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PubMed1995

Influence of a 36-h fast on the central and peripheral components of VO2 during submaximal exercise and peak oxygen uptake.

To determine if a 36-h fast affects the central and peripheral components of VO2 during submaximal exercise and peak oxygen uptake (VO2 peak), 10 physically healthy males exercised first for 10 min at approximately 60% of their VO2 peak and then to fatigue. Their cardiovascular responses were compared with those of 10 physically healthy controls (males) who were individually matched by VO2 peak values. Fasting had no significant effect on the central (heart rate, HR; stroke volume, SV; cardiac output, Q) and peripheral (arteriovenous oxygen content difference, a-vO2 diff.) components of VO2 during submaximal exercise. The respiratory exchange ratio (RER) during submaximal exercise was significantly decreased in the fasted subjects. Based on the RER, fasting altered substrate utilization of the muscle and thereby increased the contribution of fat during submaximal exercise. Fasting had no significant effect on VO2 peak, HR or O2 pulse, but RER was significantly lower during incremental exercise to fatigue. These results demonstrate that VO2 during submaximal exercise in fasted subjects is achieved by similar central and peripheral responses as found in non-fasted subjects, and that fasting does not reduce VO2 peak.

Adult↗
PubMed2003

The short-term effects of fasting on the neuroendocrine system in patients with chronic pain syndromes.

It is commonly reported that short term fasting leads to mood enhancement and emotional harmonisation. We investigated psychosocial well-being and the neuroendocrine response, assessed by nightly urinary excretion of cortisol and catecholamines, in 28 inpatients with chronic pain syndromes during and after a one-week modified fast. Twenty-two of the patients (51.4 +/- 2.7 years, BMI 26.8 +/- 1.0 kg/m2) participated in a 7-day fast with daily intake of 300 kcal/day, six control patients (47.5 +/- 4.0 years; BMI 22.9 +/- 1.1 kg/m2) received a vegetarian-based diet. With fasting significant increases of the urinary concentration of noradrenaline (17.8 +/- 3.0-27.8 +/- 3.8 microg/ml), adrenaline (1.5 +/- 0.2-3.4 +/- 0.7 microg/ml) and cortisol (26.1 +/- 3.7-40.7 +/- 6.1 microg/ml) were observed, whereas controls showed no significant endocrine changes. The neuroendocrine response to fasting was pronounced in younger subjects (age <50 years) and in the presence of a BMI >25 kg/m2, moreover the increase in cortisol excretion was significantly higher in subjects with lower baseline cortisol levels. Mood and well-being increased non-significantly in both groups. Fasting was well tolerated, and regarded as beneficial by most fasting patients. Our results show that short-term fasting leads to neuroendocrine activation and may suggest that the extent of this response is dependent on the individual metabolic and endocrine state at baseline.

Affect↗
PubMed2006

Effects of fasting on oxidative stress in rat liver mitochondria.

While moderate caloric restriction has beneficial effects on animal health state, fasting may be harmful. The present investigation was designed to test how fasting affects oxidative stress, and to find out whether the effects are opposite to those previously found in caloric restriction studies. We have focused on one of the main determinants of aging rate: the rate of mitochondrial free radical generation. Different parameters related to lipid and protein oxidative damage were also analyzed. Liver mitochondria from rats subjected to 72 h of fasting leaked more electrons per unit of O(2) consumed at complex III, than mitochondria from ad libitum fed rats. This increased leak led to a higher free radical generation under state 3 respiration using succinate as substrate. Regarding lipids, fasting altered fatty acid composition of hepatic membranes, increasing the double bond and the peroxidizability indexes. In accordance with this, we observed that hepatic membranes from the fasted animals were more sensitive to lipid peroxidation. Hepatic protein oxidative damage was also increased in fasted rats. Thus, the levels of oxidative modifications, produced either indirectly by reactive carbonyl compounds (N(epsilon)-malondialdehyde-lysine), or directly through amino acid oxidation (glutamic and aminoadipic semialdehydes) were elevated due to the fasting treatment in both liver tissue and liver mitochondria. The current study shows that severe food deprivation increases oxidative stress in rat liver, at least in part, by increasing mitochondrial free radical generation during state 3 respiration and by increasing the sensitivity of hepatic membranes to oxidative damage, suggesting that fasting and caloric restriction have different effects on liver mitochondrial oxidative stress.

Animals↗
PubMed1986

Interferon production and replication of infectious bovine rhinotracheitis virus in fasted calves.

