Fasting and refeeding cause rapid changes in intestinal tissue mass and digestive enzyme capacities of Atlantic salmon (Salmo salar L.)

Fasting and refeeding effects on gastrointestinal morphology and digestive enzyme activities of Atlantic salmon, held in tanks of seawater at 9°C and 31‰ salinity, were addressed in two trials. Trial 1: Fish (mean body mass 1190 g) were fasted for 40 days and intestines sampled at day 0, 2, 4, 11, 19 and 40. Trial 2: Fish (1334 g), fasted for 50 days, were refed and sampled at day 0, 3 and 7. Mass, length, protein, and maltase, lactase, and leucine aminopeptidase (LAP) activities were analyzed for stomach (ST), pyloric caeca (PC), proximal (PI), mid (MI), and distal intestine (DI). PC contributed 50% of gastrointestinal mass and 75% of enzyme capacity. Fasting decreased mass and enzyme capacities by 20–50% within two days, and 40–75% after 40 days. In PC, specific brush border membrane (BBM) maltase activity decreased whereas BBM LAP increased during fasting. Upon refeeding, enzyme capacities were mostly regenerated after one week. The results suggest that refeeding should start slowly with about 25% of estimated feed requirement during the first 3 days, but may then be stepped up rapidly. Investigations of digestive processes of fed fish should only be performed when intestines are feed-filled to avoid bias due to effects of fasting.     

Feeding activates protein synthesis in mouse pancreas at the translational level without increase in mRNA

To determine the mechanism of meal-regulated synthesis of pancreatic digestive enzymes, we studied the effect of fasting and refeeding on pancreatic protein synthesis, relative mRNA levels of digestive enzymes, and activation of the translational machinery. With the use of the flooding dose technique with L-[3H]phenylalanine, morning protein synthesis in the pancreas of Institute for Cancer Research mice fed ad libitum was 7.9 +/- 0.3 nmol phenylalanine.10 min(-1).mg protein(-1). Prior fasting for 18 h reduced total protein synthesis to 70 +/- 1.4% of this value. Refeeding for 2 h, during which the mice consumed 29% of their daily food intake, increased protein synthesis to 117.3 +/- 4.9% of the control level. Pancreatic mRNA levels of amylase, lipases, trypsins, chymotrypsin, elastases, as well as those for several housekeeping genes tested were not significantly changed after refeeding compared with fasted mice. By contrast, the major translational control pathway involving Akt, mTOR, and S6K was strongly regulated by fasting and refeeding. Fasting for 18 h decreased phosphorylation of ribosomal protein S6 to almost undetectable levels, and refeeding highly increased it. The most highly phosphorylated form of the eIF4E binding protein (4E-BP1) made up the 14.6% of total 4E-BP1 in normally fed animals, was only 2.8% after fasting, and was increased to 21.4% after refeeding. This was correlated with an increase in the formation of the eIF4E-eIF4G complex after refeeding. By contrast, feeding did not affect eIF2B activity. Thus food intake stimulates pancreatic protein synthesis and translational effectors without increasing digestive enzyme mRNA levels.     

Short-term fasting induces intra-hepatic lipid accumulation and decreases intestinal mass without reduced brush-border enzyme activity in mink (<Emphasis Type="Italic">Mustela vison</Emphasis>) small intestine

For many mammalian species short-term fasting is associated with intestinal atrophy and decreased digestive capacity. Under natural conditions, strictly carnivorous animals often experience prey scarcity during winter, and they may therefore be particularly well adapted to short-term food deprivation. To examine how the carnivorous gastrointestinal tract is affected by fasting, small-intestinal structure, brush-border enzyme activities and hepatic structure and function were examined in fed mink (controls) and mink that had been fasted for 1–10 days. During the first 1–2 days of fasting, intestinal mass decreased more rapidly than total body mass and villus heights were reduced 25–40%. In contrast, tissue-specific activity of the brush-border enzymes sucrase, maltase, lactase, aminopeptidase A and dipeptidylpeptidase IV increased 0.5- to1.5-fold at this time, but returned to prefasting levels after 6 days of fasting. After 6–10 days of fasting there was a marked increase in the activity of hepatic enzymes and accumulation of intra-hepatic lipid vacuoles. Thus, mink may be a useful model for studying fasting-induced intestinal atrophy and adaptation as well as mechanisms involved in accumulation of intra-hepatic lipids following food deprivation in strictly carnivorous domestic mammals, such as cats and ferrets.Communicated by I.D. Hume     

