Renal response to saline infusion in chicks of Leach's storm petrel (Oceanodroma leucorhoa)

The renal response to infusion of three different saline solutions was studied in chicks of Leach's storm petrel (Oceanodroma leucorhoa). Each of the solutions (125 mmol·1^-1 NaCl at 5.3 ml·h^-1, 250 mmol·l^-1 NaCl at 2.6 ml·h^-1, and 550 mmol·l^-1 NaCl at 1.2 ml·h^-1) provided the same delivery of Nacl but in different volumes of water. Birds infused with 125 mmol·l^-1 NaCl had a glomerular filtration rate of 25.7 ml·h^-1, a urine flow rate of 4.4 ml·h^-1, and excreted 71% of the infused Na⁺ load in the urine. With infusion of 250 mmol·l^-1 NaCl, the glomerular filtration rate was unchanged (23.3 ml·h^-1), but urine flow rate was reduced to 0.93 ml·h^-1 and only 35% of the Na⁺ load was excreted in the urine. Infusion of 550 mmol·l^-1 NaCl induced a sharp decrease in glomerular filtration rate (to 3.8 ml·h^-1) and urine flow rate (to 0.08 ml·h^-1), and only 1.4% of the infused Na⁺ was excreted in the urine. The contribution of different nephron populations to filtration was assessed by the pattern of staining of glomeruli by alcian blue infused during the last 30 min of the saline infusion. The numbers of stained glomeruli did not differ between birds infused with 125 and 250 mmol·l^-1 NaCl (59000 and 55000 glomeruli per kidney, respectively), and the patterns of staining were similar for birds in these two groups. Birds infused with 550 mmol·l^-1 NaCl had lighter staining overall and fewer stained glomeruli (37000 per kidney). This absence of staining was predominant in the smaller size classes of glomeruli, suggesting a selective shutdown of smaller (reptilian-type) nephrons during times of osmotic challenge in these birds. This may be part of an overall suite of water-conserving strategies employed by these chicks during their long confinement with irregular feeding in the nesting burrow.Abbreviations ADH antidiuretic hormone - GFR glomerular filtration rate - MT mammalian-type - P plasma inulin concentration - RT reptilian-type - U urine inulin concentration - V urine flow rate     

Water conservation and protein metabolism in northern elephant seal pups during the postweaning fast

Urine production and N output were monitored in northern elephant seal (Mirounga angustirostris) pups progressing through 10 weeks of a natural postweaning fast. Urine output declind by 84% (to 69±12 ml·day^–1) at 10 weeks (P<0.05). Glomerular filtration rate at 10 weeks was 51% of the 67±3 ml serum·min^–1 observed during week 1 (P<0.05). Urine N excretion fell by 69% to 1.2±0.17 g·day^–1, while urinary concentration increased (P<0.05). Serum urea declined from an initial 11 mmol·1^–1 to 5–7 mmol·1^–1 by 5 weeks. The fall in urinary N loss (and thus amino acid oxidation) was concomitant with depressed metabolic rate. Therefore, protein contributed little toward meeting energy demands (i.e., <4% of average metabolic rate) throughout fasting. These data indicate that fasting pups improve water conservation and minimize protein catabolism during prolonged natural fasts without an exogenous source of water.Abbreviations AA amino acid(s) - AMR average metabolic rate - ANOVA one-way analysis of variance - BMR basal metabolic rate - BUN blood urea nitrogen - EP end product - EWL evaporative water loss - [Gr]_s serum creatinine concentration - GFR glomerular filtration rate - LBM lean body mass - LML Long Marine Laboratory - MR metabolic rate - NEFA non-esterified fatty acids - RMR resting metabolic rate - TCA tricarboxylic acid - U:C ulinary urea: creatinine concentration ratio     

Activities of benthic nitrifiers in streams and their role in oxygen consumption

The in situ rates of oxygen consumption by benthic nitrifiers were estimated at 11 study sites in 4 streams. Two methods were used: an in situ respiration chamber method and a method involving conversion of nitrifying potential measurements to in situ rates. Estimates of benthic nitrogenous oxygen consumption (BNOC) rate ranged from 0–380 mmol of O₂ m^–2·day^–1, and BNOC contributed between 0–85% of the total benthic oxygen consumption rate. The activity of nitrifiers residing in the sediments was influenced by O₂ availability, temperature, pH, and substrate. Depending upon site, nitrification could approximate either first-order or zero-order kinetics with respect to ammonium concentration. The source of ammonium for benthic nitrifiers could be either totally from within the sediment or totally from the overlying water. Nitrate produced in the sediments could flux to the water above or be lost within the sediment. The sediments could act as a source (positive flux) or sink (negative flux) for both ammonium (–185 mmol·m^–2·day^–1 to +195 mmol·m^–2·day^–1) and nitrate (–135 mmol·m^–2·day^–1 to +185 mmol·m^–2·day^–1).This study provides evidence to suggest that measurements of down-stream mass flow changes in inorganic nitrogen forms may give poor estimates of in situ rates of nitrification in flowing waters.     

