Decrease In Nitrogen Excretion Research Articles

Influence of Different Methionine Sources on Performance and Slaughter Characteristics of Broilers.

Simple SummaryThe increasing public demand for efficient, sustainably produced poultry meat with simultaneous optimization of animal welfare is calling for amendments in meat production. A starting point to meet this demand consists of complete diets for broilers with reduced crude protein content, supplemented with higher amounts of crystalline amino acids. This ensures sufficient nutritional supply and decreased nitrogen excretion for environmental relief. To optimize the performance and health, despite the drastically reduced protein content (~17.5% finisher diet), the present study compared different methionine sources (methionine hydroxy analog, DL-methionine, and L-methionine) in slightly higher dosages than found in practice, in comparison to a diet meeting the methionine requirements using methionine hydroxy analog. Methionine is the first limiting amino acid and has a significant influence on the health and growth of the animals. The results of the feeding trial showed no differences concerning general health, ileal histology, and performance data of broilers before slaughter. However, the composition of the breast meat differed significantly (highest protein content and lowest fat content in the L-methionine group), and thus provides the impetus for further research.Sustainably produced poultry meat with consideration of animal health poses a challenge for broiler production. Low protein diets with high amounts of synthetic amino acids (AAs) like methionine (Met) are the consequence. In a five-week feeding trial, 360 broilers (Ross 308) assigned to four feeding groups were offered protein-reduced complete diets (starter: 20% crude protein (CP); grower: 18.5% CP; finisher: 17.5% CP), supplemented with essential AAs. The “MHA” group received DL-2-hydroxy-4-(methylthio) butanoic acid (DL-HMTBA; trade name: MHA®), groups “L” and “DL” the respective Met source in equivalent concentrations each exceeding the nutritional recommendations. “R-MHA” (“R” for “reduced”) received the minimum required level (using MHA as Met source). Performance exceeded performance goals without differences between the groups. The average feed conversion ratio (FCR) amounted to 1.35. The carcass/body weight ratio of R-MHA was significantly lower (0.782) compared to DL (0.808) and L (0.809). Breast meat of R-MHA contained significantly more fat (144 g/kg dry matter (DM)) compared to L (104 g/kg DM) and significantly lower CP content (R-MHA: 838 g/kg DM; L: 875 g/kg DM). The results indicated possible improvement in slaughter yield by protein-reduced diets supplemented with L-Met, thus recommending further research focusing on the Met influence.

Effect of different dietary protein levels and amino acids supplementation patterns on growth performance, carcass characteristics and nitrogen excretion in growing-finishing pigs

BackgroundThis study was conducted to determine the effects of different dietary protein levels and amino acids supplementation patterns in low protein diets on the growth performance, carcass characteristics and nitrogen excretion in growing-finishing pigs.Forty-two barrows (25.00 ± 0.39 kg) were randomly assigned to 7 diets. Diet 1: the high crude protein diet with balanced for 10 essential amino acids (EAAs). Diet 2: the medium crude protein diet with 2% (approx) decreased protein level of Diet 1 and balanced 10 EAAs. Diet 3: the low crude protein diet with 4% decreased protein level of Diet 1 and balanced 10 EAAs. The protein levels of Diet 4, 5, 6 and 7 were the same as that of Diet 3. Diet 4 was only balanced for lysine (Lys), methionine (Met), threonine (Thr) and tryptophan (Trp); Diet 5 and 6 were further supplemented with extra isoleucine (Ile) or valine (Val), respectively; Diet 7 was further supplemented with extra Ile + Val.ResultsOver the 112 days trial, the reduction of dietary protein by 2% or 4% with balanced10 EAAs significantly decreased nitrogen excretion (P < 0.05), but had no effects on growth performance and carcass characteristics (P > 0.05). In low protein diet, Val supplementation significantly increased body weight gain at 25–50 kg phase (P < 0.05), while Ile supplementation at 75–100 kg phase and 100–125 kg phase significantly reduced the ratio of feed to gain (P < 0.05). No effect of different dietary protein levels and amino acids supplementation patterns in low protein diets on carcass characteristics was observed (P > 0.05). The total N excretion of pigs supplemented with only Lys, Met, Thr and Trp was numerically higher than that of pigs fed with extra Ile, or Val, or Ile + Val diets.ConclusionIn low protein diet, Val is more required than Ile in the early growing phage (25–50 kg), while Ile becomes more required in the late growing and finishing phage (75–125 kg).

