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Diet-induced (taurine deficiency) dilated cardiomyopathy is reported more in large than small dogs possibly because taurine biosynthesis rate (TBR) is lower in large than small dogs. The TBR in 6 mongrels (37.9 +/- 2.1 kg) and 6 beagles (12.8 +/- 0.4 kg) was determined from the fractional dilution rate of urinary [1,2-(2)H(2)]-taurine, (d4-tau). All dogs were given a 15.6% protein, 0.60% sulfur amino acid (SAA) diet in amounts to maintain an ideal body condition score. After 3 mo, 14.6 mg/kg body weight of d4-tau was given orally and TBR determined from d4-tau to taurine ratio in urine collected each d for 6 d. Enrichments of d4-tau were determined by GC-MS. Thereafter, mongrels and beagles were paired by ranking of SAA intake per metabolic body weight per kg(0.75). Each pair received the same amount of diet/kg(0.75) for 2 wk, then TBR was again determined. Concentrations of taurine in plasma, blood, and urine and concentrations of plasma thiols were measured during each TBR determination. In Expt. 1, TBR and taurine concentrations in plasma and urine of mongrels were lower (P < 0.05) than those of beagles. In Expt. 2, TBR and taurine concentrations in blood and plasma of mongrels were lower (P < 0.05) than beagles. Together, the results support the hypothesis that large compared with small dogs have lower TBR when fed diets near-limiting in dietary SAA, but adequate to maintain ideal body condition.

Although taurine is not dietarily essential for dogs, taurine deficiency and dilated cardiomyopathy (DCM) are sporadically reported in large-breed dogs. Taurine status and husbandry were examined in 216 privately owned Newfoundlands, a giant dog breed with high incidence of idiopathic DCM (1.3-2.5%). Plasma taurine concentration was positively correlated (P < 0.01) with plasma cyst(e)ine (r = 0.37) and methionine (r = 0.35) concentrations and was similar across age, sex, neutering status, body weight, and body-condition scores. Plasma taurine concentration was low (< or =40 micromol/L) in 8% of dogs. Dogs with low plasma taurine were older, less active, had more medical problems and treatments, and had lower plasma albumin, cyst(e)ine, tryptophan, and alpha-amino-n-butyric acid concentrations than the other dogs (P < 0.05). Of 9 taurine-deficient, clinically evaluated dogs, 3 had DCM that was reversed by taurine supplementation and 1 had retinal degeneration. When given a diet apparently adequate in sulfur amino acids (5.4 g/kg) for 3 wk, 6 Newfoundlands (52.5 +/- 2.3 kg, 3.5-7 y), compared with 6 Beagles (13.2 +/- 2.3 kg, 5.5 y), had lower (P < 0.01) concentrations of plasma taurine (49 +/- 16 vs. 97 +/- 25 micromol/L) and cyst(e)ine and blood glutathione, lower (P < 0.01) de novo taurine synthesis (59 +/- 15 vs. 124 +/- 27 mg x kg(-0.75) x d(-1)), and greater (P < 0.05) fecal bile acid excretion (1.7 +/- 0.2 vs. 1.4 +/- 0.2 micromol/g). Newfoundlands would appear to have a higher dietary sulfur amino acid requirement than Beagles, a model breed used in nutrient requirement determinations.

Copper deficiency has been reported to cause a decrease in urinary taurine excretion in rats. We determined whether Cu deficiency would decrease taurine status and the hepatic activities of cysteine dioxygenase (CDO) and/or cysteine sulfinic acid decarboxylase (CSAD) in rats. Ten weanling male rats were assigned to either a Cu-adequate (+Cu) or Cu-deficient (-Cu) group. All rats consumed a Cu-deficient purified diet and water ad-libitum for 16 wk. The water for the (+Cu) group contained 20 mg Cu/L as CuSO(4). At wk 16, the groups differed (P < 0.05) in the following variables (means +/- SEM, -Cu vs. +Cu): body weight (BW), 375 +/- 19 vs. 418 +/- 2.9 g; food intake, 16.2 +/- 0.7 vs. 18.5 +/- 0.4 g/d; hematocrit, 0.294 +/- 0.027 vs. 0.436 +/- 0.027; hemoglobin, 95.2 +/- 9 vs 134 +/- 10 g/L; liver Cu, 8.7 +/- 2.0 vs. 65.9 +/- 2.5 nmol/g; plasma Cu, 0.38 +/- 0.09 vs. 13.4 +/- 0.61 micromol/L; plasma ceruloplasmin activity, 1.75 +/- 1.0 vs. 67.9 +/- 8.4 IU; relative heart weight, 0.56 +/- 0.04 vs. 0.35 +/- 0.02% BW; relative liver weight, 4.06 +/- 0.23 vs. 3.37 +/- 0.06% BW; and liver CSAD activity, 18.8 +/- 1.37 vs. 13.5 +/- 1.11 nmol x min(-1) x mg protein(-1). The groups did not differ at wk 16 in: plasma taurine, 249 +/- 14 vs. 298 +/- 63 micromol/L; whole blood taurine, 386 +/- 32 vs. 390 +/- 25 micromol/L; urinary taurine excretion, 82.5 +/- 15 vs. 52.0 +/- 8.3 micromol/d; liver taurine, 2.6 +/- 0.7 vs. 2.8 +/- 0.4 micromol/g; liver total glutathione, 6.9 +/- 0.48 vs. 6.3 +/- 0.40 micromol/g; liver cyst(e)ine, 96 +/- 7.1 vs. 99 +/- 5.3 nmol/g and liver CDO activity, 2.19 +/- 0.33 vs. 2.74 +/- 0.21 nmol x min(-1) x mg protein(-1). These findings support the conclusion that Cu deficiency does not affect body taurine status.

