Requirements for indispensable amino acids in adult humans: longer-term amino acid kinetic study with support for the adequacy of the Massachusetts Institute of Technology amino acid requirement pattern.

Twenty young men received an L-amino acid diet, supplying 140 mg N.kg-1 x d-1 and patterned as in the Egg diet for 1 wk, and then for 3 wk either a pattern based on international recommendations (modified FAO diet; n = 7), our new amino acid requirement pattern (MIT diet; n = 7), or the egg pattern (Egg diet; n = 6). At the end of the initial week, at 1 and 3 wk with the three experimental diets, and after 3 d after return to the Egg diet, an 8-h continuous intravenous infusion with [1-13C]leucine (3 h fast, 5 h fed while subjects received hourly meals supplying the equivalent of one-twelfth the daily intake) was conducted. After 3 wk with the different diets, mean daily leucine balances were lower (P < 0.01) with the FAO diet (-160 mumol.kg-1 x d-1) than with the MIT diet (-15 mumol.kg-1 x d-1). Together with changes in plasma amino acid profiles [eg, methionine increased (P < 0.05) during feeding with the FAO and Egg diets but not with the MIT diet; increased proline concentrations during the fed state (P < 0.05) with the FAO diet but not with the MIT or Egg diets] we interpret these findings to indicate that the FAO diet is not capable of maintaining amino acid homeostasis, as is the case with the MIT and Egg diets.

Phenylalanine and tyrosine kinetics for different patterns and indispensable amino acid intakes in adult humans.

In a previous paper (Am J Clin Nutr 1993;58:670-83) we described results for plasma amino acid changes, leucine kinetics, and body leucine and nitrogen balance in 20 young men receiving diets for 3 wk. The diets were based on the 1985 FAO/WHO/UNU amino acid requirement pattern (modified FAO diet; n = 7), the Massachusetts Institute of Technology (MIT) requirement pattern (MIT diet; n = 7), or the egg-protein pattern (Egg diet; n = 6). It was concluded, in comparison with the MIT and Egg diets, that the modified FAO diet was not capable of maintaining body amino acid homeostasis or balance. Here we report results from tracer studies with L-[O-2H5]phenylalanine and [2H2]tyrosine that were carried out within the same experiment. The modified FAO diet failed to maintain a mean body phenylalanine balance as determined from rates of phenylalanine hydroxylation (corrected for deuterium-isotopekinetic effects); balance was achieved with the MIT and Egg diets. These results further underscore the inadequacy of the internationally proposed amino acid requirement pattern for healthy adults. We recommend interim use of the MIT, tentative amino acid requirement values in all considerations of adult human amino acid requirements and nutrition.

Phenylalanine and tyrosine kinetics in relation to altered protein and phenylalanine and tyrosine intakes in healthy young men.

Plasma phenylalanine (Phe) and tyrosine (Tyr) turnover and the rate of conversion of phenylalanine to tyrosine (Phehyd) and of phenylalanine oxidation (Pheox) after reduced intakes of Phe and Tyr were determined in a metabolic study involving five healthy young adult men. In a pilot study, six postabsorptive young men received either 12- or 4-h infusions of [2H2]Phe and [1-13C]Tyr or [1-13C]Phe and [2H2]Tyro. From these results a primed 8-h constant infusion of [1-13C]Phe and [2H2]Tyr and [2H3]leucine was used in the metabolic study (first 3 h fasted, the 5 h fed) at the end of 1-wk periods during which subjects received an adequate nitrogen L-amino acid based-diet followed by a restricted intake of Phe and Tyr. This procedure was again repeated after 1 and 3 wk when subjects were given a diet low in both nitrogen and Phe and Tyr. Phe and Tyr fluxes were not significantly affected by diet during the fasted metabolic state but Tyr fluxes were lower when the restricted intakes were given. Compared with the rate during the fasting state, Pheox was significantly higher (P less than 0.01) when the adequate diet was consumed; Pheox and Phehyd for fed and fasted states were similar when Phe and Tyr were restricted.

Plasma proline and leucine kinetics: response to 4 wk with proline-free diets in young adults.