MRNA expression of ANT genes, productive performance and nitrogen excretion of laying hen by feeding low protein diets and amino acid supplementation

The study investigated the effects of low protein diet and amino acid supplementation on production performance of laying hens from 49–57 weeks. A total of 135 chickens were divided into 3 groups: 17%CP, 15%CP and 15%CP supplemented with amino acid (AA). The results showed that the 15% CP group consumed less feed (P less than 0.01). Adding AA to 15%CP improved feed intake, Met intake, BWG, egg mass (P less than 0.01) and egg production (P less than 0.05), while FCR and egg quality were not affected. The percentage of abdominal fat and ANT gene expression were highest in the 15%CP + AA group (P less than 0.05). Nitrogen retention in manure of 15% CP + AA hens was lower than in 17%CP (P less tahn 0.01). These results indicated that the reduced-CP diets supplemented with AA improved production performances and decreased nitrogen excretion.

Reducing the CP content in broiler feeds: impact on animal performance, meat quality and nitrogen utilization

Reducing the dietary CP content is an efficient way to limit nitrogen excretion in broilers but, as reported in the literature, it often reduces performance, probably because of an inadequate provision in amino acids (AA). The aim of this study was to investigate the effect of decreasing the CP content in the diet on animal performance, meat quality and nitrogen utilization in growing-finishing broilers using an optimized dietary AA profile based on the ideal protein concept. Two experiments (1 and 2) were performed using 1-day-old PM3 Ross male broilers (1520 and 912 for experiments 1 and 2, respectively) using the minimum AA:Lys ratios proposed by Mack et al. with modifications for Thr and Arg. The digestible Thr (dThr): dLys ratio was increased from 63% to 68% and the dArg:dLys ratio was decreased from 112% to 108%. In experiment 1, the reduction of dietary CP from 19% to 15% (five treatments) did not alter feed intake or BW, but the feed conversion ratio was increased for the 16% and 15% CP diets (+2.4% and +3.6%, respectively), while in experiment 2 (three treatments: 19%, 17.5% and 16% CP) there was no effect of dietary CP on performance. In both experiments, dietary CP content did not affect breast meat yield. However, abdominal fat content (expressed as a percentage of BW) was increased by the decrease in CP content (up to +0.5 and +0.2 percentage point, in experiments 1 and 2, respectively). In experiment 2, meat quality traits responded to dietary CP content with a higher ultimate pH and lower lightness and drip loss values for the low CP diets. Nitrogen retention efficiency increased when reducing CP content in both experiments (+3.5 points/CP percentage point). The main consequence of this higher efficiency was a decrease in nitrogen excretion (−2.5 g N/kg BW gain) and volatilization (expressed as a percentage of excretion: −5 points/CP percentage point). In conclusion, this study demonstrates that with an adapted AA profile, it is possible to reduce dietary CP content to at least 17% in growing-finishing male broilers, without altering animal performance and meat quality. Such a feeding strategy could therefore help improving the sustainability of broiler production as it is an efficient way to reduce environmental burden associated with nitrogen excretion.