Activity,milk intake and energy consumption in free-living ringed seal (Phoca hispida) pups

Measurements of growth, activity and energy consumption and estimates of milk intake were made in free-living, nursing ringed seal (Phoca hispida) pups. This was accomplished through the simultaneous use of time-depth recorders and the doubly labelled water technique. The pups spent an average of 52±7% of their time hauled out on the ice, 37±5% of the time in the water at the surface, and 11±5% of the time diving. Average daily mass gain of the pups (n=3) throughout the duration of the study period was 0.35±0.08 kg. The composition of the mass gain was 76% fat, 6% protein and 18% water. The total water flux was measured to be 52±10 ml·kg^-1·day^-1. Average CO₂ production was 0.85±0.16 ml·g^-1·h^-1, corresponding to a field metabolic rate of 0.55±0.10 MJ·kg^-1·day^-1, or 3.8±0.6 times the predicted basal metabolic rate based on body size (Kleiber 1975). Average daily milk intake was estimated to be 1379±390 ml. The field metabolic rate for the different components of seal pup activity budgets were calculated to be FMR_{haul out}=1.34 BMR, FMR_surface=6.44 BMR, and FMR_diving=5.88 BMR.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - HTO tritiated water - HT¹⁸O doubly labelled water - RQ respiration quotient - SDA specific dynamic action - TDR time-depth recorder     

Milk intake,growth and energy consumption in pups of ice-breeding grey seals (Halichoerus grypus) from the Gulf of St. Lawrence,Canada

In this study we document growth, milk intake and energy consumption in nursing pups of icebreeding grey seals (Halichoerus grypus). Change in body composition of the pups, change in milk composition as lactation progresses, and mass transfer efficiency between nursing mothers and pups are also measured. Mass transfer efficiency between mother-pup pairs (n=8) was 42.5±8.4%. Pups were gaining a daily average of 2.0±0.7 kg (n=12), of which 75% was fat, 3% protein and 22% water. The total water influx was measured to be 43.23±8.07 ml·kg^-1·day^-1. Average CO₂ production was 0.85±0.20 ml·g^-1·h^-1, which corresponds to a field metabolic rate of 0.55±0.13 MJ·kg^-1·day^-1, or 4.5±0.9 times the predicted basal metabolic rate based on body size (Kleiber 1975). Water and fat content in the milk changed dramatically as lacation progressed. At day 2 of nursing, fat and water content were 39.5±1.9% and 47.3±1.5%, respectively, while the corresponding figures for day 15 were 59.6±3.6% fat and 28.4±2.6% water. Protein content of the milk remained relatively stable during the lactation period with a value of 11.0±0.8% at day 2 and 10.4±0.3% at day 15. Pups drank an average of 3.5±0.9 kg of milk daily, corresponding to a milk intake of 1.75 kg per kg body mass gained. The average daily energy intake of pups was 82.58±19.80 MJ, while the energy built up daily in the tissue averaged 61.72±22.22 MJ. Thus, pups assimilated 74.7% of the energy they received via milk into body tissue. The lactation energetics of ice-breeding grey seals is very similar to that of their land-breeding counterparts.Abbreviations bm body mass - BMR basal metabolic rate - FMR field metabolic rate - IU international unit - RQ respiration quotient - HTO tritiated water - HT¹⁸O doubly labeled water - TBW total body water - VHF very high frequency     

Adaptation of renal function to hypotonic medium in the winter flounder (Pseudopleuronectes americanus)

