Methionine deficiency decreases protein accretion and synthesis but not tRNA acylation in muscles of chicks

The effect of supplementing a methionine-deficient, isolated soy protein diet (0.5% total sulfur amino acids) with 0.2% D,L-methionine (DL-MET) or a molar equivalent of D,L-2-hydroxy-4-(methylthio) butanoic acid (DL-HMB) was assessed in chicks over an 8-d feeding study. Chicks consumed DL-HMB diet ad libitum (HIGH) or were restricted to the level consumed ad libitum by chicks fed the basal diet. The DL-MET diet was fed at the same two levels as the DL-HMB diet. Supplementing with either methionine source resulted in significantly greater growth rate, efficiency of feed conversion, and accretion and synthesis of protein in the gastrocnemius and pectoralis muscles. These increases were greater for chicks consuming feed ad libitum as compared with feed-restricted chicks and were not affected by methionine source. Rate of muscle protein degradation appeared to increase with supplementation of either methionine source, but only when feed intake was permitted to increase. The relative in vivo conversion of DL-HMB vs. D-MET to L-MET was similar in all groups as indicated by pool sizes of methionine, tRNA(met), and tRNA(cys), and rates of protein accretion and synthesis. These data demonstrate that dietary DL-HMB and DL-MET are used with similar efficacy to support skeletal muscle protein accretion and rates of protein synthesis when feed intake is equalized.

Identification of porcine sperm plasma membrane proteins that may play a role in sperm-egg fusion

Sperm plasma membrane (PM) proteins that demonstrate affinity for egg PM preparations have the potential to be biologically important during sperm-egg binding and/or fusion. In this study four such proteins have been identified. To provide quantitative evidence for possible biological function, the large natural variation among different porcine sperm populations with regard to their ability to interact with the egg was compared with the relative binding of egg PM material to individual proteins. An aliquot from each of 24 porcine ejaculates was evaluated by the zona-free hamster ova bioassay and the remainder processed to yield sperm PM vesicles. Aliquots of sperm PM were solubilised, separated by SDS-PAGE, western blotted and probed with partially purified, biotinylated egg PM protein. Bound egg PM proteins were visualised on western blots by an avidin/biotin/horseradish peroxidase system and analysed by scanning laser densitometry. Four sperm PM proteins (62, 39, 27 and 7 kDa estimated molecular mass) were the predominant binders of egg PM. The amount of egg PM bound to the 62 kDa protein was significantly correlated with the ability of sperm from the 24 ejaculates to penetrate zona-free hamster ova (percentage of ova penetrated, p = 0.01, R = 0.65; number of penetrated sperm per ovum, p = 0.02, R = 0.63).

Free and total ion concentrations in pig digesta

Mineral bioavailability is related to the activity of the free ion or small-ligand metal ion complexes present in gastrointestinal (GI) tract digesta. Therefore, it is necessary to distinguish between total ion and free-ion/small-ligand complexes (referred to simply as "free") concentrations. Free and total cation concentration in pig digesta from various GI locations were determined. Free ions were operationally defined as those that passed through a 1,000 molecular weight cutoff filter. To test the effect of dietary supplementation on free ion concentrations, pigs were fed either basal diets of corn bran, corn grits, and soybean meal (10, 67, and 20 weight percent, respectively) or basal diets containing added Ca, Zn, Fe, and Cu. In addition, the Ca and K content of corn bran fragments retrieved from digesta was determined by energy dispersive x-ray analysis to examine whether this dietary fiber preferentially absorbed minerals, thus reducing mineral bioavailability. Free cation concentrations, expressed as a percentage of the total, averaged over all locations for both diets were: Na, 86%; K, 96%; Ca, 11%; Mg, 40%; Zn, 5%; Fe, 4%; and Cu, 11%. For Ca, Mg, Zn, and Cu, the free:total cation concentration ratios differed (P < .05) between upper and lower GI tract. Mineral supplementation did not alter free:total ratios of any ion in the GI tract. For supplemented diets, mineral concentrations generally were higher throughout the GI tract, as were concentrations of free Ca. Free concentrations of Zn and Cu in the jejunum and ileum were higher (P < .01) with supplemented diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of insulin-like growth factor-I and binding protein-3 expression in oMtla-oGH transgenic mice

