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PubMed1990

Secretory pattern of growth hormone, insulin, and related metabolites in growing male turkeys: effects of overnight fasting and refeeding.

The effect of an overnight fast on the secretory profile of growth hormone (GH), insulin, and related metabolites [glucose, nonesterified fatty acids (NEFA) and triglycerides (TG)] was determined in two separate experiments with 8- and 9-wk-old male turkeys. Toms were provided feed ad libitum or were fasted 20 h prior to sampling. Blood samples (.6 to .7 mL) were collected every 10 min for 8 h from the toms showing a positive weight gain between cannulation and the initiation of the experiment. Overall and baseline, GH levels were higher for the fasted birds versus the fed birds. The GH peaks for the fasted birds were of shorter duration than those for the fed birds, but were more frequent. The plasma NEFA levels of the fasted birds were higher than those of the fed birds. Plasma TG was lower for the fasted than the fed group. Insulin, which was secreted in a pulsatile fashion, was lower for the fasted versus the fed birds. Fasting produced no change in plasma glucose. A separate group of fasted males was refed after 4 h of sampling; the plasma levels of GH, insulin, and metabolites returned to those observed in birds given feed ad libitum within 30 min of refeeding. There appeared to be no relation between the pulsatile release of GH and the circulating levels of NEFA.

Animal Feed↗

PubMed1999

Translocation of protein kinase C isoforms in rat muscle in response to fasting and refeeding.

Weanling rats were offered food ad libitum, or fasted for 18 h, or fasted and refed for times ranging from 5 to 30 min. Five protein kinase C (PKC) isoforms (alpha, epsilon, zeta, theta and mu) were detected in the hindlimb muscles by Western immunoblotting. PKC forms epsilon and theta were abundant in plantaris, but not in soleus muscle, and no difference in localization was detected between fed rats and those fasted for 18 h. PKC forms alpha and mu were affected by fasting and refeeding. PKC-mu was found only in the cytosolic fraction of the plantaris muscle of the fasted animal, but in the fully-fed animals it was also associated with the membrane fraction. The pattern of localization observed in the fully-fed state was restored in the fasted rats by 20 min refeeding. In contrast, PKC-alpha was not detected in the cytosolic fraction of the plantaris in fasted animals but rapidly reappeared there on refeeding, being restored to 20% and 80% of the fed value within 5 and 30 min of refeeding respectively. The timing of these changes was correlated with the increase in serum insulin concentration, which was significantly elevated above the fasted value by 5 min and at subsequent times. These data suggest a possible role for PKC isoforms alpha and mu in the metabolic changes that occur in skeletal muscle on transition between the fasted and the fed state.

Animals↗

PubMed2001

Cystatin C is an independent predictor of fasting and post-methionine load total homocysteine concentrations among stable renal transplant recipients.

BACKGROUND: An increased prevalence of hyperhomocysteinemia with an increased incidence of cardiovascular disease events has been reported among stable renal transplant recipients (RTRs). Preliminary studies in a small number of these individuals have shown that serum creatinine and cystatin C, both markers of kidney function and glomerular filtration rate, are independent determinants of fasting tHcy concentrations; however, determinants of tHcy concentrations after a methionine load have not been studied. METHODS: We determined the prevalence of both fasting and 4-h post-methionine load (PML) tHcy concentrations in 78 stable RTRs and compared the role of cystatin C with the role of serum creatinine as determinants of fasting and PML tHcy. RESULTS: Of the 78 RTRs, 21 (26.9%) had fasting and PML tHcy within the respective reference intervals, and 57 (73.1%) had increased plasma tHcy. Of these 57 RTRs, 22 had fasting hyperhomocysteinemia, 9 had PML hyperhomocysteinemia, and 26 had combined hyperhomocysteinemia (both fasting and PML). Unadjusted Pearson correlations showed that fasting plasma tHcy correlated with both cystatin C (r = 0.564; P <0.001) and creatinine (r = 0.519; P <0.001) and that increases in PML tHcy modestly correlated with cystatin (r = 0.205; P = 0.072), but not creatinine (r = 0.057; P = 0.624). General linear regression modeling with stepwise analysis of covariance showed that both cystatin C (partial R = 0.554; P <0.001) and creatinine (partial R = 0.535; P <0.001) were independent predictors of fasting tHcy, but of the two, only cystatin C (partial R = 0.242; P = 0.035) was an independent predictor of increased PML tHcy. CONCLUSIONS: Clinically stable RTRs have an excess prevalence of moderate hyperhomocysteinemia, and additional cases can be detected by methionine loading. Both creatinine and cystatin C are independent predictors of fasting tHcy in these individuals; however, only cystatin C is a determinant of tHcy concentration after a methionine load, probably because cystatin C is a more sensitive marker of glomerular filtration rate than serum creatinine.