Summary The kidneys of winter flounders transferred to hypotonic medium were investigated for glomerular and tubular handling of fluid and electrolytes and for the urinary excretion of proteins. Media were sea water (925 mosm·kg^–1) and brackish water (70 mosm·kg^–1).In sea water, the urine was hypertonic to the plasma in 7 fish of this study. Urine flow rate was correlated with the GFR. After adaptation to brackish water a delay of 1 to 3 days was observed until the kidneys switched from fluid retention to the excretion of large amounts of dilute urine. GFR and urine flow rate were increased from 0.61±0.08 to 1.58±0.29 ml·h^–1·kg^–1 and from 0.14±0.02 to 0.68±0.08 ml·h^–1·kg^–1, respectively . With increased filtered load the tubular reabsorption of fluid decreased from 74±2.4% to 45±11.2%. The excretion rates of sodium and potassium were increased due to decreased fractional sodium and potassium reabsorption. The urinary excretion of divalent cations, however, was reduced because the net tubular reabsorption of calcium was increased and the net secretion of magnesium was diminished.Both the urinary total protein concentration and the protein pattern showed no significant change, but the rate of protein excretion was increased from 0.21±0.04 to 0.60±0.05 mg·h^–1·kg^–1. The comparison of protein patterns obtained from urine and serum samples revealed that high molecular weight (HMW) proteins prevail in the serum whereas low molecular weight (LMW) proteins dominate in the urine. The diminished quantity of the HMW-protein fraction in the urine thus may reflect size selectivity of the glomerular filtration barrier for serum proteins also in the winter flounder.Abbreviations BW brackish water - SW sea water - GFR glomerular filtration rate - HMW heigh molecular weight - LMW low molecular weight     

Water and sodium requirements of field populations of house mice (Mus domesticus) and short-tailed mice (Leggadina lakedownensis) on Thevenard Island, in the arid Pilbara region of Western Australia

The coexistence of the Lakeland Downs short-tailed mouse Leggadina lakedownensis and house mouse Mus domesticus on Thevenard Island, in the arid north of Western Australia, prompted a study to compare their seasonal water and sodium metabolism using tritiated water and sodium-22 as tracers. Fractional water influx rates for M. domesticus (40.3 ± 1.6% total body-water day⁻¹) were significantly higher than those for L. lakedownensis (25.3 ± 1.2% total body-water day⁻¹). Water effluxes were higher in both species of mouse after the passage of a cyclonic storm near the study site. Water flux differences remained significant between species when turnover rates were scaled with body mass. A comparison of water influx rates of M. domesticus with those predicted for field populations of other eutherian rodents showed that rates for M. domesticus on Thevenard Island were higher than expected. In contrast, water influx rates for L. lakedownensis did not differ significantly from expected values for a desert rodent. Rates of sodium influx for M. domesticus (41.7 ± 3.6 mmol kg⁻¹ day⁻¹) were over twice those of L. lakedownensis (19.7 ± 4.8 mmol kg⁻¹ day⁻¹), and were reflected in the significantly higher concentrations of sodium ingested in the diet, and excreted in the urine, of M. domesticus. Furthermore, the rate of water influx was positively correlated with the rate of sodium influx in M. domesticus, suggesting that they were obtaining both water and sodium from the one dietary source. There was no evidence to suggest that mice of either species were experiencing water or sodium stress, because water and sodium influxes and effluxes remained in balance. These results suggest that M. domesticus on Thevenard Island had a higher-than-expected daily water requirement, and may represent a mesic deme of house mice that have yet to adapt to the island environment. Accepted: 9 May 1999     

Water and energy metabolism in the rock hyrax (Procavia habessinica)

Summary The influence of ambient temperature and water supply on water metabolism and O₂-consumption was measured in rock hyraxes (Procavia habessinica).With ad libitum food and water (control), water turnover rates of hyraxes were significantly lower than the general eutherian mean; water turnover rates were 61.4, 44.1 and 55.1 ml·kg^–0.82·24 h^–1 at 20, 27 and 35°C respectively. When greens were fed ad libitum but no drinking water was given, water turnover rate at 20°C was twofold higher, but at 27 and 35°C it was similar to that in control experiments.Water turnover rates were significantly reduced when no drinking water and only 25 g greens per day were offered (25.8, 22.0 and 29.3 ml·kg^–0.82·24 h^–1 at 20, 27 and 35°C respectively). Highest urine osmolality (3,200 mosm·kg^–1) was recorded at 20°C.Oxygen consumption under control conditions was 43% below that predicted on the basis of body weight for most eutherian mammals. The thermoneutral zone ranged from 27 to 35°C, and the basal metabolic rate was 165 kJ·kg^–0.75·h^–1.     

