Sodium Turnover Research Articles

Comparative Investigation of Copper Tolerance and Identification of Putative Tolerance Related Genes in Tardigrades.

Tardigrades are microscopic aquatic animals renowned for their tolerance toward extreme environmental conditions. The current study is the first to investigate their tolerance toward heavy metals and we present a novel tardigrade toxicant tolerance assay based on activity assessments as a measure of survival. Specifically, we compare tolerance toward copper in four species representing different evolutionary lineages, habitats and adaptation strategies, i.e., a marine heterotardigrade, Echiniscoides sigismundi, a limno-terrestrial heterotardigrade, Echiniscus testudo, a limno-terrestrial eutardigrade, Ramazzottius oberhaeuseri, and a marine eutardigrade, Halobiotus crispae. The latter was sampled at a time of year, when the population is predominantly represented by aberrant P1 cysts, while the other species were in normal active states prior to exposure. Based on volume measurements and a general relation between body mass and copper tolerance, expected tardigrade EC50 values were estimated at 0.5–2 μg l−1. Following 24 h of exposure, tolerance was high with no apparent link to lineage or habitat. EC50s (95% CI), 24 h after exposure, were estimated at 178 (168–186) and 310 (295–328) μg l−1, respectively, for E. sigismundi and R. oberhaeuseri, whereas E. testudo and H. crispae were less affected. Highest tolerance was observed in H. crispae with a mean ± s.e.m. activity of 77 ± 2% (n = 3) 24 h after removal from ~3 mg l−1 copper, suggesting that tardigrade cysts have increased tolerance toward toxicants. In order to identify putative tolerance related genes, an E. sigismundi transcriptome was searched for key enzymes involved in osmoregulation, antioxidant defense and copper metabolism. We found high expression of Na/K ATPase and carbonic anhydrase, known targets for copper. Our transcriptome, furthermore, revealed high expression of antioxidant enzymes, copper transporters, ATOX1, and a Cu-ATPase. In summary, our results indicate that tardigrades express well-known key osmoregulatory enzymes, supporting the hypothesis that copper inhibits sodium turnover as demonstrated for other aquatic organisms. Tardigrades, nevertheless, have high tolerance toward the toxicant, which is likely linked to high expression of antioxidant enzymes and an ability to enter dormant states. Tardigrades, furthermore, seem to have a well-developed battery of cuproproteins involved in copper homeostasis, providing basis for active copper sequestering and excretion.

Effects of fludrocortisone on water and sodium intake of C57BL/6 mice

Little is known about steroidal control of thirst- and salt-appetite behaviors of mice. The current study investigates effects of fludrocortisone acetate (FCA), a steroid with potent glucocorticoid and mineralocorticoid effects, on thirst- and salt-appetite responses of C57BL/6 mice. Treatment with FCA produced dose-dependent (5, 10, and 25 mg/kg) increases in both magnitude and duration of water and sodium intake. Chronic elevation of water and saline intake was achieved with daily injections of FCA. Daily injection of FCA, when only 0.9% saline was available, produced a remarkably rapid increase in saline intake. A single injection of FCA stimulated brisk diuresis and natriuresis in fluid-restricted animals. This work is the first to demonstrate copious water drinking by mice in response to FCA. The results are discussed in terms of the possibility that the renal effects of FCA promote increases in water and sodium turnover and thereby, increases in water and sodium ingestion.