Indispensable amino acids are neither synthesized nor stored in animals and are rapidly depleted when not provided by the diet. To maintain homeostasis, organisms must sense deficiency of an indispensable amino acid and implement a repletion strategy. In rats and birds, the anterior piriform cortex houses the detector, but its mechanism has evaded description for >50 years. Recently, rapid detection of amino acid depletion was shown behaviorally when naive animals, pre-fed a low nitrogen diet, terminated their first deficient meal within 20 min. The general amino acid control system of yeast, which is activated by amino acid deprivation via deacylated tRNA, was found to be active in rodent brain, showing conservation of amino acid sensory mechanisms across eukaryotic species.

When pyrroloquinoline quinone (PQQ) is added to an amino acid-based, but otherwise nutritionally complete basal diet, it improves growth-related variables in young mice. We examined PQQ and mitochondrial function based on observations that PQQ deficiency results in elevated plasma glucose concentrations in young mice, and PQQ addition stimulates mitochondrial complex 1 activity in vitro. PQQ-deficient weanling mice had a 20-30% reduction in the relative amount of mitochondria in liver; lower respiratory control ratios, and lower respiratory quotients than PQQ-supplemented mice (2 mg PQQ/kg diet). In mice from dams fed a conventional laboratory diet, but switched at weaning to the basal diet, plasma glucose, Ala, Gly, and Ser concentrations were elevated at 4 wk (PQQ- vs. PQQ+), but not at 8 wk. The relative mitochondrial content (ratio of mtDNA to nuclear DNA) also tended (P

The percentage of protein that dogs voluntarily choose and the effect of palatability on the quantity selected were determined. Six beagles were offered a choice of two isoenergetic purified diets containing 0 vs. 25, 9 vs. 32, 18 vs. 32, 18 vs. 48 and 25 vs. 48% metabolizable energy from protein (MEp). To examine whether palatability modifies the choice, the dogs were offered 0 vs. 25% MEp, with the 0% protein diet containing 2.9 times more sucrose than the diet containing 25% MEp. To determine the effect of concentration of protein in the diet on dietary choice and plasma amino acid concentrations (PAA), dogs were adapted to 9% MEp, followed by a choice of diets containing 9 vs. 32% MEp. The choice was repeated after adaptation to a diet containing 32% MEp. Dogs selected diets to obtain 21-27% of the MEp (mean, 25% MEp; median, 27% MEp) when sucrose was kept at 6.4%. When the protein-free diet contained 25% sucrose, dogs selected 17% of MEp, but increased food intake to ingest about the same amount of protein per day. PAA did not correlate linearly with protein intake. Food intake and total PAA were the lowest after consumption of the 9% MEp diet. We conclude that when fed equally bland diets, dogs select food to ingest approximately 25% MEp. As a palatability enhancer, sucrose increases food intake and selection of the diet containing the higher sucrose concentration.

Breath hydrogen (H(2)) concentration, an indicator of intestinal microbial abundance, was determined in cats given purified and commercial canned and dry-type diets. Before measurements, the cats were fed diets for more than 2 wk and habituated to a daily feeding interval of 4 hr. Breath H(2) concentrations were determined before a meal (approximately 25% daily MER) and then every 20 min for 8 hr or hourly for 10 hr. A clear rise above baseline breath H(2) concentrations, 1-2 ppm, was not observed in 6 males given a casein-based purified diet. A mean (+/- SEM) peak breath H(2) concentration of 22 +/- 4 ppm was observed in 6 other males, 6.3 hr after ingestion of a canned diet with protein, fat, and carbohydrate proportions similar to those of the purified diet. Area-under-the-curve (AUC) breath H(2) responses to the canned diet were substantially greater (p0.05) than responses observed in 5 males given a dry-type diet, but similar to responses observed in 12 males given an uncooked form of the canned diet. Gamma irradiation to inactivate microbes in the uncooked diet did not affect the breath H(2) response. Breath H(2) responses to 2 other canned and 2 other dry-type diets were evaluated in 8 adult females using a 4 x 4 Latin-square design. Peak and AUC responses to the canned diets were similar but approximately 2 times greater (p0.05) than responses to the dry diets. Relative to dry-type diets, canned diets induce a substantially greater breath H(2) production, and therefore appear to support a greater intestinal microbial population.

The objective of this study was to determine the copper requirement of female cats (queens) for gestation. Cuproenzyme activities were evaluated to identify a noninvasive indicator of copper status. This study used a depletion-repletion model. Specific pathogen-free queens (n = 28) were adapted to a purified diet; after consuming a copper-depletion diet (0.8 mg Cu/kg diet) for 4 mo, they were randomly allocated to three dietary treatment groups receiving copper sulfate at 4.0, 5.8 or 10.8 mg Cu/kg diet. Four queens underwent liver biopsies at two time points during the study. Plasma samples were analyzed for copper concentrations, extracellular superoxide dismutase, ceruloplasmin and diamine oxidase activities. Only liver copper concentrations were responsive to dietary copper intake. The dietary concentration of copper had a significant effect on the time taken for queens to conceive (P = 0.04). There was a negative linear relationship between dietary copper (x = Cu mg/kg diet) and the mean time (y = days) for queens to conceive (y = 43.38-2.87x; R(2) = 0.97). The current NRC recommendation of 5 mg/kg diet copper for cats appears marginal for optimal reproduction.

EXPANDED ABSTRACT Experiments with rats (Heger 1990, Stucki and Harper 1962), chicks (Bedford and Summers 1985, Stucki and Harper 1961), turkeys (Bedford and Summers 1988) and pigs (Wang and Fuller 1989) have shown optimal growth rates when the dietary essential amino acid (EAA) 3 nitrogen to total nitrogen (E:T) ratios were between 0.4 and 0.65. It has been consistently found that diets containing only EAA (E:T 5 1.0) yield poor growth rates. Taylor et al. (1996) showed that in kittens fed diets that contain EAA as the sole source of nitrogen [E:T 5 1.0, with the EAA pattern proportionate to the NRC requirements (NRC 1986)], weight loss results. Plasma amino acid concentrations of methionine (and possibly arginine) suggested toxicities of these amino acids. Also, marked depressions in the concentrations of proline and asparagine suggested that these amino acids might be conditionally essential. A near-maximal growth rate for the group receiving all EAA (E:T 5 1.0) was achieved when methionine and arginine were limited to not more than 2.25 times the NRC requirements. No response was obtained with proline and/or asparagine supplementation to the all-EAA diet or when these two amino acids were removed from the control diet. Thus asparagine and proline are clearly dispensable under all conditions tested thus far. These results suggest that the poor growth rates recorded in other species given only EAA (E:T 5 1.0) diets are the result of an intolerance of one or more EAA, rather than a metabolic inability of animals to synthesize dispensable amino acids (DAA) at a rate fast enough for rapid growth, as previously suggested by Harper (1974). Here we report the results of weight gains of kittens fed a wide range of crude protein (CP) levels at various E:T ratios in which excesses of essential amino acids that depress weight gains were avoided. Materials and methods. A control purified diet (CD) was