Secretion of electrolytes,protein and urea by the mandibular gland of the common wombat (Vombatus ursinus)

Saliva was collected from the mandibular glands of anaesthetized common wombats (Vombatus ursinus) to ascertain maximal flow rates, salivary compostion and possible adaptations, particularly PO₄ ^3- secretion, to assist digestion. After temporary catheterization of the main duct through its oral opening, salivary secretion was evoked at flow rates ranging from 0.02±0.002 (±SEM) ml·min^-1 (0.7±0.07 l·min^-1·kg body weight^-1) to 0.4±0.05 ml·min^-1(14±1.9 l·min^-1·kg body weight^-1) by ipsilateral intracarotid infusion of acetylcholine. The [Na⁺] (15±5.1 to 58±8.6 mmol·l^-1) and [HCO₃ ^-] (35±1.9 to 60±1.9 mmol·l^-1) were positively correlated with salivary flow rate. The [K⁺] (58±5.2 to 30±2.4 mmol·l^-1), [Ca²⁺] (10.4±1.67 to 4.1±0.44 mmol·l^-1), [Mg²⁺] (0.94±0.137 to 0.17±0.032 mmol·l^-1), [Cl^-] (71±9.2 to 45±6.0 mmol·l^-1), [urea] (9.3±0.79 to 5.1±0.54 mmol·l^-1), H⁺ activity (29±1.6 to 17±1.6 nEq·l^-1) and amylase activity (251±57.4 to 92±23.3 kat·l^-1) were negatively correlated with flow. Both concentration and osmolality fell with increasing flow at the lower end of the flow range but osmolality always increased again by maximal flow whereas the relation between protein and flow was not consistent at the higher levels of flow and stimulation. Salivary [PO₄ ³⁺] was not correlated with flow and at 3–14% of the plasma concentration was extremely low. Thus, in contrast to its nearest relative, the koala (Phascolarctos cinereus), the wombat secretes little PO₄ ³⁺ presumably because it does not need high levels of PO₄ ³⁺ in its saliva to facilitate microbial digestion of plant fibre.Abbreviations bw body weight - ww wet weight     

Renal,respiratory and ionic regulation in Atlantic salmon (Salmo salar L.) kelts following transfer from fresh water to seawater

Summary Atlantic salmon may return to the sea after spawning in fresh water. These fish, known as kelts, reportedly show a limited ability to hypoosmoregulate. However, this study shows that fresh-water-adapted kelts exposed to seawater demonstrate rapid adaptation (within 48 h) in osmoregulatory parameters to values characteristic of seawater-adapted salmonids. The urine flow rate falls from 1.2 to 0.2 ml·kg^-1·h^-1 within 24 h. Over the same period, urine osmolality increases from 48 mosmol·kg^-1 to become isosmotic with the plasma, and Mg²⁺ secretion by the kidney tubules elevates the urine concentration from 0.5 to 100 mmol·l^-1. As is characteristic for marine teleosts, kelts drink seawater and process the ingested water in the gut to replace body water lost by osmosis to the hyperosmotic medium. Seawater exposure causes a marked hypoxia, arterial oxygen tension falling by 43% within minutes and persisting for at least 4 days at this low level. This is associated with large changes in blood pH and acid-base balance. The physiological mechanisms involved in adaptation to a hyperosmotic external medium are discussed, and the osmoregulatory capacity of kelts is compared with that of salmon at other stages of the life cycle.Abbreviations FW fresh water - GFR glomerular filtration rate - Hb haemoglobin - Hct haematocrit - MCHC mean cell haemoglobin concentration - pH_a pH in arterial blood - P _aO₂ partial pressure of oxygen in arterial blood - SEM standard error of mean - SW seawater - UFR urine flow rate     

Mechanisms of fluid and ion secretion by the parotid gland of the kangaroo,Macropus rufus,assessed by administration of transport-inhibiting drugs