Three groups of calves were inoculated intranasally with infectious bovine rhinotracheitis (IBR) virus, to determine any effects of a 3-day fast on virus replication and interferon (IFN) production measured in nasal secretions (NS). One group ("fasted") was inoculated 24 h after onset of the fast and another ("refed") at the end of fasting, immediately before refeeding. A third ("control") group was inoculated but not fasted. In fasted calves, overall mean virus excretion (during the first 5 postinoculation days) did not differ from that in control calves, though average virus excretion was higher on days 3 and 4, 24 and 48 h after refeeding. In refed calves, overall mean virus excretion was lower (p less than 0.05), yet on day 5 these calves secreted two times more IFN than nonfasted calves. Analysis of the overall data (all 5 postinoculation sampling days) showed that fasted calves produced more IFN (p less than 0.05), with IFN titers sometimes exceeding 1000, than either control nonfasted calves or refed calves. We conclude that fasting enhanced the ability of calves to produce IFN, and this did not result from increased IBR virus replication.

Animals↗
PubMed1996

Effects of metoclopramide on fasting-induced TSH suppression.

Short-term caloric deprivation leads to suppression of TSH secretion in healthy subjects, but the mechanism of this effect is unknown. Since dopamine inhibits TSH secretion at physiologic levels, increased endogenous dopamine activity may cause the TSH suppression observed during fasting. To test this hypothesis, 11 healthy subjects underwent four studies: (1) Baseline-subjects were allowed ad libitum food. (2) MCP-subjects were allowed ad libitum food and received iv metoclopramide (MCP) at 30 micrograms/kg/h over 48 h. (3) Fasting-subjects received no caloric intake for 56 h. (4) Fasting+MCP-subjects fasted for 56 h, and received iv MCP during the final 48 h of the study. Serum TSH levels were measured every 15 min during the final 24 h of each study, and a TRH stimulation test was performed at the conclusion of each study: 56 h of fasting decreased 24 h mean TSH levels and TSH pulse amplitude by 40%, with blunting of the TSH response to TRH. MCP infusions increased 24 h mean TSH levels and TSH pulse amplitude 26-34%, with no differences between the fasting and nonfasting studies. MCP infusions did not normalize TSH levels, TSH responses to TRH, or serum T3 levels during fasting. These data suggest that endogenous dopaminergic activity does not play a major role in fasting-induced TSH suppression in healthy subjects.

Adolescent↗
PubMed2001

Whole-body and adipose tissue glucose metabolism in response to short-term fasting in lean and obese women.

BACKGROUND: Alterations in glucose metabolism during early fasting may be an important trigger of the hormonal and metabolic responses to fasting. OBJECTIVE: The purpose of this study was to determine whether glucose metabolism in response to brief starvation differs in lean and abdominally obese women. DESIGN: We evaluated whole-body glucose metabolism by use of stable-isotope tracer methods and glucose uptake in subcutaneous abdominal adipose tissue by use of arteriovenous balance in 7 lean [58 +/- 2 kg; body mass index (BMI; in kg/m(2)): 21 +/- 5] and 6 abdominally obese (96 +/- 2 kg; BMI: 36 +/- 1) women after 14 and 22 h of fasting. RESULTS: Between 14 and 22 h of fasting, whole-body glucose production and disposal declined in both groups (P < 0.05), but the reduction was 50% greater in lean than in obese women (P < 0.05). The decline in glucose uptake at 22 h of fasting was also lower in obese (0.11 +/- 0.04 micromol*100 g(-1) x min(-1)) than in lean (0.26 +/- 0.03 micromol x 100 g(-1) x min(-1)) women (P < 0.05). Decreases in plasma insulin and leptin concentrations between 14 and 22 h of fasting were also lower in obese than in lean women (insulin: 20 +/- 3% and 32 +/- 5%; leptin: 18 +/- 3% and 37 +/- 6%; both P < 0.05). CONCLUSIONS: The normal decline in glucose production and uptake that occurs during early fasting is blunted in women with abdominal obesity. These alterations in glucose metabolism are associated with a blunted decline in circulating concentrations of both insulin and leptin, which may explain some of the differences in the metabolic response to fasting observed between lean and abdominally obese persons.

Abdomen↗
PubMed2005

Decreases in fasting leptin and insulin concentrations after acute energy restriction and subsequent compensation in food intake.

