Rate Of Amino Acid Catabolism Research Articles

Inhibition of the mTORC1/NF-κB Axis Alters Amino Acid Metabolism in Human Hepatocytes

In addition to serving as the building blocks for protein synthesis, amino acids can be used as an energy source, through catabolism. The transamination, oxidative deamination, and decarboxylation processes that occur during amino acid catabolism are catalyzed by specific enzymes, including aspartate aminotransferase (AST), glutamate dehydrogenase (GDH), glutamic acid decarboxylase (GAD), and ornithine decarboxylase (ODC); however, the overall molecular mechanisms through which amino acid catabolism occurs remain largely unknown. To examine the role of mechanistic target of rapamycin complex 1 (mTORC1) on amino acid catabolism, mTORC1 was inactivated by rapamycin or shRNA targeting Raptor, versus activated by overexpressing Rheb or amino acids in human hepatocytes. The expression of amino acid catabolic genes and related transcription factor was investigated by RT/real-time PCR and western blot analysis. A few types of amino acid metabolite were examined by ELISA and HPLC analysis. The data showed that inactivated mTORC1 resulted in inhibition of NF-κB and the expression of AST, GDH, GAD, and ODC, whereas activated mTORC1 enhanced NF-κB activation and the expression levels of the catabolism-associated genes. Further, inhibition of NF-κB reduced the expression levels of AST, GDH, GAD, and ODC. mTORC1 upregulated NF-κB activation and the expression of AST and ODC in response to glutamate and ornithine treatments, whereas rapamycin inhibited the utilization of glutamate and ornithine in hepatocytes. Taken together, these results indicated that the mTORC1/NF-κB axis modulates the rate of amino acid catabolism by regulating the expression of key catabolic enzymes in hepatocytes.

Upregulation of Glucose Production by Increased Dietary Protein in the Adult Cat (Felis catus)

Domestic cats are strict carnivores with a high requirement for protein, from which they derive their energy and glucose needs. Shuttling of amino acid carbon through glucose may also increase utilization of amino acids that are normally oxidized as protein intake increases. The objective of this study was to measure the effect of dietary protein intake on endogenous glucose production in the cat. Eighteen cats from the colony at the Centre for Feline Nutrition at Massey University were fed one of three low carbohydrate diets containing 15, 45, or 65% of their metabolizable energy as crude protein. After 3 weeks, cats were administered a primed continuous infusion of [U‐13C] glucose for 5 hours and blood was sampled. Mass isotopomer distribution analysis of plasma glucose was used to determine glucose production. Endogenous glucose production from all sources was 1.2‐ and 1.3‐times greater in cats fed 45 and 65% crude protein compared to those fed 15% crude protein (P < 0.05). Contribution of the Cori cycle to gluconeogenesis was not different among diets and averaged 32.6 ± 1.41%, whereas non‐Cori cycle flux of endogenous glucose production (net gluconeogenesis) was greater in cats fed 45 and 65% (1.92 vs 2.29 and 2.47 g glucose × kg BW−1 × d−1, P < 0.05). Increased gluconeogenesis in cats fed high protein diets suggests that part of the increased rate of amino acid catabolism and oxidation in these cats is the result of increased amino acid carbon cycling through glucose.Support or Funding InformationResearch funding was provided by the Animals and Society Research Fund, BRCSRA.

The role of host cell physiology in the productivity of the baculovirus-insect cell system: Fluxome analysis of Trichoplusia ni and Spodoptera frugiperda cell lines.

The Insect Cell-Baculovirus Expression Vector System (IC-BEVS) is broadly used for the production of recombinant proteins and vaccine manufacture, yet the host physiological aspects that contribute to productivity are to be disclosed. This work provides the first quantitative analysis of the metabolic fluxes of High Five cells. This analysis was conducted in comparison with Sf9 cells, another major host for biologicals production via BEVS. Moreover, herein is presented, for the first time, quantitative data of the relative contribution of sugars and amino acids catabolism to the activity of the TCA cycle in Sf9 and High Five cells. High Five cells metabolic activity was markedly influenced by the amino acids concentration in culture medium, which determine the rates of amino acid catabolism, carbon overflow and by-product formation. This characteristic of High Five cells was reflected in the activities of anaplerotic metabolism and the TCA cycle, which may not work as a true cycle as a function of medium composition. This was not the case for Sf9 cells, in which the glucose carbon incorporation in the TCA cycle was significantly higher and lactate production minor. Following infection, the decrease in by-product accumulation rates was accompanied by an increase in net ATP synthesis in Sf9 and High Five cells, although through distinct mechanisms cell-line dependent. The impact of baculovirus infection on cellular metabolic status highlights the capacity of this virus to re-direct the cellular fluxome toward ATP production to support replication and progeny generation. These results pave the way to deepen our knowledge on the relationship between a host cell and the virus, contributing to disclosing the metabolic determinants that contribute to productivity. Biotechnol. Bioeng. 2017;114: 674-684. © 2016 Wiley Periodicals, Inc.