Amino acid-imbalanced (IMB) diets induce an acute amino acid deficiency and hypophagic responses in most animals. The neural circuits underlying these responses are unknown. To ascertain potential neural circuits involved in the recognition of IMB, we measured the concentrations of norepinephrine, dopamine, serotonin, their metabolites and 20 amino acids in 14 rat brain areas in three studies. Rats were prefed a basal diet with L-amino acids as the protein source for at least 1 wk. For the experiments, either threonine or isoleucine IMB diet was offered for 2.5 or 3.5 h. Brains were taken before (using a mildly IMB diet) or after (using moderately or severely IMB diet) food intake was significantly (P < 0.05) depressed. Brain areas were dissected and analyzed for monoamines, metabolites and amino acids. Only in the anterior piriform cortex (APC), a brain area that may contain the amino acid chemosensor, was the limiting amino acid lower in IMB groups than in controls across all of the experiments. Before the onset of the anorectic response to the IMB diets, monoaminergic activity was affected in areas that have recognized monosynaptic connections with the APC. We propose a circuit for the neural responses in the initial recognition of acute amino acid deprivation that begins with activation of the APC and includes areas in the hindbrain and hypothalamus. After a significant hypophagic response, serotonergic indicators were altered in areas of the taste pathway and the limbic system. These results suggest that different circuits mediate the initial recognition and secondary conditioned responses to IMB diets.

Incomplete agreement exists on the relative potency of amino acids in stimulating endocrine secretion of cholecystokinin (CCK). Species and methodological variations have been suggested to account for the apparent inconsistencies. In the present research, the CCK-releasing potency of dietary amino acids was evaluated in cats using plasma CCK-like immunoreactivity (CCK-LI) as an indicator of CCK secretion rather than pancreatic protein and enzyme secretion, as has been used in past research. Oral-gastric administrations of a casein-simulating amino acid mixture increased (P < 0.05) plasma CCK-LI but not to the extent of that observed for casein or sodium oleate. The response in plasma CCK-LI to administrations of 50 mM solutions of amino acids was significant (P < 0.05) for tryptophan, phenylalanine, leucine, and isoleucine and the response increased linearly (P < 0.01) with increasing amino side-chain hydrophobicity. Control administrations of water and saline also evoked elevation in plasma CCK-LI, but the responses were so transient that amino acid effects were not obscured. This was substantiated by the finding of a significant linear (P < 0.001) dose response to phenylalanine administration. Cholecystokinin-8, 33 and 58 were among the CCK molecular forms identified by HPLC in plasma after administrations of phenylalanine and water. The present findings indicate that lipophilic amino acids released during digestion account for at least part of the endocrine CCK response in cats to ingested protein. The greater CCK-releasing potency observed for intact protein relative to free amino acids may have been the result of a slow digestive release of amino acids, elaboration of peptide secretogogues or protection of protease-sensitive releasing factors.

This study determined the effect of a commercial dry expanded (complex) diet and purified diet on methotrexate (MTX) toxicity and pharmacokinetics in the cat. Twelve cats were randomized to receive a purified diet or a complex diet for 21 days. They were then given an intravenous bolus injection of MTX at a dose of 10 mg/kg (160 mg/M2). Cats fed the purified diet had severe enteritis, characterized by depression, lethargy, diarrhea, and vomiting. Cats receiving the complex diet remained mentally bright, alert, and responsive throughout the post-chemotherapy period, and only one of six cats in this dietary group developed mild diarrhea 48 hr after MTX administration. Methotrexate was associated with a significant (P < 0.0001) reduction in the total white blood cell (WBC) counts in cats receiving the purified and complex diets. The elimination of MTX appeared to follow a three-compartment model of elimination. Plasma MTX concentrations at all time points examined were virtually identical in cats receiving the purified and complex diets. The terminal half-life of MTX in cats receiving the complex and purified diets was 1.75 ± 0.44 hr and 2.77 ± 0.8 hr, respectively. The similarity of plasma MTX concentrations and pharmacokinetic parameters in both dietary groups suggests that dietary alterations may influence enterotoxicity directly rather than altering exposure to MTX.

Most experiments conducted to determine the optimal essential amino acid (EAA) nitrogen to total nitrogen (E:T) ratio in rats, chicks and other species have shown that weight gain and nitrogen retention are optimal when the ratio is between 0.5 and 0.65. Two experiments were conducted to determine if weight gains of kittens fed EAA as a sole source of dietary nitrogen were equivalent to those of kittens fed a control diet that contained equal amounts of EAA and dispensable amino acids (DAA). In the first experiment, kittens fed diets that contained only EAA lost weight. Amino acid analysis of plasma showed that the concentration of methionine was 9.1 times that of controls, supporting the premise that the weight loss that occurred was the result of an adverse effect of excess methionine. Also, plasma threonine and arginine were elevated whereas proline and asparagine were very low. In the second experiment, feeding lower concentrations of methionine and arginine in a diet containing only EAA resulted in weight gains and nitrogen retention that were not significantly different from results for kittens fed the control diet (E:T ratio = 0.5). The addition of proline and asparagine to this EAA diet or their removal from the control diet did not improve or reduce weight gain or nitrogen retention. It is concluded that the decreased weight gain found in kittens (and probably other species) fed only EAA is the result of an adverse effect of excesses of methionine and possibly other EAA, and not the inability to synthesize DAA. If excesses of certain EAA are avoided, near-maximal weight gain can be achieved without any DAA in the diet.

