimated. Patients with high serum phosphate levels were found to be more likely to exhibit greater proteinuria, higher FGF23 levels, and lower klotho levels. The 24-h EP/GFR increased and the 24-h TRP/GFR decreased with increasing proteinuria and CKD progression. Simple mediation analyses showed that 15.4% and 67.9% of the relationship between proteinuria and the serum phosphate level were mediated by the FGF23/klotho ratio and 24-h EP/GFR, respectively. Together, these two factors accounted for 73.1% of the relationship between serum markers. These findings suggest that proteinuria increases the 24-h EP/GFR via the FGF23/klotho axis as a compensatory mechanism for the increased phosphate burden well before the reduction in renal function is first seen.

Urinary stone risk factors in the descendants of patients with kidney stone disease.

Evidence has indicated that immediate family members of nephrolithiasis patients had high opportunity to develop stones. However, they are usually not regarded to be at risk, since it is unclear if there are any lithogenic abnormalities found in non-stone-forming nephrolithiasis relatives. Our aim was to investigate urinary metabolic abnormalities in the children of nephrolithiasis patients, compared with the general population. The 24-h urinary metabolic profile was studied for 28 calcium oxalate nephrolithiasis patients (NL) and 46 of their descendants (ND), as well as 40 non-stone-forming volunteers (V) and 34 of their descendants (VD). There was no difference between age, gender, and serum creatinine between NL vs. V (parental groups) and ND vs. VD (descendant groups). High urinary oxalate in nephrolithiasis and urinary calcium in their descendants was detected. In addition, an elevated urinary excretion rate of calcium, phosphate, protein, and albumin, along with low citrate excretion and high urinary supersaturation was observed in both the nephrolithiasis patients and their descendants. Approximate 17.8-24.4% of the nephrolithiasis descendants had a urinary supersaturation higher than the nephrolithiasis level, but none was found in VD group. The level of urinary supersaturation index was correlated with urinary protein and albumin excretion in nephrolithiasis family. It was demonstrated that nephrolithiasis offspring carried several urinary metabolic risks predisposing to stone formation which are similar to their parents, and about one in every five nephrolithiasis children had nephrolithiasis level urinary supersaturation.

Nonlinear disposition of lithium in rats and saturation of its tubular reabsorption by the sodium-phosphate cotransporter as a cause.

We previously reported the contribution of sodium-phosphate cotransporter to the tubular reabsorption of lithium in rats. In the present study, the dose dependency of the renal handling of lithium was examined in rats. When lithium chloride at 1.25mg/kg, 2.5mg/kg and 25mg/kg was intravenously injected as a bolus, the areas under the plasma concentration-time curve of lithium until 60minutes were calculated to be 6.23mEq·min/l, 8.77mEq·min/l and 64.6mEq·min/l, respectively. The renal clearance of lithium and its fractional excretion increased with increments in the dose administered. The renal clearance of lithium strongly correlated with the urinary excretion rate of phosphate in the 1.25mg/kg group (r = 0.840) and 2.5mg/kg group (r = 0.773), whereas this correlation was weak in the 25mg/kg group (r = 0.306). The infusion of foscarnet, a typical inhibitor of sodium-phosphate cotransporter, decreased the fractional reabsorption of lithium in rats administered lithium chloride at 2.5mg/kg, but did not affect it in rats administered 25mg/kg. These results demonstrate the nonlinearity of the renal excretion of lithium in rats, with the saturation of lithium reabsorption by the sodium-phosphate cotransporter potentially being involved.