The effects of removing proline from the diet on plasma leucine and proline kinetics were investigated. After a 1-wk control period, during which young adult men received a diet containing a complete L-amino acid mixture, seven subjects were given for 4 wk a diet devoid of proline (group 1); six received a diet devoid of proline, arginine, aspartate, glutamate, and serine (group 2); and seven continued with the complete diet (group 3). At the end of the control and 4-wk periods subjects were given a continuous, (3-h fast, 5-h fed) intravenous infusion of L-[1-13C]leucine and L-[5,5-2H]proline. Plasma proline was reduced significantly, especially during the fed state, in groups 1 and 2 after the 4-wk diet periods. Small but statistically significant (P < 0.05) reductions occurred in nonoxidative leucine disappearance and leucine appearance during the fasted state in group 2. Proline fluxes decreased by approximately 50% in fasted and fed states in groups 1 and 2. Mean de novo proline synthesis during the fasted state declined markedly (P < 0.05) after 4 wk in groups 1 and 2.

Source and amount of dietary nonspecific nitrogen in relation to whole-body leucine, phenylalanine, and tyrosine kinetics in young men.

We studied the effects of amount and source of nonspecific nitrogen (NSN) on the oxidation of leucine and hydroxylation of phenylalanine. In phase 1, seven adult males received for 6 d diets providing indispensable amino acid intakes to meet the 1985 FAO/WHO/UNU (FAO) requirements or our proposed requirement values (MIT). During one diet period with each diet, the NSN of the basal diets (total nitrogen intake: 107 mg N.kg-1.d-1) was increased to a total of 160 mg N.kg-1.d-1. On the morning of day 7, an 8-h constant intravenous tracer-infusion protocol (3-h fast; 5-h fed state) was conducted with L-[1-13C]leucine, L-[ring-2H5]phenylalanine, and L-[3,3,2H2]-tyrosine as tracers. In phase 2, six subjects were given three diets for 6 d, supplying 107 mg N.kg-1.d-1; NSN was a mixture of dispensable amino acids in which glutamine accounted for 0%, 12.5%, and 100% of total NSN. Leucine oxidation and phenylalanine hydroxylation rates and whole-body leucine and phenylalanine balances were unaffected by addition of supplemental NSN to the diets in phase 1 or by amino acid source of NSN in phase 2. Leucine and phenylalanine balances were lower (P < 0.05) for FAO compared with MIT diets.

Phenylalanine and tyrosine kinetics in young men throughout a continuous 24-h period, at a low phenylalanine intake.

We determined the daily rates of whole-body phenylalanine oxidation (phe-Ox) and hydroxylation (phe-OH) in young men receiving [1-13C]phenylalanine and [2H2]tyrosine via primed, constant intravenous (n = 5) or oral (n = 7) infusions for a consecutive 24 h (12-h fast followed by 12-h fed period), and given a low-phenylalanine (21.9 mg.kg-1.d-1), no-tyrosine, but otherwise adequate L-amino acid-based diet for 6 d before the tracer study. Estimates of the daily rates of phe-Ox and phe-OH were significantly higher (P < 0.001) for the subjects receiving the oral tracer, with estimates of phe-Ox obtained with the oral tracer during the 12-h fast period being close to those predicted from similar 24-h leucine kinetic studies (Am J Clin Nutr 1994;59:1000-11). There was generally poor agreement between the measured 24-h rates of phe-Ox and phe-OH compared with the daily rates as predicted from the last hour of the 12-h fast and 5th hour of feeding. From the 24-h data, daily phenylalanine balances were estimated to be positive with the intravenous-tracer protocol and negative with the oral-tracer group. Our results question the adequacy of current international recommendations for aromatic amino acid requirements in healthy adults.

Methionine and cysteine kinetics at different intakes of cystine in healthy adult men.

We investigated plasma methionine and cysteine kinetics in eight healthy adult men receiving for 6 d each of five L-amino acid diets supplying 13 mg methionine.kg-1.d-1 without cystine or 6.5 mg methionine.kg-1.d-1 plus 0, 5.2, 10.5, or 20.9 mg cystine.kg-1.d-1. On the morning of day 7, primed, constant intravenous infusions of L-[2H3-methyl, 1-13C]methionine and L-[3,3-2H]cysteine were given for 8 h (for the first 3 h subjects remained in a fasted state and for the next 5 h received small, equal meals at hourly intervals to achieve a fed state). Methionine and cysteine fluxes and rate of methionine oxidation were estimated from plasma methionine and cysteine labeling and 13C in expired air. Methionine oxidation declined (P < 0.05) with lowered methionine intake. Cysteine flux was similar across diets and dietary cystine did not affect tracer methionine oxidation. If there is a sparing effect of dietary cystine on the methionine requirement in adults, it probably takes place during the "first-pass" removal of these amino acids within the splanchnic region.