BACKGROUND: The decrease in leptin after energy restriction is a starvation signal to the brain. Several studies have found an association between this decrease and subjective appetite; however, no solid data are available on the acute decrease in fasting leptin concentration and subsequent caloric compensation. OBJECTIVE: The objective was to assess the effect of acute decreases in fasting leptin concentrations, induced by energy restriction, on subsequent energy intake compensation. We hypothesized that men with a large decrease in fasting leptin concentrations would have larger ad libitum energy intakes than would men with a small decrease in leptin. DESIGN: Thirty-four male unrestrained eaters [age: 23 +/- 3 y; body mass index (in kg/m(2)): 22.3 +/- 1.6] participated in a semicontrolled intervention study. Fasting serum leptin and insulin concentrations were measured before and 2 d after 62% energy restriction. Energy intake was measured on the 2 following days on which food was provided ad libitum. RESULTS: During energy restriction, fasting leptin and insulin concentrations decreased by 27.2% (95% CI: -34.4%, -19.9%) and 30.7% (95% CI: -41.0%, -20.4%), respectively. Subjects consumed 143 +/- 27% of their estimated energy requirements (18.3 +/- 2.9 MJ) on the first day and 124 +/- 20% (16.0 +/- 2.6 MJ) on the second day of ad libitum intake. No significant correlations were observed between decreases in fasting leptin or insulin concentrations and subsequent ad libitum energy intake; however, decreases in insulin were correlated with an increase in carbohydrate intake (r=-0.49, P < 0.01). CONCLUSION: Although fasting leptin concentrations decreased significantly during energy restriction and subjects showed compensatory behavior during subsequent ad libitum food intake, no association was observed between the decrease in fasting leptin concentrations and caloric compensation.

Adult↗
PubMed2006

Higher fasting plasma concentrations of glucagon-like peptide 1 are associated with higher resting energy expenditure and fat oxidation rates in humans.

BACKGROUND: Glucagon-like peptide 1 (GLP-1) is a gut hormone that decreases appetite and promotes satiety. Its role in energy metabolism regulation is still poorly understood. OBJECTIVE: The aim of the study was to investigate the relation of fasting plasma GLP-1 concentrations to rates of energy expenditure (EE) and substrate oxidation-ie, respiratory quotient (RQ). DESIGN: Forty-six glucose-tolerant white subjects (22 men, 24 women) aged 18-49 y whose adiposity spanned a wide range [body mass index (in kg/m2): 18.5-50] were studied in an inpatient clinic. Main outcome measures included resting EE and RQ (ventilated hood technique), body composition (dual-energy X-ray absorptiometry), and fasting plasma concentrations of GLP-1, pancreatic polypeptide, glucose, and insulin. RESULTS: Fasting plasma GLP-1 concentrations were positively associated with resting EE (after adjustment for age, sex, and body composition) and negatively correlated with RQ (after adjustment for age, sex, and percentage body fat) and fasting plasma pancreatic polypeptide concentrations (both before and after adjustment for age, sex, percentage body fat, and fasting plasma glucose and insulin concentrations). Adjustment for fasting plasma pancreatic polypeptide concentrations, a marker of parasympathetic outflow to the gut, attenuated the strength of the association of fasting plasma GLP-1 concentrations with resting EE and RQ. CONCLUSIONS: Higher fasting plasma GLP-1 concentrations are associated with higher rates of EE and fat oxidation independent of age, sex, and body composition. The autonomic nervous system may have a role in this relation. This effect, along with the established role of GLP-1 in promoting satiety, may further foster its therapeutic potential in the treatment of obesity.

Absorptiometry, Photon↗
PubMed2003

Rats habituated to chronic feeding restriction show a smaller increase in olfactory bulb reactivity compared to newly fasted rats.

During the 1970s, the multiunit reactivity of the olfactory bulb to food odor was extensively shown to increase before their usual meal in rats habituated to having a single 2 h daily meal compared to the same rats recorded after their usual meal. More recently, we reported dramatic modifications of mitral cell single-unit reactivity in adult rats following a simple a manipulation of the olfactory environment--exposure to an odor. The present study aimed at testing the hypothesis that a simple behavioral change such as habituation to chronic food restriction may induce profound changes in olfactory bulb responsiveness compared to occasional fasting. We compared mitral cell reactivity in non-fasted rats, in rats fasted during 22 h for the very first time, and in rats habituated during 15 days to a chronic 22 h food restriction. Mitral cell single-unit reactivity was found to increase less in rats habituated to fasting than in newly fasted rats. Indeed, the proportion of mitral cell responses to food and non-food odors was significantly higher in rats habituated to fasting than in non-fasted rats, but lower than in newly fasted rats. The proportion of simple unsynchronized and synchronized responses of 1b and 2b types was also lower in habituated rats whereas the proportion of complex synchronized responses of 4b type increased. This decreased responsiveness in habituated rats, similar to that observed in rats repeatedly exposed for 20 min per day to an odor during six consecutive days in our previous studies, is discussed with respect to olfactory bulb plasticity.