Growth hormone (GH)-transgenic mice provide a model for studying hormonal regulation of gene products responsible for efficient lean growth. Insulin-like growth factor-I (IGF-I) and IGF binding protein-3 (BP-3) are two products involved in mediating the growth promoting actions of GH. Mice carrying the ovine metallothionein la-ovine growth hormone (oMtla-oGH) transgene were used to study GH regulation of IGF-I and BP-3 expression because these mice do not exhibit elevated basal oGH levels without transgene stimulation by exogenous zinc. C57B1/6XCBA mice with (transgenic = TG) and without control = C) the oMtla-oGH transgene were activated (+ Zn) or inactivated (-Zn) by the addition or removal of 25 mM zinc sulfate in the drinking water. Plasma IGF-I and BP-3 levels were determined by radioimmunoassay and western ligand blotting, respectively. Hepatic IGF-I and BP-3 mRNA levels were determined by slot-blot analysis. TG+Zn mice had higher plasma IGF-I (p < 0.05) and hepatic IGF-I mRNA (p < 0.05) levels as compared to TG-Zn, C+Zn and C-Zn mice. Plasma IGF-I and hepatic IGF-I mRNA levels in TG-Zn mice were not different from C+Zn and C-Zn mice. Removal of Zn decreased hepatic IGF-I mRNA levels to C levels in TG mice. Plasma BP-3 and hepatic BP-3 mRNA levels in TG+Zn mice were increased (p < 0.05) as compared to TG-Zn, C-Zn and C+Zn. Plasma BP-3 and hepatic BP-3 mRNA levels did not differ between TG-Zn, C-Zn and C+Zn mice. Expression of the transgene also increased the level of plasma BP-3 during pregnancy as compared to that observed for pregnant C mice. We conclude that oGH regulates IGF-I and BP-3 expression in the oMtla-oGH transgenic mouse model system.

Dietary energy source and density modulate the expression of immunologic stress in chicks

To determine how dietary energy level and source influence feed intake, growth and energy partitioning drug immunologic stress, growing chicks were fed diets based on cornstarch and casein with varying energy densities and injected every other day for 6 d with either saline (control), Salmonella typhimurium lipopolysaccharide or heat-killed Staphylococcus aureus. Salmonella typhimurium lipopolysaccharide decreased growth and feed consumption at low energy densities. When the dietary energy density was increased above 13.4 kJ/g using cornstarch, but not corn oil, the growth depressing effect of immunogens was eliminated. Immunologically stressed chicks had a greater proportion of gain in visceral organs and less in the carcass, regardless of the nutrient density of the diet. Immunologic stress decreased intake of metabolizable energy of chicks fed a diet with low nutrient density and increased it for those fed a diet with high nutrient density. Chicks injected with S. typhimurium lipopolysaccharide lost more energy as heat than controls when differences in metabolizable energy intakes were accounted for and modified their preference between two diets differing in metabolizable energy density and fat content as a result of the challenge. Control chicks selected between the 11.7 and 14.2 kJ/g diets to obtain an energy density of 13.2 kJ/g compared with 12.5 kJ/g in the S. typhimurium lipopolysaccharide-challenged chicks. The S. typhimurium lipopolysaccharide-challenged chicks consumed similar amounts of the low energy diet but decreased intake of the high energy diet.

Source of amino acids for tRNA acylation. Implications for measurement of protein synthesis

