Nitrogen Excretion Rates Research Articles

Glomerular structure in IDDM women with low glomerular filtration rate and normal urinary albumin excretion.

Eight women with insulin-dependent diabetes mellitus (IDDM) with low creatinine clearance rate (CCR) and normal urinary albumin excretion (UAE) were compared with three other groups of diabetic women: 19 with normal creatinine clearance rate (CCR) and UAE, 7 with normal CCR and microalbuminuria, and 7 with low CCR and microalbuminuria. The four groups were similar in age, duration of diabetes, HbA1, incidence of urinary tract infection, prevalence of bladder neuropathy, and urinary urea nitrogen excretion rate. The prevalence of hypertension was similar among the groups, although mean arterial pressure was higher in the low CCR and microalbuminuria group. Renal area index was lower in the low CCR and normal UAE groups than in the other groups of diabetic patients, but was not different from normal. Morphometric measures of mesangial expansion and estimates of arteriolar hyalinosis and global glomerulosclerosis were increased to a similar degree in the low CCR and normal UAE, normal CCR and microalbuminuria, and low CCR and microalbuminuria groups compared with the group without abnormalities of renal function. Therefore, it is likely that diabetic glomerulopathy is, at least in part, responsible for the loss of glomerular filtration rate seen in the low CCR and normal UAE patients. Thus, the definition of incipient nephropathy may have to be expanded beyond the concept of microalbuminuria if longitudinal study of such patients reveals an increased risk of the subsequent development of overt nephropathy. Finally, screening for diabetic kidney disease among IDDM patients should include determination of glomerular filtration rate and measurement of UAE and blood pressure, especially among women.

Protein Turnover Rates in Sick, Premature Neonates during the First Few Days of Life

Rates of protein turnover were measured in 19 infants during the first few days of life while they were receiving i.v. glucose. The technique consisted of a continuous i.v. infusion of L-[1-13C]leucine to measure whole body leucine flux and determination of total urinary nitrogen excretion to assess leucine oxidation rates. Subsequent to each of the studies, the decision to start total parenteral nutrition (TPN) was made by the clinician concerned, with the result that seven infants did not start TPN and 12 did. There were significantly greater urinary nitrogen excretion (p less than 0.001) and lower rates of whole body protein synthesis (p = 0.024) and breakdown (p = 0.015) in those who did start TPN compared with those who did not. The marked difference in nitrogen excretion between the two groups suggests that this could be a useful determinant for deciding which neonate should start TPN.

Refeeding after the late increase in nitrogen excretion during prolonged fasting in the rat

Recovery of body mass, food intake and body composition was studied in the laboratory rat after the late increase in nitrogen excretion that characterizes prolonged fasting in mammals and birds. The rats lost 43% of their body mass during 13 days of food deprivation. They all regained their prefasting body mass within a shorter period of 11 days of refeeding. These results confirm that the late increase in nitrogen excretion in rats, as in spontaneously fasting birds, is reversible and is a part of the physiological adaptations to long-term food deprivation. Water intake of the rats continuously decreased during fasting, and the animals virtually stopped drinking as protein utilization increased. On refeeding, changes in water intake paralleled those in food intake. The refed rats progressively increased their daily food intake, that was always higher than the prefasting value (8.0–10.4 vs. 6.7% of body mass). The comparison of organ weights between fed and ad lib refed rats of similar body weight indicates that muscle mass was regained earlier than body fat during refeeding. The laboratory rat therefore appears to be a good experimental model to investigate the metabolic and behavioural changes that occur during spontaneous anorexia and refeeding in wild animals.