Toxicokinetic Toxicodynamic (TKTD) Modeling of Ag Toxicity in Freshwater Organisms: Whole-Body Sodium Loss Predicts Acute Mortality Across Aquatic Species

ToxicoKinetic ToxicoDynamic (TKTD) models are considered essential tools to further advance acute toxicity prediction of metals for a range of species and exposure conditions, but they are currently underutilized. We present a mechanistic TKTD model for acute toxicity prediction of silver (Ag) in freshwater organisms. In this new approach, we explicitly link relevant TKTD processes to species (physiological) characteristics, which facilitates model application to other untested freshwater organisms. The model quantifies the reduction in whole-body sodium concentration over time as a function of the target site inhibition over time, the target site density and the species-specific sodium turnover rate. Freshwater species are assumed to die instantly when they have lost a critical amount of their initial whole-body sodium concentration. Results show that mortality is significantly related to sodium loss (r(2) = 0.86) for various aquatic organisms and exposure durations. The model accurately predicts lethal effect concentrations for different freshwater organisms, including Daphnia magna, rainbow trout and juvenile crayfish, and is able to capture the observed size-specific variation of nearly 2 orders of magnitude in empirical LC50s.

Evaluation of salt appetite in brain specific 11β hydroxysteroid dehydrogenase type 2 knockout (11βHSD2−/−) mice

Male brain specific 11βHSD2−/− mice and floxed controls were individually housed in metabolic cages and basal water turnover assessed over 4 days. In separate studies mice were given access to 2 bottles containing water and 1.5% NaCl and salt preference measured over 7 days. The role mineralocorticoid receptor (MR) in salt appetite was evaluated using spironolactone s.c.Basal water and sodium turnover and plasma sodium concentrations were not altered by the deletion of 11βHSD2 in the brain. When given access to NaCl brain specific 11βHSD2−/− mice displayed a significant salt preference, 70% of total fluid intake was accounted for by NaCl. Salt appetite was significantly reduced by MR blockade. Sodium was not retained in the null mice; increased salt intake resulted in significant natriuresis and polyuria.Deletion of 11βHSD2 in the brain, which is specifically expressed in the nucleus of the solitary tract (NTS) in mice, resulted in an increased salt appetite. Activation of MR is implicated since spironolactone significantly reduced NaCl intake. These data are the first demonstration of salt appetite occurring in the absence of sodium depletion and with normal renal function. They suggest that activation of MR on 11βHSD2 positive neurons in the NTS increases salt appetite. Funded by the British Heart Foundation.

M1366 Surgical Exclusion of the Upper Gastrointestinal Tract in Man Increases Turnover of Body Sodium

M1366 Surgical Exclusion of the Upper Gastrointestinal Tract in Man Increases Turnover of Body Sodium

Sublethal copper exposure induces respiratory stress in common and gibel carp but not in rainbow trout

Rainbow trout, common carp, and gibel carp were exposed to sublethal Cu levels (1.0 or 1.7 μM) for 1 week. In rainbow trout, arterial oxygen tension ( P aO 2 ) remained normal and there was no indication of anaerobic metabolism. P aO 2 was considerably lower in common and gibel carp and Cu exposure decreased this further. The decrease was transient for common carp but persistent in gibel carp and coincided with an elevation in arterial carbon dioxide tension ( P aCO 2 ) indicating that all gas exchange was compromised in both cyprinid species. The disturbed gas exchange resulted in acidosis, which was respiratory and metabolic for common carp but mainly respiratory for gibel carp. Gibel carp produced ethanol as end product of their alternative anaerobic pathway. The hypothesis that hypertrophy and hyperplasia, resulting in increased diffusion distances, are reducing P aO 2 appeared invalid. Hypoventilation seems a more likely cause. Ionoregulatory parameters responded more uniform among species. Fast and pronounced decreases in plasma sodium and chloride developed for all three species, independent of the observed gill damage. Rainbow trout lost 20% of their plasma Na in the first 3 days, while common and gibel carp had only lost 13 and 16% respectively at that time. This difference might be crucial when challenged with Cu exposure and allow a fish to survive the first shock phase and supports it the hypothesis that sodium turnover is a key factor in predicting Cu toxicity.

Validation of 22 Sodium Turnover in Estimating Sodium and Food Intake in an Amphibian (Bufo marinus)

We measured the relationship between the amount of sodium ingested by 10 adult toads (Bufo marinus) and the turnover rate of tracer amounts of 22sodium injected into each animal. There was a good relationship (r2 = 0.76) with the isotope turnover technique overestimating measured sodium intake by approximately 9%. We suggest that reliable estimates of food consumption can be obtained in free-living amphibians using this technique, provided the sodium content of the diet and the extent of transdermal sodium influx are known.