Estimates of protein-synthesis rates using radioisotopes require accurate measurement of the specific radioactivity of the label in protein and in the precursor pool over time. Although the extracellular and intracellular pools of amino acids are easiest to sample, the tRNA pool is the direct precursor and is the appropriate pool for sampling. To test if the intracellular or extracellular pools reflect the tRNA specific radioactivity, a chicken macrophage cell line was incubated in medium containing either 0.23 mM-leucine and 14.5 microCi of [3H]leucine (tracer dose) or 2.3 microM-leucine plus 145.0 microCi of [3H]leucine (flooding dose). At both leucine levels, the tRNA specific radioactivity reached a plateau quickly, but did not equilibrate with either the extracellular or intracellular specific radioactivity within 30 min, and remained closer to that of protein. In a second experiment, proteins in chicken macrophages were labelled with [3H]leucine for 2 days. Labelling medium was removed, and the cells were washed free of residual free [3H]leucine and incubated with medium containing either 0.23 mM- or 2.3 mM-leucine (unlabelled). The specific radioactivity of leucyl-tRNA leucine reached a plateau within 2 min and remained considerably closer to that in the protein than that in intracellular or extracellular pools for at least 60 min. These results suggest that amino acids from protein degradation are a primary source for charging tRNA. When protein-synthesis rates are estimated by label incorporation, use of extracellular or intracellular specific-radioactivity values result in a marked underestimation.

Effects of somatotropin and substrates on patterns of liver metabolism in lactating dairy cattle

Objectives of this study were to quantitate metabolite fluxes in ruminant liver and to delineate effects of recombinant bST on patterns of nutrient metabolism by liver. Nineteen multiparous cows ranging in previous lactational performance from 6400 to 13,500 kg per 305-d lactation were treated with either placebo or bST (40 mg/d) from wk 11 to 18 of lactation. Liver tissue was collected at slaughter. Tissue slices were incubated with various 14C-labeled substrates, and rates of conversion of label to CO2 and metabolites were measured. In vivo recombinant bST treatment increased in vitro conversion of [1-14C]propionate and [2-14C]acetate to glucose more than twofold. At 2.5 mM propionate, bST-treated cows converted propionate to glucose at 90% efficiency. Recombinant bST increased [14C]bicarbonate incorporation into glucose five-fold. Overall, bST treatment resulted in greater C flow from propionate and acetate through the TCA cycle. Acetate had only small effects on propionate metabolism and no effects on lactate plus pyruvate metabolism. Unexpectedly, propionate decreased acetate conversion to ketone bodies. Suggested mechanisms for this observation include depletion of coenzyme A and allosteric regulation of carnitine palmitoyltransferase I by methylmalonyl-coenzyme A formed from propionate. In summary, bST treatment resulted in increased rates of gluconeogenesis and oxidation in liver in support of lactation.

Kinetics of amino acid extraction by lactating mammary glands in control and sometribove-treated Holstein cows

Studies of mammary arteriovenous difference were conducted on multiparous lactating Holstein cows (n = 21) on d 35, 70, 105, and 126 of lactation to examine kinetic relationships between arterial concentration and mammary gland extraction of AA. Additionally, these cows were paired by previous lactational performance and assigned to bST-treated or control groups to examine the effect of bST treatment on AA concentration and extraction by lactating mammary glands. Treated cows were injected daily with 40 mg of recombinant bST from d 71 through 126 of lactation. Arterial concentrations of Asp, Ser, Asn, Gly, beta-aminoisobutyrate, and Met were increased. Concentrations of Val, Ile, Leu, Phe, Orn, and Lys were decreased in bST-treated cows compared with controls. Increased extractions of Asp and Met by mammary glands in treated versus control cows were correlated positively with treatment-induced changes in arterial concentrations of these AA. However, increased mammary extractions of Arg, cystathionine, Leu, and Lys by bST-treated compared with control cows were not correlated with bST-induced changes in arterial concentrations of these AA. Extractions of Asn, His, Thr, Arg, Tyr, Met, cystathionine, cystine, Ile, Phe, Orn, Glu, Gly, Tau, Cit, Leu, and Val were correlated linearly with arterial concentrations (r2 greater than .15) of each AA. Extractions of Asp, Glu, Ser, Asn, Gly, Gln, Tau, His, Cit, Thr, Pro, Tyr, Val, cystine, Ile, Leu, Trp, Orn, and Lys also were correlated with arteriovenous differences of Met.