The economic and environmental value of genetic improvements in fattening pigs: An integrated dynamic model approach1

The selection of animals for improved performance affects the profitability of pig fattening and has environmental consequences. The goal of this paper was to examine how changes in genetic and market parameters impact the biophysical (feeding patterns, timing of slaughter, nitrogen excretion) and economic (return per pig space unit) results describing pig fattening in a Finnish farm. The analysis can be viewed as focusing on terminal line breeding goals. An integrated model using recursive stochastic dynamic programming and a biological pig growth model was used to estimate biophysical results and economic values. Combining these models allowed us to provide more accurate estimates for the value of genetic improvement and, thus, provide better feedback to animal breeding programs than the traditional approach, which is based on fixed management patterns. Besides the benchmark scenario, the results were simulated for 5 other scenarios. In each scenario, genotype was improved regarding daily growth potential, carcass lean meat content, or the parameters of the Gompertz growth curve (maturing rate [], adult weight of protein [α], and adult weight of lipid mass []). The change in each parameter was equal to approximately 1 SD genetic improvement (ceteris paribus). Increasing , , daily growth potential, or carcass lean meat content increased the return on pig space unit by €12.60, €7.60, €4.10, or €2.90 per year, respectively, whereas an increase in decreased the return by €3.10. The genetic improvement in and resulted in the highest decrease in nitrogen excretion calculated in total or per kilogram of carcass gain but only under the optimal feeding pattern. Simulated changes in the Gompertz growth function parameters imply greater changes in ADG and lean meat content than changes in scenarios focusing on improving ADG and lean meat content directly. The economic value of genetic improvements as well as the quantity of nitrogen excreted during the fattening period largely depends on feeding. Improved genotypes can require changes in pig management pattern. Estimating the influence of the genotype on the nitrogen excretion without considering changes in the management pattern can result in flawed conclusions. To improve overall economic performance and to decrease the environmental footprint of fattening pig production, the pig producer can adjust the herd management pattern according to the pigs' genetics.

Optimizing feed efficiency and nitrogen excretion in growing rabbits by increasing dietary energy with high-starch, high-soluble fibre, low-insoluble fibre supply at low protein levels

A total of 282 crossbred rabbits of both genders were divided into six experimental groups and fed ad libitum six diets formulated in a 2×3 factorial arrangement based on three dietary energy levels (low, approximately 8.45MJ/kg; medium, 9.9MJ/kg: and high, 11.5MJ/kg) and two crude protein levels (15% and 17%). The increase of dietary energy was obtained by a simultaneous increase of dietary starch (9.1%, 13.7%, and 17.9%) and soluble fibre (4.8%, 7.1%, and 9.4%) at the expense of acid detergent fibre (23.0%, 18.0%, and 13.5%). Growth performance and nitrogen excretion from weaning until slaughter, and digestive traits were monitored. The increase of dietary energy enhanced the apparent digestibility of dry matter (50.8%, 60.5%, and 71.5%; P<0.001), gross energy (50.3%, 59.7%, and 70.7%; P<0.001), soluble fibre (73.1%, 77.8%, and 82.9%; P<0.10), and neutral detergent fibre (16.1%, 29.0%, and 48.1%; P<0.001). In the caecum, the total volatile fatty acid (VFA) content increased (63.0, 79.2, and 78.5mmol/L; P<0.05), and the propionate rate decreased (4.0%, 4.2%, and 3.5% mol VFA; P<0.05); in the jejunum, the villi-to-crypt ratio tended to decrease (4.18, 3.89, and 3.57; P<0.10). The increase of dietary energy supply decreased feed intake (181g/d, 157g/d, and 135g/d; P<0.001), which improved feed conversion ratios (3.98, 3.40, and 2.87; P<0.001), and decreased nitrogen excretion (3.15g/d, 2.56g/d, and 1.93g/d; P<0.001). The increase of dietary energy significantly decreased mortality (15.8%, 4.9%, and 4.9%; P<0.05). When dietary crude protein increased from 15% to 17%, apparent digestibility increased for dry matter, crude protein, total dietary fibre, and gross energy (P<0.01). Growth performance during the trial was not affected, but nitrogen excretion decreased significantly (2.73g/d vs. 2.37g/d; P<0.001). In conclusion, the increase of dietary energy by the simultaneous increase of dietary starch and soluble fibre to replace insoluble fibre optimized feed efficiency and controlled nitrogen excretion in growing rabbits with positive effects on digestive traits and health. The reduction in dietary protein level was determined to be an useful strategy to reduce farm nitrogen excretion.