The 24-h pattern and rate of leucine oxidation, with particular reference to tracer estimates of leucine requirements in healthy adults.

Daily leucine oxidation and derived values for whole-body leucine balance, obtained by continuous measurement throughout a 24-h period, were compared with those predicted from short-term measurements during fasted and fed states in five healthy adults studied during two 6-d experimental diet periods, each immediately followed by a 24-h continuous intravenous tracer infusion of L-[1-13C]leucine. Leucine intake was either 14 or 38.3 mg.kg-1.d-1. Mean measured daily leucine oxidation (mg leucine.kg-1.d-1) was 27.8 and 45.2 for the 14- and 38.3-mg intakes, respectively. Oxidation rates predicted by extrapolation of rates measured during the final hour of fasting (15 h after last meal) and the 5th h of feeding were approximately 12% higher (P < 0.01) than measured rates for both diets. For the prediction based on the 12th h of fasting and 5th h of feeding, it was 4% higher or 0.4% lower than measured rates for the 38.3- and 14- mg intakes, respectively. Hence, relatively small differences exist between measured vs predicted estimates of daily leucine oxidation and balance. These studies support previous conclusions that the current, international requirement value for leucine in healthy adults is far too low.

Validation of the tracer-balance concept with reference to leucine: 24-h intravenous tracer studies with L-[1-13C]leucine and [15N-15N]urea.

The validity of tracer-derived estimates of whole-body leucine balance was investigated. Seven healthy young adult subjects received an adequate protein diet for 6 d; at 1800 on the last day, L-[1-13C]leucine and [15N-15N]urea were given as primed, continuous intravenous infusions for 24 h. Subjects were in a fasting state for the first 12 h and at 0600 on day 7 they then received hourly 10 equal meals to achieve a fed state. Total leucine intake (diet plus tracer) was 89.4 mg.kg-1.d-1. Mean daily leucine oxidation was equivalent to 89.5 +/- 3.3 mg leucine/kg. The predicted daily oxidation rate, from measurements made during the last hour of the fast and the fifth hour of the fed period, was 91.2 +/- 5.8 mg/kg (P = 0.25 from measured). Measured and predicted whole-body leucine balances were 0.76 +/- 2.99 and -0.98 +/- 5.54 mg/kg, respectively (P = 0.25). Urea production exceeded urea excretion by 20%; daily protein oxidation was the same when estimated from leucine oxidation or nitrogen excretion. Thus, the tracer-balance concept is valid, and reliable predictions of total daily leucine oxidation and whole-body leucine balance can be obtained from short-term measurements of leucine oxidation during fasted and fed states.

Twenty-four-hour intravenous and oral tracer studies with L-[1-13C]phenylalanine and L-[3,3-2H2]tyrosine at a tyrosine-free, generous phenylalanine intake in adults.

The daily rates of whole-body phenylalanine oxidation and hydroxylation were determined in young men receiving [1-13C]phenylalanine and [2H2]tyrosine via primed, constant intravenous (n=3) or oral (n=5) infusion for 24 consecutive hours (12-h fast followed by 12-h fed period), and given a generous phenylalanine (100 mg.kg-1.d-1), tyrosine-free, but otherwise adequate L-amino acid-based diet for 6 d before the tracer study. Our hypothesis was that subjects would be in whole-body phenylalanine equilibrium. Estimates of the daily rates of phenylalanine oxidation (phe-ox) and hydroxylation (phe-OH) were significantly higher for the subjects receiving the oral compared with intravenous tracer (P<0.01 for both comparisons), with the estimates of phe-ox obtained with oral tracer during the 12-h fast period being close to those predicted from similar 24-h leucine kinetic studies. The precision of the agreement between the measured 24-h rates of phe-ox and phe-OH compared with the predicted daily rates by extrapolation from the last hour of the 12-h fast and fifth hour of the fed period was poor. From the 24-h data, daily phenylalanine balances were estimated to be positive for both the intravenous and oral tracer protocols, although it was less positive for the oral tracer group. These results imply that the [13C]phenylalanine probe underestimated whole-body irreversible loss of phenylalanine, and suggest that daily phenylalanine balance in earlier 24-h phenylalanine-tyrosine tracer studies at low phenylalanine intakes may have been overestimated. Studies involving [13C]tyrosine as tracer will be required to further assess whole-body aromatic amino acid balance.