Shifting Patterns of Nitrogen Excretion and Amino Acid Catabolism Capacity during the Life Cycle of the Sea Lamprey (Petromyzon marinus)

The jawless fish, the sea lamprey (Petromyzon marinus), spends part of its life as a burrow-dwelling, suspension-feeding larva (ammocoete) before undergoing a metamorphosis into a free swimming, parasitic juvenile that feeds on the blood of fishes. We predicted that animals in this juvenile, parasitic stage have a great capacity for catabolizing amino acids when large quantities of protein-rich blood are ingested. The sixfold to 20-fold greater ammonia excretion rates (J(Amm)) in postmetamorphic (nonfeeding) and parasitic lampreys compared with ammocoetes suggested that basal rates of amino acid catabolism increased following metamorphosis. This was likely due to a greater basal amino acid catabolizing capacity in which there was a sixfold higher hepatic glutamate dehydrogenase (GDH) activity in parasitic lampreys compared with ammocoetes. Immunoblotting also revealed that GDH quantity was 10-fold and threefold greater in parasitic lampreys than in ammocoetes and upstream migrant lampreys, respectively. Higher hepatic alanine and aspartate aminotransferase activities in the parasitic lampreys also suggested an enhanced amino acid catabolizing capacity in this life stage. In contrast to parasitic lampreys, the twofold larger free amino acid pool in the muscle of upstream migrant lampreys confirmed that this period of natural starvation is accompanied by a prominent proteolysis. Carbamoyl phosphate synthetase III was detected at low levels in the liver of parasitic and upstream migrant lampreys, but there was no evidence of extrahepatic (muscle, intestine) urea production via the ornithine urea cycle. However, detection of arginase activity and high concentrations of arginine in the liver at all life stages examined infers that arginine hydrolysis is an important source of urea. We conclude that metamorphosis is accompanied by a metabolic reorganization that increases the capacity of parasitic sea lampreys to catabolize intermittently large amino acid loads arising from the ingestion of protein rich blood from their prey/hosts. The subsequent generation of energy-rich carbon skeletons can then be oxidized or retained for glycogen and fatty acid synthesis, which are essential fuels for the upstream migratory and spawning phases of the sea lamprey's life cycle.

Early myocardial dysfunction in the diabetic heart: current research and clinical applications

Patients with diabetes mellitus have a high incidence of heart failure, which contributes significantly to their increased cardiovascular morbidity and mortality. One of the major complications of diabetes is the development of cardiomyopathy, a condition characterized by defects of contractile function in the absence of significant coronary artery disease or systemic hypertension. Experimental data in animal models show that contractile depression begins as early as 1 week after induction of diabetes, and the dysfunction is related to an isomyosin distribution shift from V 1 with high adenosine triphosphatase (ATPase) to V 3 with low ATPase activity. Moreover, diabetes is associated with an increased or poorly regulated rate of amino acid catabolism at the cardiac level. Abnormal responses to acute left ventricular (LV) overload induced by exercise (isometric or isotonic) have been demonstrated in patients with diabetes. Impaired augmentation of LV ejection fraction occurs in up to 40% of patients with diabetes. Analysis of the LV afterload-pump function (LV circumferential wall stress-ejection fraction) relationship shows that defective contractile recruitment is the main cause of this anomaly. Exercise-induced LV dysfunction may be the first manifestation of cardiac involvement in patients with diabetes. Increasing the supply of amino acids in addition to conventional therapy significantly attenuates this phenomenon. Although the precise underlying pathophysiologic mechanism is not completely known, these observations may eventually be important in designing an optimal dietary or supplemental approach for patients with diabetes in order to prevent progressive myocardial dysfunction.