Relationship of early lactation and bovine somatotropin on nutrient uptake by cow mammary glands

Twenty-one multiparous lactating dairy cows with previous 305-d milk production records varying from 5900 to 13,600 kg were used to investigate effects of bST administration and stage of lactation on nutrient plasma arterial concentrations and arterial-venous differences across the mammary glands (uptake). On d 71 and continuing until d 126 of lactation, cows were injected with 40 mg of sometribove (bST group) or bicarbonate buffer (placebo group). Arterial and venous blood plasma samples were collected over a 12-h period on d 35, 70, 105, and 126 of lactation. Plasma concentration of glucose was 7% higher in midlactation compared with early lactation cows. Plasma concentration of acetate decreased from 2.11 to 1.87 mM in placebo versus bST-treated cows. Plasma arterial concentration and uptake of D-beta-hydroxybutyrate were .52 and .18 mM higher, respectively, in early versus midlactation cows. Concentration and uptake of NEFA were elevated in both early lactation and bST-treated cows. Triacylglyceride concentrations were 24 and 19% lower in early lactation and bST-treated cows compared with midlactation cows receiving placebo. Likewise, uptake of triacylglyceride was reduced in early lactation and with bST treatment compared with midlactation. The mediation of nutrient delivery and uptake by the mammary gland appears to be markedly similar between early lactation and bST-treated cows, suggesting a similarity between these physiological states and the homeostatic and homeorhetic mechanisms regulating nutrient partitioning in the lactating dairy cow. In early compared with midlactation cows receiving placebo, uptakes of D-beta-hydroxybutyrate and NEFA were reduced, and triacylglyceride uptake increased.

Patterns of nutrient uptake by the mammary glands of lactating dairy cows

Twenty-one multiparous lactating dairy cows with previous 305-d milk production records varying from 5900 to 13,600 kg were used to examine patterns of nutrient uptake by the mammary glands. On d 71 and continuing until d 126 of lactation, animals were injected daily with 40 mg of sometribove (bST group) or bicarbonate buffer (control group). Arterial and venous blood plasma samples were collected over a 12-h period on d 35, 70, 105, and 126 of lactation. Regression equations developed to evaluate linear effects of plasma arterial concentrations on net arterial-venous difference across the mammary glands demonstrated that, for acetate, NEFA, and D-beta-hydroxybutyrate, plasma arterial concentration accounted for over 50% of variation in uptake by the mammary glands. Additionally, a sigmoidal equation fitted the relationship between D-beta-hydroxybutyrate plasma arterial concentration and mammary gland uptake (r2 = .70). Triacylglyceride concentration was less effective in predicting uptake (r2 = .25). Administration of bST did not alter patterns of nutrient uptake, but a fourfold increase in NEFA uptake was predicted for bST-treated cows from this study, using NEFA concentrations from the literature. These observations indicate that plasma concentrations of acetate, NEFA, D-beta-hydroxybutyrate, and triacylglyceride are major determinants of uptake by the mammary glands. Factors other than plasma concentration, such as mammary gland biosynthetic capacity, availability of other nutrients, and blood flow, determine uptakes of glucose, lactate, and total and free cholesterol (r2 less than or equal to .03).

Whole blood and plasma amino acid uptakes by lactating bovine mammary glands

The objective of the experiment was to determine the contribution of red blood cells to transport of individual amino acids to lactating bovine mammary glands. Blood samples were collected from coccygeal and subcutaneous abdominal veins of 21 lactating Holstein cows on d 35, 70, 105, and 126 of lactation. Samples were collected every 20 min for 12 h. Subsamples of whole blood and plasma were pooled by hour and day. Hourly plasma samples and daily whole blood and plasma samples were analyzed for amino acid concentration. Plasma glutamate concentration was stable throughout the 12-h collection period, indicating that sample collection did not perturb amino acid homeostasis. Therefore, data from pooled daily samples were used for subsequent comparisons. Whole blood arteriovenous differences of phosphoserine, aspartate, glutamate, hydroxyproline, phosphoethanolamine, serine, asparagine, glycine, glutamine, taurine, histidine, citrulline, threonine, alanine, beta-aminoisobutyrate, carnosine, arginine, proline, alpha-aminobutyrate, tyrosine, valine, methionine, cystine, isoleucine, leucine, phenylalanine, tryptophan, ornithine, and lysine differed significantly from plasma arteriovenous differences. Uptakes of individual amino acids from plasma were poorly correlated with uptake from whole blood. These data clearly indicate that uptake data derived from plasma do not adequately represent whole blood amino acid uptake.