Kinetics of plasma arginine and leucine in pediatric burn patients.

The dynamic status of whole-body arginine and leucine was investigated in eight severely burned (mean 55% of body surface area) pediatric patients (mean age 5.3 y) at a mean of 16 d after their initial injury. Plasma amino acid kinetics were estimated by using primed constant intravenous infusions of L-[13C-guanidino]arginine and L-[I-13C]leucine given for 4 h. Each patient was studied twice within 2 d. The patients were studied either in a "basal" state, which involved removal of amino acids from the total parenteral nutrition (TPN) solution for 8 h before the tracer study, or while receiving complete TPN. Nitrogen intake was 0.58 +/- 0.08 g.kg-1.d-1 with nonprotein energy intake equivalent to 197 +/- 29 kJ.kg-1.d-1. Plasma leucine and arginine fluxes (mumol.kg-1.h-1) were 208 +/- 35 and 108 +/- 18 for basal and 290 +/- 38 and 195 +/- 22 for TPN periods, respectively. Leucine oxidation was 42 +/- 7 and 59 +/- 9 mumol.kg-1.h-1 for basal and TPN periods, respectively, indicating a higher rate of leucine loss in the absence of a leucine intake than that expected for healthy individuals. The arginine kinetic data implied little net de novo arginine synthesis and further suggested increased rates of arginine degradation from burn injury. The expected rate of urea excretion, based on the basal rate of leucine oxidation, agreed closely with the measured output of urinary urea. These findings suggest that arginine is a conditionally indispensable amino acid for maintaining body protein homeostasis and nutrition in severely burned pediatric patients. The metabolic response of these children appears to be quantitatively similar to that for severely burned adult patients.

Kinetic measurement of the urinary production rate of cortisol in male piglets: is the prerequisite 'collection until all label has disappeared' necessary?

Urinary cortisol production rate (CPR) was calculated by two different methods in five male piglets (about 3 kg bodyweight) injected i.v. with 40-120 kBq tritiated cortisol ([3H]F. After administration of [3H]F, urine was obtained from four consecutive collections for the following 2 days, during which 80-100% of the label was recovered. Total radioactivity in the urine was measured and used to calculate the total rate constant of 0.115 +/- 0.011 h-1 and, from this, the mean biological half-life (t1/2) of 6.0 +/- 0.6 h (S.D.; n = 4). It was found that the mass ratio of the two principal urinary cortisol metabolites tetrahydrocortisone (THE) and tetrahydrocortisol (THF) was strikingly less than 1.0 (0.4 +/- 0.1; n = 14), which is the reverse of that observed in older pigs, neonatal infants and man. To calculate CPR conventionally, the cumulative specific activities of THE and THF were calculated for the 2-day period of urine collection. The apparent mean CPR values on the basis of THE and THF were calculated as 11.5 +/- 1.6 (n = 5) and 12.8 +/- 3.3 (n = 5) mumol/day respectively, and 12.1 +/- 1.4 (n = 5) mumol/day for the average of THE and THF. The second method for calculating CPR consisted of determining the masses of THE and THF (mumol) per fraction of dose (m/fd) (fd refers to the ratio of radioactivity in the metabolite and dose) at different times after administration of [3H]F. The calculated m/fd values, which are synonymous with the dose divided by the specific activities of the metabolites, and the different times of urine collection were analysed by linear regression. The resulting slope is equal to the CPR. The CPR derived by this method for the average of THE and THF, 10.1 +/- 0.91 mumol/day was significantly (P less than 0.014) lower than that derived conventionally, 12.1 +/- 1.40 mumol/day. This second method may be used when CPR is determined in neonatal infants by means of nonradioactive, deuterated or 13C-enriched cortisol, where the extent of negative feedback by the relatively high dose of exogenous steroid on cortisol secretion must be kept as low as possible. This method also allows urine collections to be used at times when the tracer is still being excreted.

Measurement of the cortisol production rate in two sisters with 17 alpha-hydroxylase deficiency using [1,2,3,4-13C]cortisol and isotope dilution mass spectrometry.