Early myocardial dysfunction in the diabetic heart: current research and clinical applications

Patients with diabetes mellitus have a high incidence of heart failure, which contributes significantly to their increased cardiovascular morbidity and mortality. One of the major complications of diabetes is the development of cardiomyopathy, a condition characterized by defects of contractile function in the absence of significant coronary artery disease or systemic hypertension. Experimental data in animal models show that contractile depression begins as early as 1 week after induction of diabetes, and the dysfunction is related to an isomyosin distribution shift from V1 with high adenosine triphosphatase (ATPase) to V3 with low ATPase activity. Moreover, diabetes is associated with an increased or poorly regulated rate of amino acid catabolism at the cardiac level. Abnormal responses to acute left ventricular (LV) overload induced by exercise (isometric or isotonic) have been demonstrated in patients with diabetes. Impaired augmentation of LV ejection fraction occurs in up to 40% of patients with diabetes. Analysis of the LV afterload-pump function (LV circumferential wall stress-ejection fraction) relationship shows that defective contractile recruitment is the main cause of this anomaly. Exercise-induced LV dysfunction may be the first manifestation of cardiac involvement in patients with diabetes. Increasing the supply of amino acids in addition to conventional therapy significantly attenuates this phenomenon. Although the precise underlying pathophysiologic mechanism is not completely known, these observations may eventually be important in designing an optimal dietary or supplemental approach for patients with diabetes in order to prevent progressive myocardial dysfunction.

Ammonia toxicity in fish

Ammonia is present in the aquatic environment due to agricultural run-off and decomposition of biological waste. Ammonia is toxic to all vertebrates causing convulsions, coma and death, probably because elevated NH 4 + displaces K + and depolarizes neurons, causing activation of NMDA type glutamate receptor, which leads to an influx of excessive Ca 2+ and subsequent cell death in the central nervous system. Present ammonia criteria for aquatic systems are based on toxicity tests carried out on, starved, resting, non-stressed fish. This is doubly inappropriate. During exhaustive exercise and stress, fish increase ammonia production and are more sensitive to external ammonia. Present criteria do not protect swimming fish. Fish have strategies to protect them from the ammonia pulse following feeding, and this also protects them from increases in external ammonia, as a result starved fish are more sensitive to external ammonia than fed fish. There are a number of fish species that can tolerate high environmental ammonia. Glutamine formation is an important ammonia detoxification strategy in the brain of fish, especially after feeding. Detoxification of ammonia to urea has also been observed in elasmobranches and some teleosts. Reduction in the rate of proteolysis and the rate of amino acid catabolism, which results in a decrease in ammonia production, may be another strategy to reduce ammonia toxicity. The weather loach volatilizes NH 3, and the mudskipper, P. schlosseri, utilizes yet another unique strategy, it actively pumps NH 4 + out of the body.

Ammonia functions as a regulatory molecule to mediate adjustments in glomerular filtration rate in response to changes in metabolic rate

In mammals, varying in size from mouse to elephant there is a close linkage between metabolic rate (MR) and glomerular filtration rate (GFR). This linkage has evolved because of the necessity to excrete nitrogenous wastes generated predominately by amino acid catabolism. A similar linkage is observed in birds, reptiles and fish, although in the latter vertebrate group gill excretion rate and GFR need to be considered as an interdependent co-ordinated system. A change in the rate of amino acid catabolism will result in a change in the rate of production of nitrogenous wastes requiring excretion and hence GFR (or GFR plus gill excretory rate in fish) must be appropriately re-set. It is hypothesized that ammonia functions as a regulatory molecule to mediate adjustments in excretory rate (GFR or GFR plus gill excretory rate) in response to such changes in amino acid catabolism.

Free amino acids and osmoregulation in the intertidal pulmonate Onchidium tumidium

The aim of this study is to elucidate the osmoregulatory capabilities of the intertidal pulmonate Onchidium tumidium. Our results indicate that O. tumidium could tolerate hyperosmotic stress more effectively than hypoosmotic stress. In 10% seawater (SW), it was capable of maintaining its plasma hyperosmotic and hyperionic to the external medium. However, it rapidly gained weight in 10% SW, and no restoration of body weight was observed. In contrast, in 90% SW it was able to recover its body weight partially. In a hyperosmotic medium, accumulation of intracellular free amino acids (FAA) was responsible for cell volume regulation. The accumulated FAA might originate from protein catabolism, which occurred in the internal organs (IO). In contrast, the relatively smaller amination:deamination ratio of glutamate dehydrogenase in the body wall (BW) and IO of specimens exposed to hypoosmotic stress might lead to a higher rate of amino acid catabolism. This was supported by the greater ammonia contents in the BW and IO of, and higher rate of ammonia excretion by, specimens exposed to 10% SW.