Previous work indicates that the essential amino acid requirements for kittens are not positively correlated with the concentration of dietary nitrogen as they are in other species. In the studies presented here, the interaction between graded levels of threonine and dietary crude protein was investigated. Dose-response curves were generated using six 4 x 4 Latin squares. Each square represented one concentration of threonine (4.0, 5.0, 6.0, 7.0, 9.0 or 12.0 g/kg diet) and four concentrations of crude protein (150, 200, 300 and 500 g/kg diet). Food intake, weight gain, nitrogen retention and plasma amino acids were measured. There was no strong positive relationship between the threonine requirement of kittens and dietary crude protein. Increasing crude protein when threonine was limiting in the diet increased growth and food intake under some conditions, whereas under other conditions food intake and growth were decreased in a manner consistent with an amino acid imbalance response. An additional experiment was done to verify some of these findings. The requirement for threonine was found to increase from 5.0 g/kg diet at 150 and 200 g crude protein/kg diet to 6.0 g/kg diet when crude protein was 300 or 500 g/kg diet. The requirement for crude protein in the kitten appears to be between 200 and 300 g/kg diet.

The effect of acid–base status on self-selection of dietary protein was examined in three groups of adult male cats fed 20% soybean-protein and lactalbumin diets formulated to produce acidic, neutral or alkaline status. In two experiments, cats were offered a choice between the 20% protein diets or (1) the same diet with additional protein as casein (49% total crude protein) or (2) the same diet with added soybean-protein and lactalbumin (43% crude protein). Casein contained 0·63 mmol H + /g and caused all three groups to avoid the high casein diets by day 4. The high soybean-protein–lactalbumin diets did not contain added acid but would produce some extra acid upon catabolism of the sulfur-containing amino acids. Again, all three groups avoided the high protein diets by day 4. In a third choice trial, cats adapted to three low protein diets containing appropriate electrolytes to cause neutrality, acidemia or alkalemia, were offered a choice between: neutral vs. acidic; acidic vs. neutral or basic vs. acidic. The cats chose the neutral, neutral and basic diet respectively, restoring or maintaining acid–base homeostasis for each situation. The diets producing acidosis lowered serum sodium and potassium concentrations. We conclude that cats select appropriate diets in an attempt to maintain acid–base homeostasis.

In a crossover design, cats were fed a canned heat-processed diet (18 g dry matter/kg initial body wt) either with (+) or without (-) antibiotics [a mixture of penicillin G, procaine (25 mg/18 g diet) and tetracycline (50 mg/18 g diet)]. The (-/+) group received no antibiotics during the first 5-wk period and received antibiotics during the second 5-wk period; the (+/-) group received the reverse. Plasma, whole blood, urinary and fecal concentrations of taurine, fecal bile acid excretion and cholyltaurine hydrolase activities were measured. Consumption of antibiotics for 5 wk resulted in a lower rate of depletion of plasma taurine. Taurine concentrations decreased more over the first 5 wk in cats in the (-/+) group than in cats in the (+/-) group [from 116 +/- 26 to 26 +/- 6 mumol/L (-/+) and from 109 +/- 6 to 77 +/- 7 mumol/L (+/-) for plasma, and from 546 +/- 8 to 292 +/- 29 mumol/L (-/+) and from 560 +/- 11 to 431 +/- 20 mumol/L (+/-) for whole blood]. Urinary total taurine excretions during the 5th week were 54 mumol/d for the (-/+) group and 135 mumol/d for the (+/-) group (pooled SEM, +/- 13). Fecal total taurine excretions during the 5th week were 184 and 53 mumol/d for the (-/+) and (+/-) groups, respectively, (pooled SEM +/- 9). Most of the fecal taurine was unconjugated (free). Fecal bile acid excretions during the 5th week were 235 +/- 18 and 106 +/- 11 mumol/d for the (-/+) and (+/-) groups, respectively. Dietary antibiotics suppressed fecal cholyltaurine hydrolase activity of cats. Fecal cholyltaurine hydrolase activities during the 5th week were 279 +/- 54 and 42 +/- 10 nmol cholic acid released.min-1.g dry feces-1 in the (-/+) and (+/-) groups, respectively. After the crossover, mean values for the groups were reversed, showing that the observed changes were due to the antibiotic treatment. These results support the hypothesis that the dietary taurine requirement of cats is largely determined by the extent of microbial degradation of taurine in the gastrointestinal tract.

The purpose of this study was to evaluate the use of urinary 3-methylhistidine excretion as an index of in vivo skeletal muscle protein degradation in cats. The criterion for validation was the rapid and quantitative excretion of an intravenously administered dose of radiolabeled 3-methylhistidine (3-methyl-14C). Four adult cats were maintained in individual metabolism cages and allowed free access to a purified diet (43.5% protein) and water for 4 weeks. The cats were then injected intravenously with 740 kBq 3-[14C]methylhistidine dihydrochloride diluted in 1 mL of saline. Twenty-four-hour urine samples were collected for 7 days. Total radioactivity in each urine sample was determined by direct counting. Quench correction was determined by using an external standard. The mean (±SEM) cumulative urinary recovery of 3-[14C]methylhistidine from the four cats was 94.9 ±3.5% at 48 hr following radioisotope injection. The mean (±SEM) cumulative urinary recovery of radioactivity from the four cats was 103.9 ± 2.2% at 7 days following radioisotope administration. There was no detectable radioactivity found in expired CO2 and negligible amounts (mean ± SEM: 0.6 ± 0.5%) in the feces. Chromatography of urinary amino acids and radioactive urine metabolites revealed no significant radioactivity in any other peak besides 3-methylhistidine. Acid hydrolysis of urine resulted in no increase in 3-methylhistidine content or urine, indicating that there is no significant acetylation of 3-methylhistidine in this species. On the basis of these results, 3-methylhistidine does not appear to be metabolized and should therefore be a valid index of in vivo skeletal muscle protein degradation in the cat. Urinary 3-methylhistidine excretion should be useful for studying how nutritional, hormonal, and other physiological or pathological factors cause losses or gains in skeletal muscle protein in this species.