Strategies for mitigation of nitrogen environmental impact from swine production

This work presents strategies that can be implemented in order to minimize the environmental impact of swine slurry on soil, water, and air. This reduction can be achieved through decrease in nitrogen excretion and ammonia emissions. The correct feed formulation according to animal requirements, the increase in diet digestibility and improvement in animal performance can reduce nitrogen excretion. The use of additives either in the diet or in the manure as well as some equipment rearrangements can reduce ammonia emission.

Effect of decreasing ideal protein levels on performance results and nitrogen efficiency of growing-finishing gilts

This study examined the effect of decreasing ideal protein concentrations on performance and nutrient efficiency. The experimental diets contained 100%, 90%, 80% or 70% of the ideal dietary protein level (Diet 100%, 90%, 80% and 70%, respectively) estimated in previous experiments with pigs of the same genetic background. The four different treatments were divided among 16 pens of six pigs each. The average initial and final body weight were 20.8 ± 1.1 and 107 ± 3 kg, respectively. Three-phase feeding was applied (BW 20–40 kg, 40–70 kg and 70–110 kg). The dietary ileal digestible (ID) methionine + cystine, threonine, tryptophan, isoleucine, valine, and leucine contents expressed as percent of ID lysine were 63, 72, 22, 60, 68, and >100%, respectively. The lysine to protein ratio was kept constant at 6.8%. Between 21 and 106 kg BW the best performance was achieved on Diet 90%. Diet 70% led to significantly worse results. Although lean meat percentage did not differ, protein content of the carcass was lower on Diet 70% than on Diets 90% and 100%. Decreased protein concentrations increased crude protein efficiency and consequently decreased nitrogen excretion most at the 80% level. If protein varies together with digestible amino acid content, it can be concluded that Diet 80% may be the best choice for the environment and for profitability. If protein content stays at a fixed level, Diet 90% may be the safest choice.

Impact of supplementation with bicarbonate on lower-extremity muscle performance in older men and women

This study describes the impact of bicarbonate treatment for 3 months on net acid excretion (NAE), nitrogen excretion, and muscle performance in older men and women. Bicarbonate reduced NAE, and the decrement was associated with a decrease in nitrogen excretion. Treatment also improved muscle power and endurance in the women. Bicarbonate enhances muscle performance during strenuous exercise, but its effect on performance during normal activity in older subjects is unknown. In this trial, healthy subjects age 50 and older were randomized to 67.5 mmol of bicarbonate or to no bicarbonate daily for 3 months. Changes in lower-extremity muscle power, endurance, urinary nitrogen, and NAE were compared across treatment groups in the 162 participants included in the analyses. In the men and the women, bicarbonate was well tolerated, and as expected, it significantly decreased NAE. The change in NAE correlated with change in nitrogen excretion in women (r = 0.32, P = 0.002) with a similar trend in men (r = 0.23, P = 0.052). In the women, bicarbonate increased double leg press power at 70% one repetition maximum by 13% (P = 0.003) compared with no bicarbonate and improved other performance measures. Treatment with bicarbonate had no significant effect on muscle performance in the men. Ingestion of bicarbonate decreased nitrogen excretion and improved muscle performance in healthy postmenopausal women. The bicarbonate-induced decline in NAE was associated with reduced nitrogen excretion in both men and women. These findings suggest that bicarbonate merits further evaluation as a safe, low-cost intervention that may attenuate age-related loss of muscle performance and mass in the elderly.