Renal damage induced by the pesticide methyl parathion in male Wistar rats

ABSTRACTLittle information is apparently available regarding the nephrotoxic effects induced by pesticides. The aim of this study was to examine the influence of low doses of methyl parathion (MP) on the structure and function of the kidney of male Wistar rats. A corn oil (vehicle) was administered to control rats, whereas treated rats received MP at 0.56 mg/kg orally (1/25 of LD50), every third day, for 8 weeks. At the end of each week following MP exposure, creatinine and glucose levels were measured in plasma, while glucose, inorganic phosphate, total proteins, albumin, and activity of γ-glutamyltranspeptidase (GGT) were determined in urine. Kidney histological study was also performed. Compared with control rats, MP significantly increased plasma glucose and creatinine levels accompanied by decreased urinary flow rate and elevated urinary excretion rates of glucose, phosphate, and albumin. Further, the activity of GGT in urine was increased significantly. The proximal cells exhibited cytoplasmic vacuolization, positive periodic acid Schiff inclusions, and brush border edge loss after 2 or 4 weeks following MP treatment. Finally, renal cortex samples were obtained at 2, 4, 6, and 8 weeks of MP treatment, and the concentrations of reduced glutathione (GSH) and glutathione peroxidase (GPx) activity were measured. The mRNA expression levels of BAX and tumor necrosis factor-α (TNF-α) were also determined (RT-PCR). MP significantly decreased renal GSH levels, increased GPx activity, as well as downregulated the mRNA expression of TNF-α and BAX. Densitometry analysis showed a significant reduction in TNF-α and BAX mRNA expression levels at 2 and 4 weeks following MP treatment. Low doses of MP produced structural and functional damage to the proximal tubules of male rat kidney.

Ecological interactions modulate responses of two intertidal mussel species to changes in temperature and pH

Predicted climate change scenarios for the end of this century suggest a substantial warming and ocean acidification of sea surface waters. Physiological performance of marine coastal organisms will be affected leading to changes in whole communities. In particular, ocean acidification poses an important threat for shelled molluscs. Nevertheless, climate change impacts are species-specific and responses may even differ among species that play a similar role in the ecosystems. Currently, two mussel species, the native Mytilus galloprovincialis Lamarck 1819 and the non-indigenous Xenostrobus securis Lamarck 1819, share the same habitat along shores in the inner part of the Galician Rias Baixas (NW Spain) forming mixed patchy clumps. Here, we used an experimental approach in mesocosms to evaluate the effects of increasing temperature and acidification on mussel clumps of different composition (monospecific and mixed clumps). Our model systems were artificially constructed clumps resembling those found on rocky shores. Responses to environmental stressors were measured on several functioning variables at the individual (i.e. survivorship, growth, condition index and composition of shell) and clump level (i.e. respiration, ammonia and phosphate excretion rates). The decrease of pH had a lethal effect and reduced growth on the native mussels. The invader was more resilient although individual responses were very often shaped by the composition of the clump. The reduced pH and, especially the high temperature conditions, tended to cause an increase in respiration rates of all types of clumps. Interactions between the two species seemed to modulate many effects at both individual and clump levels highlighting the complexity of responses when considering multiple stressors.

Biodeposition, respiration, and excretion rates of an introduced clam Mercenaria mercenaria in ponds with implications for potential competition with the native clam Meretrix meretrix in Shuangtaizi estuary, China

This study aimed to evaluate the potential impacts of an introduced clam Mercenaria mercenaria on estuarine ecosystem, and implications for the niche competition with a native clam Meretrix meretrix. The biodeposition, respiration, and excretion rates of M. mercenaria were determined seasonally using a sediment trap and a closed respirator in field. The biodeposition rates of M. mercenaria were 0.06–0.37 g/ (ind.·d), and the respiration rates were 0.31–14.66 mg/(ind.·d). The ammonia and phosphate excretion rates were 0.18–36.70 and 1.44–14.87 μg/(ind.·d), respectively. The hard clam M. mercenaria may discharge dry deposits up to 2.1×105 t, contribute 18.3 t ammonia and 9.0 t phosphate to culture ponds, and consume 7.9×103 t O2 from ponds annually. It suggested that the hard clam M. mercenaria might play an important role in pelagic-benthic coupling in pond ecosystem through biodeposition and excretion. A comparison of the key physiological parameters of the introduced clam M. mercenaria and the native clam Meretrix meretrix suggested that M. mercenaria had a niche similar to that of Meretrix meretrix in Shuangtaizi estuary and might have a potential competition with Meretrix meretrix for habitat and food if M. mercenaria species escaped from the culture pond or artificially released in estuarine ecosystem.

Physiological and molecular responses of the goldfish (Carassius auratus) kidney to metabolic acidosis, and potential mechanisms of renal ammonia transport.