Value of raw soybeans and soybean oil supplementation in sow gestation and lactation diets: a cooperative study

A cooperative study using 215 sows during two parities (349 litters) was conducted at six stations to determine the effect of raw soybeans in gestation and lactation diets on sow and litter performance. Sows were bred and allotted to fortified corn diets containing either soybean meal (control) or raw soybeans. A corn-soybean meal-soybean oil diet, isocaloric to the raw soybean diet, was included as a third treatment at three stations. All diets contained 14% CP. These diets were fed during both gestation and lactation through two parities. The daily gestation feed intake ranged from 1.8 to 2.3 kg/sow, depending on station. During lactation, the sows were allowed ad libitum access to their respective diets. Gestational weight gain was not influenced by diet, but sows fed raw soybeans consumed less (P less than .01) feed during lactation and had greater (P less than .01) lactational weight loss and their pigs were lighter in weight (P less than .05) both at 21 d and at weaning (varied between 3 and 5 wk of age). Sows fed the diet with supplemental oil had reproductive and lactational performance similar to those fed the control diet. Milk obtained at d 10 to 14 of lactation from sows fed raw soybeans had lower (P less than .05) protein content than milk from sows fed the other two diets, but fat content of the milk tended to be increased by raw soybeans or by added soybean oil. Return to estrus was not affected by diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced male reproductive capacity in mice with high genetic potential for post-weaning growth

Male reproductive capacity was examined in 5 lines of mice which differed markedly in mature body weight (30-73 g) due to selection for growth and/or substitution of the high growth gene (hg). Testes weight ranged from 0.75-0.77% of body weight in control lines to 0.33% in the largest mice which had the hg gene in a growth selected background. Both selection for growth and the hg gene in a control background reduced absolute testes size (0.200 and 0.207 g vs 0.236 and 0.228 g in control lines) as well as relative testes size although body weight was increased by at least 50%. Although the combination of growth background and hg gene reduced sperm production per g testis compared to the outbred control, the primary cause of reduced sperm production per mouse in lines containing either the growth background or the hg gene alone was reduced absolute testes size. At 24, but not at 11, weeks of age, the hg gene reduced sperm motility. In these lines, high genetic potential for post-weaning growth was associated with decreased male reproductive capacity.

Energy-dispersive X-ray analysis of the mineral content of corn bran treated in vitro and by passage through the pig gastrointestinal tract

Energy-dispersive X-ray (EDX) analysis was tested as a method for examining the mineral contents of corn bran loaded in vitro or passed through the GI tract of pigs. Particles of dry-milled corn pericarp treated in vitro or retrieved from the stomach, ileum, and colon of killed pigs were prepared as microtomed bulk specimens directly embedded in resin. Because of heterogeneity caused by differences in substrate cell density and mineral content, X-ray count averages for a number of different specimens had a coefficient of variation greater than or equal to 0.24. Detectable amounts of K, Ca, S, and P, but not Na, Cu, Fe, or Zn were found in specimens of initial bran. Although detectable concentrations of Cu, Fe and Zn could be loaded in vitro, these elements generally were not detected in bran retrieved from the pig GI tract. During GI tract passage, sodium was loaded onto bran mainly in the small intestine and unloaded in the large intestine. Calcium was loaded in the stomach and unloaded mainly in the small intestine. At each GI tract location, content of Na, Ca, K, and P in retrieved bran was greater than in the initial bran. EDX microprobe methods can be applied successfully to plant tissues treated in vitro and in vivo to investigate interactions with minerals in a diet.

On the application of compartmental models to radioactive tracer kinetic studies of in vivo protein turnover in animals

A mathematical framework is presented for unifying and extending the various compartmental models and formulae used to calculate fractional protein synthesis and degradation rates in animals from data obtained by infusing labelled amino acids. It is shown how the various schemes can be derived as special cases of the product-precursor model or some three-pool variant. Three-compartment representations, which circumvent the need to measure the specific radioactivity of the precursor pool, are proposed. The mathematical solutions are generally presented in a form that is amenable to parameter estimation by non-linear least squares. The problems of measuring the true precursor pool for protein synthesis are addressed, and theoretical consideration is given to assaying aminoacyl-tRNA.