Partition of energy metabolism in the surgical newborn

Variations in energy expenditure (EE) and substrate utilization were investigated in 12 surgical neonates (body weight, 2.81 ± 0.15 kg) receiving total parenteral nutrition (TPN) at an energy intake of 66.34 ± 2.16 kcal/kg/d in a thermoneutral environment of 32°C to 34°C. Respiratory gas exchange was continuously recorded for 12 hours by a computerized, open-circuit indirect calorimeter. Physical activity was monitored on a modified Freymond scale. Urine was collected over 3 days, including the time of the calorimetry study to determine the urinary nitrogen excretion rate. Oxygen consumption, carbon dioxide production, nonprotein respiratory quotient, and EE were calculated according to the principles of indirect calorimetry for each 30-minute period and for the entire 12 hours. During the indirect calorimetry study the patients were receiving a fat-free TPN mixture consisting of 10% glucose and 2% amino acids ( GL AA ) for 8 hours. The fat-free TPN was interupted by an isocaloric and isovolemic infusion of Intralipid 10% (IL) for 4 hours. The effect of physical activity on EE was evaluated separately according to the macronutrient intake ( GL AA for 8 hours v IL for 4 hours) and then combined throughout the 12 hours of intravenous alimentation. The neonates were resting during 80% of the 12-hour study time (range, 38% to 90%). The partition of EE expressed as mean ± SEM in kcal/kg/d was: total EE 48.5 ± 2.1; resting EE 43.9 ± 1.6; energy cost of activity 4.6 ± 1.3. Resting EE ranged from 33 to 51 kcal/kg/d and correlated positively with body weight ( r = .96; P = .0001), body length ( r = .79; P = .002), and body surface area ( r = .95; P = .0001). The coefficient of variation for resting EE was higher between subjects (12%) than between each 30-minute period (9%). No significant differences were found in daily resting EE between 30-minute and 12-hour measurements. Total EE correlated positively with the percentage of time spent for crying/total body movement ( r = .65; P = .012). EE variability among surgical neonates receiving TPN in a thermoneutral environment, depends on interindividual differences during rest and activity. Resting EE can be accurately estimated by indirect calorimetry from 30-minute measurements. Physical activity contributes up to 9% of the total EE. Substrate utilization in these patients was not effected by the vigorous muscular activity.

Effect of Feeding on Nitrogen Excretion of Japanese Flounder Paralichthys olivaceus.

Measurements of the rate of nitrogen excretion were carried out with fed and starved Japanese flounder of 163 to 575g in body weight at 20°C. Ammonia-N and urea-N excretion of the starved fish were 0.20±0.05mg-N/100g/h and 0.04±0.02mg-N/100g/h, respectively. Immediately after feeding, the rate of ammonia-N excretion per hour of the flounder became 3 to 4 times that of the starved fish. These elevated rates continued for 12, 30 and more than 36h, at 0.5, 1.0 and 1.5% rations, respectively. In contrast to ammonia-N excretion, the rate of urea-N excretion per hour of the fed fish showed a major peak during the period of 6-12 or 12-24h after feeding. In Japanese flounder fed on the pelleted diet containing 7.5% of nitrogen at average ration of 0.5%, it is estimated that 32% of the consumed nitrogen was excreted as ammonia-N, about 5% as urea-N and 8% as faeces-N within 24h after feeding.

Nitrogen Excretion by Artemia franciscana.

Dry weight and nitrogen content in the San Francisco Bay brine shrimp as well as their am-monia and Kjeldahl nitrogen excretion rates are presented as the log-log linear regressions with respect to the body length. The nitrogen content per dry weight was fairly constant in any size of shrimp (7.8%). However, the slopes of dry weight and nitrogen content changed greatly at the length of 0.8mm and slightly at about 6mm. In the smallest group, the slope was -0.2 ?? 0.2, but it was 2.1-2.2 and 2.7-2.9 in the middle and the largest groups, respectively. The mature male was heavier than the female of the same length. The ammonia nitrogen was about 68% in the total nitrogen excreted. The total nitrogen turnover rate at 28°C ranged 6-22% per day for the shrimp of 4-10mm in length and decreased as the shrimp grew.

Excretion of ureide and other nitrogenous compounds by the root system of soybean at different growth stages

Direct excretion of nitrogenous compounds into a N-free nutrient solution, which was allowed to drip onto the root system of soybean (Glycine max (L) Merr. cv. Kurosengoku) was examined at different growth stages; vegetative, flowering and pod-filling. Considerable amounts of nitrogenous compounds were excreted at all the growth stages, with the highest amount recorded at the pod-filling stage. The root was found to be the major site of N compound excretion and its dry weight was linearly correlated with N amount excreted. Maximum nitrogen excretion rate during vegetative and flowering stages was recorded during the ‘day’, however at the pod-filling stage, the highest was recorded during the ‘night’. Ureide was excreted at all growth stages, but the highest amount was recorded at the pod-filing stage. The root was found to be the active site of ureide excretion. Composition of the total nitrogen examined i. e. ureide, soluble proteins, ammonia and amino acids, was found to be changing during the growth stages, suggesting possible different major pathways of excretion at different plant age. Among the N compounds monitored, were soluble proteins, ammonia and amino acids. Only a few of the several amino acids found in the root tissues were observed in the ‘excreted solution’, notably phosphoserine and phosphoethanolamine, at all the growth stages, whilst γ-amino-butyric-acid and serine were observed in trace amounts during vegetative and flowering stages. Quantitatively the ammonia found in the ‘excreted solution’ was far greater than in the tissues.