The effects of heat processing (Maillard reaction) and addition of antibiotics to diets on the metabolism of taurine in adult cats were studied. Groups of four cats were given daily 22 g/kg body weight one of four purified diets based on casein and starch. All diets contained the same major ingredients as the control (diet 1), except for starch substitutions. Diet 2 was autoclaved ; in diet 3, 50 g glucose replaced 50 g starch before autoclaving ; in diet 4, only the casein component was autoclaved with 50 g glucose before addition to the diet. Diets were fed for 5 wk, then a mixture of antibiotics was added to all diets and they were fed for a further 5 wk. In the first (no antibiotics) period, cats given the Maillard reaction products (diets 3 and 4) had a significant depletion of plasma and whole blood taurine and had twice the fecal, but less than half the urinary total taurine excretion of control cats. The addition of antibiotics to the diets restored plasma and whole blood concentration in cats given diets 3 and 4, reduced fecal and increased urinary taurine excretion, and decreased fecal cholyltaurine hydrolase activity. These results suggest that Maillard reaction products promote an enteric flora that favors degradation of taurine and decreases recycling of taurine by the enterohepatic route.

The nitrogen requirements of cats during gestation and lactation were determined. Purified diets containing 200, 250, or 300 g protein (N × 6.25)/kg diet, calculated ME = 20 kJ/g) and ≥ 1.5 times the minimal essential amino acid requirement of the growing kitten were fed for ≥ one month before mating and through gestation and lactation. Results during gestation showed that there were no significant differences among treatments in number and size of kittens at birth and suggested that 200 g protein/kg diet was adequate. Treatments had little effect on kitten weight gains at week one or two. By the third week, kitten weight gains were significantly higher for the higher levels of dietary protein. Queens fed the 200 g protein/kg diet had a lower PCV at 6 weeks lactation than queens fed the 250 or 300 g protein/kg diet. Essential amino acid concentrations in plasma at 3 week lactation indicated that two to five of the essential amino acids may have been limiting, even though they were all added in the diet at 1.5 times that of the kitten growth requirement. Results suggest that the protein requirement of the queen during gestation is not greater than 200 g protein/kg diet and the requirement during lactation appears to be between 250 and 300 g protein/kg diet containing 250 g fat/kg diet.

Freshly passed feces were collected from cats (n = 5-7) given cooked and uncooked commercial canned-type diets, casein and soy protein containing purified diets and a commercial extruded diet. The feces were anaerobically cultured in medium containing either taurine, taurocholic acid or [2-3H]taurine for 24 h at 37 degrees C. Taurine degradation in cultures was greatest for cultures from cats receiving diets reputed to cause taurine depletion. Diaminopimelic acid in feces indicated that differences in taurine degradation rate among groups was associated with differences in bacterial numbers in feces. After 6 h of incubation,10% of taurocholate and60% of taurine remained. Nearly all the tritium on the labeled taurine was recovered as water. These results indicate that deconjugation and deamination are the initial steps in microbial catabolism of taurocholic acid and that enteric microbial growth may be a major determinant of dietary taurine requirement of cats.

Despite the lack of precise information on the requirements for many of the nutrients essential for cats and dogs and the paucity of information on the availability of nutrients in foods, many commercial diets support excellent growth, reproduction, and maintenance. However, these diets use empirical information that cannot be readily applied to the formulation of new diets. Progress in companion animal nutrition requires more precise information on requirements for various life stages (especially reproduction and maintenance), along with values for the bioavailability of nutrients in dietary ingredients. There is virtually no information on the bioavailability of nutrients for companion animals in many of the common dietary ingredients used in pet foods. These ingredients are generally byproducts of the meat, poultry and fishing industries, with the potential for wide variation in nutrient composition. Claims of nutritional adequacy of pet foods based on the current Association of American Feed Control Official (AAFCO) nutrient allowances ("profiles") do not give assurances of nutritional adequacy and will not until ingredients are analyzed and bioavailability values are incorporated. The AAFCO feeding test provides a superior method for assessing nutritional adequacy to the profile, although the current protocol has procedural and interpretative limitations.

This study was conducted to determine the effect of excess leucine on the dietary choice of kittens. The basal diets contained 16% (low nitrogen) or 24% (adequate nitrogen) amino acids and were limiting in isoleucine and valine. The addition of leucine to either of these basal diets has been shown to cause a transitory adverse effect on the growth and food intake of kittens. In separate experiments each basal diet was used to test three sets of choices: basal vs. basal + 10% leucine; basal + alanine vs. basal + leucine (isonitrogenous) and basal vs. basal + alanine. When offered basal vs. basal + excess leucine, the kittens chose significantly more of the excess leucine diet regardless of the level of nitrogen in the basal diet. When offered an isonitrogenous choice of excess alanine vs. excess leucine, the kittens selected somewhat more of the excess leucine diets over the excess alanine diets; this selection was sustained longer in kittens fed low nitrogen. In the third choice experiment (basal vs. basal + alanine), the group offered the low nitrogen diets exhibited no preferences, and the group offered adequate-nitrogen diets selected significantly more of the excess alanine diet. These results for kittens are opposite to those for rats, a species that will select a low protein basal or even a protein-free diet over a diet containing excess leucine.