Relative to the gills, the mechanisms by which the kidney contributes to ammonia and acid-base homeostasis in fish are poorly understood. Goldfish were exposed to a low pH environment (pH4.0, 48 h), which induced a characteristic metabolic acidosis and an increase in total plasma [ammonia] but reduced plasma ammonia partial pressure (PNH3). In the kidney tissue, total ammonia, lactate and intracellular pH remained unchanged. The urinary excretion rate of net base under control conditions changed to net acid excretion under low pH, with contributions from both the NH4 (+) (∼30%) and titratable acidity minus bicarbonate (∼70%; TA-HCO3 (-)) components. Inorganic phosphate (Pi), urea and Na(+) excretion rates were also elevated while Cl(-) excretion rates were unchanged. Renal alanine aminotransferase activity increased under acidosis. The increase in renal ammonia excretion was due to significant increases in both the glomerular filtration and the tubular secretion rates of ammonia, with the latter accounting for ∼75% of the increase. There was also a 3.5-fold increase in the mRNA expression of renal Rhcg-b (Rhcg1) mRNA. There was no relationship between ammonia secretion and Na(+) reabsorption. These data indicate that increased renal ammonia secretion during acidosis is probably mediated through Rhesus (Rh) glycoproteins and occurs independently of Na(+) transport, in contrast to branchial and epidermal models of Na(+)-dependent ammonia transport in freshwater fish. Rather, we propose a model of parallel H(+)/NH3 transport as the primary mechanism of renal tubular ammonia secretion that is dependent on renal amino acid catabolism.

Eucalanoid copepod metabolic rates in the oxygen minimum zone of the eastern tropical north Pacific: Effects of oxygen and temperature

The eastern tropical north Pacific Ocean (ETNP) contains one of the world’s most severe oxygen minimum zones (OMZs), where oxygen concentrations are less than 2µmolkg−1. OMZs cause habitat compression, whereby species intolerant of low oxygen are restricted to near-surface oxygenated waters. Copepods belonging to the family Eucalanidae are dominant zooplankters in this region and inhabit a variety of vertical habitats within the OMZ. The purpose of this study was to compare the metabolic responses of three species of eucalanoid copepods, Eucalanus inermis, Rhincalanus rostrifrons, and Subeucalanus subtenuis, to changes in temperature and environmental oxygen concentrations. Oxygen consumption and urea, ammonium, and phosphate excretion rates were measured via end-point experiments at three temperatures (10, 17, and 23°C) and two oxygen concentrations (100% and 15% air saturation). S. subtenuis, which occurred primarily in the upper 50m of the water column at our study site, inhabiting well-oxygenated to upper oxycline conditions, had the highest metabolic rates per unit weight, while E. inermis, which was found throughout the water column to about 600m depth in low oxygen waters, typically had the lowest metabolic rates. Rates for R. rostrifrons (found primarily between 200 and 300m depth) were intermediate between the other two species and more variable. Metabolic ratios suggested that R. rostrifrons relied more heavily on lipids to fuel metabolism than the other two species. S. subtenuis was the only species that demonstrated a decrease in oxygen consumption rates (at intermediate 17°C temperature treatment) when environmental oxygen concentrations were lowered. The percentage of total measured nitrogen excreted as urea (% urea-N), as well as overall urea excretion rates, responded in a complex manner to changes in temperature and oxygen concentration. R. rostrifrons and E. inermis excreted a significantly higher % of urea-N in low oxygen treatments at 10°C. At 17°C, the opposite trend was observed as E. inermis and S. subtenuis excreted a higher % of urea-N in the high oxygen treatment. This unique relationship has not been documented previously for crustacean zooplankton, and warrants additional research into regulation of metabolic pathways to better understand nitrogen cycling in marine systems. This study also compared metabolic data for E. inermis individuals captured near the surface versus those that were resident in the deeper OMZ. Deeper-dwelling individuals had significantly higher nitrogen excretion rates and O:N ratios, suggesting an increased reliance on lipids for energy while residing in the food-poor waters of the OMZ.