Kemp's Ridley Sea Turtle Waste Characterization Study: Precursor to a Recirculating Holding System Design

AbstractThe decreasing population of the endangered Kemp's ridley sea turtle (Lepidochelys kempi) has necessitated research into more cost effective captive nurseries. Captive nurseries are an attempt to increase the survival of the Kemp's ridley past the first year of life. Presently, Kemp's ridleys are reared in captivity at the Headstart rearing facility in Galveston, Texas. This facility consists of a labor intensive, flow‐through system. Alternatively, recirculating systems permit development of inshore facilities with decreased labor and operating costs. This paper presents baseline excretion data necessary for designing filtration units required for water quality maintenance in recirculating holding systems. The total ammonia nitrogen excretion rate based on a 24 hour isolation period (fed) was fairly constant at 0.19 mg N/g‐turtle‐day, while the BOD5 loading rate was highly variable, averaging nearly 0.50 mg O2/g‐turt1e‐day. In addition, comparisons of filtered versus nonfiltered samples suggest that a suspended solids removal mechanism prior to the filtration unit would dramatically decrease BOD5 and, thus, improve filter efficiency and increase its capacity.

Effects of Foods Rich in Polyphenols on Nitrogen Excretion in Rats

The extent to which tea, cocoa and carob (foods rich in polyphenols) influence fecal nitrogen (N) excretion was investigated in rats. The studies took into account the methylxanthine contents of tea and cocoa as well as the poor digestibility of cocoa nitrogen. Balance measurements indicated that all three food sources significantly increased fecal nitrogen excretion relative to methylxanthine-matched control diets (p less than 0.01). In the case of cocoa, virtually all the increase could be attributed to the poor digestibility of cocoa protein itself (estimated to be only 28-30% of total N in cocoa powder). There appeared to be no other effects. With extracts of tea and carob, however, the increased excretion of N in feces resulted either from a decreased digestibility of other dietary protein, through interaction with their polyphenols, or from a stimulation of the excretion of endogenous (body) nitrogen. With respect to the latter possibility, a preliminary investigation with the stable isotope of nitrogen (15N) showed that tea produced a marked increase in the excretion of endogenous nitrogen. These studies, therefore, indicate that foods rich in polyphenols have varying effects on N excretion in feces and that, in the case of tea at least, the loss of endogenous nitrogen may be a major contributing factor.

Zooplankton of tikehau atoll (Tuamotu archipelago) and its relationship to particulate matter

The standing stock and taxonomic composition of zooplankton (>200 μm) were monitored in the lagoon of Tikehau atoll from April 1985 to April 1986. These data were supplemented by two 10 d studies on the variability, structure and functioning of the pelagic ecosystem. The biomass of animals >200 μm comprised 50% of the total biomass of all organisms from 35 to >2000 μm. The zooplankton populations were characterized by successive blooms of copepods, larvaceans, pteropods and salps, probably arising from the periodic input of detritus from the reef during windy periods. As a result, the ecosystem was not in a steady state and the data for the fluxes of organic matter are presented separately for April 1985 and April 1986. Using the C:N:P ratio method, net growth efficiencies, K2, were calculated for total mesozooplankton, mixed copepods, and two planktonic species, Undinula vulgaris and Thalia democratica. Combined with nitrogen and phosphorus excretion rates, these K2 values enabled the assessment of production rates. On a 24 h basis, P:B ratios (%) were close to 100 for the total zooplankton and 54, 34 and 800 for mixed copepods, U. vulgaris and T. democratica, respectively. These ratios are 5.7 times lower than that recorded for phytoplankton. High productivity may be ascribable to the high density of seston, the high temperature (29.5°C), and the kind of organisms present. Zooplankton production equalled 38 and 30% of 14C uptake during April 1985 and April 1986, respectively. Ingestion of animals >35μm was calculated by means of assimilation efficiencies and amounted to 17 and 7% of particulate organic carbon, 100 and 38% of living carbon, and 64 and 140% of primary production during the two periods, respectively. Finally, inorganic exduring was 32 and 18% of phytoplankton nitrogen and phosphorus requirements. A model based on the dimensional structure of the pelagic food-web, has been drawn to illustrate the biomass and carbon, nitrogen and phosphorus fluxes in the study area. The lagoon appears to export part of its planktonic biomass, which is 4.2 times lower one sea mile outside the main pass connecting the lagoon to the open ocean.