Estimation of Urea Production Rate With [15N2]Urea and [13C]Urea to Measure Catabolic Rates in Diabetes Mellitus

For verifying catabolic states in insulin-dependent patients and dogs the method estimating urea production rates with 13C and with doubly 15N labeled urea, respectively, has been established. For a fast steady state of urea tracer dilution, a prime of 600 times the continuous infusion rate had to be injected. Urea was isolated from plasma samples by protein precipitation and cation exchange chromatography with a consecutive derivatization of the dried urea fraction (trimethylsilyl derivatives). The masses of the fragment ions m/z 189 (14N14N), 190 (14N15N) and 191 (15N15N) urea are monitored to estimate the [15N2]urea frequency in the overall body urea pool in mol percent excess (MPE). 1 to 15 ng of derivatized urea were measured efficiently. An excellent correlation between expected standard and measured MPE (r = 0.9977) was achieved from solutions containing 1 to 7% [15N2]urea. The interassay coefficient of variation amounted to < 10% for a [15N2]urea portion of ≥ 3%. Normoglycemic diabetic patients who were treated with insulin overnight showed significantly higher urea production compared to healthy controls (9.22 ± 2.07 vs. 5.4 ± 0.32 μmol·kg−1 · min−1; p < 0.05). Measurements in chronic diabetic dogs proved an increased rate of amino acid catabolism (+ 20% urea production) in systemic versus portal application of insulin in paired studies. This increased nitrogen load in diabetics may accelerate progression of diabetic nephropathy. - Thus, the established stable isotope technique may serve as a sensitive and useful indicator of amino acid catabolism in clinical and experimental research.

Are dietary protein requirements altered in diabetes mellitus?

Authorities in the United States and Canada have recently advised persons with diabetes to limit their protein intake to the level recommended for normal adults, and consider further reductions in the presence of incipient renal disease. This recommendation ignores metabolic data indicating that conventional insulin therapy fails to fully normalize the abnormal protein metabolism characteristic of untreated diabetes. The residual abnormality is an increased or poorly regulated rate of amino acid catabolism. It is proposed in this review that the large amount of protein in the customary diet compensates for this increased amino acid catabolism, and thus protects many diabetic individuals from protein malnutrition. If this is true, protein restriction to a level that still meets the requirement of an individual with normal insulin metabolism could be too little for someone with diabetes. The current assumption that the protein requirement in diabetes is equal to the value set for normal individuals should be reconsidered.

Protein requirements of adults from an evolutionary perspective

It is argued that the observed minimum needs for protein and individual amino acids by adult humans and animals may merely reflect the diet that their predecessors consumed in the course of their evolution. The ability to adapt to diets with a lower proportion of protein than was ever encountered in practice would have given no competitive advantage. This can explain the limited ability to reduce rates of amino acid catabolism. The protein requirement of domestic cats, obligate carnivores, corresponds to approximately 20% of their energy requirement. Humans adapt to lower levels (approximately 6%). Some urge that higher protein intakes, resulting in higher rates of protein synthesis and turnover, are desirable and that, in general, the more prosperous and successful groups eat more protein. But cause and effect may be reversed. Are higher rates of turnover and catabolism necessarily beneficial? Objective data are still not available.

Efflux and accumulation of amino nitrogen in relation to the volume of rat renal inner medullary cells exposed to media of variable osmolality