Twelve weanling kittens (6 male and 6 female) were given six purified l -amino acidbased diets for periods of 10 days each in accordance with a 6×6 balanced latin square design. Diets contained either 5.5, 7.0 or 15 g, of either the d -or l -isomer of methionine/kg of diet. Neither food intake nor body weight gains of kittens were significantly different between kittens fed d -and l -methionine diets. Nitrogen retention of female kittens and of male and female kittens combined was significantly greater when fed the l -as compared to the d -methionine diets. When dietary methionine was just under the requirement (7 g/kg diet), weight gain and nitrogen retention of the d methionine group as compared to l -methionine group, respectively was 80% and 73% whereas below and above the requirement, the weight gain and nitrogen retention of the d -methionine groups was 90–106% of that of the L-methionine groups. Total methionine and D-methionine concentrations in plasma were significantly higher after ingestion of the d -than l -methionine diets for combined sexes. Plasma of kittens ingesting the d -methionine diet had 20–30% of the methionine present as d -methionine. Plasma half/cystine and cystathionine were significantly lower for the female and combined sexes after ingestion of the d -as compared to the l -methionine diets. Male kittens also had significantly lower plasma cystathionine after ingesting the d -than the l -methionine diets. The weanling kitten utilizes d -methionine well for growth; but N retention and plasme amino acids indicate that the efficiency of utilization of d -methionine for tissue growth may be lower than that for l -methionine.

Male albino rats, trained to eat over a 3-h period, reduced their food intake from 0·38 ± 0·04 g of a low-protein diet to 0·14 ± 0·03 g of a high-protein diet, within 1 min following diet presentation. Since this occurred before the metabolic effects of a high-protein diet should be seen, we suggest that, although neophobia could play a role, poor initial palatability may be a significant factor in this early depression in food intake. To differentiate initial palatability from responses to metabolic feedback, we designed a feeding paradigm using positive or negative taste cues and a 6-h feeding period. Pre-treatment with a 6% casein diet containing 0·15% quinine HCl resulted in near equal consumption of a 75% casein and a 6% casein unadulterated diet during the first 30 min after introduction of the diets. Later, the rate of consumption of the high-protein diet was lower than of the lower-protein diet, likely the result of post-absorptive factors. We suggest that prevention of the early reduction in food intake due to initial palatability may facilitate study of post-absorptive response(s) to high-protein diets.

The effect of dietary protein source (soybean vs. casein) and taurine status on kinetics of [24-14C] and [taurine-2-3H]taurocholic acid was determined by isotope dilution in 10 adult male cats (six taurine-replete and four taurine-depleted). Taurine-replete cats were fed 1500 mg taurine/kg purified diets containing either 435 g/kg casein (1500 Cas) or soybean protein (1500 Soy) in a crossover design. Taurine-depleted cats were fed the soybean protein diet with no taurine (0 Soy). Specific activity of [14C]- and [3H]taurocholic acid in bile was determined for 6 d following a pulse dose of dual-labeled taurocholic acid. Taurocholic acid pool size was significantly greater in cats when fed the 1500 Soy diet than when fed the 1500 Cas or than in cats fed the 0 Soy diet. Total entry rate, irreversible loss rate and recycling rate of [taurine-2-3H]taurocholic acid and the irreversible loss rate of [24-14C]taurocholic acid tended to be greater in cats when fed the 1500 Soy than the 1500 Cas diet. Irreversible loss rates of taurocholic acid in taurine-replete cats fed the 1500 Soy diet were significantly greater than in taurine-depleted cats, 356 vs. 120 mumol/d [24-14C]taurocholic acid and 445 vs. 56 mumol/d [taurine-2-3H]taurocholic acid. The fraction of taurocholic acid was greater, and the fraction of taurochenodeoxycholic and taurodeoxycholic acids lower in cats when fed the 1500 Soy than when fed the 1500 Cas diet. Taurine-depleted cats had less taurocholic, taurochenodeoxycholic, and taurodeoxycholic acids and greater glycocholic and cholic acids than taurine-replete cats fed the 1500 Soy diet. This study demonstrates that both dietary protein source and taurine status affect taurocholic acid kinetics and bile acid composition in cats.

Dietary selection and intake of a threonine-imbalanced diet were evaluated after increasing the concentration of the dietary limiting amino acid in the prepyriform cortex. Selection against the threonine-imbalanced diet in favor of a protein-free diet was reversed when 2 or 4 nmol threonine was injected bilaterally into the prepyriform cortex. However, intake of the threonine-imbalanced diet was significantly increased only after injection of 2 nmol threonine. The reduced intake of the threonine-imbalanced diet, compared to the basal diet, after injection of 4 nmol threonine was not the result of an excess in the concentration of amino acid (or nitrogen) injected into the PPC because intake of the threonine-basal diet was not reduced when 4 nmol threonine was administered. Intake of the threonine-imbalanced diet was also increased after injection of 2 nmol threonine plus 2 nmol isoleucine but not after injections of 2 nmol isoleucine. The changes in food intake when an imbalanced diet is fed appear to be the result of at least two separable responses: recognition of a diet as having an amino acid imbalance, as indicated by dietary choice, and reduction in food intake. The results of this study indicate that changing the concentration of the dietary limiting amino acid in the prepyriform cortex influenced dietary selection and food intake separately.

The effect of inhibiting protein synthesis within the prepyriform cortex (PPC) on intake of an amino acid imbalanced diet was evaluated in rats receiving bilateral injections of the dietary limiting amino acid (DLAA). Injection of the DLAA into the PPC increased intake of the imbalanced diet by 150% and incorporation of [3H]leucine into the trichloroacetic acid insoluble fraction of PPC homogenates by 248%. Coinjection of puromycin (100 mumol/L) or actinomycin D (10 mumol/L) blocked the increase in intake of the imbalanced diet but had no effect on intake of the basal diet. Puromycin blocked the increase in intake of the imbalanced diet whether injected with the DLAA or 6 h later. Selection of the imbalanced diet over a protein-free diet when the DLAA was administered was blocked by co-injecting puromycin or actinomycin D. The results indicated that the increased intake and the reversal of aversion to the imbalanced diet when the DLAA was injected into the PPC required de novo protein synthesis. The proteins necessary for the feeding response seemed to have a short half-life and seemed to require synthesis of new mRNA. We conclude that changes in concentration of the DLAA within the PPC influenced protein synthesis at the genomic level.