Respiration and nitrogen excretion by the squid Loligo forbesi

Respiration and nitrogen excretion rates of mature adult Loligo forbesi were investigated at the Roscoff Laboratory (North Brittany, France) during individual short-term incubation experiments in January 1986. The squids were in post-digestive condition and not actively swimming. Both oxygen uptake and nitrogen excretion are continuous processes. The metabolic rates of this active nektonic species (145 ml kg-1 h-1 oxygen uptake, 18.56 μg g-1 h-1 ammonia excretion) are distinctly higher than those of benthic cephalopods. Proteins constitute the main metabolic substrate for energetic needs. Besides ammonia, urea is also continuously released, in amounts ranging from 5 to 16% of ammonia-excretion values.

Phosphorus and nitrogen excretion rates of zooplankton from the eutrophic Loosdrecht lakes, with notes on other P sources for phytoplankton requirements

Phosphorus and nitrogen excretion rates by zooplankton communities from two eutrophic and shallow Dutch lakes were measured in laboratory. The variations in excretion rates in the lakes (May–October) were caused mainly by fluctuation in zooplankton biomass. Mean summer excretion rates (June–September) were 2.4 and 0.9 µg PO4ăP·1−1·d−1 in Lake Loosdercht and Lake Breukeleveen, respectively. This difference between the lakes was caused mainly by the lower zooplankton biomass in Lake Breukeleveen. The excretion of 2.4 µg PO4ăP·1−1·d− compared with the calculated P-demand of phytoplankton of 8.0 µg PO4ăP·1−1·d−1 is substantial in the summer (June–September) and far more important than the external P-supply of 0.4 µg P·1−1·d−1 and sediment release of 0.5 µg P·1−1·d−1. Both temperature and composition of zooplankton affected the weight specific excretion rates of the zooplankton community. The weight specific community excretion rates of P and N increased with temperature (exponential model); 1–8 μg PO4ăP·mg−1 zooplankton-C·d−1 and 5–42 µg NH3ăN·mg−1 zooplankton-C·d−1 (10°C–20°C).

Grazing, defecation and excretion rates of copepods from inter-island channels of the Canadian Arctic archipelago

Zooplankton (>800 μm) and water samples were collected at night at eleven stations in Parry Channel and adjacent waters, between 28 August and 14 September 1986. Chlorophyll concentrations varied between ≈17 μg l-1 at the surface at one station in Wellington Channel, Canada, and ≈1.5 μg l-1 throughout the top 30 m at one station in Byam Martin Channel, Canada. In tows from 0 to 50 m the zooplankton community at all stations was dominated by varying proportions of three species,Calanus hyperboreus, C. glacialis andMetridia longa. Levels of chlorophyllderived pigments inC. hyperboreus Stages V, IV and III were correlated with the concentration of chlorophyll at the chlorophyll maximum. Defecation rate constants, measured for the different stages where present, were variable but not correlated with ambient chlorophyll concentrations. Ammonia excretion was measured simultaneously for the communities in which defecation was being measured in the invividual species and stages. In these experiments the rate of ammonia accumulation decreased significantly over the period during which the copepods were actively defecating (usually the first 3 h) and then tended to a constant level (over the next 18 to 20 h). The time courses of ammonia accumulation could be described by a model comprised of the sum of a straight line and a saturating curve. For seven experiments the ammonia release given by the asymptote of the saturating component was correlated with the estimate of community defecation, obtained by summing the individual defecations, suggesting that the two processes were closely associated. Weight specific defecation and weight specific “defecation-associated” ammonia excretion were both correlated with ambient chlorophyll concentration. The ratio of initial to basal ammonia excretion rate varied between 2 and 20, so that “defecation-associated” ammonia release may be important in the estimation of in vivo nitrogen excretion or regeneration rates.

