Changes in plasma glucose and liver glycogen following the administration of gluconeogenic precursors to the starving fowl

Physiology and behavior of the hen during induced molt

Feed deprivation has been adopted by the commercial egg industry to induce molt because it is the easiest method to apply and produces the best results. Feed deprivation, however, raises concerns about animal welfare. Birds respond to long-term feed deprivation in three phases. The first phase lasts at most a few days, during which physiological and behavioral adjustments ultimately reduce protein catabolism and energy expenditure. A temporary increase in plasma corticosterone may be observed at this time. Corticosterone promotes gluconeogenesis, helping to maintain plasma glucose levels in the initial stage of the fast. The corticosterone increase may also be linked to increased activity in feed-deprived birds. Hens have been observed to manifest temporarily increased levels of alertness and activity during the first 48 h of feed deprivation. Aggressive behavior of hens also has been observed to increase briefly during the first day of feed deprivation. The second phase is the longest, during which proteins are spared and lipids are catabolized to provide energy. This phase may last several months in some species; in the chicken it can continue more than 20 d. Hens show increasing amounts of resting behavior during this phase. The third phase begins when protein catabolism accelerates. A pathological stage eventually is reached when the bird will cease activity and no longer eat. The phased response to feed deprivation optimizes a tradeoff between the need to maintain constant levels of plasma glucose to sustain activity and the need to preserve critical body structures such as muscles and organs. Hens are capable of vigorous activity throughout feed deprivation periods typical of induced molts, which do not appear to take birds beyond the second phase of fasting. Hens having undergone extended fasts may also have improved livability. Alternative induced molting methods are being sought to reduce animal welfare concerns. The methods of current interest involve alteration of feeding regimen and cause at least some body weight loss. These alternative methods should be evaluated to ensure that they do not actually make aspects of hen welfare worse compared to feed withdrawal, which might happen if hens perceive feed restriction without being allowed to progress fully into the second phase of adaptation to feed deprivation.

Early changes in plasma hormones and metabolites during fasting in king penguin chicks

Chicks of the king penguin (Aptenodytes patagonica) can tolerate a fast of 4-6 months during the subantarctic winter. The aim of this work was to study their initial response to food deprivation. Nine chicks were starved for 18 days. Two phases of starvation were defined according to changes in the specific daily loss in body mass: it decreased by 92% in phase I (6.6 +/- 0.3 days) and remained steady and low in phase II. Phase I was marked by a large decline in protein utilization, indicated by decreases in plasma levels of alanine (58%), uric acid (89%) and urea (76%) together with a decrease in circulating corticosterone (60%) and thyroxine (75%). In phase I, plasma insulin concentration decreased (61%) in some birds, but did not change in others; plasma pancreatic glucagon was stable whereas gut-glucagon decreased by 75%. Free fatty acids and beta-hydroxybutyrate concentrations gradually rose during the fast to 5 to 6 times pre-fast levels. Glycemia remained unchanged. Phase II was characterized by no change in plasma concentrations of protein-derived metabolites and by no or little change in circulating hormone levels. From comparison with previous data, we conclude that there are similar early adjustments to food deprivation in king penguin chick, rat and man: (1) a decrease in resting metabolic rate, (2) a decrease in protein utilization, and (3) mobilization of fat stores. The key adaptations to long-term fasting in these species are therefore effectiveness in protein sparing and ability to prolong this situation.(ABSTRACT TRUNCATED AT 250 WORDS)

Uricoteley:its nature and origin during the evolution of tetrapod vertebrates

The hepatic mechanism for detoxication of ammonia formed during amino acid gluconeogenesis in uricotelic vertebrates requires the intramitochondrial synthesis of glutamine by glutamine synthetase. This glutamine then serves as a precursor of uric acid in the cytosol. The evolutionary development of uricoteley thus required the localization of glutamine synthetase in liver mitochondria. The mechanism for the mitochondrial import of glutamine synthetase in uricotelic vertebrate liver is not yet known. Tortoises, extant relatives of the stem reptiles, possess both the ureotelic and uricotelic hepatic systems. It therefore seems likely that the genetic events allowing the mitochondrial localization of glutamine synthetase in liver occurred in the amniote amphibian ancestors of the stem reptiles. The selection of ureoteley by the theropsids and of uricoteley by the sauropsids were major events in the divergence and subsequent evolution of these two lines. Once established in the sauropsid line, uricoteley has persisted through to the higher reptiles, crocodilians, and birds. Uricoteley was in part responsible for the radiation of the archosaurs during the Triassic as a water-conserving mechanism in the adult, thereby allowing them to invade the arid environments of that period. Contrary to dogma, uricoteley was probably of minor significance in the development of the cleidoic egg. Neither mammalian nor avian embryonic liver tissues catabolize amino acids to any great extent, so it is inappropriate to attribute to them a kind of "waste" nitrogen metabolism.