Possible mechanisms of primary fluid formation by macropodine parotid glands were investigated in anaesthetized red kangaroos using ion transport inhibitors. Carotid plasma amiloride concentrations of 0.05–0.5 mmol·l^-1 progressively reduced a stable acetylcholine-evoked half-maximal flow rate of 2.0±0.04 to 0.22±0.024 ml·min^-1 (mean±SEM). Concurrently, saliva bicarbonate concentration and secretion fell (135±1.6 to 67±1.7 mmol·l^-1 and 272±7.6 to 15±2.6 mol·min^-1, respectively); [phosphate], [chloride] and [sodium] rose and [potassium] and osmolality were unaltered. High-rate cholinergic stimulation did not increase saliva flow beyond 11±1.0% of that for equivalent pre-amiloride stimulation. Equipotent levels of amiloride and methazolamide given concurrently were no more effective at blocking flow and bicarbonate secretion than when given separately. Furosemide (up to 2 mmol·l^-1), bumetanide (up to 0.2 mmol·l^-1) and ethacrynate (1 mmol·l^-1) in carotid plasma had no effect on salivary flow or ion concentrations. During methazolamide blockade, furosemide did not curtail the concurrent increase in salivary [chloride]. Chlorothiazide at 0.25–1.0 mmol·l^-1 caused progressive depression of saliva flow and [bicarbonate], and elevation of [chloride]. 4-acetamido-4-isothiocyanatostilbene-2,2 disulphonic acid at 0.1 mmol·l^-1 was without effect, whereas at 0.5 mmol·l^-1 it stimulated fluid secretion and increased saliva [protein], [sodium], [potassium], [bicarbonate] and osmolality. Concurrently, mean arterial blood pressure and pulse pressure fell and heart rate, haematocrit and carotid artery plasma flow rose. These responses were absent if saliva flow was kept constant by reduction in cholinergic stimulation during 4-acetamido-4-isothiocyanatostilbene-2,2 disulphonic acid administration. It is concluded that secretion of primary fluid by the kangaroo parotid is initiated mainly (>90%) by secretion of bicarbonate which is formed in the endpiece cells from CO₂ delivered by the circulation. No evidence was found for initiation of fluid secretion by chloride transport involving basolateral Na⁺-K⁺-2Cl^- symports, Na⁺-Cl^- symports or Cl^-/HCO ₃ ^- antiports.Abbreviations CA carbonic anhydrase - CAI carbonic anhydrase inhibitors - MAP mean arterial blood pressure - PAH p-aminohippurate - SITS 4-acetamido-4-isothiocyanatostilbene-2,2 disulphonic acid     

Field metabolic rates of instrumented Adélie penguins using double-labelled water

Summary Adélie penguins (Pygoscelis adeliae) carrying dummy instruments were used to determine field metabolic rates using double-labelled water. All penguins injected with double-labelled water showed a marked loss of body mass (-4.5%) during the period of the experiments (20–131 h), irrespective of the time of the breeding season. Total body water averaged 57.3% and water flux estimates of field metabolic rates correlated with double-labelled water estimates of field metabolic rate (r ²=0.68), indicating that Adélie penguins do not ingest significant amounts of sea water. Brooding Adélie penguins had a mean field metabolic rate of 10.1 W·kg^-1 and at sea a field metabolic rate of 13.3 W·kg^-1, both of which compare well with previously published estimates based on time/activity budgets and respirometry. Mean field metabolic rate in penguins with crèching chicks was 14.1 W·kg^-1, and the birds spent 65 h absent from the nest as opposed to previous estimates of 7.1 W·kg^-1 and 21 h. The effects of weather, disturbance and manipulation on the behaviour and field metabolic rate of penguins late in the breeding season are discussed. Adélie penguins (crèching chicks) equipped with externally attached instruments spent more time absent from the nest than noninstrumented controls (76 vs 54 h), but had a lower field metabolic rate.Abbreviations ANOVA analysis of variance - DLW double-labelled water - FMR field metabolic rate - MR metabolic rate - RMR resting metabolic rate - TBW total body water - VSMOW Vienna standard mean ocean water - WF water flux     

Effect of Cooking on Speciation and In Vitro Bioaccessibility of Hg and As from Rice,Using Ordinary and Pressure Cookers

Rice is the most widely consumed staple food for a large part of the world’s human population, and owing to environmental pollution, it is a major source of human exposure to mercury (Hg) and arsenic (As). We evaluated the impact of cooking on the speciation and bioaccessibility of Hg and As from rice in this study. Results show that the dominant Hg and As species in rice from Guangzhou market in China were their inorganic forms (iHg and iAs), respectively. The cooking process modified the levels of Hg and As. Average Hg and As bioaccessibility in raw rice was 69.74 and 80.32%, respectively. Hg bioaccessibility decreased to 46.22 and 42.37% for pressure- and ordinary-cooked rice, respectively. In contrast, As bioaccessibility remained unchanged except after cooking with a large amount of water. Protein denaturation and the amount of soluble and volatile forms determine the bioaccessibility of Hg and As in cooked rice by being released into the cooking water or into the air. From the bioaccessibility data, the average established daily intake (EDI) values of Hg and As from pressure-cooked rice for children and adults were 0.034 and 0.025 μg kg⁻¹ day⁻¹ (Hg), and 0.735 and 0.559 μg kg⁻¹ day⁻¹ (As), respectively. This study provides novel insights into Hg and As exposure due to rice cooking.