Protein Nutrition, Exercise and Aging

Aging is associated with remarkable changes in body composition. Loss of skeletal muscle, a process called sarcopenia, is a prominent feature of these changes. In addition, gains in total body fat and visceral fat content continue into late life. The cause of sarcopenia is likely a result of a number of changes that also occur with aging. These include reduced levels of physical activity, changing endocrine function (reduced testosterone, growth hormone, and estrogen levels), insulin resistance, and increased dietary protein needs. Healthy free-living elderly men and women have been shown to accommodate to the Recommended Dietary Allowance (RDA) for protein of 0.8 g · kg−1 · d−1 with a continued decrease in urinary nitrogen excretion and reduced muscle mass. While many elderly people consume adequate amounts of protein, many older people have a reduced appetite and consume less than the protein RDA, likely resulting in an accelerated rate of sarcopenia.One important strategy that counters sarcopenia is strength conditioning. Strength conditioning will result in an increase in muscle size and this increase in size is largely the result of increased contractile proteins. The mechanisms by which the mechanical events stimulate an increase in RNA synthesis and subsequent protein synthesis are not well understood. Lifting weight requires that a muscle shorten as it produces force (concentric contraction). Lowering the weight, on the other hand, forces the muscle to lengthen as it produces force (eccentric contraction). These lengthening muscle contractions have been shown to produce ultrastructural damage (microscopic tears in contractile proteins muscle cells) that may stimulate increased muscle protein turnover. This muscle damage produces a cascade of metabolic events which is similar to an acute phase response and includes complement activation, mobilization of neutrophils, increased circulating an skeletal muscle interleukin-1, macrophage accumulation in muscle, and an increase in muscle protein synthesis and degradation. While endurance exercise increases the oxidation of essential amino acids and increases the requirement for dietary protein, resistance exercise results in a decrease in nitrogen excretion, lowering dietary protein needs. This increased efficiency of protein use may be important for wasting diseases such as HIV infection and cancer and particularly in elderly people suffering from sarcopenia. Research has indicated that increased dietary protein intake (up to 1.6 g protein · kg−1 · d−1) may enhance the hypertrophic response to resistance exercise. It has also been demonstrated that in very old men and women the use of a protein-calorie supplement was associated with greater strength and muscle mass gains than did the use of placebo.

Effects of nutritional history on nitrogen assimilation in congeneric temperate and tropical scleractinian corals

The nutritional history of corals is known to affect metabolic processes such as inorganic nutrient uptake and photosynthesis, but little is known about how it affects assimilation efficiency of ingested prey items or the partitioning of prey nitrogen between the host and symbiont. The temperate scleractinian coral Oculina arbuscula and its tropical congener Oculina diffusa were acclimated to three nutritional regimes (fed twice weekly, starved, starved with an inorganic nutrient supplement), then fed Artemia nauplii labeled with the stable isotope tracer 15N. Fed corals of both species had the lowest assimilation efficiencies (36–51% for O. arbuscula, 38–57% for O. diffusa), but were not statistically different from the other nutritional regimes. Fed and starved corals also had similar NH4+ excretion rates. This is inconsistent with decreased nitrogen excretion and reduced amino acid catabolism predicted by both the nitrogen recycling and conservation paradigms. In coral host tissue, ~90% of the ingested 15N was in the TCA-insoluble (protein and nucleic acids) and ethanol-soluble (amino acids/low molecular weight compounds) within 4 h of feeding. The TCA-insoluble pool was also the dominant repository of the label in zooxanthellae of both species (40–53% in O. arbuscula, 50–60% in O. diffusa). However, nutritional history had no effect on the distribution of prey 15N within the biochemical pools of the host or the zooxanthellae for either species. This result is consistent with the nitrogen conservation hypothesis, as preferential carbon metabolism would minimize the effects of starvation on nitrogen-containing biochemical pools.

Effects of exercise on senescent muscle.