Sodium and Calcium Balance in Mozambique Tilapia, Oreochromis mossambicus, Raised at Different Salinities

Mozambique tilapia, Oreochromis mossambicus, born and raised in five salinities, viz. (relatively soft) fresh water, 25, 50, 75% and full-strength sea-water, were analyzed for ionoregulatory performance (in particular sodium and calcium handling) and growth. This tilapia regulates its blood serum mineral composition rather effectively; however, in sea-water serum concentrations of sodium, chloride and calcium (in males only) were increased, as was the serum osmolarity. In sea-water, the total body sodium pool was significantly enlarged. With increasing salinity, sodium turnover increased. Serum calcium levels and the total body calcium pool were more strictly controlled than those of sodium. The lowest density of chloride cells in opercular epithelium and the lowest branchial Na +-K +-ATPase activity were observed in 50% sea-water; these values were higher in fish kept in waters of lower or higher salinities. Fish grew more rapidly in brackish water. Fish kept in brackish water appeared to depend on food-related calcium for growth as branchial calcium uptake provides no more than 20% of growth related Ca-accumulation.

Validation of 22 Sodium to Estimate Food Intake of Bears

We measured the turnover of exchangeable sodium in black bears (Ursus americanus) and grizzly bears (U. arctos horribilis) with 22 sodium ( 22 Na) and tested the procedure for its usefulness as a predictor of food intake. Sodium excretion had a strong, positive correlation with sodium intake (r 2 = 0.97; SEE = 3.8). 22 Na equilibrated with the exchangeable Na pool within 105 minutes (t = 1.844, P < 0.05), and sodium flux was linearly related to sodium intake (r 2 = 0.87; SEE = 10.5). Diets with sodium contents greater than 5 mg Na/g dry matter (DM), between 2 and 5 mg Na/g DM, and less than 2 mg Na/g DM induced biological half-lives of sodium of 8.8 ± 2.5, 19.3 ± 3.5, and 70.5 ± 25.0 days, respectively. Sodium flux rates greater than 75 mg/kg-day and sample sizes of 5-10 animals are required to reduce the error of predicting food intake to less than 10%. This technique is suited for bears consuming primarily meat diets (i.e., winter kill carrion, neonatal ungulates, or spawning salmonids).

Water and energy balance of the thorny devil Moloch horridus: is the devil a sloth?

Abstract Rates of turnover of water, energy and sodium were measured for free-ranging thorny devils (Moloch horridus), which are myrmecophagous agamid lizards, in a semi-arid Western Australian habitat. There were significant differences in body water content and water turnover rate (WTR) measurements for cool, wet, average and hot periods, although the field metabolic rate (FMR) and sodium turnover (NaTR) rate did not differ significantly between weather conditions. The thorny devil had a substantially lower field WTR during dry periods (10-15 ml kg-1 d-1) than expected for semi-arid and arid lizards, although the WTR was higher in wet conditions (30-35 ml kg-1 d-1). The field metabolic rate of thorny devils (0.134 ml CO2 g-1 h-1) was only slightly less than that expected for a semi-arid/lizard (0.178 ml CO2 g-1 h-1), despite the apparently slothful nature of the thorny devil. The sodium turnover rate of the thorny devil (1.5-2.5 mmol kg-1 d-1) was within the range reported for other semi-arid/arid lizards. The field metabolic rate of the thorny devils suggests that they consume about 750 ants per day. The ratio of water to energy turnover measured for thorny devils in the field (0.11 ml H2O kj-1) was the same as that predicted from the composition of ants and their digestibility by thorny devils (0.11 ml H2O kj-1). However, the ratios of sodium-to-energy turnover (30 μmol Na+ kj-1) and sodium-to-water turnover (277 μmol ml H2O-1) were substantially higher than expected ratios (10 and 89 respectively).