Bioenergetics of growth of a cyprinid, Phoxinus phoxinus: the effect of ration, temperature and body size on food consumption, faecal production and nitrogenous excretion

Food consumption, faecal production and nitrogen excretion by minnows, Phoxinus phoxinus, weighing 1–5.5 g were studied at five rations ranging from starvation to ad libitum and four temperatures ranging from 5 to 15°C.The maximum rate of food consumption (Cmax) was related to body weight (W) and temperature (T) by the relationship: Cmax=aWb1Tb2. There were significant daily variations in Cmax, which tended to decline over time. Absorption efficiency increased with increasing ration size and decreasing temperature. Body weight had no significant effect on the faecal production. The equation F= aCb1eb2 T described the relationship between faecal production (F), food consumption (C) and temperature. Ammonia‐N predominated over urea‐N in the excreta of most experimental fish. The proportion of urea‐N in the total nitrogen excreted was generally higher at lower rations than at higher rations. Rates of nitrogen excretion increased with increased ration size and were, to a lesser extent, influenced by temperature. Body weight had no significant effect on the nitrogen excretion by feeding minnows. The equation N = a+blT+b2C described the effects of food consumption and temperature on nitrogen excretion (N) other than urea‐N excretion. The relationship between urea‐N excretion (Nu), food consumption and temperature was described by the equation Nu= aeb1T((C+1)b2.On the average, 11 % of food energy was lost in faecal production and nitrogen excretion by minnows feeding on whiteworms, Enchytraeus spp.

Long-term starvation in Xenopus laevis daudin—I. Effects on general metabolism

1. 1. The influence of starvation for 12 months on different physiological parameters was studied in the South African clawed toad, Xenopus laevis Daudin. 2. 2. During starvation for 12 months the animals lost between 35 and 45% of the initial body weight depending on sex. 3. 3. The experimental analysis of the starvation period showed two distinct phases. In females the first phase lasting about 4–6 months was characterized by a reduced oxygen consumption of about 30% of the fed state, a reduced nitrogen-excretion rate and decreased plasma concentrations of urea and lactate. An elevation of lipid utilization can be concluded from an increase in total lipids in plasma. Plasma glucose did not change significantly for four months of starvation. 4. 4. A transition to the second phase of starvation was characterized by a new start of decreasing oxygen consumption. 5. 5. In the second phase of starvation there was a short and small increase in metabolic activity followed again by a decrease. The increase in the nitrogen-excretion rate and plasma urea together with the declining concentration of proteins in plasma indicated an intensified protein catabolism. The plasma glucose concentration decreased continuously during this phase. 6. 6. Aldosterone and corticosterone in plasma were first shown to be reduced after 2–4 months of starvation and remained unchanged for the duration of the experiment.

Effects of varying doses of methionine sulfoximine on liver glutamine synthetase activity and time courses of blood and urinary nitrogenous compounds in the chicken ( Gallus domesticus)

1. 1. The activity of liver glutamine synthetase was inhibited to 7–12% of the control activity by an intracardiac injection with methionine sulfoximine (MSM) at dosages of 20,50, 75 and 100 mg/kg body wt. 2. 2. Plasma glutamine concentrations in all the MSM treatments decreased sharply, then reached steady-state levels within 0.5–2.5 hr, which were almost proportional to a dose of MSM. 3. 3. Blood ammonia concentration sharply increased to a steady-state level attained at 4.5 hr, which was proportional to a dose of MSM. The excretion rate of urinary ammonia augmented linearly up to the dose-dependent maximum rates within 2–5 hr. 4. 4. Plasma uric acid concentration dropped linearly by about 6.4 mg/100 ml at doses of 50, 75 and 100 mg MSM and by 3.7 mg/100 ml at a dose of 20 mg MSM within 2.5 hr, then recovered a little. 5. 5. The decreases in excretion rates of urinary uric acid for the first 4 hr were almost the same at doses of 50 mg and larger, being twice as large as that of the control chicken. 6. 6. Any doses of MSM affected neither the time course of excretion rate of total urinary nitrogen nor its total amounts for 7 hr after MSM treatment.