Animals↗
PubMed1986

Changes in energy metabolite and regulatory hormone concentrations and net fluxes across splanchnic and peripheral tissues in fed and progressively fasted ewes.

Effects of fasting on glucose, ketone bodies, free fatty acids (FFA), insulin and glucagon metabolism were studied in eight fed, five 1-d-fasted and five 3-d-fasted ewes. The 3-d fast decreased blood glucose from 55 to 49 mg/dl due to a 40% reduction in its splanchnic output. Plasma FFA increased from 280 to 872 and 912 microM in 1- and 3-d-fasted ewes concomitant with increased omental and peripheral release. Hepatic uptake of FFA increased three- and fourfold and was concentration-dependent. Consequently, hepatic release of acetoacetate and beta-hydroxybutyrate increased from -43 and 276 to 90 and 1304 mumol/min, respectively, in 3-d-fasted ewes. Alimentary ketogenesis ceased entirely due to lack of substrate and gut tissue was actually utilizing both ketone bodies by d 3 of fast. Lower hindquarter utilization of both ketone bodies increased with increasing circulating concentrations. Insulin seemed to be the major mechanism of regulation of glucose, FFA and ketone body metabolism since pancreatic production and arterial concentrations of insulin decreased with progressive fasting. No changes were observed in glucagon concentrations or net fluxes, and therefore the role of glucagon was passive and secondary to that of insulin.

Animals↗
PubMed1987

Effect of short fasts on the development of tibial dyschondroplasia in chickens.

The length of time each day that feed is available to young broiler-type chickens significantly influenced the development of tibial dyschondroplasia. Birds that were fasted for 8 or 10 h per day had reduced incidences of tibial dyschondroplasia as compared to birds fed ad libitum (5-11% vs. 59-68%). When birds were fasted for only 2 or 4 h each day there was no significant effect on the development of tibial dyschondroplasia. Birds fasted for 8 h every other day or every 4th d had lower incidences of tibial dyschondroplasia compared to ad libitum fed controls. Fasting for 8 h on the 4th d or the 4th and 8th d of a 20-d experiment had no effect on the incidence of tibial dyschondroplasia as compared to controls. Except for the daily fasting there was little effect of fasting on 20-d body weight or gain per feed intake. Fasting increased the percent bone ash in the tibia in all experiments. Fasting had no effect on total calcium, ultrafilterable calcium, dialyzable phosphorus or growth hormone levels in plasma taken from the birds the 18th and 19th day. The hour of the day that the birds were bled had a significant influence on the plasma total calcium, dialyzable phosphorus and growth hormone levels.

Animals↗
PubMed1987

Beneficial effects of exercise on growth of rats during intermittent fasting.

An 8-wk trial was conducted to compare the effects of exercise and intermittent fasting, either singly or combined, on growth responses of rats. Four-week-old male Wistar rats, 85-110 g each, were assigned to one of four groups (n = 9): control, exercise on a motor-driven treadmill, fasting every other day (EOD) and fasting EOD and exercise combined. At the end of the trial, the exercised rats had consumed 7% less feed, had gained 7% less weight and had 36% less carcass fat than the control rats. Fasting on alternate days markedly reduced the growth rate of the young rats. Fasted-EOD rats weighed less than half as much as the control rats, had 64% less carcass fat and 51% less lean mass and had smaller livers, kidneys, hearts, tibias and tibialis anterior muscles. The addition of exercise to the fasting EOD regimen improved the growth of the animals. When the fasted-EOD rats were also exercised, they gained 29% more weight, consumed 11% more feed and had carcasses that contained 29% more lean mass and 18% less fat than the fasted-EOD rats. The data suggest that exercise may be beneficial where feed restriction is episodic, allowing some capacity for catch-up growth.

Animals↗
PubMed1994

Nitrogen balance, plasma free amino acid concentrations and urinary orotic acid excretion during long-term fasting in cats.