Field Metabolism and Turnover in the Golden Bandicoot (Isoodon-Auratus) and Other Small Mammals From Barrow Island, Western-Australia

Barrow Island, which lies about 90 km north of Onslow off the arid Western Australian Pilbara coast, experienced its driest year on record in 1990 with a total of only 122.4 mm of rain. Golden bandicoots captured in November 1990 evidenced poor condition and mean body mass was a low 242.6 +/- 10.9 g with-a total body water content (TBW) of 76.3 +/- 1.4%. Despite this substantial loss of body water and solids, the animals maintained water and electrolyte balance during the period of turnover [water influx 79.5 +/- 6.9 v. efflux 83.3 +/- 5-7 mL (kg0.82 day)-1 and sodium influx 4.9 +/- 0.7 v. efflux 5.3 +/- 0.7 mmol (kg day)-1]. By April 1991, although only a further 37.4 mm of rain had been recorded on Barrow Island, the condition of the bandicoots had improved markedly, as a result of exploitation of insect resources, and their mean body mass had increased to 306.5 +/- 22.6 g and TBW decreased to 62.5 +/- 1.4% (both P &lt; 0.001), the latter reflecting enhanced fat stores. This general improvement in condition of the bandicoots was in marked contrast to that of other herbivorous marsupials on the island. Rates of water and sodium turnover of the golden bandicoots were, however, not significantly different from those measured in the previous November, Field Metabolic Rates (FMRs), measured with doubly labelled water ((HHO))-H-3-O-18, were extremely low, averaging only 0.45 +/- 0.26 mL CO2 (g h)-1, which is very close to laboratory estimates of 0.35 +/- 0.09 mL O2(g h)-1 for the basal metabolic rate of this species. A major cyclone struck Barrow Island on 3 March 1992, with 162 mm of rain falling in 24 h, and turnover measurements in May of that year revealed a substantial increase in rates of water flux. Mean body mass further increased to 332.6 +/- 8.5 g and TBW averaged 61.8 +/- 1.1%. Water turnover rates were significantly elevated when compared with April of the previous year with an influx of 112.5 +/- 7.3 and an efflux of 119.0 +/- 7.6 mL (kg0.82 day)-1 respectively (both P = 0.001). Rates of sodium turnover, however, were only slightly lower at 3.6 +/- 0.5 and 4.1 +/- 0.5 mmol (kg day)-1 for influx and efflux respectively (P = 0.056 for influx only), suggesting a slight decrease in the average sodium content of the diet. The volume of water required to maintain hygric balance was estimated by regression analysis at 26.7 mL day-1 [=88.3 mL (kg0.82 day)-1] in November 1990, and 33-9 mL day-1 [=85.2 mL (kg0.82 day)-1] in May 1992, following rain. The FMR of eight bandicoots was very significantly elevated to 1.39 +/- 0.23 mL CO2 (g h)-1 after rain, which is substantially higher than even the FMR of 0.91 +/- 0.07 mL CO2(g h)-1, or 644 kJ day-1, reported for the closely related southern brown bandicoot (Isoodon obesulus) studied in the region of Perth by Nagy et al. (1991). Turnover rates of water and sodium for two rodent species, the Barrow Island mouse (Pseudomys nanus) and the rock rat (Zyzomys argurus), were very similar to those recorded for golden bandicoots in the dry period, but FMRs were a little higher at 0.80 +/- 0.26 and 0.59 +/- 0-36 mL CO2(g h)-l respectively. The FMR of Barrow Island mice increased very significantly to a mean of 2.73 +/- 0.50 mL CO2(g h)-l after rain, but rock rats were not caught at this time. The data document the impressive ability of these mammals to avail themselves of extremely limited resources and maintain physiological homoiostasis under conditions of extreme aridity.