Temporal focusing of nitrogen release by a periodically feeding herbivorous reef fish

The reef-dwelling jewel damselfish Plectroglyphldodon lacrymatus (Quoy & Gaimard) exhibited a marked diel periodicity in nitrogenous excretion and defecation rates. This temporal “focusing” of soluble and particulate-faecal nitrogen release on the latter part of the day correlated strongly with the pattern of feeding activity. There was a lag after feeding began each day of ≈ 5–6 h before defecation accelerated, but no such lag was apparent in the case of excretion. Both excretion and defecation, however, did lag behind feeding at the end of the day, for they remained above their respective minimum rates for ≥ 8 h after feeding had ceased. Gut evacuation rates were variable, while the excretion of nitrogenous waste appeared to take ≈24 h and to be subject to a physiological rhythm. Defecation, most of which occurred at a single site in each territory, was far more important in the generation of nitrogen by the fish than was excretion. In laboratory experiments the faeces took up ammonium, but in the field most faeces were probably removed quickly by ophiocomine brittlestars and pulled down into interstices of the reef. Nearly all of the nitrogen egested, but perhaps only one-third of that excreted, was transferred initially to the reef framework below the fish's territory.

An experimental study of microflagellate bacterivory: further evidence for the importance and complexity of microplanktonic interactions

By simulating an upwelling event in a laboratory microcosm, it was possible to promote the development of a natural and diverse planktonic community. An initial bacterioplankton community which developed in response to phytoplankton growth was dominated by small coccoid forms (0,14–0,2 μm3) of the genera Vibrio and Pseudomonas. This group was heavily exploited by the heterotrophic microflagellate Pseudobodo sp. (30 μm3). Later, the bacterioplankton community was dominated by large rods (0,7 μm3) which the flagellates seemed unable to exploit. A Lotka-Volterra predator-prey model fitted to the observed data indicated that the flagellates consumed 2,4 times their carbon body mass per day or 19 bacteria·flagellate−1·h−1 when prey were not limiting. Clearance rates were inversely proportional to prey density and ingestion rate, ranging from 2 × 10−3 to 20 × 10−3) μℓ·flagellate−1·h−1. At typical field densities of bacteria and heterotrophic flagellates in the southern Benguela region, between 5 and 30 percent of the water column could be cleared per day. Specific growth rates of the flagellates were positively related to prey density, the maximal rate being 0,84 · d−1. Their initially faster growth rates allowed bacteria to increase in numbers despite predation. The growth yield of the flagellates (34–36 per cent) was also positively related to food density. Such low values suggest inefficient transfer of carbon to higher trophic orders but considerable nitrogen regeneration. Nitrogen excretion rates were approximately 6–7 μg N·mg dry weight−1·h−1, comparable to other flagellates but faster than ciliates. These rates are comparable with in situ measurements of NH+4-N excretion in pycnoclinal regions based on 15N isotope studies but are only about 20 per cent of measured rates in surface waters. This is interpreted to mean that, in pycnoclinal regions where the relative input of "new" nitrogen is high, there are few regenerative steps and the model describes them satisfactorily. In surface waters, observed rates of excretion can only be accounted for by many regenerative steps in a highly complex food chain in which the cumulative total of nitrogen excretion at each step amounts to that based on 15N labelling studies.

Relative Protein Metabolism in Rotifer Brachionus calyciflorus PALLAS, in Relation to Temperature

AbstractIn the temperature range of 10 to 35°C the relationships of the oxygen consumption and nitrogen excretion rates to temperature in Brachionus calyciflorus PALLAS can be described by an exponential function where Q10 is equal to 2.45 or 2.18, respectively. Temperature adaptation within the range studied resulted in stabilisation of relative protein metabolism which accounted for nearly 50 per cent of the total metabolic loss.

Respiration and excretion by oceanic salps

Rates of oxygen consumption and ammonium nitrogen excretion were measured on the solitary and/or aggregate generations of ten species of oceanic salps collected by SCUBA divers during cruises in the Atlantic Ocean (1982–1985). Species that were visibly more active had higher metabolic rates than did less active species. Rates were 1.5 to 2 times lower and O:N ratios were lower when salps were held before incubation than when incubation began at the time of collection. Respiration rate showed a better relationship to length than to weight, suggesting that metabolic activity may be connected mainly with swimming. O:N ratios were between 13 and 28 for most species and generations, but higher and more variable in Pegea spp. Exretion of urea was low or undetectable. Rates of metabolic demand (turnover) ranged from 9.7 to 99% body carbon d-1 and 6.4 to 55.6% body nitrogen d-1.