Sodium-phosphate cotransporter mediates reabsorption of lithium in rat kidney

Lithium, used for the treatment of bipolar disorders, is reabsorbed via sodium-transport system in the proximal tubule. This step causes intra-/inter-individual difference of lithium disposition, and it has not been unclear which transporter contributes. In this study, we examined effect of foscarnet and parathyroid hormone (PTH), inactivators for sodium-phosphate cotransporter, and phlorizin, a typical inhibitor for sodium-glucose cotransporter, on the disposition of lithium in rats. Their intravenous administration stimulated urinary excretion of phosphate or glucose. After the intravenous injection of lithium chloride as a bolus, plasma concentration of lithium decreased time-dependently. The renal clearance of lithium was calculated to be 0.740ml/min/kg in control rats, and this was 26.7% of creatinine clearance. Foscarnet and PTH significantly increased the renal clearance of lithium and its ratio to creatinine clearance, suggesting that they prevented the reabsorption of lithium. No effect of phlorizin on the renal handling of lithium was recognized. In control rats, the renal clearance of lithium showed a strong correlation with the renal excretion rate of phosphate, compared with creatinine clearance. These findings suggest that sodium-phosphate cotransporter reabsorbs lithium in the rat kidney. Furthermore, its contribution was estimated to be more than 65.9% in the lithium reabsorption. And, this study raised the possibility that therapeutic outcome of lithium is related with the functional expression of sodium-phosphate cotransporter in the kidney.

Potentially life-threatening phosphate diabetes induced by ferric carboxymaltose injection: a case report and review of the literature.

We report the case of a 45-year-old female patient who developed phosphate diabetes after administration of ferric carboxymaltose. Ten days after the second dose, she complained of intense fatigue and blood analysis showed a phosphate plasma level of 0.93 mg/dL with phosphate excretion rate of 23%. She received phosphate supplementation which resulted in phosphate clearance improvement which persisted for two months. We reviewed other cases described in the literature and would draw attention to this rare but potentially life-threatening side effect.

The Role of Distubances of Phosphate Metabolism in Metabolic Syndrome

Abstract Background and Aims: Metabolic syndrome represents a cluster of cardiovascular risk factors and reached epidemic proportions. It was hypothesized that disturbances in phosphate metabolism may represent a feature of the metabolic syndrome. The aim of the study was to investigate the relationship between phosphate levels and the presence of metabolic syndrome components, as well as the putative mechanism for reduced phosphate level in metabolic syndrome. Materials and Methods: We enrolled 155 subjects: 64 with metabolic syndrome and 91 controls. Biochemical parameters of the metabolic syndrome study population were compared with the healthy population. Results: Patients with metabolic syndrome showed significantly lower phosphate (46%) and magnesium levels compared with controls (22.7%) (p&lt;0.001). Women showed significantly greater serum phosphate levels than men (3.32 mg/dl versus 3.18 mg/dl) (p&lt;0.03). Serum magnesium levels did no differ significantly between men and women. Fractional phosphate excretion rates in patients with metabolic syndrome were similar with controls (10.1±10.2% vs 13.1±9.9%), as well as fractional magnesium excretion (3.1±1.6% vs 2.8±1.3%). Conclusions: Patients with metabolic syndrome show significantly lower phosphate and magnesium concentrations compared to controls. This reduction is likely to be attributed to internal redistribution of phosphate and is more pronounced as the number of components of metabolic syndrome increases

Nutrient recycling by coastal macrofauna: intra- versus interspecific differences

In the context of global change, improving our understanding of how species communities shape ecosystem functioning and stability is a key issue. Therefore, we have to adopt a functional approach by considering the role of organisms in ecosystem processes. Nutrient recycling is important for sustaining primary productivity in aquatic systems but has been largely overlooked for macro-organisms. In a Mediterranean coastal ecosystem we found that per capita ammonium and phosphate excretion rates for the 9 dominant nektonic macrofauna species exceeded those of 3 benthic bivalves by factor 100. Body mass and species identity together significantly explained these interspecific differences in excretion rates. Significant differences in the effect of body mass on nutrient excretion rates were also found among the 7 fish species. More studies are needed to further explore the biological determinants of the intra-and interspecific variability of excretion rates as well as their consequences on marine ecosystem functioning.

Increased renal dopamine and acute renal adaptation to a high-phosphate diet

The current experiments explore the role of dopamine in facilitating the acute increase in renal phosphate excretion in response to a high-phosphate diet. Compared with a low-phosphate (0.1%) diet for 24 h, mice fed a high-phosphate (1.2%) diet had significantly higher rates of phosphate excretion in the urine associated with a two- to threefold increase in the dopamine content of the kidney and in the urinary excretion of dopamine. Animals fed a high-phosphate diet had a significant increase in the abundance and activity of renal DOPA (l-dihydroxyphenylalanine) decarboxylase and significant reductions in renalase, monoamine oxidase A, and monoamine oxidase B. The activity of protein kinase A and protein kinase C, markers of activation of renal dopamine receptors, were significantly higher in animals fed a high-phosphate vs. a low-phosphate diet. Treatment of rats with carbidopa, an inhibitor of DOPA decarboxylase, impaired adaptation to a high-phosphate diet. These experiments indicate that the rapid adaptation to a high-phosphate diet involves alterations in key enzymes involved in dopamine synthesis and degradation, resulting in increased renal dopamine content and activation of the signaling cascade used by dopamine to inhibit the renal tubular reabsorption of phosphate.