     

Pulmonary diffusing capacity in reptiles (Relations to temperature and O2-uptake)

Summary Pulmonary CO-diffusing capacity (D l _CO), lung volume, pulmonary perfusion and O₂-uptake were measured by non-invasive techniques in the lizardsVaranus exanthematicus andTupinambis teguixin (mean body weight 2.2 kg for both species).The CO-diffusing capacity was at 25–27°C 0.059 mlstpd·kg^–1·min^–1·Torr^–1 inVaranus, which is 47% greater than the value of 0.040 mlstpd·kg^–1·min^–1·Torr^–1 inTupinambis. The lung volume ofVaranus was 36 ml·kg^–1 and that ofTupinambis 20 ml·kg^–1. At 35–37°C the diffusing capacity of lizard lungs are about 25% of those for mammals of comparable size.InVaranus pulmonary CO-diffusing capacity increased with temperature from 0.027 mlstpd·kg^–1·min^–1·Torr^–1 at 17–19 °C to 0.075 mlstpd·kg^–1·min^–1·Torr^–1 at 35–37 °C. This change closely matched a concomitant increase of O₂-uptake. Pulmonary perfusion increased from 27 ml·kg^–1·min^–1 to 55 ml·kg^–1·min^–1 within this temperature range.The study emphasizes that pulmonary diffusing capacity cannot be fully evaluated without information on pulmonary perfusion and O₂-uptake. In reptiles and other ectotherms diffusing capacity must be reported at specified body temperature.     

Alcoholic fermentation of glucose and xylose by Pichia stipitis,Candida shehatae,Saccharomyces cerevisiae and Zymomonas mobilis: oxygen requirement as a key factor

Summary To investigate simultaneous alcoholic fermentation of glucose and xylose derived from lignocellulosic material by separate or co-culture processes, the effect of oxygen transfer rate (OTR) on the fermentation of 50 g/l xylose by Pichia stipitis NRRL Y 7124 and Candida shehatae ATCC 22984, and the fermentation of 50 g/l glucose by Saccharomyces cerevisiae CBS 1200 and Zymomonas mobilis ATCC 10988 was carried out in batch cultures. The kinetic parameters of the xylose-fermenting yeasts were greatly dependent on the OTR. The optimum OTR values were found to be 3.9 and 1.75 mmol·1^–1·h^–1 for C. shehatae and P. stipitis, respectively. By contrast the fermentative parameters of S. cerevisiae were poorly affected by the OTR range tested (0.0–3.5 mmol·l^–1·h^–1) Under these conditions the ethanol yields ranged from 0.41 g·g^–1 to 0.45 g·g^–1 and the specific ethanol productivity was around 0.70 g·g^–1·h^–1. Z. mobilis gave the highest fermentative performance under strictly anaerobic conditions (medium continually flushed with nitrogen): under these conditions, the ethanol yield was 0.43 g·g^–1 and the average specific ethanol productivity was 2.3 g·g^–1·h^–1. Process considerations in relation to the effect of OTR on the fermentative performance of the tested strains are discussed. Offprint requests to: J. P. Delgenes     

Secretory capacity of the lachrymal salt gland of hatchling sea turtles,Chelonia mydas

Summary The lachrymal salt glands ofChelonia mydas were functional when hatchlings emerged from the nest. Osmotic concentrations up to 720 mosmol kg^–1 were recorded in spontaneously produced tears (salt gland secretions). When injected with a Na⁺ load (1500–2700 mol (100 g)^–1) newly emerged hatchlings produced tears ranging in osmotic concentration from 1000–1900 mosmol kg^–1 with Na⁺ secretion rates from single glands of 200–475 mol (100 g·h)^–1. In these circumstances the rate of sodium excretion, via the salt glands, was equivalent to the sodium content of 0.2 to 0.5 ml of sea water per hour. Since the apparent drinking rate of hatchlings within the first two days of entering sea water was approximately 0.5 to 1.7 ml per day, the excretion of Na⁺ imbibed by drinking is well within the secretory capacity of the lachrymal salt glands.In feeding hatchlings extraordinarily high Na⁺ secretion rates were induced by Na⁺ loading. Hatchlings which were loaded with Na⁺ by injection (1500–5400 mol (100 g)^–1) produced tears having osmotic concentrations between 1500 and >2000 mosmol kg^–1. The Na⁺ secretion rates from single glands were 750–4185 mol (100 g·h)^–1 with extremely high short term rates of 10700 mol (100 g·h)^–1 (50 mol min^–1 for 28 g hatchlings).In terms of gland mass the highest long term secretion rate translates into 21 mmol of Na⁺ per gram of salt gland per hour and is the highest secretion rate yet recorded for a reptilian salt gland. This rate is almost three times the highest rate recorded for sea snakes (8 mmol g·h^–1) and is similar to rates commonly observed in avian salt glands (25 mmol g·h^–1).Secretion by the lachrymal salt glands was initiated by increased blood concentrations of Na⁺ or K⁺, K⁺ being as effective as Na⁺ but with the composition of the teras being virtually unchanged compared to tears from Na⁺ stimulated hatchlings. Preliminary experiments indicated that secretion was not initiated by increased Cl^– concentration in the blood or by increased volume or osmotic concentration of the blood.Abbreviation O.P. osmotic pressure     