Brown fat activity in fasted and refed rats

Four days of fasting in the rat reduced brown-adipose-tissue (BAT) mass, mitochondrial protein, and tissue protein content. Specific binding of guanosine diposphate (GDP) to BAT mitochondria was depressed by 55% in 4d-fasted rats. Rats fasted for 3 d, and then refed a single carbohydrate meal (40 kJ), showed a significant increase in specific GDP-binding (27% above fasted) 24 h later, and a large increase in total binding. Specific activities of cytochrome oxidase and -glycerophosphate dehydrogenase in BAT mitochondria were not significantly affected by fasting or refeeding. These results suggest that BAT may be partly responsible for the fall in metabolic rate associated with fasting and the delayed increase after carbo-hydrate refeeding. These effects may be due to changes in the mitochondrial proton-conductance pathway in brown fat.     

Physiological and morphological responses to the first bout of refeeding in southern catfish (Silurus meridionalis)

Many animals experience fasting because of the high temporal and spatial sporadicity of food availability. Once food is available, animals use external energy to restore their depressed functional performance. In the present study, the physiological and morphological responses to the first bout of refeeding in juvenile southern catfish (Silurus meridionalis) were characterized. Fish that had undergone long-term fasting (fasted for 32 days, the S32 group) exhibited a lower resting metabolic rate ( $ {\dot{\text{M}}} $ O_2rest decreased by 49 %), lower peak metabolic rate ( $ {\dot{\text{M}}} $ O_2peak decreased by 24 %), greater energy expenditure (increased by 15 %) during specific dynamic action (SDA) and longer duration SDA response (increased by 41 %) than those of a control group (S0 group, fasted for 0 days). The S32 group showed a significantly reduced peak gastric evacuation rate (0.131 g meal h^?1) compared with the S0 group (0.315 g meal h^?1). The S0 group also had a shorter gastric evacuation time (36 h) than either of the two fasting groups (both 64 h). The S32 group displayed a higher minimum gastric pH (3.1) than the S0 and S16 groups (2.6). Refeeding did not trigger an increase in the wet mass of the gastrointestinal tract, whereas the liver wet mass of the S0 and the two fasting groups increased significantly with refeeding. The trypsin and lipase of the S0 group showed higher mass-specific activities and organ capacities than either of the two fasting groups at certain specific time points. A similar result was found for aminopeptidase activity. Multiple loach meals equaling 6 % of the body weight of the fed fish completely restored the liver morphology within the S16 but not the S32 group. Our results suggest that the regulation of the digestive performance of the gastrointestinal tract in S. meridionalis that are finishing their first small meal after fasting is delayed compared with that of nonfasting fish and that it is similar to the characteristics (lower $ {\dot{\text{M}}} $ O_2peak, greater SDA and a longer duration of the SDA response) of the refeeding SDA.     

The response of lipoprotein lipase to feeding and fasting. Evidence for posttranslational regulation