Strength conditioning will result in an increase in muscle size and this increase in size is largely the result of increased contractile proteins. The mechanisms by which the mechanical events stimulate an increase in ribonucleic acid synthesis and subsequent protein synthesis are not well understood. Lifting weight requires that a muscle shorten as it produces force (concentric contraction). Lowering the weight, however, forces the muscle to lengthen as it produces force (eccentric contraction). These lengthening muscle contractions have been shown to produce ultrastructural damage (microscopic tears in contractile proteins muscle cells) that may stimulate increased muscle protein turnover. This muscle damage produces a cascade of metabolic events that is similar to an acute phase response and includes complement activation, mobilization of neutrophils, increased circulation of skeletal muscle interleukin-1, macrophage accumulation in muscle, and an increase in muscle protein synthesis and degradation. Although endurance exercise increases the oxidation of essential amino acids and increases the requirement for dietary protein, resistance exercise results in a decrease in nitrogen excretion, lowering dietary protein needs. This increased efficiency of protein use may be important for wasting diseases such as human immunodeficiency virus infection and cancer and particularly in elderly people suffering from sarcopenia. Research has indicated that increased dietary protein intake (as much as 1.6 g protein x kg x day ) may enhance the hypertrophic response to resistance exercise. It also has been shown that in very old men and women the use of a protein-calorie supplement was associated with greater strength and muscle mass gains than the use of placebo.

Protein nutrition and resistance exercise.

Strength conditioning will result in an increase in muscle size and this increase in size is largely the result of increased contractile proteins. The mechanisms by which the mechanical events stimulate an increase in RNA synthesis and subsequent protein synthesis are not well understood. Lifting weight requires that a muscle shorten as it produces force (concentric contraction). Lowering the weight forces the muscle to lengthen as it produces force (eccentric contraction). Eccentric contractions produce ultrastructural damage that may stimulate increased muscle protein turnover and a cascade of metabolic events which is similar to an acute phase response and includes complement activation, mobilization of neutrophils, increased circulating and skeletal muscle interleukin-1 and macrophage accumulation. While endurance exercise increases the oxidation of essential amino acids and increases the requirement for dietary protein, resistance exercise results in a decrease in nitrogen excretion, lowering dietary protein needs. Research has indicated that increased dietary protein intake (up to 1.6 g protein x kg(-1) x d(-1)) may enhance the hypertrophic response to resistance exercise. It has also been demonstrated that in very old men and women the use of a protein-calorie supplement was associated with greater strength and muscle mass gains than did the use of placebo.

Insulin-like growth factor 1 has beneficial effects, whereas growth hormone has limited effects on postoperative protein metabolism, gut integrity, and splenic weight in rats with chronic mild liver injury.

Both growth hormone (GH) and insulin-like growth factor 1 (IGF-1) improve protein metabolism after surgical insult in subjects without liver disease. However, these effects in chronic liver injury, in which the GH-IGF-1 axis is impaired, have not been investigated. We examined the anabolic effects of GH and IGF-1 after gastrectomy in rats with chronic mild liver injury. Rats with chronic mild liver injury induced by thioacetamide were used. After gastrectomy, the rats were randomized into vehicle control, GH, and IGF-1 groups. In the latter two groups, 0.8 IU/kg/d of GH or 4 mg/kg/d of IGF-1 was infused for 72 hours. Anabolic effects were assessed by body weight change, 3-methylhistidine (3-MH) excretion, nitrogen excretion, and whole-body protein turnover. Organ weights, plasma levels of glucose, insulin, and IGF-1, tissue IGF-1 levels, hepatic messenger RNA (mRNA) content, and intestinal structure were also determined. Both GH and IGF-1 decreased nitrogen excretion. IGF-1, but not GH, increased postoperative body weight, whole-body protein turnover, and splenic weight. IGF-1 reduced atrophy of the intestinal mucosa. GH treatment increased hepatic IGF-1-mRNA and the plasma IGF-1 level, whereas IGF-1 treatment increased the plasma IGF-1 level with no change in the hepatic IGF-1-mRNA content. There were no significant differences in plasma glucose or insulin levels among the three groups. Neither GH nor IGF-1 affected the gastrocnemius muscle IGF-1 level. IGF-1 has beneficial effects, whereas GH has only limited effects on post-operative protein metabolism, gut integrity, and splenic weight in chronic mild liver injury.