Secretion by the mandibular gland of the red kangaroo (Macropus rufus) during isoprenaline infusion

Summary Intracarotid infusion of isoprenaline, either alone or in combination with acetylcholine infusion was used to stimulate salivation by the mandibular glands of anaesthetized red kangaroos. Isoprenaline alone (0.20–1.25 mol·kg^–1·min^–1) elicited flow rates ranging from 0.014 to 0.239 ml·min^–1 (1.21–28.1 l·g gland^–1·min^–1). Salivary concentrations of sodium, chloride, phosphate and urea were negatively correlated with flow, whereas potassium, calcium, magnesium, hydrogen ion, bicarbonate, protein, and osmolality were poorly correlated with flow. Relative to cholinergic saliva produced at equivalent flow rates, isoprenaline-evoked saliva had higher osmolality, saliva/plasma urea ratios and concentrations of protein, potassium, magnesium, bicarbonate, and phosphate, but lower sodium, chloride and hydrogen ion levels. At a steady salivary flow (0.5 ml·min^–1), superimposition of isoprenaline infusion (0.15 mol·kg^–1·min^–1) on a pre-existing acetylcholine infusion reduced the rate of acetylcholine administration necessary to maintain flow, increased osmolality and the concentrations of protein, urea, potassium, calcium, magnesium, bicarbonate and phosphate and decreased sodium, chloride and hydrogen ion in the saliva. Salivary amylase activity was low and highly variable and the amylase activity/protein ratio fell substantially during isoprenaline stimulation. These results support the conclusion that the enzyme is of extrinsic origin. The response of the kangaroo mandibular gland to isoprenaline stimulation was very similar to that reported for rat mandibular gland, suggesting that the same ion transport phenomena underlie mandibular secretion in both species and probably in therian mammals generally.     

Effects of 3 days of carbohydrate supplementation on muscle glycogen content and utilisation during a 1-h cycling performance

This study compared the effects of supplementing the normal diets of six trained cyclists [maximal oxygen uptake O_2max) 4.5 (0.36)l · min⁻¹; values are mean (SD)] with additional carbohydrate (CHO) on muscle glycogen utilisation during a 1-h cycle time-trial (TT). Using a randomised crossover design, subjects consumed either their normal diet (NORM) for 3 days, which consisted of 426 (137) g · day⁻¹ CHO [5.9 (1.4) g · kg⁻¹ body mass (BM)], or additional CHO (SUPP) to increase their intake to 661 (76) g · day⁻¹ [9.3 (0.7) g · kg⁻¹ BM]. The SUPP diet elevated muscle glycogen content from 459 (83) to 565 (62) mmol · kg⁻¹ dry weight (d.w.) (P < 0.05). However, despite the increased pre-exercise muscle glycogen stores, there was no difference in the distance cycled during the TT [40.41 (1.44) vs 40.18 (1.76) km for NORM and SUPP, respectively]. With NORM, muscle glycogen declined from 459 (83) to 175 (64) mmol · kg⁻¹ d.w., whereas with SUPP the corresponding values were 565 (62) and 292 (113) mmol · kg⁻¹ d.w. Accordingly, both muscle glycogen utilisation [277 (64) vs 273 (114) mmol · kg⁻¹ d.w.] and total CHO oxidation [169 (20) vs 165 (30) g · h⁻¹ for NORM and SUPP, respectively] were similar. Neither were there any differences in plasma glucose or lactate concentrations during the two experimental trials. Plasma glucose concentration averaged 5.5 (0.5) and 5.6 (0.6) mmol · l⁻¹, while plasma lactate concentration averaged 4.4 (1.9) and 4.4 (2.3) mmol · l⁻¹ for NORM and SUPP, respectively. The results of this study show that when well-trained subjects increase the CHO content of their diet for 3 days from 6 to 9 g · kg⁻¹ BM there is only a modest increase in muscle glycogen content. Since supplementary CHO did not improve TT performance, we conclude that additional CHO provides no benefit to performance for athletes who compete in intense, continuous events lasting 1 h. Furthermore, the substantial muscle CHO reserves observed at the termination of exercise indicate that whole-muscle glycogen depletion does not determine fatigue at this exercise intensity and duration. Accepted: 25 November 1996     