SALT AND WATER BALANCE IN FIELD POPULATIONS OF THE TERRESTRIAL CRAB GECARCOIDEA NATALIS

ABSTRACT Water and salt balance in the terrestrial crab Gecarcoidea natalis were examined in the laboratory and in free-ranging animals on Christmas Island, Indian Ocean. Under laboratory conditions the drinking rate was low (1.6 ± 1.0 ml · 100 g-1 · d-1) but filtration rate (which equaled urine flow) was much higher (10.5 ± 4.71 ml·100 g―1·d―1). The isosmotic urine was released to the branchial chambers and a small portion (0.54 ± 0.48 ml· 100 g-1 ·d-1) was eventually released as dilute excretory fluid ([Na] 3.85 ± 1.25 mmol·1―1) after reabsorption of ions by the gills. The remainder was ingested and reabsorbed. The system offers flexibility to cope with varying conditions, since the filtration rate is high and both volume and concentration of released fluid can be adjusted. Water efflux, estimated by tritium exchange in field animals, was high even in dry conditions (7.1 ± 1.45 ml·100 g-1·d-1, T½ = 5.25 ± 0.95 d-1) and doubled during wet weather (13.8 ± 2.93 ml·100 g-1 ·d-1, T½ = 2.7 ± 0.56 d '). The tritium method was considered to overestimate efflux of unlabeled water under the experimental conditions, but even so measured turnover was much greater than in laboratory conditions. Sodium turnover in the field was also high ranging from 231.3 ± 24.4 µmol· 100 g-1 ·d-1, T½ = 31.7 ± 4.69 d-1 in dry weather conditions to 439.3 ± 86.3 µmol· 100 g 1 ·d―1, T½ = 18.5 ± 4.89 d-1 in rainy weather. Sodium in the diet (predominantly fallen leaves) accounted for sodium intake, while output was partitioned between feces and excreted fluid. The discrepancy between tritiated water and sodium turnovers in laboratory and field data indicated that field animals had a considerable reserve of osmoregulatory capacity. Crabs participating in the annual breeding migration to the sea underwent a substantial fall in the osmolality of the hemolymph during their journey. On arrival at the coast the crabs remained in contact with sea water for several hours during which time the ion concentrations of their hemolymph returned to the normal range. It is suggested that this dipping behavior functions primarily in osmoregulation.

Corticotropin-releasing factor enhances sodium and water intake/excretion in rabbits

Sodium and water intake and excretion of wild rabbits was studied during intracerebroventricular (icv) infusion of corticotropin-releasing factor (CRF). Icv infusion of 200 and 600 pmol/h for 22 h induced changes in the ingestive and general behaviour animals. Increased consumption of 0.5 M NaCl solution was observed during the day of infusion, accompanied by increased sodium excretion, and food intake was decreased. The rabbits maintained the high sodium turnover, together with a high water turnover, for 2–3 days after the icv infusion stopped. Icv infusion of CRF induced strange behaviour in wild rabbits, they appeared to react with fright to normal daily events around them. The strange behaviour started about two hours after the beginning of icv infusion and disappeared immediately after the infusion stopped. On the basis of present and earlier observations, that systemic administration of adrenocorticotropin (ACTH) and adrenal steroid hormones induce increased sodium turnover, it is proposed that changes in the sodium and water metabolism might constitute part of the general stress reaction of the body.