The rate of efflux of 2-amino[ 14C]isobutyric acid (AIB) from pre-loaded slices of rat renal inner medulla has been followed during incubation in media whose osmolality was varied between 350 and 2500 mosmol/kg H 2O by adjustment of NaCl and urea concentrations. Efflux was biphasic, and it was assumed that the second, slower phase represented mainly cellular loss of AIB. As a function of cell volume (water content) the mean net rate of 2nd phase efflux declined far more abruptly (−36%) during an increase in external osmolality from 350 to 720 mosmol/kg than during further increase to 2500 mosmol/kg, over which range the rate of efflux fell by only a further 12%. Conversely, relative decrements of steady-state cell water contents during these two transitions were −17% and −37%, respectively. It is probable that in strongly hyperosmolal media (above 720 mosmol/kg) reduction in the rate of amino acid catabolism, with resultant cellular accumulation, becomes more important than passive efflux as a determinant of cell amino nitrogen content, and that this is caused by the enzyme-destabilizing effect of high intracellular concentrations of permeant urea. This interpretation is supported by the finding in the present study that trimethylamine N-oxide, which is known to counteract the destabilzing effect of urea, completely inhibited the accumulation of amino nitrogen (ninhydrin-positive substances) in media stronger than 720 mosmol/kg, as well as leading to further reduction of steady-state cell water contents, but was without effect on either variable in more dilute media. It is proposed that, under the conditions of this investigation, amino acids contribute to cell volume maintenance mainly by efflux and by metabolic accumulation under mildly and strongly hyperosmolal conditions, respectively, and that this interpretation is consistent with recent findings on the fluctuations in medullary levels of Na +, urea and total amino nitrogen in the intact kidneys of rats during acute water diuresis and oliguria (Law, R.O. (1991) Pflügers Arch. 418, 442–446).

Effect of Exercise on Amino Acid Concentrations in Skeletal Muscle and Plasma

Protein is not normally an important energy fuel for exercising muscle. In spite of this, there is a significant increase in the rate of amino acid catabolism during exercise. This is secondary to the exercise-induced increase in several metabolic processes, such as hepatic gluconeogenesis and the citric acid cycle, where amino acid carbon is utilized. The suppression of protein synthesis during an exercise bout leaves amino acids available for catabolism. There is some evidence that basal amino acid concentrations in plasma and muscle may be higher in trained than in untrained individuals. In the rat, the concentration of free amino acids is higher in slow-twitch than in fast-twitch muscles. With short-term exercise, the transamination of glutamate by alanine aminotransferase leads to increased levels of alanine in muscle and plasma, and an increased release of alanine from the muscle. At the same time, the muscle and plasma glutamate concentrations are markedly decreased. The plasma glutamine level is elevated with short-term exercise, but changes in muscle glutamine concentration are more variable. With prolonged exercise, there is a depletion of the plasma amino acid pool, which may be explained by an increased consumption in organs other than muscle. With the exception of alanine, we found, however, that the muscle levels of free amino acids are kept stable throughout a 3.5-h exercise period. There is a significant activation of branched-chain amino acid metabolism with prolonged exercise, and the current data indicate that this is more pronounced in endurance-trained subjects than in untrained controls.

Nitrogen excretion and O:N ratios in reef corals: Evidence for conservation of nitrogen

Rates of ammonia excretion, and respiration to excretion (atomic O:N) ratios were measured for three species of scleractinian coral from the Bahamas, during August 1986 and March 1987, to test the hypothesis that zooxanthellate reef species have lower rates of amino acid catabolism and higher dependence on lipid and carbohydrate catabolism than nonzooxanthellate species. Freshly collected individuals of two reef species,Montastrea annularis andAcropora cervicornis, have significantly lower mean ammonia excretion rates [51 ± 66 nmol (mg-at N)−1 h−1 and 192 ± 172 nmol (mg-at N)−1 h−1, respectively] than those of the tropical nonzooxanthellate speciesTubastrea coccinea [257 ± 68 nmol (mg-at N)−1 h−1]. The temperate nonzooxanthellate coralAstrangia poculata has mean excretion rates [632 ± 242 nmol (mg-at N)−1 h−1] which are much higher than those of all three tropical species. O:N ratios for the two reef species were generally greater than 300, while those of the nonzooxanthellate species ranged from 17 to 39 forT. coccinea and from 8 to 12 forA. poculata. The two reef species conserve nitrogen by having relatively low rates of amino acid catabolism, and support most of their metabolic needs by catabolizing the lipids and carbohydrates they receive from their zooxanthellae. The tropical nonzooxanthellate species has lower rates of ammonia excretion and respiration, and higher O:N ratios than the temperate nonzooxanthellate coral, which may be an indication that the former has less food available to it. The ammonia production rates of the reef species would support doubling times (growth rates) of the zooxanthellae of 13 to 22 d. These growth rates agree with observed rates obtained by mitotic index methods, and with suggestions that growth of zooxanthellae within many corals may be nitrogen-limited.