[1,2,3,4-13C]cortisol was i.v. administered to two sisters aged 11 yr (patient I) and 3 yr (patient II) who suffer from 17 alpha-hydroxylase deficiency. This is the first time that the cortisol production rate (CPR) in patients with 17 alpha-hydroxylase deficiency has been measured with a stable labelled tracer using the urinary method. The urine was collected for 3 days. High-performance liquid chromatography (HPLC) of approximately 100 ml urine extracts was carried out to isolate the small amount of cortisol metabolites excreted. The cortisol metabolites were oxidized to 11-oxo-aetiocholanolone. The isotope dilution in the methyl oxime tert-butyldimethylsilyl ether derivatives was measured by selected ion monitoring gas chromatography/mass spectrometry (GC/MS). The CPR calculated from tetrahydrocortisone (THE) and the cortolones was 765 and 536 nmol/day, respectively in patient I. The CPR in patient II was only calculated from THE and was 62 nmol/day. If radioactive labelled cortisol had been used, much larger quantities of urine would have been needed for isolation of sufficient mass of metabolites, even then purification may have been difficult. Steroid profiling of 1 ml urine samples by GC and identification by GC/MS revealed high concentrations of pregnenolone, progesterone, 11 beta-hydroxy progesterone and corticosterone metabolites. Tetrahydrocorticosterone and 5 alpha-tetrahydrocorticosterone were found in urine at elevated excretions of 2.5 and 5.7, 0.9 and 2.0 mumols/24 h, in patients I and II respectively. No cortisol metabolites were detected by routine GC or GC/MS as the low amounts excreted co-eluted with the relatively abundant corticosterone metabolites.

Phenylalanine conversion to tyrosine: comparative determination with L-[ring-2H5]phenylalanine and L-[1-13C]phenylalanine as tracers in man.

The in vivo rate of conversion of phenylalanine to tyrosine (PheOH) can be estimated using combinations of stable isotope-labeled phenylalanine and tyrosine. We have compared in four healthy adult men the rates of phenylalanine conversion to tyrosine based on the following pairs of primed, continuous tracer infusions administered simultaneously: (1) L-[ring-2H5]phenylalanine and 2H2-tyrosine with a 2H4-tyrosine prime, and (2) L-[1-13C]phenylalanine and 2H2-tyrosine with a 1-13C-tyrosine prime. Phenylalanine oxidation was determined from measurement of 13CO2 excretion in expired air. Tracers were given for 8 hours, with subjects being in the postabsorptive state during the first 3 hours and in the fed state during the remaining 5 hours. Mean (+/- SD) rates (mumol.kg-1.h-1) of phenylalanine conversion to tyrosine for fasted and fed states, respectively, were 5.1 +/- 2.9 and 6.8 +/- 3.4 with 2H5-phenylalanine and significantly higher (P < .05) at 11.1 +/- 5.6 and 12.7 +/- 7.7 with 13C-phenylalanine as tracer. Phenylalanine oxidation was 9.9 +/- 2.0 and 13.5 +/- 2.6, respectively, for fasted and fed states, and these mean values did not differ (P > .1) from the rate of phenylalanine conversion to tyrosine determined using 13C-phenylalanine. These results indicate the need for caution in interpreting kinetic aspects of phenylalanine metabolism when based on isotopic data from multideuterated phenylalanine.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma arginine kinetics in adult man: response to an arginine-free diet.

To explore the response of whole-body arginine metabolism to a change in arginine intake, plasma arginine kinetics were investigated in eight healthy adult men who received an L-amino acid diet supplying an Arg-rich or Arg-free intake for 6 days before undergoing a tracer study on day 7. The tracer protocol lasted for 8 hours. For the first 3 hours subjects remained in the postabsorptive (fasted) state, and during the following 5 hours they consumed small meals at 30-minute intervals. Primed continuous intravenous infusions of L-[guanidino-13C]arginine, L-[5,5,5-2H3]leucine, and [15N2]urea were administered to estimate plasma amino acid fluxes and the rate of urea production. For the fasted and fed states, plasma arginine fluxes (mumol.kg-1.h-1, mean +/- SD) were 69 +/- 8 and 87 +/- 12 (P < .01), respectively, for the Arg-rich diet and 63 +/- 14 and 51 +/- 7 (P < .01, from Arg-rich) for the Arg-free diet. Compared with the Arg-rich results, fed-state plasma arginine and ornithine concentrations were decreased (P < .01) and citrulline concentration was increased (P < .01) during the Arg-free diet period. Leucine fluxes and rates of urea production did not differ between the diet groups. The lower fed-state arginine flux in subjects receiving the Arg-free compared with the Arg-rich diet appears to be entirely due to the decreased rate of entry of arginine from the intestine in the former group.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma arginine and leucine kinetics and urea production rates in burn patients.