Kidney gluconeogenesis: its importance to net glucose synthesis during the development of chick embryos

A technique is described for the preparation of viable isolated kidney tubules from chick embryos. Assessment of the potencies of various possible gluconeogenic precursors indicates that kidney is the site of net glucose synthesis from physiologically relevant precursors during embryonic life. The plasma concentrations of physiological gluconeogenic precursors was determined and the rates of glucose synthesis by tubules was measured from a precursor mixture which stimulated plasma contents.

Effect of starvation and protein-feeding on blood amino acid compartmentation of domestic fowl hatchlings

The amino acid concentrations in plasma and blood cells of 5-day old domestic fowl hatchlings that received either standard feeding, protein-feeding or were starved have been determined. The effects of 5-day starvation or protein feeding did not alter significantly the combined amino acid concentration of blood plasma, but decreased blood cell levels. The patterns of individual amino acid changes observed in starvation or protein-feeding were similar in both groups when compared with those of controls. However, starvation-induced effects were actually more marked than those observed in protein-fed animals. The patterns of change with starvation of individual amino acids in the hatchling blood compartments were very different from those observed in mammals subjected to short or medium-term starvation. The mechanisms controlling circulating amino acid concentrations act in both situations studied to maintain the plasma amino acid concentrations despite marked changes in the availability of 2-amino nitrogen energy to the animal; changes in blood amino acid compartmentation buffering plasma amino acid availability.

Hormonal effects and the control of gluconeogenesis from sorbitol, xylitol and glycerol in perfused chicken liver

Addition of sorbitol or xylitol to perfused chicken liver caused a biphasic increase in the rate of glucose production. The second increase correlated with a decrease in the lactate to pyruvate ratio. Increased glucose production in response to the addition of glycerol was not biphasic. Aminooxyacetate inhibited both the inherent second increase in glucose production and stimulatory effects of alanine and pyruvate. The stimulatory effects of norepinephrine and glucagon on gluconeogenesis from sorbitol decreased in the presence of methylene blue. Only the stimulatory effect of norepinephrine was inhibited by aminooxyacetate.

Effect of starvation and a protein diet on the amino acid metabolism enzyme activities of the organs of domestic fowl hatchlings

The activities of alanine and aspartate transaminases, adenylate deaminase, glutamine synthetase and glutamate and xanthine dehydrogenases have been measured in liver, yolk sac membrane, intestine and breast and leg muscle of domestic fowl hatchlings receiving for 3 or 5 days either a standard diet or hard boiled eggwhite as well as in 3 or 5 days starved animals. The patterns of activation of amino acid metabolism enzymes were fully comparable in protein-fed and starved groups with respect to fed controls; the differences with respect to the latter became more marked in 5- than in 3-days old chicks. In 5-days old chicks intestine alanine transaminase activity increased in parallel to that of liver in protein-fed animals but not in those starved, in agreement with an enhanced alanine transfer between both organs under this situation. Both, starvation and protein-feeding, induced a general decrease in the amino acid metabolizing ability of muscle. Glutamine (but not alanine) synthetizing capabilities were enhanced.

Pattern of protein profiles of reproductive organs after induced bilateral cryptorchidism in albino rats

Bilateral cryptorchidism was induced surgically in albino rats and pattern of protein profiles was studied in reproductive organs. Cryptorchidism activated tissue proteolysis leading to overall degradation in soluble and structural protein fractions and in amino acids leading to prevalence of negative nitrogen balance in the reproductive organs. The testicular hypoalbuminic and hypoglobulinic conditions seem to be responsible for oligo-astheno-spermia associated with cryptorchidism.