The regulation of adipose tissue lipoprotein lipase (LPL) was examined in rats fed or fasted overnight, and was found to be controlled posttranslationally. LPL catalytic activity decreased by 50% after fasting while LPL mRNA levels and rates of synthesis increased nearly 2-fold; enzyme mass remained unchanged. The distribution of LPL within the endoplasmic reticulum (ER) and Golgi/post-Golgi secretory pathway was assessed by differentiating between LPL high mannose and complex forms. After fasting, the majority of LPL is in the high mannose ER form (65%, 0.97 micrograms/g wet weight tissue), whereas the LPL complex form comprises only 35% (or 0.52 micrograms/g). After refeeding, however, the Golgi-derived LPL complex form predominates (65%, 1.03 micrograms/g) over the high mannose ER form (35%, 0.55 micrograms/g). Kinetic analysis suggests that high mannose LPL disappears with a half-life of t0.5 = 40 min in both fed and fasted rats, indicating that the redistribution of LPL mass during feeding/fasting does not arise by differential retention within ER. Instead, the fractional catabolic rate of complex LPL within the Golgi/post-Golgi secretory compartment can be calculated to be 3.5-fold greater in fasting. In heart, changes in LPL activity in response to feeding/fasting are also not due to differences in mRNA levels or rates of synthesis. Based on these findings, a model of LPL posttranslational regulation is proposed and discussed.     

Differences in the expression of lipolytic-related genes in rat white adipose tissues

We have investigated in vivo whether the gene expression of the beta3-adrenergic receptor (beta3-AR), perilipin A, hormone-sensitive lipase (HSL), and adipocyte lipid-binding protein (ALBP/aP2) is regulated in a site-specific manner. To induce lipolysis and discriminate between short- and long-term modifications, rats were submitted to an experimental fast for one or five days followed or not by refeeding. The mRNA encoding beta3-AR in retroperitoneal adipose tissue (RP) was significantly increased by one and five days of fasting (4-fold) and then lowered by one day of refeeding (2-fold) compared to fed rats. The reverse trend was observed for perilipin A expression in one day fasted rats. HSL mRNA concentrations were significantly induced (2.2-fold) by five days of fasting relative to fed animals and remained high after refeeding. ALBP/aP2, peroxisome proliferator-activated receptor gamma, and CAAT/enhancer binding protein alpha mRNA levels were essentially unaffected by dietary manipulations. Fasting and/or refeeding were similarly ineffective at regulating gene expression in SC. These data provide a molecular basis for regional differences at different steps of the lipolytic process.     

Physiological responses to short-term fasting among herbivorous,omnivorous, and carnivorous fishes

We explored the integrated role of dietary specialization and feeding periodicity on the response of the gastrointestinal tract of teleosts fishes to short-term (7–10 days) fasting and refeeding. Fasted and fed herbivorous grass carp (Ctenopharyngodon idella), omnivorous channel catfish (Ictalurus punctatus), and carnivorous largemouth bass (Micropterus salmoides) were compared for digestive organ masses, intestinal morphology, gastrointestinal pH, and the specific activities and total intestinal capacities of the intestinal hydrolases aminopeptidase (APN) and maltase and intestinal nutrient transporters. All three species experience intestinal hypertrophy with feeding as noted by significant increases in enterocyte dimensions. Of the three, only I. punctatus experienced a postprandial increase in intestinal length, and only C. idella experienced significant modulation of intestinal microvillus length. Feeding resulted in acidification of the stomachs of I. punctatus and M. salmoides. Predicted to exhibit a relatively modest set of postprandial responses because of their more frequent feeding habits, C. idella only experienced increases in APN and maltase activity with feeding and no significant regulation of nutrient uptake. Significant regulation of hydrolase activities and nutrient uptake were exhibited by I. punctatus and M. salmoides, with I. punctatus experiencing the most comprehensive set of responses. As predicted by food habits, there was an interspecific gradient in intestinal length and glucose uptake extending from longer intestines and greater glucose uptake for the herbivorous C. idella, intermediate lengths and glucose uptake for the omnivorous I. punctatus, and shorter intestines and reduced glucose uptake for the carnivorous M. salmoides. Among teleosts fishes, short episodes of fasting lead to significant alterations in intestinal form and function that are rapidly restored with feeding.     

The effects of fasting and refeeding on serum parathormone and calcitonin concentrations in young and old male rats.