The purpose of this study was to ascertain the changes in nitrogen balance, plasma free amino acid concentrations, urinary orotic acid excretion and body weight during long-term fasting in adult obese cats. Results from eight cats that fasted rather than eat an unpalatable diet are reported. After 5 to 6 wk of weight loss, six of the eight cats developed signs of hepatic lipidosis, and the livers of all cats were severely infiltrated with lipids. Cats lost (mean +/- SE) 33.2 +/- 1.4% of their pre-fasting body weight. Mean nitrogen balance (+/- SE) was -547 +/- 54 mg.d-1.kg-2/3 for the first week, and then the net nitrogen losses decreased to a plateau (-303 +/- 52 mg.d-1.kg-2/3) after 4 wk. Fasting was associated with a decrease in plasma concentration of essential amino acids. When plasma amino acid concentrations were considered individually, concentrations of alanine, methionine, taurine, citrulline, arginine and tryptophan decreased the most (> or = 50%), whereas concentrations of glutamine, glutamate and ornithine significantly increased. Orotic acid was not detected in the urine during the fast. After 1 wk of fasting, obese cats had reduced nitrogen excretion, but not to the same extent as has been shown in obese humans or obese rats. It is suggested that the availability of several amino acids may become limiting for liver protein synthesis during fasting and that these deficiencies may contribute to the development of hepatic lipidosis. Orotic acid was not linked to hepatic lipidosis caused by fasting in cats.

Amino Acids, Essential↗
PubMed2003

Performance and physiological parameters of broiler chickens subjected to fasting on the neonatal period.

Broiler chicks aged 12 h after hatching were allotted according to a block design in a 7 x 2 factorial schedule of 14 treatments and four replications of 50 chicks each one. The main experimental factors were fasting for 0, 6, 12, 18, 24, 30, and 36 h after chick placement and sex. Independent of sex, fasting had a negative linear effect on weight and productivity of broilers at market age (42 d) without affecting feed conversion or mortality index. Groups subjected to 18 and 36 h of fasting after placement, corresponding to 30 and 48 h posthatching fasting, had lower biometrical values for small intestine (length, weight, and size; villus height; and crypt depth) than chicks fed immediately after placement. According to the Pearson test, BW of birds at 21 and 42 d were significantly correlated to BW at 7 d (r=0.77) and 21 d (r=0.45), respectively. Males performed better than females but had higher mortality rates. Fasting did not influence serum concentrations of corticosterone or sexual steroid hormones. Nevertheless, early signs of sexual dimorphism arose from the high estradiol (E2) concentration on female serum. Heterophil:lymphocyte ratio was not different among treatments, indicating that early fasting did not seem to be a stress factor 21 or 42 d after fasting. The results suggested a maximum fasting of 24 h after hatching in order to preserve broiler productivity at market age.

Aging↗
PubMed1990

Induction of type II T4-5'-monodeiodinase activity in brown adipose tissue in fasted mice.

In order to study the effect of starvation on brown adipose tissue (BAT) type II 5'-monodeiodinating activity (5'MDI), type II 5'MDI was measured in vitro in the presence of 20 mM dithiothreitol, 1 mM propylthiouracil, 2 nM thyroxine (T4) and appropriate amounts of 600 X g infranatant of BAT from fed control or 3 day fasted mice, with or without daily T4 replacement (1.2 micrograms/100 g bw) during starvation. I- released from 125I-T4 was measured by ion-exchange column chromatography. Activity of BAT 5'MDI was markedly elevated in the 3 day fasted group (133 +/- 28 fmol I-/h per mg protein vs. 26 +/- 6.4; p less than 0.05). Kinetic studies using BAT infranatant suggested that fasting-induced activity is associated with a similar change in the Vmax, but no demonstrable change in apparent Km of T4 monodeiodination. T4 replacement during fasting, which normalized both serum T4 and T3 in fed and 3 day fasted groups, did not stop the increase of BAT 5'MDI in the fasted group (p less than 0.01). The data suggest that: (1) the fasting-induced increase in BAT 5'MDI is due mainly to the changes in capacity rather than the affinity of the enzyme, and (2) the fasting-induced increase in BAT 5'MDI is not mediated entirely through changes in serum thyroid hormone concentration.

Adipose Tissue↗
PubMed1990

Carbohydrate tolerance improves with fasting in obese subjects with noninsulin-dependent (type II) diabetes.