Validation of Estimating Food Intake in Gray Wolves by 22 N Turnover

We studied 22 sodium ( 22 Na) turnover as a means of estimating food intake in 6 captive, adult gray wolves (Canis lupus) (2 F, 4 M) over a 31-day feeding period. Wolves were fed white-tailed deer (Odocoileus virginianus) meat only. Mean mass-specific exchangeabke Na pool was 44.8±0.7 mEq/kg; there was no difference between males and females. Total exchangeable Na was related (r 2 =0.85, P<0.009) to body mass. Overall, 22 Na turnover overestimated Na intake by 9.8±2.4% after 32 days. Actual Na intake was similar in males and females; however, Na turnover (P<0.05) and the discrepancy (P<0.01) between turnover and actual Na intake were greater in females than males. From Day 8 to the end of the study, the absolute difference (mEq) between Na intake and Na turnover remained stable. Sodium turnover (mEq/kg/day) was a reliable (r 2 =0.91), P<0.001) estimator of food consumption (g/kg/day) in wolves over a 32-day period. Sampling blood and weighing wolves every 1-4 days permitted identification of several potential source of error, including change in size of exchangeable Na pools, exchange of 22 Na with gastrointestinal and bone Na, and rapid loss of the isotope by urinary excretion

Seasonal changes in material and energy balance associated with reproduction in the green lizard, Lacerta viridis, in western France

Abstract Rates of turnover of oxygen, water and sodium were measured in free-ranging and captive Lacerta viridis in western France during their period of reproduction in May, and again in late autumn prior to their entering winter hibernation. Rates of C02 production and turnover of water and sodium in captive lizards showed little significant variation and these animals appeared to be buffered to a large extent from environmental changes, even though they were exposed to external climatic influences. Overall means for rates of CO2 production in free-ranging individuals did not vary statistically between seasons but considerable individual variation was observed during the breeding season in May. The animals could be divided into 'active' and 'inactive' groups on the basis of their rate of CO2 production and other significant differences were apparent between these two groups: 'active' individuals had increased rates of sodium turnover, lower body water contents and lost body mass during the period of observation whereas the 'inactive' individuals gained mass over the same period. These data suggest that not all individuals necessarily participate in the activity associated with breeding in spring in this species and further behavioural studies would seem appropriate in the light of these physiological data. Calculation of the 'Water Effectiveness Index' for this species from the ratio of water to energy turnover suggests that Lacerta viridis is a profligate utiliser of available resources when compared with similar-sized species of lizards inhabiting desert environments.

Evaluation of the accuracy of 22Na and tritiated water for the estimation of food consumption and fat reserves in passerine birds

We validated the use of 22Na and 3H for the measurement of food intake, total body water, and fat reserves in free-living passerines. The close correlation between sodium intake and blood sodium turnover (r2 = 0.98) and the narrow 95% confidence limits on the relationship (± 11% for Na consumption over 6.0 mmol) show that the 22Na technique may give precise estimates of food intake for individuals. The 3H technique does not provide precise measures of fat reserves in individuals because estimates of body fat have an error term ranging from 25 to 150%. However, it is sufficiently precise to allow the comparison of fat reserves between groups of birds. We provide a field test showing that adult Cliff Swallows have 60.3% lower fat reserves during a second breeding attempt compared with the first.

Effect of available surface water on levels of antidiuretic hormone (lysine vasopressin) and water and electrolyte metabolism of the Rottnest Island quokka ( Setonix brachyurus)

A sensitive radioimmunoassay was developed to measure circulating levels of the neuro-hypophysial peptide lysine vasopressin (LVP) in the marsupial quokka ( Setonix brachyurus), which is abundant on Rottnest Island off the coast of Western Australia. Animals from locations on the island where free water is completely absent were compared in midsummer with animals from sites where brackish water is available and utilized by the quokkas. In the animals from West End, where free water is absent, circulating levels of LVP averaged 89.2 ± 19.6 pg/ml, which was significantly higher than the mean level of 35.6 ± 15.8 pg/ml measured in individuals collected from the Lakes site with access to brackish drinking water. Rates of water and sodium turnover, measured with isotopes, were significantly greater in Lakes than West End animals, as were renal clearances of sodium, chloride, urea, and total osmolytes. Despite an obvious osmotic diuresis resulting from the ingestion of salty water, the Lakes animals were in better physical condition at the end of summer than the West End animals which lack free water, and these latter individuals showed signs of slight dehydration with elevated plasma and urinary electrolyte concentrations and osmolalities.