Effect of varying dietary zinc intake of weanling mouse pups during recovery from early undernutrition on growth, body composition and composition of gain

Catch-up growth during recovery from undernutrition is characterized by rapid body weight gain often marked by disproportionately high fat gain. In this study dietary zinc intake of mouse pups during recovery from undernutrition affected composition of gain as well as growth. Mouse pups were undernourished during the suckling period and then fed 25% casein recovery diets containing 5, 10, 40 or 110 micrograms Zn/g diet. Pups given dietary zinc levels of 40 micrograms Zn/g ad libitum achieved recovery body weights and had normal body composition. However, previously undernourished pups given marginal levels of dietary zinc (10 micrograms Zn/g diet) had similar food intakes, similar final body weights, lower lean body mass gains and greater fat gains (males only) than controls. Pups fed low zinc diets (5 micrograms Zn/g diet) were unable to attain recovery body weight and had less protein gain than previously undernourished animals fed higher zinc-containing diets or healthy pups fed the same zinc levels. The results were consistently more pronounced in males. Thus dietary zinc deficiency during catch-up growth after undernutrition limited both recovery and protein gain, whereas marginal dietary zinc intake limited protein gain in mice.

Effects of dietary excesses of the branched-chain amino acids on growth, food intake and plasma amino acid concentrations of kittens

The effect of excesses of the branched-chain amino acids (BCAA), particularly leucine, on growth, food intake and plasma amino acid concentrations were investigated in kittens. Effects of excess leucine were tested in kittens fed five basal diets that varied in their nitrogen and amino acid contents. Compared to rats, kittens were much less sensitive to excesses of the BCAA. Addition of 10% leucine to basal diets that provided nitrogen just at or below the minimal requirement of kittens resulted in no change or increased growth and food intake of kittens when the isoleucine and valine concentrations in the basal diet were just at or slightly in excess of the kitten's minimal requirements for those amino acids. An adverse effect of leucine added to low nitrogen basal diets was observed only when isoleucine and valine were provided below the kitten's requirement (80% of requirement). When basal diets containing adequate nitrogen (24% amino acids) were tested, the addition of leucine (10%) resulted in an adverse effect when isoleucine and valine were provided at 80% of the kitten's requirement and in mild growth depressions when isoleucine and valine were provided at 1.1 times the requirement. Leucine-induced growth depression was alleviated by the addition of isoleucine and valine at 0.5%, indicating that excess leucine caused a BCAA antagonism or an amino acid imbalance. With the addition of leucine to the basal diets, there were consistent decreases in concentrations of alanine and tyrosine in plasma but no consistent depressions in the concentrations of isoleucine and valine.

Energetics of protein synthesis in mice with a major gene for growth

The effect of the level of food intake on protein synthesis rate in carcass, liver, gastrointestinal tract (GIT) and heart, kidneys and lungs (HKL) was determined in male mice with a major gene for rapid postweaning gain (line Ch) and normal controls (line CH) at 31 d of age. In both lines of mice, food restriction lowered carcass, HKL and liver absolute protein synthesis rates (ASRs) while GIT protein ASR was not affected by food intake. As a result, whole-body protein ASR increased with increasing food intake. It was estimated that heat production from protein synthesis (HrpsE) was responsible for 8.3 and 10.8% of the maintenance energy requirement of CH and Ch mice, respectively. It was also calculated that HrpsE represents 19.4 and 18.3% of the heat increment of growth of CH and Ch mice, respectively. Energetic efficiencies of protein deposition in CH and Ch mice were 58.6 and 66.7%, respectively.

Delayed excretion of 3-methylhistidine in goats

The purpose of this study was to evaluate the use of 3-methylhistidine (3MH) as an index of muscle protein degradation in dairy goats. The criterion for validation was the rapid and quantitative excretion of radiolabeled 3MH. Three adult dry does and four bucks were confined to metabolism cages and injected with 5 ml of L-3-[14C]methylhistidine dihydrochloride (4 microCi/mL) diluted in normal saline. The does' urine was collected from catheters and the bucks' urine from stainless steel separators protected with fecal collection bags. The daily urine samples were analyzed for labeled amino acid. Urinary recovery of radioactivity from all does was less than 33% after 3 d and was proceeding at less than 5% d. After 9 d, total recovery was less than 50% of total dose for the does. Elimination rates were slightly higher and more variable for the yearling bucks (25-63% after 4 d). On the basis of these data, 3MH does not appear to be a valid index of muscle protein degradation in either male or female dairy goats.