The role of adrenal function in the anorectic response and adaptation of rats to a diet with an isoleucine (Ile) imbalance was investigated. In the first of four experiments, rats were fed a mildly Ile-imbalanced diet after treatment with metyrapone, and inhibitor of glucocorticoid synthesis. In two separate experiments, rats were presented with either a mildly or severely Ile-imbalanced diet (4.93 and 9.86% imbalanced amino acid mixture, respectively) after bilateral adrenalectomy. Finally, the effects of ICS 205-930, a serotonin-3 receptor antagonist, on the intake of mildly Ile-imbalanced diet were tested in adrenalectomized animals. In each experiment a 2 X 2 factorial design was used. Neither metyrapone nor adrenalectomy altered the initial depression in the intake of an imbalanced diet. The adaptation phase in the response of adrenalectomized rats fed a mildly Ile-imbalanced diet was not different from that of controls, but adrenalectomized rats fed severely Ile-imbalanced diets were unable to adapt. Adrenalectomy did not alter the anti-anoretic activity of ICS 205-930 in this model. These results suggest that adrenal hormones are not necessary for the initial anoretic response or adaptation of rats to an Ile-imbalanced diet, nor are they implicated in the anti-anorectic effect of serotonin-3 blockade.

The objective of this study was to determine the fate of a pulse-labeled oral dose of uniformly labeled [14C]taurine in cats fed four separate diets. The diets were a heat-processed commercial diet, the same diet frozen-preserved and two purified diets containing 0 or 1325 mg taurine/kg. The commercial formulations contained 1070 mg taurine/kg dry matter (by analysis). The excretion of 14C in CO2, urine and feces was monitored. Significant quantities of 14CO2 were produced, with greater amounts excreted by cats fed the heat-processed commercial diet (9.4% of initial dose) than by those fed the frozen-preserved diet (0.09%), indicating extensive taurine degradation by the intestinal microflora. Purified diet groups were intermediate between the two commercial diet groups. Carbon-14 excreted in urine peaked at 24 h and was highest for cats fed the frozen-preserved commercial diet or 1325 mg taurine/kg purified diet. Carbon-14 excreted in feces was highest for cats fed the two commercial diet formulations, with peak amounts at 48-72 h. Because the frozen-preserved commercial diet had previously been shown to maintain plasma taurine concentration, whereas the heat-processed diet did not, these results indicate that processing affects the digestive and/or absorptive process in a manner that increases the catabolism of taurine by gastrointestinal microorganisms.

The essential amino acid requirements of several species are affected by the level of dietary nitrogen. In chicks, pigs and rats, individual essential amino acid requirements are positively correlated with the level of dietary nitrogen. Preliminary experiments indicated that this may not be true for the kitten. Growth and nitrogen retention were used to examine the nature of this response in kittens. A comprehensive set of dose response curves were completed using six latin squares. Each square represented one of the following concentrations of dietary methionine3: 0.15, 0.25, 0.35, 0.45, 0.60 or 0.90% and four concentrations of dietary nitrogen: 15, 20, 30 and 50% crude protein. Plasma amino acid concentrations and selected hor mone concentrations (insulin/glucose, cortisol, somatomedin C, T3 and T4) were also measured. When methionine was limiting, increasing dietary nitrogen did not produce an amino acid imbalance, but rather increased weight gains and nitrogen retention in kit tens. The methionine requirement of the kitten was not positively correlated with the level of dietary ni trogen, but instead was similar for each level of dietary nitrogen tested. Plasma methionine concentrations increased with increasing dietary methionine. At di etary methionine concentrations above the require ment of the kitten (0.40%) (2), plasma methionine de creased with increasing dietary nitrogen. At 0.25 and 0.45% dietary methionine, insulin/glucose ratios and cortisol and somatomedin C concentrations were not significantly different between the levels of dietary ni trogen. At 0.25 and 0.45% dietary methionine, total T3 and T4 concentrations increased significantly (P < 0.05) as dietary nitrogen increased. In conclusion, the methionine requirement of kit tens is not positively correlated with the level of di etary nitrogen as it is in other species, but rather it is similar for each level of dietary nitrogen tested. Weight gains and nitrogen retentions increased in kittens fed diets limiting in methionine as dietary nitrogen in creased. The mechanism by which increasing dietary nitrogen increases weight gains and nitrogen reten tions of kittens when methionine is limiting is not yet clear.

Using a continuous recording computerized system, an experiment was conducted to examine the feeding and drinking patterns of the cat. Four diets; 1), dry commerical; 2), canned commercial; 3), casein based purified cats during 8 consecutive 7–10 day periods. Mean daily dry matter intake was greater (P

1. The dynamics of insulin and glucagon secretion by the isolated perfused cat pancreas was studied in response to glucose and amino acid stimuli. 2. Insulin secretion is biphasic in response to either glucose or amino acid stimuli. 3. Glucose caused a much more pronounced first phase release than did a complete amino acid mixture; whereas glucose and the amino acid mixture stimulated late second phase insulin secretion equipotently. 4. The same amino acid mixture produced a biphasic secretion of glucagon characterized by a rapid and transient spike-release which was followed by a substantial, relatively steady-state, second secretory phase. 5. Various combinations of glucose and amino acids resulted in insulin secretion which suggests a simple additive stimuli phenomenon; whereas no such additive effect was observed with respect to amino acid stimulation of glucagon secretion. 6. Instead, various of the amino acids appear to stimulate maximal glucagon secretion independently. 7. Glucose failed to cause a suppression of amino acid induced glucagon release. 8. The quantitative aspects of this study suggest that the cat pancreas is very responsive to amino acid modulation of hormone release, a fact which may well reflect the high amino acid content of the cat's diet.