To determine the effects of short-term fasting on carbohydrate tolerance, 10 obese women with noninsulin-dependent diabetes mellitus (NIDDM) were studied with meal tolerance tests before and after 3 days of fasting. After 3 days' fast, basal serum glucose declined from 15.2 +/- 0.9 to 7.5 +/- 0.7 mmol/L (273 +/- 17 to 135 +/- 13 mg/dL) (mean +/- SEM, p less than 0.001) and the glycemic response to the test meal (area under the glucose curve) improved by 31%. There were no changes in basal or postprandial insulin levels but a slight increase in serum c-peptide. Resting metabolic rate and the thermic effect of food were unchanged. There was a slight but insignificant change in basal and postprandial free fatty acid levels and a significant elevation of basal beta-hydroxybutyrate levels. Blood lactate rose significantly (from 0.9 to 2.0 mM) during the initial meal tolerance test, but no rise in lactate was seen in the meal tolerance test after fasting. Two subgroups of patients were identified based on the degree of glycemic improvement after short-term fasting. Those with lesser improvement in serum glucose showed overnight rises in serum glucose during the period of fasting (the dawn phenomenon), while those patients who normalized serum glucose showed a steady fall in serum glucose. This finding may help to predict the glycemic response to long-term calorie restriction. Carbohydrate tolerance improves in obese diabetic (NIDDM) women after 3 days of fasting, in contrast to the impairment of glucose tolerance seen in lean or obese nondiabetic subjects after fasting.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxybutyric Acid↗
PubMed2003

Fasting blood glucose is independently associated with resting and exercise blood pressures and development of elevated blood pressure.

OBJECTIVE: To assess whether fasting blood glucose is independently related to blood pressure at rest and during exercise, and to development of elevated blood pressure. DESIGN: Cross-sectional and prospective cohort study of 2014 apparently healthy middle-aged men. METHODS: The baseline survey included carefully standardized blood pressure measurements at rest and during exercise testing, an intravenous glucose tolerance test and a panel of fasting blood tests, including fasting blood glucose. Results from 7-years follow-up provided data on development of elevated blood pressure. RESULTS: Strong associations were found between quartiles of fasting blood glucose and baseline resting and/or exercise levels of blood pressure, and also development of elevated blood pressure over 7 years. Physical fitness, calculated from an exercise test, had a strong modulating effect on blood pressure at all levels of fasting blood glucose. In multivariate models - after adjusting for intravenous glucose tolerance, physical fitness, age, body mass index, triglycerides and cholesterol - fasting blood glucose was strongly associated with blood pressure at rest (coefficient = 2.83, P = 0.0004) and during exercise (coefficient = 6.57, P < 0.0001), and further to development of treated hypertension and/or elevated blood pressure [odds ratio (OR), 1.17; 95% confidence interval (CI), 1.05-1.31]. CONCLUSION: In healthy non-diabetic and non-hypertensive men, strong associations were found between fasting blood glucose and blood pressure at rest and during exercise and to development of elevated blood pressure after 7-years follow-up. Fasting glucose metabolism deserves scrutiny when studying the pathogenesis of hypertension.

Adult↗
PubMed1985

Influences of fasting and water intake on plasma refill during hemorrhagic shock.

The hyperglycemic response to hypovolemia has been regarded as an essential osmotic force for promoting the early phase of the internal restoration of plasma volume. Our previous studies of rats fasted 24 hours revealed that they did not develop the hyperglycemic response to hemorrhage observed in fed animals but they had a similar hyperosmotic response. The solutes responsible for the hyperosmolality in the fasted animals were primarily products of anaerobic glycolysis, rather than glucose which accounted for most of the hyperosmolality in fed animals. Plasma refill as reflected by a fall in the hematocrit (Hct) and survival time was significantly reduced in the fasted animals. This study was undertaken to test the hypothesis that the failure of fasted rats to exhibit a normal restoration of plasma volume after hemorrhage may reflect the detrimental effects of fasting on the state of hydration and on the plasma oncotic pressure of the fasted animals rather than the absence of a hyperglycemic response. Four groups of anesthetized rats (280-380 gm) were bled acutely and maintained at an arterial pressure of 40 mm Hg. Before hemorrhage animals in Group A were well fed, those in Groups B, C, and D were fasted for 24 hours. Rats in Group B were induced to drink by addition of sodium chloride in their water, rats in Group C spontaneously had a normal fluid intake, and rats in Group D had a significant reduction in their 24-hour fluid intake. The results demonstrated that 24 hours of fasting led to a loss of body weight of 7 to 10% and a fall in the concentration of plasma total protein of 12 to 17% in all rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