Although fasting and refeeding reveal the existence of age-related changes in carbohydrate and lipid metabolism, the effects of aging on mineral metabolism in refed animals are unknown. We therefore investigated hormonal regulation of calcium metabolism in young (4 months) and old (26 months) male rats fasted for 48 hours and then refed for 4 or 24 hours. Serum concentrations of total and ionized calcium and parathormone were similar in control young and old rats. Serum calcitonin level was higher, and the concentrations of albumin and inorganic phosphate and alkaline phosphatase activity were lower in fed old rats. In young fasted rats, the serum ionized and total calcium was decreased, and phosphate concentration was increased. In old rats, fasting resulted in the increase of serum parathormone level. Fasting reduced serum alkaline phosphatase activity to a similar extent in both age groups. In young rats, refeeding for 24h normalized serum calcium and phosphate levels and alkaline phosphatase activity, and decreased serum concentrations of PTH and calcitonin. In old refed rats, serum calcitonin concentration was raised by 77% compared to fed or fasted animals, whereas parathormone levels were normalized. Our results indicate that old fasted or refed rats maintain normal serum calcium concentration in a different way than young animals, possibly through the increase in serum levels of parathormone and/or calcitonin. Thus, dietary manipulations such as fasting and refeeding constitute an interesting model for the investigation of the effects of aging on the hormonal regulation of serum calcium level.     

Effects of fasting and refeeding on antral, duodenal, and serum gastrin levels and on colonic thymidine kinase activity in rats

Antral, duodenal, and serum gastrin levels and colonic thymidine kinase activity were determined in 1- to 4-day-fasted rats and after refeeding of 4-day-fasted rats for 3-24 h. The effect of pentagastrin on colonic thymidine kinase activity was also determined. Total deprivation of food caused a drastic reduction in gastrin concentrations in serum and tissues. After 4 days of fasting, serum gastrin levels in most animals fell below the present detection limit of the assay (10-15 pg/ml), and antral and duodenal gastrin levels decreased to 15 and 50% of the respective initial fed control. After 9 and 24 h of refeeding, gastrin concentration in serum and antrum had increased to about 35% of the initial fed level. On the other hand, refeeding for 3-24 h produced no significant change in duodenal gastrin concentration. Fasting for 1-4 days resulted in a 60-70% reduction in colonic thymidine kinase activity, compared to the initial fed control. Refeeding caused a prompt stimulation in the enzyme activity, which after 6 h was found to be 72% above the 4-day-fasted group. Daily injection of pentagastrin, at doses between 125 and 500 micrograms/kg, during a 4-day fasting period resulted in a significant stimulation in colonic thymidine kinase activity, compared to the saline-treated control. The maximal stimulation of an enzyme activity 90% higher than in the saline control was attained with a pentagastrin dose of 125 micrograms/kg. Higher doses decreased the maximal stimulatory effect of pentagastrin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intermittent fasting during winter and spring affects body composition and reproduction of a migratory duck

We compared food intake, body mass and body composition of male and female black ducks (Anas rubripes) during winter (January-March). Birds were fed the same complete diet ad libitum on consecutive days each week without fasting (control; nine male; nine female) or with either short fasts (2 day x week(-1); nine male; nine female), or long fasts (4 day x week(-1); eleven male; twelve female). We continued treatments through spring (March-May) to measure the effect of intermittent fasts on body mass and egg production. Daily food intake of fasted birds was up to four times that of unfasted birds. Weekly food intake of males was similar among treatments (364 g x kg(-1) x week(-1)) but fasted females consumed more than unfasted females in January (363 g x kg(-1) x week(-1) vs. 225 g x kg(-1) x week(-1)). Although both sexes lost 10-14% body mass, fasted females lost less mass and lipid than unfasted females during winter. Total body nitrogen was conserved over winter in both sexes even though the heart and spleen lost mass while the reproductive tract and liver gained mass. Intermittent fasting increased liver, intestinal tissue and digesta mass of females but not of males. Fasting delayed egg production in spring but did not affect size, fertility or hatching of the clutch. Females on long fasts were still heavier than controls after laying eggs. Thus black ducks combine flexibility of food intake with plasticity of digestive tract, liver and adipose tissue when food supply is interrupted during winter. Females modulate body mass for survival and defer reproduction when food supply is interrupted in spring.     