Effect of a major gene for growth on protein synthesis in mice

Rates of protein synthesis of mice with a major gene (hg) for rapid postweaning gain (line Ch) and their normal counterparts (line CH) were determined at 21, 31 and 42 d of age with an intraperitoneal injection of a flooding dose of 14C-leucine. A preliminary experiment demonstrated that the relationship between the specific activities of leucine in acid-soluble supernatants and carcass protein corresponded to the theoretical precursor-product relationship, indicating that the method is valid for estimating protein synthesis rates. Using this method at 21, 31 and 42 d of age, whole-body protein fractional synthesis rates (FSR) were 43.7, 32.7 and 29.1%/d and 41.9, 32.6 and 33.1%/d for lines CH and Ch, respectively. Although differences between lines were not significant, FSR decreased with age. Absolute synthesis rate (ASR), where ASR = (FSR) X (whole body protein), was greater (P less than .001) at 21, 31 and 42 d of age in line Ch as compared with CH, and increased (P less than .001) with age. The relative contributions of liver, gastrointestinal tract, heart-kidney-lung and remaining carcass to whole body protein ASR were not affected by line, but did change (P less than .05) with age. Whole body protein fractional breakdown rate (FBR), calculated as FSR minus whole body protein fractional growth, indicates that differences between lines CH and Ch whole-body FSR and(or) FBR exist only between 24 and 33 d of age, and that the maximum value of this difference probably does not exceed 10%.

Growth characteristics, protein synthesis, and protein degradation in muscles from fast and slow-growing chickens

Developmental changes in muscle growth were studied in Single Comb White Leghorn (SCWL) and broiler-type (B) chickens. The extensor digiti communus (EDC) and ulnaris lateralis (UL) muscles were chosen for study because these muscles can be maintained in vitro, permitting the direct measurement of the fractional rate of protein synthesis (FSR) and the fractional rate of degradation (FDR). These muscles were removed from chicks at 1, 5, 10, and 20 days of age. Muscles for B were heavier, grew at a faster rate, and had greater fractional rates of growth than muscles from SCWL. Muscle protein concentrations were similar for SCWL and B. The deoxyribonucleic acid (DNA) concentrations were greater in EDC muscles from SCWL than B at all time periods. Concentrations of DNA were greater in UL muscles from SCWL than B after Day 1. The FSR and FDR were measured in muscles incubated in vitro. At 9 days of age, FSR in broiler and SCWL chicks was not significantly different in either muscle. The FDR was 12 and 19% lower in broiler EDC and UL muscles, respectively, demonstrating that broiler EDC and UL muscles accrete protein at a greater rate and more efficiently than SCWL muscles because of a slower rate of protein degradation. The FSR and FDR were also compared in B and SCWL chicks of 8 and 11 days, respectively, with equal DNA unit sizes. The FSR in B was 27 and 13% greater in EDC and UL muscles, respectively, demonstrating that protein synthesis per nucleus is greater in B chicks.

Relative contributions of hyperplasia and hypertrophy to growth in cattle

The relationship between postweaning DNA accumulation and body weight was calculated for a reference growing steer. Accumulation of DNA (hyperplasia) was calculated from patterns of protein accretion derived from literature data and protein-to-DNA ratios (Pro/DNA) measured in samples of muscles from chuck, round and plate, hides, intestines, rumens and livers of steers slaughtered at body weights ranging from 150 to 700 kg. Amounts of protein relative to DNA found in muscles from chuck, round and plate were used to estimate Pro/DNA changes in carcass. Corresponding values from intestines, rumen and liver were used to estimate Pro/DNA patterns for viscera. This ratio increased in carcass until animals reached body weights of approximately 300 kg and leveled off thereafter. No cell enlargement was evident in viscera. Thus, postweaning protein accretion in carcass results from both cell enlargement (hypertrophy) and DNA accumulation (hyperplasia) until body weights of 300 kg are attained, subsequent growth appeared to be hyperplastic in nature. In viscera, hyperplasia was the primary determinant of protein accretion.