The influence of fasting on chicken liver metabolites, enzymes and mitochondrial respiration

Chicken liver mitochondria were isolated in relatively pure form as indicated by electron microscopy and marker enzyme assay. The rate of respiration, respiratory control index and ADP/O ratios with several different substrates indicated that chicken liver mitochondria are more uncoupled than rat liver mitochondria. Chickens have ten-fold higher malate concentrations in liver than do rats, 2-oxoglutarate was also more abundant in chicken livers. Fasted birds had a five-fold increase in beta-hydroxybutyrate as compared with fed birds; whereas malate and lactate concentrations decreased. Fasted birds had increased levels of isocitrate dehydrogenase (NADP dependent) and lactate dehydrogenase in the cytosol, and increased malate dehydrogenase (NAD dependent), isocitrate dehydrogenase (NADP dependent) and malic enzyme activities in the mitochondria.

Ketogenesis in chick embryo isolated hepatocytes

Isolated hepatocytes from 17-day chick embryos exhibit high endogenous rates of ketogenesis. The addition of long-chain fatty acids stimulated ketogenesis with potency ordered as follows: palmitate greater than oleate greater than stearate. Octanoate produced a slight stimulation of ketogenesis when added at low concentrations (less than 0.25 mM). At higher concentrations the effect of octanoate was inhibitory. The addition of glucose to incubations failed to lessen endogenous ketogenesis whereas propionate, pyruvate and lactate produced inhibition. Ketogenesis from both endogenous sources and added fatty acids was not altered by the addition of glucagon, insulin, adrenalin or vasopresin.

Changes in glucose and lipid metabolism in starved or starved-refed Japanese quail (coturnix coturnix japonica) in relation to fine structure of liver cells

1. Metabolic response of adult quail to fasting or refeeding was studied by measuring the main blood and hepatic metabolites. Moreover, the fine structure of hepatocytes in these physiological conditions was described. 2. Starvation or refeeding did not affect glycemia in male as in female quails. 3. Fasting had no effect on plasma free fatty acids in female quails, whereas plasma triglycerides were markedly decreased. 4. In fasted quails, there was an active ketogenesis with a high 3-hydroxybutyrate/acetoacetate ratio. 5. Ultrastructural aspect of liver parenchymal cells from fasted quails revealed alterations in the quantity of glycogen, smooth endoplasmic reticulum, lysosomes and in the form of the rough endoplasmic reticulum. 6. The significance of these morphological changes was discussed in relation to an hormonal stimulation.

A comparison of the effects of infection with Eimeria maxima and dietary restriction on weight gain, plasma metabolites and liver glycogen in the immature fowl, Gallus domesticus

The effects of Eimeria maxima or restricted pair-feeding on weight gain, plasma concentrations of protein, glucose, free fatty acids (FFA) and uric acid and liver glycogen were compared in immature fowl. Food intake/kg body weight and weight gain decreased during the acute phase of infection (days 5-7) while weight loss was prolonged for an extra day compared with pair-fed birds. During recovery, food intake/kg body weight of infected birds was greater than that of non-infected controls but there was no evidence for an increase in growth rate compared with controls when body weight was considered. Growth rate of pair-fed birds was greater than that of infected birds during recovery, indicating their better use of ingested food. Liver glycogen and plasma protein concentration were decreased during the acute phase of infection but the concentrations of plasma glucose, free fatty acid (FFA) and uric acid were not affected. In pair-fed birds liver glycogen was depleted, concentrations of plasma glucose and uric acid decreased and FFA increased, and these changes persisted for the remainder of the experiment. The findings are similar to those in birds whose food has been withheld and were probably due to the pattern of food intake imposed by the experimental protocol. It is concluded that the metabolic differences between infected and pair-fed birds are of doubtful significance.