We measured plasma arginine and leucine kinetics and rates of urea production (appearance) in 12 severely burned patients (mean body surface burn area, 48%) during a basal state (low-dose intravenous glucose) and while receiving routine, total parenteral nutrition ([TPN] fed state) including an L-amino acid mixture, supplying a generous level of nitrogen (mean, 0.36 g N.kg-1.d-1). The two nutritional states were studied in random order using a primed 4-hour constant intravenous tracer infusion protocol. Stable-nuclide-labeled tracers were L-[guanidino-13C]arginine, L-[1-13C]leucine, [18O]urea, and NaH13CO3 (prime only), with blood and expired air samples drawn at intervals to determine isotopic abundance of arginine, citrulline, ornithine, alpha-ketoisocaproate ([KIC] for leucine), and urea in plasma and 13CO2 in breath. Results are compared with data obtained in these laboratories in healthy adults. Leucine kinetics (flux and disappearance into protein synthesis) indicated the expected higher turnover in burn patients than in healthy controls. Mean leucine oxidation rates are also higher and compared well with values predicted from urea production rates, provided that urea nitrogen recycling via intestinal hydrolysis is taken into account. The plasma urea flux was also higher than for normal subjects. Arginine fluxes as measured in the systemic whole body, via the plasma pool, were correspondingly higher in burned patients than in healthy controls and were in good agreement with values predicted from leucine-KIC kinetics. However, systemic whole-body arginine flux measured via the plasma pool was only 20% of the arginine flux estimated from the urea flux plus the rate of protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Stable isotope dilution analysis of cystine in granulocyte suspensions as cysteine: a powerful method for the diagnosis, the follow-up, and treatment of patients with cystinosis.

A stable isotope dilution method was developed for the determination of cystine in granulocytes. Granulocytes were isolated from blood samples of treated cystinosis patients. Cystine in the granulocyte suspension was decoupled from proteins and converted to cysteine by treatment with a tri-butyl phosphine solution. Tertiary butyldimethyl silyl derivatives were prepared and analyzed by gas chromatography/mass spectrometry. Selective ion monitoring was carried out at m/z 304.3 (M-159 and m/z 406.4 (M-57) for the natural, and at m/z 306.3 and 408.4 for the labelled compound. [3,3,3',3'-2H]-DL-cystine was used as internal standard for the isotope dilution analysis. Concentrations of cystine in granulocytes could be accurately measured. There was a distinct difference in cystine concentrations in healthy individuals and treated patients.

Determination of medium chain acyl-CoA dehydrogenase activity in cultured skin fibroblasts using mass spectrometry.

Medium chain acyl-CoA dehydrogenase deficiency, a defect of mitochondrial beta-oxidation, is one of the most frequently occurring among inborn errors of metabolism. We describe a rapid and sensitive gas chromatographic/mass spectrometric method allowing reliable assessment of medium chain acyl-CoA dehydrogenase activity in cultured skin fibroblasts. We investigated MCAD activity in three presumed medium chain acyl-CoA dehydrogenase deficient (MCADD) patients and 10 control subjects. The medium chain acyl-CoA dehydrogenase activity determined in three patients was 1.0 +/- 0.4 nmol.min-1.mg-1 protein (mean +/- SD; range: 0.6-1.4) and in controls it was 2.8 +/- 1.0 nmol.min-1.mg-1 protein (mean +/- SD; range: 1.6-4.4).

Body water content and turnover in cats fed dry and canned rations.

Body water content and total body water turnover in cats fed commercially available dry food and then given canned rations were determined with tritiated water. Cats during the feeding of either ration did not differ in body water content or turnover. Cats during the feeding of the dry ration derived a greater fraction of their total water turnover from drinking water, and these cats drank more water per gram of dry matter intake than when fed the canned ration. On the basis of total water intake, however, those given the canned ration had significantly greater water intake per gram of dry matter; also, their total water turnover per gram of dry matter was greater. Compared with other animals, cats have a similar ratio of body water to body solids, but the rate of water turnover per unit of body weight is slower.