Energetic efficiency of protein and fat deposition in mice with a major gene for rapid postweaning gain

Previous research demonstrated the existence of a major gene (hg), expressed as a homozygous recessive, that increases postweaning growth 60% in C57B1/6 mice (line Ch) compared to the same genetic stock without the major gene (line CH). Effects of the hg gene on the partial energetic efficiencies of protein and fat deposition in mice between 21 and 42 d of age were examined by using comparative slaughter data and multiple regression techniques. Efficiency estimates for fat deposition were biologically impossible and unstable, probably as a result of high correlations between the independent variables (multicollinearity). Use of biased regression techniques gave rise to biologically possible estimates for efficiencies of fat and protein gain. However, biased regression procedures introduced subjectivity in an otherwise objective analysis. Since these regression techniques produce biologically possible estimates, the physiological implications of the results are discussed in relation to protein and fat turnover. Although the usefulness of these statistical methods for predictive purposes is not questioned, it is concluded that they do little toward advancing our understanding of energy metabolism. Rather, we suggest that mechanistic models be used wherein specific biological processes are presented separately and effects of energy intake on these processes accommodated explicitly.

Gluconeogenesis in isolated lamb hepatocytes

Isolated sheep hepatocytes were used to obtain estimates of kinetic parameters, identify substrate preference and interactions and study regulation of gluconeogenesis. Respective Vmax estimates for propionate, pyruvate and alanine conversion to glucose were 59.5, 12.8 and 21.5 mol glucose formed X (h X g dry weight)-1. Respective KS estimates for propionate and pyruvate were 1 mM and 18 to 40 microM. Rates of lactate utilization varied among cell preparations, possibly because of loss of lactate dehydrogenase during isolation. Dihydroxyacetone and glycerol were utilized for glucose synthesis at similar rates of 8.6 and 8.7 mumol glucose formed X (h X g dry weight)-1, respectively. Respective rates of glucose synthesis from 5 mM fructose and 10 mM galactose were 63.2 and 31.4 mumol X (h X g dry weight)-1. Maximum rates of pyruvate carboxylase and phosphoenolpyruvate carboxykinase were estimated to be 101.6 and 160.4 mumol substrate converted X (h X g dry weight)-1, respectively. Neither butyrate nor acetate accelerated gluconeogenesis from propionate while acetate increased glucose synthesis from pyruvate, presumably through activation of pyruvate carboxylase. Glucagon stimulated gluconeogenesis from propionate. Dibutyrylcyclic AMP mimicked the effect of glucagon, implying that the glucagon effect is translated via the adenyl cyclase system as in rats. The kinetic parameters established in these experiments should be useful in future experiments and in computer modeling analyses of ruminant liver and whole animal metabolism where Michaelis-Menten type equations are widely used.

Relationships among dietary protein, feed intake and tissue protein turnover in lactating rats

Effects of protein and energy intake on tissue protein synthesis and degradation were studied in rats fed 12, 24 and 36% protein diets at 100, 70, 50 and 30% of ad libitum intake begining on d 7 of lactation. Rates of protein synthesis were measured in liver, mammary, abdominal viscera and remaining carcass of rats on d 10 of lactation. Tissue protein loss was estimated as the difference in tissue protein from d 7 to 14. Data were analyzed using stepwise multiple quadratic regression to define response surfaces of protein loss, synthesis and degradation to intake of protein and energy. Protein loss increased with restriction of energy and protein intake in all tissues. However, carcass protein synthesis and degradation did not vary systematically with either energy or protein intake. Energy intake restriction increased visceral protein turnover while protein intake restriction decreased rate of protein turnover. Liver protein loss increased with decreased dietary protein due to increased liver protein degradation. Decreased energy intake also increased liver protein loss without directly affecting rate of synthesis or degradation. Mammary protein synthesis decreased very slightly with energy restriction while decreased protein intake sharply inhibited protein synthesis.