Effect of fasting on body composition and responses to stress in sunshine bass

The integrated responses of the hormonal regulation of growth and stress in sunshine bass (Morone chrysops X Morone saxatilis) as regulated by feed deprivation were investigated. Groups of fish were fed 1.5% of the body weight per day or offered no feed for 4 weeks. Another group of fish was not fed for 3 weeks and feed was offered during the fourth week. Fish in each group were sampled immediately before or after a 15-min low water confinement stressor after each week of the experiment. Liver mass and liver glycogen content were decreased after one week of fasting and remained low until the end of the study. However, both recovered after a week of refeeding. Intraperitoneal fat was significantly lower after two weeks of fasting and did not recover after a week of refeeding. None of these components were affected by confinement stress. Plasma glucose in unstressed fish was generally unaffected by fasting or refeeding; however, plasma glucose increased after confinement stress in fed but not in fasted fish. The cortisol stress response was unaltered by fasting and remained robust. Plasma IGF-I generally decreased in fasted fish but was not significantly lower than fed fish until the fourth week. A week of refeeding did not restore plasma IGF-I concentrations. Plasma IGF-I concentrations were higher in confinement stressed fed fish after two and four weeks but were unchanged in the fourth week. There was no change in the plasma IGF-I concentrations in fasted or refed fish due to the stress. Liver weight and liver glycogen were essentially depleted after 2 weeks of fasting. The reduction of liver glycogen greatly reduced the glucose response to stress; however, the cortisol stress response was maintained for at least four weeks of fasting. Intraperitoneal fat was decreased very little after 4 weeks of fasting. Plasma IGF-I concentrations were reduced only after 3 weeks of fasting.     

Metabolic control of phosphorylase conversion in muscle. Effect of fasting and refeeding on the response of rat diaphragm glycogen phosphorylase, cyclic AMP Dependent protein kinase, and phosphorylase b kinase to adrenergic stimulation.

The influence of fasting and refeeding on the response to adrenergic stimulation of several enzymes involved in glycogen metabolism has been investigated in the isolated, intact rat diaphragm. The in vitro response of the phosphorylase system to terbutaline was found to decrease markedly following fasting. A pronounced increase in this response was seen upon refeeding. This increased responsiveness was normalized by incubation of isolated tissues with palmitate (1.5 mM). Plasma free fatty acid concentration was increased in fasted rats compared to the value found in refed animals. The effect of terbutaline on cyclic AMP concentration and protein kinase activity was not significantly influenced by fasting and refeeding while fasting decreased the effect of terbutaline upon phosphorylase b kinase. Diaphragm glycogen levels were reduced by more than 50% in rats fasted for 24 hours and were significantly increased upon refeeding compared to fed rats. The results indicate that the nutritional state can modulate the sensitivity of the interconverting system for phosphorylase. It is suggested that this modulation might depend upon fatty acid metabolism.     

Leptin concentrations in plasma and follicular fluid from prepubertal gilts as influenced by fasting, refeeding and insulin.

This study's aim was to examine whether fasting and refeeding would influence leptin levels in both plasma and follicular fluid from prepubertal gilts, and whether insulin affects leptin levels in fasting gilts. In experiment 1, four gilts were fasted for 72 h and then refed. Blood samples were withdrawn during normoalimentation, at the end of fasting, and for 4 h after refeeding. All samples were assayed for leptin; alternate samples were assayed for insulin, glucose and non-esterified fatty acids (NEFA). Fasting caused a decrease in leptin, glucose and insulin levels in plasma, while NEFA concentrations increased. In experiment 2, four gilts were given insulin as a bolus (0.2 IU/kg body weight) after 68 h of fasting. Blood samples were collected every 15 min around insulin administration and were assayed for leptin, insulin and glucose. This experiment shows that insulin administration increases leptin levels during fasting. In experiment 3, gilts were ovariectomized during normal alimentation (n=4), after 48 h of fasting (n=4), and after 48 h of realimentation following 48 h of fasting (n=4). Leptin levels in both plasma and follicular fluid collected after 48 h of fasting were significantly lower than those observed during normoalimentation or refeeding. In conclusion, a transient increase in insulin during fasting is effective in restoring leptin concentrations; in addition, leptin levels in follicular fluid parallel those in plasma.     