Osmoregulation in Crocodilians

Recent crocodilians live primarily in freshwater habitats. However two species ( Crocodylus acutus and C. porosus ) are estuarine specialists; two others ( C. niloticus and C. johnstoni ) that are primarily found in fresh water, have estuarine populations. Routes of uptake of water and sodium include drinking, feeding and associated incidental drinking, and integumental and buccal diffusion. Routes of loss include faeces-cloacal fluid, lingual salt glands, integumental and buccal diffusion, and respiratory loss. The least understood route of salt and water exchange is that of the oral and buccal epithelia, which are much more permeable to water and sodium than the general integument. The freshwater alligator ( Alligator mississippiensis ) osmoregulates in a manner typical for an amphibious reptile. Body sodium turnover is low and the general integument is quite low in permeability to sodium. Water turnover is more rapid (in terms of molar exchange) but still relatively low for an aquatic reptile. Most water exchange occurs across the integument and buccal epithelia. The presence of lingual salt glands in freshwater crocodilians remains enigmatic, as does the failure of these exocrine glands in estuarine species to respond to saline loading. Secretion does occur after injection of the parasympathetic stimulant methacholine chloride. The “salt water crocodile” ( C. porosus ) possesses a suite of osmoregulatory adaptations similar to those found in other estuarine reptiles. Water and sodium balance are maintained primarily by an extremely low general permeability to sodium, by economies in water loss, and by excretion of excess sodium by the lingual salt glands. Further work is needed to examine newly hatched C. porosus , and the possibility of ontogenetic change in lingual gland function in C. acutus. The importance of incidental drinking of sea water during feeding (recently discovered in turtles) needs to be evaluated in crocodilians. The use of osmoregulatory data in interpretation of the evolutionary history of the genus Crocodylus needs to be viewed with caution. The hypothesis that all species of Crocodylus originated from the transoceanic migration of a saline-tolerant form may not be the most parsimonious explanation.

Water and Sodium Turnover and Estimated Food Consumption Rates in Free-Living Fairy Prions (Pachyptila turtur) and Common Diving Petrels (Pelecanoides urinatrix)

Water and sodium influx rates of fairy prions (Pachyptila turtur) and common diving petrels (Pelecanoides urinatrix) were measured in the field by means of isotope turnover techniques. The influx rates were similar and high in both species: about 800 mL H₂O/kg · d and 170 mmol Na/kg · d Seawater ingestion represented 17% of water influx and 35% of sodium influx in P. turtur, and 9% and 21%, respectively, in P. urinatrix. It was estimated that P. turtur and P. urinatrix consumed krill at rates of 704 ± 157 and 854 ± 173 g/kg·d, respectively. The water and energy turnover rates of fairy prions and common diving petrels are compared with those of other foraging seabirds; allometric regressions with slopes of 0.64 and 0.61 were derived for water influxes and metabolic rates, respectively.

Different patterns of cellular sodium turnover in essential hypertension.

Erythrocyte sodium turnover was studied in 22 men aged 56 years who had been treated for hypertension for 7 years. Investigations were performed during treatment, and 1 and 4 weeks after withdrawal of therapy, and when hypertension had returned (blood pressure greater than or equal to 170/105 mmHg). Hypertension returned early in 11 patients (group A) and late in 11 patients (group B). There was no difference in blood pressure, therapy, body weight or peripheral resistance between the groups, but group A had a greater left ventricular mass. Intra-erythrocyte sodium was determined by flame photometry. Sodium influx and the rate constant of sodium efflux were calculated from uptake values of 22Na. In group B the return of hypertension was accompanied by a tendency for an increase in intra-erythrocyte sodium and a decrease in sodium efflux. In group A opposing changes were seen, so that significant differences occurred in sodium efflux and intra-erythrocyte sodium between the groups occurred at the reappearance of hypertension. The results are compatible with the appearance of a membrane abnormality in patients with a slow return of hypertension, whereas other mechanisms, e.g. increased sympathetic activity, may be associated with the more rapid rise in blood pressure in the other group.