The effect of carbonic anhydrase inhibitors on secretion by the parotid and mandibular glands of red kangaroos Macropus rufus

Summary The effects of carbonic anhydrase inhibitors on secretion by macropodine parotid and mandibular glands were investigated using anaesthetized red kangaroos. In the parotid gland, acetazolamide (500 mol·l^-1) reduced a stable acetylcholine-evoked, half-maximal flow rate of 2.02±0.034 to 0.27±0.023 ml·min^-1 (87% reduction). Concurrently, salivary bicarbonate concentration and secretion fell (129.4±1.46 to 80.9±1.63 mmol·l^-1 and 264.8±7.96 to 22.3±2.30 mol·min^-1, respectively), phosphate and chloride concentrations rose (14.0±0.79 to 27.6±0.85 mmol·l^-1 and 5.6±0.25 to 27.5±1.32 mmol·l^-1, respectively), sodium concentration and osmolality were unaltered, and potassium concentration fell (8.8±0.33 to 6.4±0.29 mmol·l^-1). High-rate cholinergic stimulation during acetazolamide blockade was unable to increase salivary flow beyond 11±0.9% of that for equivalent unblocked control stimulation. However, superimposition of isoprenaline infusion on the acetylcholine stimulation caused a three-fold increase in the blocked flow rate. These treatments were accompanied by small increases in salivary phosphate and chloride concentrations but not bicarbonate concentration. Methazolamide infusion caused similar changes in parotid secretion. In the mandibular gland, acetazolamide infusion had no effect on salivary flow rate during either low- or high-level acetylcholine stimulation. Acetazolamide caused no alterrations in salivary electrolyte secretion at low flow rates, but curtailed the rise in bicarbonate concentration associated with high-level acetylcholine stimulation. Acetazolamide administration did not affect the increase in salivary flow rate associated with isoprenaline infusion, but did block the concomitant increase in bicarbonate concentration and secretion substantially. It was concluded that neither cholinergic nor adrenergic stimulation of mandibular fluid secretion depends on secretion of bicarbonate derived from catalysed hydration of CO₂, but a substantial proportion of the increase in bicarbonate secretion during isoprenaline administration, which is probably ductal in origin, is so dependent. In contrast to other salivary glands, including the ovine parotid, fluid secretion by the kangaroo parotid gland during cholinergic stimulation is largely dependent (about 90%) on secretion of bicarbonate derived from hydration of CO₂ catalysed by glandular carbonic anhydrase. Fluid secretion during adrenergic stimulation is not bicarbonate dependent.Abbreviations b.w. body weight - PAH p-aminohippurate - PCO₂ partial pressure carbon dioxide - PCO₂ partial pressure of oxygen     

Drinking rates and Na+ effluxes in response to temperature change in two species of marine flatfish: dab,Limanda limanda and plaice,Pleuronectes platessa

The relationship between fish mass and drinking rate in two species of flatfish, dab and plaice, weighing between 1 and 150 g was investigated. Both plaice and dab showed increased drinking rates with increasing fish mass, although — when calculated on a weight-specific basis — the increase was negligible. Fish were acclimated to winter and summer temperatures of 9 and 14°C, respectively. In winter both species were acutely transferred to 5, 14 and 21°C and in summer to 5, 9, 21 and 25°C. Drinking rates, Na⁺ efflux and body ion content were measured. Dab showed lower drinking rates than plaice (e.g. the weight-specific drinking rates of summer-and winter-acclimated dab were 0.12±0.01 and 0.06±0.006 ml·h^-1·100 g^-1, respectively, compared to that of plaice which were 0.25±0.02 ml·h^-1·100 g^-1 in summer and 0.17±0.02 ml·h^-1·100g^-1 in winter). Summer dab exhibited decreased weight-specific drinking rates at 5, 9 and 25°C, while winter dab increased drinking at 21°C. Winter plaice also showed increased drinking at 21°C and a decrease at 5°C, but in contrast summer plaice did not increase drinking at either 21 or 25°C but showed a decrease at 5 and 9°C. Winter dab and plaice showed similar Na⁺ efflux rates but summer dab showed higher efflux at all temperatures except 5°C. The data indicates that (a) the osmoregulatory function of plaice is much weaker than that of dab at higher temperatures (>20°C) and (b) mass has a greater effect on drinking and Na⁺ efflux rates than temperature; although when calculated on a weight-specific basis neither drinking nor efflux showed any variation with fish mass suggesting that these functions occur at similar intensities across the entire weight range.Abbreviations ANOVA analysis of variance - ⁵¹Cr-EDTA ⁵¹chromium ethylenediaminetetra-acetic acid - SW sea water