Metabolic rates and carbon budget of early developmental stages of the marine cyclopoid copepod Oithona davisae

The genus Oithona has been considered the most abundant and ubiquitous copepod in the world's oceans. However, despite its importance, the metabolism of its developmental stages (nauplii and copepodites), crucial to explain their evolutionary success, is almost unknown. We determined respiration rates, ammonium and phosphate excretion rates, and the net growth efficiencies of early developmental stages of Oithona davisae as related to stage, body weight, temperature, and food availability. Respiration and excretion rates increased with increasing body weight and were positively related to temperature and food. Specific respiration rates of nauplii and copepodites varied from 0.11 to 0.55 d−1 depending on stage, body weight, temperature, and food availability. Metabolic C:N ratios were higher than 14, indicating lipid‐oriented metabolism. Assimilation efficiencies and net growth efficiencies ranged from 65% to 86% and from 23% to 32%, respectively, depending on body weight, stage, and temperature. Assimilation efficiencies and net growth efficiencies estimated using the respiration rates of nauplii with food were 1.7 times higher and 0.6 times lower, respectively, than those calculated using respiration rates of nauplii without food. Therefore, the use of respiration rates measured in filtered seawater led to substantial bias on the estimations of zooplankton carbon budget. O. davisae developmental stages exhibited similar assimilation and growth efficiencies but lower carbon‐specific respiratory losses than calanoid copepods. Hence, the low metabolic costs of Oithona compared with calanoids may be one reason for their success in marine ecosystems.

Self-pollutant loading from a suspension aquaculture system of Japanese scallop ( Patinopecten yessoensis) in the Changhai sea area, Northern Yellow Sea of China

Bivalve filter feeders that have been suspension-cultured intensively produce significant amounts of particulate biodeposits (feces and pseudofeces) and dissolved metabolic wastes (mainly ammonia and phosphate) that may negatively impact the aquaculture environment. In this study, monthly biodeposition rates, as well as ammonia and phosphate excretion rates, of three-age-cohort Japanese scallops ( Patinopecten yessoensis) cultured in the Changhai sea area, Northern Yellow Sea of China were investigated in situ using a sediment trap and a closed respirator, respectively, to evaluate self-pollutant loading in this system. Results showed an age effect and obvious seasonality in these rates for P. yessoensis. The biodeposition rates for 1, 2, and 3-yr-old P. yessoensis ranged from 0.01–0.66, 0.09–1.28, and 0.18–2.25 g dry material ind − 1 d − 1 , respectively. Manifested lower values in the biodeposition rates occurred in summer and winter, while higher values appeared in spring and autumn, which were mainly attributable to the effects of water temperature and seston concentration. The Japanese scallops released considerable amounts of ammonia, ranging from 0.02–0.86, 0.05–1.69, and 0.05–3.96 mg ind − 1 d − 1 for 1, 2, and 3-yr-old specimens, respectively. Excretion rates for PO 4–P ranged from 0.03–0.39, 0.09–1.18, and 0.18–2.65 mg ind − 1 d − 1 for 1, 2, and 3-yr-old scallops, respectively. An extrapolation of the results showed that annual biodeposit production could reach as high as 1.42 × 10 6 t dry matter, or 1.30 × 10 5 t POM, 3.48 × 10 4 t POC, and 4.83 × 10 3 t PON, with an annual NH 4 +–N production of 1.50 × 10 3 t and PO 4 3−–P production of 1.07 × 10 3 t by all current suspension-cultivated scallop populations in the Changhai sea area. Results of our study suggest that the potential impact of self-pollutants by filter-feeding bivalves on the environment should not be neglected given the large scale and high density of bivalve culture in the Changhai sea area and in the coasts of China. However, the type and extent of environmental impact generated by self-pollutant loading in this area remain unknown because of the lack of hydrographic conditions.