The effect of fasting and refeeding on the composition and synthesis of triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines in rat liver

Refeeding a high-sucrose, fat-free diet to fasted rats caused drastic alterations in the fatty acid composition of hepatic diacylglycerols, triacylglycerols, and phosphatidylcholines. However, the fatty acid profile of phosphatidylethanolamines did not change significantly. These results suggest that the fatty acid composition of diacylglycerols may influence the distribution of diacylglycerols among triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines. Fasting and refeeding also affected the activities in vitro of a number of enzymes responsible for the formation of triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines. The activity of hepatic phosphatidate phosphatase increased fourfold upon refeeding. However, fasting the rats did not affect the activity of this enzyme despite the reduced triacylglycerol synthesis in the fasted liver in vivo. Fasting and refeeding induced alterations in the activities of diacylglycerol acyltransferase, cholinephosphotransferase, and ethanolaminephosphotransferase which correlated reasonably well with the changes observed in the synthesis of triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines in vivo, although the changes in diacylglycerol acyltransferase were too moderate. The changes in the activity of cholinephosphate cytidylyltransferase, which is suggested to catalyze the rate-limiting step in the formation of CDP-choline, ran parallel with the alterations in the synthesis of phosphatidylcholines in vivo. No such correlation was found between the activity of ethanolaminephosphate cytidylyltransferase and the rate of phosphatidylethanolamine synthesis. The present results indicate that the synthesis of triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines is controlled by the availability of the various substrates as well as by the activities of several enzymes involved in these processes.     

Effect of fasting and refeeding on the activities of monoamine oxidase and antioxidant enzymes in rat hypothalamus and brown adipose tissue

Fasting for 48 h and the same period of recovery induced by 48 h refeeding increased rat hypothalamic monoamine oxidase (MAO) activity. However, in the interscapular brown adipose tissue (IBAT), only refeeding induced a significant elevation of the enzyme activity. As far as hypothalamic antioxidative enzymes are concerned, the copper zinc superoxide dismutase (CuZnSOD) activity was decreased in refed rats only. However, in the IBAT both food deprivation and refeeding induced a significant decrease in catalase (CAT) activity. Under the influence of fasting the adrenal glands were strongly activated as judged by the increased dopamine-beta-hydroxylase (DBH) activity and decreased cholesterol concentration. Refeeding brought both parameters to control levels indicating full recovery of these glands. As expected, fasting for 48 h induced a significant decrease in serum glucose but an increase in FFA concentrations. Thus, it can be concluded that both fasting and refeeding resulted in increased activation of hypothalamic MAO, whereas CuZnSOD activity was decreased only by refeeding. However, in the IBAT only refeeding increased MAO activity whereas both fasting and refeeding decreased that of CAT. In conclusion, it may be assumed that food deprivation for 48 h and the same duration of refeeding influenced MAO and antioxidative enzymes activities in the rat hypothalamus and IBAT in a tissue specific manner.     

Insulin-like growth factor I and glucagon-like peptide-2 responses to fasting followed by controlled or ad libitum refeeding in rats