Rate of whole-body protein synthesis in the rat as calculated from fractional oxidation of leucine, valine, or methionine

In the steady state, the ratio of the rate of utilization for whole-body protein synthesis of any essential amino acid to its rate of oxidation should be the same as the ratio of the peak fraction of a dose of tracer incorporated into protein (F) to the fraction oxidized (1-F) provided that negligible tracer remains in the free amino acid pool or remains unabsorbed in the gut. The total rate of amino acid catabolism (C) can be estimated from the rate of urinary excretion of urea nitrogen (N) plus ammonia N. Hence the rate of whole-body protein synthesis (S) can be estimated as CF (1 − F) . This method, which is not new, was explored as follows: (1) Radioactivity in the leucine of whole-body protein of rats after intravenous (IV) injection of labeled leucine was shown to plateau from three to nine hours. (2) The fractions of labeled leucine, valine, and methionine remaining in the gut six hours after enteral injection were 1.2 ± 0.4% (SD), 1.2 ± 0.4%, and 7.1 ± 2.9%, respectively; thus, enterally administered methionine cannot be used for this purpose. (3) Oxidation of [1- 14C]-labeled leucine or valine, measured from 14CO 2 excretion, was found to be the same whether these isotopes were given IV or enterally. (4) Negligible radioactivity remained in the free leucine of plasma within one hour after injection of labeled leucine. (5) The rates of whole-body protein synthesis, estimated from cumulative 14CO 2 excretion for six hours after enteral or IV injection of [1- 14C]-labeled leucine or valine, or after IV injection of [1- 14C]-labeled methionine did not differ from one another by more than 7%. Mean S was 73 mg 100 g body wt/h . These results support the validity of this technique for determining whole-body protein synthesis.

Dynamic models for the transport of various substances in the placenta

The rate of efflux of 2-amino[14C]isobutyric acid (AIB) from pre-loaded slices of rat renal inner medulla has been followed during incubation in media whose osmolality was varied between 350 and 2500 mosmol/kg H2O by adjustment of NaCl and urea concentrations. Efflux was biphasic, and it was assumed that the second, slower phase represented mainly cellular loss of AIB. As a function of cell volume (water content) the mean net rate of 2nd phase efflux declined far more abruptly (−36%) during an increase in external osmolality from 350 to 720 mosmol/kg than during further increase to 2500 mosmol/kg, over which range the rate of efflux fell by only a further 12%. Conversely, relative decrements of steady-state cell water contents during these two transitions were −17% and −37%, respectively. It is probable that in strongly hyperosmolal media (above 720 mosmol/kg) reduction in the rate of amino acid catabolism, with resultant cellular accumulation, becomes more important than passive efflux as a determinant of cell amino nitrogen content, and that this is caused by the enzyme-destabilizing effect of high intracellular concentrations of permeant urea. This interpretation is supported by the finding in the present study that trimethylamine N-oxide, which is known to counteract the destabilzing effect of urea, completely inhibited the accumulation of amino nitrogen (ninhydrin-positive substances) in media stronger than 720 mosmol/kg, as well as leading to further reduction of steady-state cell water contents, but was without effect on either variable in more dilute media. It is proposed that, under the conditions of this investigation, amino acids contribute to cell volume maintenance mainly by efflux and by metabolic accumulation under mildly and strongly hyperosmolal conditions, respectively, and that this interpretation is consistent with recent findings on the fluctuations in medullary levels of Na+, urea and total amino nitrogen in the intact kidneys of rats during acute water diuresis and oliguria (Law, R.O. (1991) Pflügers Arch. 418, 442–446).

Effects of protein anabolic hormones on rates of protein degradation and protein loss in the fasting dog.

NITROGEN storage induced in the adult female dog with either growth hormone (Bartlett and Gaebler, 1952) or testosterone propionate (Bartlett, 1953) is characterized by a higher rate of protein synthesis and a lower rate of amino acid catabolism than is observed in the same animal during nitrogen balance. The size of the nitrogen pool is increased during nitrogen storage induced with growth hormone (Bartlett and Gaebler, 1952) and is unaffected by testosterone propionate (Bartlett, 1953). Administration of growth hormone plus testosterone propionate induced marked nitrogen storage and gain in body weight in the adult female dog, yet produced no change in the rate of protein synthesis, decreased the rate of amino acid catabolism, and decreased the size of the nitrogen pool (Bartlett, 1953). This latter finding, which seemed of particular interest, was interpreted as being due to a decreased rate of protein degradation. In order to test this interpretation, we have extended our studies to the fasting animal.