Metabolites of citric acid cycle, carbohydrate and phosphorus metabolism, and related reactions, redox and phosphorylating states of hepatic tissue, liver mitochondria and cytosol of the pigeon, under normal feeding and natural nocturnal fasting conditions

1. The metabolite profile of intact pigeon liver differs greatly from that of pigeon liver homogenates or of the isolated perfused pigeon liver. 2. As compared to the rat liver, there are much higher glycerol-3-phosphate, Pi, and malate contents of the pigeon liver, and much lower 6-phosphogluconate, fructose-1,6-diphosphate, phosphoenolpyruvate, ammonium, ATP, and the sum of adenine nucleotides. The other metabolites in livers of both species do not differ significantly. 3. Pigeon liver mitochondria concentrate phosphoenolpyruvate completely, and accumulate lactate against a concentration gradient. There are rather high mitochondrial malate, glutamate, and aspartate, but low mitochondrial alpha-ketoglutarate and adenine nucleotides. 4. Cytosolic Pi concentration is 1,5-fold higher than mitochondrial one in the fed pigeon liver and 4-fold lower than that in the starved liver. Cytosolic phosphorylation potential, and NAD+/NADH and NADP+/NADPH ratios are from 3- to 7-fold lower than those in the rat liver. 5. In contrast to the rat liver, cellular glucose-1-phosphate, glucose-6-phosphate, fructose-1,6-diphosphate, glutamate, alpha-ketoglutarate and aspartate increase in the starved pigeon liver, and glycerol-3-phosphate, phosphoenolpyruvate, Pi, and adenine nucleotides decrease. Cellular and cytosolic phosphorylation potentials rose without any change in cytosolic NAD+/NADH and NADP+/NADPH ratios. 6. It is concluded that pigeon liver differs from mammalian one and therefore it is of special interest for metabolic studies.

Gluconeogenesis in isolated chicken (Gallus domesticus) liver cells

1. Gluconeogenesis was studied in isolated avian hepatocytes. The highest rate of glucose production obtained was from lactate, followed by dihydroxyacetone, glyceraldehyde, and fructose. Alanine was converted to glucose at only about 4% the rate of lactate. 2. Addition of 10 mM sorbitol, xylitol, or ethanol to the hepatocytes increased glucose production from pyruvate 25-40%, while glycerol addition increased it only 9%. 3. Addition of beta-hydroxybutyrate had no effect on glucose production from lactate or pyruvate. 4. Addition of octanoate had no effect on glucose production from pyruvate, but depressed it from lactate at 5 mM. 5. Differences in the formation of glucose from various substrates suggest some basic differences in the mode of glucose production between the chick and the rat and guinea-pig.

Hepatic gluconeogenesis in chickens

Gluconeogenesis by isolated hepatocytes resulted in glucose release but insignificant rates of glycogen synthesis. The effectiveness of precursors was similar for hepatocytes from fed and starved chickens except for impaired gluconeogenesis from pyruvate when compared to lactate in lactate starved chicken hepatocytes. The impairment was caused by limitations in cytosolic NADH production as a result of the mitochondrial location of phosphoenolpyruvate carboxykinase in chicken liver. The order of effectiveness of precursors on hepatic gluconeogenesis was generally similar to the effects of precursors on increasing the plasma glucose concentration in vivo. The exceptions were caused by interactions with other precursors in vivo. The alteration of the NADH/NAD+ ratio by ethanol and ATP/ADP ratio by adenosine could play significant roles in the control of precursor conversion to glucose. Physiological glucagon concentrations stimulated gluconeogenesis from precursors entering the pathway both above and below the level of triose phosphates, and its effect were mimicked by dibutyryl cyclic AMP. Previous results on the effects of precursor and glucagon injection on the plasma glucose concentration of chickens in vivo can largely be explained by effects at the hepatic level. Isolated chicken and rat hepatocytes share many common features. Qualitatively the ordering of gluconeogenic effectiveness was similar but quantitive differences existed as a result of differing activities and cellular locations of enzymes. Neither preparation readily synthesised glycogen and the sensitivity to glucagon was similar.

Glucose phosphorylation and dephosphorylation in chicken liver

1. Glucokinase was absent from chicken liver and only the low Km hexokinases, inhibited by AMP, ADP but not ATP, were present. 2. The Km of chicken liver glucose-6-phosphatase for glucose-6-phosphate was reduced from 5.65 to 3.75 mM following starvation, and the enzyme was inhibited by glucose. 3. Starvation of chickens for 24 hr slightly lowered the hexokinase activity and doubled glucose-6-phosphatase activity; it did not change subcellular distribution of the enzymes. Oral glucose rapidly restored the activities to fed values. 4. It was concluded that glucose uptake into, and efflux from, chicken hepatocytes, was regulated by the activity and kinetic characteristics of glucose-6-phosphatase and by the glucose-6-phosphate concentration, and that the hexokinases had little regulatory function.