Luminal nutrients stimulate structural and functional regeneration in the intestine through mechanisms thought to involve insulin-like growth factor I (IGF-I) and glucagon-like peptide-2 (GLP-2). We investigated the relationship between IGF-I and GLP-2 responses and mucosal growth in rats fasted for 48 h and then refed for 2 or 4 days by continuous intravenous or intragastric infusion or ad libitum feeding. Fasting induced significant decreases in body weight, plasma concentrations of IGF-I and bioactive GLP-2, jejunal mucosal cellularity (mass, protein, DNA, and villus height), IGF-I mRNA, and ileal proglucagon mRNA. Plasma IGF-I concentration was restored to fed levels with 2 days of ad libitum refeeding but not with 4 days of intravenous or intragastric refeeding. Administration of an inhibitor of endogenous GLP-2 (rat GLP-2 3-33) during ad libitum refeeding partially attenuated mucosal growth and prevented the increase in plasma IGF-I to fed levels; however, plasma GLP-2 and jejunal IGF-I mRNA were restored to fed levels. Intragastric refeeding restored intestinal cellularity and functional capacity (sucrase activity and sodium-glucose transporter-1 expression) to fed levels, whereas intravenous refeeding had no effect. Intestinal regeneration after 4 days of intragastric or 2 days of ad libitum refeeding was positively associated with increases in plasma concentrations of GLP-2 and jejunal IGF-I mRNA. These data suggest that luminal nutrients stimulate intestinal growth, in part, by increased expression of both GLP-2 and IGF-I.     

The effects of starvation and refeeding on plasma amino acid levels in carp, Cyprinus carpio L., 1758

Plasma amino acid (AA) levels of carp, Cyprinus carpio L., 1758, were analysed after various periods of starvation as well as after 12 days of refeeding. The levels were compared to control groups, which had been previously fasted for 24 h. A positive correlation between dietary and plasma essential amino acid (EAA) concentrations was observed in all of the control groups.
The effect of starvation on the dynamics of AA concentration was different according to the period of starvation. Fasting already produced a decrease of total α-AA levels at 2 days, and these low levels were maintained until 5 and 8 days. These short periods of fasting affected the levels of EAA (especially branched-chain AA) more than those of non-essential amino acids (NEAA). The only AA that increased was Ala, which rose at 5 days of starvation, surpassing the levels of the control group. These high levels were maintained until 19 days of starvation.
A different situation was observed at 19 days, when an important increase of total α-AA levels was produced, the branched-chain AA being the most notable among EAA and Glu/Gln among NEAA. Later, at 50 days of starvation, total α-AA, EAA (except Leu and Ile) and NEAA decreased.
After 50 days of starvation, 12 days of refeeding did not modify the levels of EAA and NEAA, and their concentrations were lower than those of the control group, which presented an increase of total AA at this time. The differences observed on the changes of individual AA levels are discussed.     

Effect of dietary polyamines and alpha-difluoromethylornithine on regulation of intestinal Na+/H+ exchanger

Polyamines are compounds required for initiation of rapid cellular growth and differentiation in many cell types. Ornithine decarboxylase is the rate limiting enzyme in polyamine synthesis. Fasting and refeeding regulates the activity of ornithine decarboxylase and polyamine content in the intestinal tract. We tested the hypothesis that polyamines regulate cell growth via the Na+/H+ exchanger which is believed to be intimately involved in cell growth. Ileal Na+/H+ activity was therefore examined in control, fasted, refed fasted, and in rats given the specific inhibitor of ornithine decarboxylase alpha-difluoromethylornithine. A well-validated ileal brush border membrane vesicles for the study of Na+/H+ exchange activity was utilized. Fasting markedly decreased while refeeding stimulated Na+/H+ exchange activity at all times studied (P less than 0.05-0.001). Maximal uptake of Na+ at 5 min was 3.12 +/- 0.05, 2.5 +/- 0.05 and 2.22 +/- 0.05 nmol/mg protein in refed, control and fasted rats respectively. Kinetics of amiloride sensitive Na+/H+ exchanger showed a Vmax of 17.1 +/- 3.5, 8.0 +/- 0.64 and 4.7 +/- 1.1 nmol/mg protein per 5 s in refed fasted, control and fasted rats respectively Km values were not significantly different between the groups studied. 2% alpha-difluoromethylornithine given in the drinking water abolished the stimulation in Na+/H+ exchange activity in refed fasted rats. These results suggest a close relationship between polyamines and Na+/H+ activity in the intestinal mucosa of rats.     

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.