Bilateral double electrolytic overlapping lesions were placed in dorsal-lateral hippocampus of male 230 g rats, and their food intake responses to the ingestion of diets containing disproportionate amounts of amino acids were examined. Rats with such lesions and intact control rats maintained their normal intakes of the 6% casein basal diet or a threonine basal amino acid diet postoperatively. However, they exhibited marked initial food intake depression, similar to that of intact rats, when fed the threonine imbalanced amino acid diet. Also, animals with lesions in certain areas of the dorsal-lateral hippocampus showed facilitated adaptation to the amino acid imbalanced diet. Similar severe reduction in food intake with relative lack of adaptation were observed in both the intact controls and rats with hippocampal lesions when fed amino acid diets completely devoid of threonine. Initial food intake of rats with hippocampal lesions was inhibited drastically as was the case with the intact controls when fed a 75% casein high protein diet. All rats, either intact or lesioned, showed similar slow adaptation patterns with the prolonged ingestion of the high protein diet. The initial food intake responses and facilitated adaptation of the animals bearing lesions in certain areas of the hippocampus suggest that such areas are not crucially involved in the inhibition of food intake of rats fed disproportionate amounts of dietary amino acids. Rather, such areas of lesions in the hippocampus may play a role in a system governing the behavioral adaptation of the intake of amino acid imbalanced diets but not of diets containing amino acids in general excess. This would also indicate that different mechanisms control the intake of amino acid imbalanced diets and diets containing amino acids in excess.

In order to examine the mechanism of the effect of dietary amino acids on hepatic polysome aggregation and protein synthesis, tRNA charging levels (tRNA acylated with amino acids) were measured in the livers of rats meal-fed (trained to eat for 2 hours/day) a 15% casein diet at the high and low point of polysome aggregation, and of meal-fed and control-fed (ad libitum feeding from 1800 to 0800 hours) rats fed an isoleucine deficient diet. The charging levels of tRNAs for two of the amino acids tested, namely isoleucine and phenylalanine, did not drop with the diurnal changes that occur in polysome aggregation, whereas, the feeding of an isoleucine deficient diet resulted in a 25% decrease in the ile-tRNA charging levels. Although it is not clear how amino acid supply regulates polysome aggregation and protein synthesis, it would not appear to be mediated via a decrease in tRNA charging levels.

The essentiality of dietaryargininewas ex amined in adult humans with three biochemical indices: plasma levels of ammonium and amino acids and urinary orotic acid excretion. Three male and two female subjects participatedin the 10-d study. Subjects consumed an i- amino acid diet containing 0.74 g protein equivalent/kg body weight on d 1-5; these amino acid concentrations were doubled on d 6-10. The diet was devoid of arginine on d 3-8. Daily urine was collected and blood samples were drawn on 6 of the 10 d at 0, 0.5, 1, 2, 3 and 4 h after the breakfastmeal. Whenargininewas removed from the diet, urinaryorotic acid did not increase, in contrast to what has been reportedin most otheranimalspecies tested. Plasma ammonium concentrations remained within nor mal limits throughout the study. A small postprandialde crease in plasma arginineconcentrationwas observedwhen the arginine-deficientdiet was consumed; this decline dis appeared when the diet was resupplied with arginine.The results of this study suggest that over the short term the adulthuman's capacityforde novo argininesynthesis when fed a dietarydeficiencyof arginineis sufficientforthe main tenance of normal cellular metabolism. J. liutr. 117: 1734-1739, 1987.

Previous experiments have demonstrated that cats fed an arginine free purified amino acid diet (-Arg) could be protected from hyperammonemia by the inclusion of ornithine in the diet. Experiments reported here show that diets containing ornithine added at an equimolar (+Orn) or five times equimolar (+5 Orn) to replace arginine in the +Arg basal diet (2.0% Arg . HCl), were incapable of maintenance of body weight. Growing kittens fed a -Arg +Orn and -Arg +5 Orn diets had a daily rate of body weight loss of 6.5 +/- 0.6 and 7.9 +/- 2.2 g, respectively, which is somewhat less than the mean rate of weight loss of kittens fed diets devoid of most of the other amino acids indispensable for the kitten. When citrulline was added to a -Arg diet at an equimolar level to the arginine in the +Arg basal diet, growth rates were equivalent. The mean plasma free ornithine concentration of kittens receiving the -Arg +5 Orn diet was about 33 times higher than when they were fed the +Arg diet. For kittens fed the -Arg + Orn and -Arg +5 Orn diets the mean plasma free arginine was less (but significant only for the -Arg + Orn diet) than that observed for the basal diet. When the -Arg + Cit diet was fed, plasma free arginine concentration was similar and plasma free citrulline was about 18 times higher than when these cats were fed the basal diet.

The dietary potassium requirements of weaning kittens given basal diets containing either a "normal" (33%) or "high" (68%) level of protein were determined. Potassium as KHCO3 was added to give concentrations of 0.1, 0.2, 0.3, and 0.4% for the 33% protein diet and 0.3, 0.4, 0.5, and 0.6% for the 68% protein diet. Excluding the highest concentrations of potassium used, body weight gains within diets were positively and linearly related to potassium concentration. Within both levels of dietary protein, concentration of potassium is plasma was linearly related to dietary potassium; however, for the same dietary potassium concentrations, kittens receiving the high protein diet had lower concentrations of potassium in plasma than kittens given he normal protein diet. Body weight gains were greater for kittens given the 68% protein diets than those receiving the 33% protein diet. The dietary potassium requirements of kittens were estimated as being in the range of 0.3% to 0.5% for 33% and 68% protein diets.

The effect of deleting each of the amino acids known to be essential for the young rat was determined in post weanling kittens fed a purified diet containing only L-amino acids as the source of dietary nitrogen. When any one of the 10 amino acids (arginine, lysine, histidine, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan, valine) were deleted from the diet food intake decreased, the kittens lost weight, and there was a dramatic drop in each corresponding amino acid in the blood plasma; indicating that each of the above amino acids is essential for the kitten. Deletion of all the amino acids except the 10 essential amino acids plus alanine resulted in a decreased weight gain to about 1/3 normal; indicating that although all the other amino acids could be synthesized, one or more of the dispensable amino acids may be required for maximal growth. When any one of the essential amino acids was decreased to one-half that present in the basal diet, there was no decrease in weight gain, indicating that the high protein requirement of the kitten is not the result of an unusually high requirement for the essential amino acids.