Effects of lactulose and lactitol on protein digestion and metabolism in conventional and germ free animal models: relevance of the results to their use in the treatment of portosystemic encephalopathy.

Protein digestion and metabolism have been studied in laboratory rats and miniature pigs to investigate the mechanisms of action of lactulose and lactitol when used in the treatment of patients with portosystemic encephalopathy. Lactulose (beta-D-galactopyranosyl-(1----4)-beta-D-fructofuranose) and lactitol (beta-D-galactopyranosyl-(1----4)-D-glucitol) increased the excretion of nitrogenous material in the faeces and decreased nitrogen excretion in the urine in a similar degree to that reported for human patients. In studies with germ free rats given lactulose no such effect was observed, suggesting that, for lactulose at least, these effects are mediated by the gut flora. Measurement of the alpha-, epsilon-diaminopimelic acid content of the faeces confirmed that the enhancement of faecal nitrogen was due to an increased contribution from bacteria. The similarity in the results for lactulose and lactitol suggests that, from the perspective of protein metabolism, lactitol acts in a similar way to lactulose in the treatment of portosystemic encephalopathy.

Does hyperketonemia affect protein or glucose kinetics in postabsorptive or traumatized man?

Leucine and glucose turnover were measured using simultaneous infusions of [ 13C]leucine and [ 2H]glucose before and during an infusion of Na dl-hydroxybutyrate (Na dl-HB) in overnight-fasted patients the day before and 3 days after total hip replacement. The ketone body infusion before surgery resulted in a significant increase in plasma leucine concentration and leucine turnover, while glucose concentration and turnover decreased. Surgery increased leucine turnover. Ketone body infusion after surgery caused a further increased leucine turnover while turnover fell as before surgery. We suggest that exogenous ketone bodies decrease hepatic glucose production and probably stimulate a rise in protein synthesis above breakdown leading to a decreased nitrogen excretion as observed by other investigators. Despite the metabolic adaptation to trauma, this response was not affected by surgery.

Effect of a protein-free diet on muscle protein turnover and nitrogen conservation in euthyroid and hyperthyroid rats.

Although protein turnover in skeletal muscle is increased in hyperthyroidism and decreased in hypothyroidism, a deficient protein intake tends to increase serum T3 (tri-iodothyronine) while decreasing muscle protein turnover. To determine whether this diet-induced decrease in protein turnover can occur independent of thyroid status, we have examined muscle protein turnover and nitrogen conservation in hyperthyroid rats fed on a protein-free diet. After inducing hyperthyroidism by giving 20 micrograms of T3/100g body wt. daily for 7 days, groups of euthyroid and hyperthyroid animals were divided into subgroups fed on basal and protein-free diets. Muscle protein turnover was measured by N tau-methylhistidine excretion and [14C]tyrosine infusion. Urinary nitrogen output of euthyroid and hyperthyroid animals fed on the protein-free diet was also measured. Although hyperthyroidism increased the baseline rates of muscle protein synthesis and degradation, it did not prevent a decrease in these values in response to protein depletion. Furthermore, hyperthyroid rats showed greatly decreased nitrogen excretion in response to the protein-free diet, although not to values for euthyroid rats. These findings suggest that protein depletion made the experimental animals less responsive to the protein-catabolic effects of T3.

Whole body protein breakdown rates and hormonal adaptation in fasted obese subjects.

Fasting is known to result in marked decreases in urinary urea nitrogen excretion over a 7-day period. In the present studies, changes in whole body protein breakdown rates and in the circulating levels of a number of hormones involved in protein anabolism and catabolism were systematically studied in nine obese subjects after 12 h and after 7 days of fasting. Whole body protein breakdown rates, measured with a primed continuous infusion of L-[U-14C]lysine, were decreased after 7 days of fasting (1.54 +/- 0.12 g/kg . day) compared to those after 12 h of fasting (1.96 +/- 0.10 g/kg . day). Plasma insulin decreased and glucagon increased after 7 days of fasting, resulting in an increased glucagon to insulin molar ratio. Plasma cortisol, urinary free cortisol excretion plasma rT3 levels, and branched chain amino acid levels increased after 7 days of fasting. Serum lysine levels, used for the calculations of whole body protein breakdown rates, were not changed. We conclude: 1) decreased whole body protein breakdown contributes significantly to the decreased nitrogen excretion observed with fasting in obese subjects; and 2) a decrease in circulating levels of free T3 may lead to this adaptive decrease in protein breakdown in fasted obese subjects, since the other hormones measured either did not change or changed in a catabolic direction.

Endocrine effects on nitrogen excretion in the euryhaline teleost, Salmo gairdnerii

Several of the hormones known to be active in the induction of parr-smolt transformation and the migration of salmonids to salt water were administered to nonsmolt freshwater rainbow trout to assess their effects on the nitrogen excretion of fed and starved individuals. Somatotrophin and thyroxine decreased nitrogen excretion in the fed fish, whereas cortisol was without effect. In the starved fish, cortisol caused an increase in the excretion of nitrogen, but somatotrophin and thyroxine were ineffective. Simultaneous administration of cortisol and somatotrophin to nonsmolt freshwater fish produced a pattern of nitrogen excretion similar to that observed in freshwater smolt and salt water fish, decreasing the nitrogen excretion of fed fish but inducing an increase in starved fish. It is suggested that the hormones responsible for the regulation of euryhalinity in rainbow trout have an important influence on the different specific growth and nitrogen excretion rates found at the various stages in its life history.

Diagnostic and prognostic value of short-term metabolic response to human growth hormone in short stature.

Metabolic tests of the response to three days of administration of human growth hormone (HGH) have been done on 55 patients aged 6·2 to 20·3 years. 22 had `isolated9 growth hormone deficiency (or hyposomatotrophic short stature, HS), 16 CNS tumours or multiple hormone deficiencies, 6 short stature associated with low birthweight, 3 psychosocial short stature, 4 Turner9s syndrome, 1 hereditary short stature, and 3 uncertain diagnosis. Height was measured at 3-monthly intervals for a full year, then HGH was given for a full year and the difference in rate, that is the acceleration during the growth hormone year, was calculated. The height measurements were all done by one measurer in 45 of the patients. In the metabolic test there were 5 baseline days followed by 3 days of a single injection of 10 IU HGH, then 2 final days. The means for urinary nitrogen excretion, blood urea, and urinary calcium excretion were calculated for the 5 baseline days and for the last 2 HGH days plus the one subsequent day. The difference between the means is given as a percentage of baseline values. The children with isolated growth hormone (GH) deficiency had a greater decrease in nitrogen excretion (33±3%) than the low birthweight cases and small children (7±5%), but there was overlap between individuals in the isolated deficiency group (range 12 to 66%) and the rest (range -12% to 42%); 2 deficient children were below a dividing line of 20%, and 1 Turner9s syndrome and 3 psychosocial short stature children were above it. The tumour and multiple deficiency patients had an average fall of 40±3% and showed no overlap with the low birthweight group. Blood urea and calcium excretion gave a worse separation. Within the isolated deficiency and the tumour and multiple deficiency groups there was no relation between any metabolic parameter and the amount of growth acceleration in the first year of HGH treatment. In the HS, though not in the tumour patients, there was a correlation (-0·60) between the decrease in percentage nitrogen excretion and peak GH level on stimulation and between per cent decrease in urinary nitrogen excretion and per cent decrease in blood urea (0·76). We conclude that the differential diagnostic value of the short-term metabolic test is very limited now that we have tests of GH response; and that in cases of isolated GH or multiple pituitary hormone deficiency the result of the metabolic test does not predict at all the height acceleration obtained on HGH treatment.