Adult↗

PubMed2001

Fasting-induced changes in the expression of genes controlling substrate metabolism in the rat heart.

During fasting, when overall metabolism changes, the contribution of glucose and fatty acids (FA) to cardiac energy production alters as well. Here, we examined if the heart is able to adapt to such fasting-induced changes by modulation of its gene expression. Rats were fed ad libitum or fasted for 46 h, resulting in reduced circulating glucose levels and a 3-fold rise in FA. Besides changes in the cardiac activity or content of proteins involved in glucose or FA metabolism, mRNA levels also altered. The cardiac expression of genes coding for glucose-handling proteins (glucose transporter GLUT4, hexokinase I and II) was up to 70% lower in fasted than in fed rats. In contrast, the mRNA levels of various genes involved in FA transport and metabolism (FA translocase/CD36, muscle-type carnitine palmitoyl transferase 1, long-chain acyl-CoA dehydrogenase) and of the uncoupling protein UCP-3 increased over 50% in hearts of fasted rats. Surprisingly, mRNA levels of the fatty acid- activated transcription factors PPARalpha and PPARbeta/delta were reduced in hearts of fasted rats, whereas in livers, fasting led to a marked rise in PPARalpha mRNA. Reducing FA levels by nicotinic acid administration during the final 8 h of fasting did not affect the expression of the majority of metabolic genes, but totally abolished the induction of UCP-3. In conclusion, the adult rat heart responds to changes in nutritional status, as provoked by 46 h fasting, through adjustment of glucose as well as FA metabolism at the level of gene expression.

Acyl-CoA Dehydrogenase↗

PubMed1992

The effect of fasting on cell proliferation in the gastric mucosa of the 14-day-old suckling rat.

1. The effect of fasting on cell proliferation in the gastric mucosa was investigated in 14-day-old suckling Wistar rats. 2. The renewal of the epithelial cells of the corpus of the stomach was evaluated by DNA labelling and counting arrested metaphases in fifty 14-day old rats fasted for 18 to 21 h and in fifty control suckling rats of the same age. The animals were sacrificed at 3 h intervals over a 24-h period. 3. The metaphase arrest method was also used to estimate the rate of entry of cells into mitosis in the gastric glands of 26 rats under both feeding and fasting conditions. In addition to the proliferative indices, the number of epithelial cells, and the heights of the glands and mucosa were measured morphometrically in 20 rats. 4. No significant differences in the rate of entry of cells into mitosis (number of cells in fasted = 0.49 +/- 0.077 cells 100 cells-1 h-1), in the number of epithelial cells (fasted = 241.2 +/- 24.3 cells/0.023 mm2) or in the height of the gastric glands (fasted = 194 +/- 5.4 microns) of fasted and control rats were observed. Both labelling and metaphase indices (means +/- SEM) were significantly higher (P < 0.01) in the fasted (13.9 +/- 0.57% and 1.3 +/- 0.07%, respectively) suckling rats than in the controls (7.9 +/- 0.39% and 0.9 +/- 0.05%, respectively). 5. These data indicate that fasting stimulates cell proliferation in the gastric mucosa of suckling rats rather than decreasing proliferation, as is the case for adult rats.

Animals↗

PubMed2003

The effect of fasting on the parameters of the antioxidant defence system in the blood of vegetarian human subjects.

OBJECTIVES: Although the evidence is strong that fasting has anti-tumor, anti-inflammatory and anti-ageing actions, the mechanisms responsible for these phenomena are still unclear. An ameliorated antioxidative defence with fasting may be the cause of such effects. The objective of the present work was to determine the influence of fasting on antioxidant systems in healthy young vegetarian humans. DESIGN AND METHODS: We measured Trolox Equivalents Antioxidant Capacity (TEAC) of plasma, erythrocytes superoxide dismutase (SOD) activity, blood glutathione peroxidase (GPx) activity, level of total blood non-proteic thiols (TBNT), plasma ceruloplasmin activity, plasma level of NO metabolites (the sum of nitrites and nitrates, NOx), in 18 healthy young humans (age 20-27 years) after 12h (overnight fasting) and 80h of fasting. RESULTS: Trolox Equivalents Antioxidant Capacity of plasma, the level of total blood nonproteic thiols, plasma ceruloplasmin activity and plasma concentration of nitrites and nitrates were significantly increased after 80h of fasting. Superoxide dismutase activity and glutathione peroxidase activity were lower after 80h of fasting. CONCLUSIONS: Our results suggest that fasting induces the "reorganisation" of antioxidative defence lines: fasting increases especially plasma protective systems (total antioxidant capacity of plasma, plasma ceruloplasmin activity) and decreases an erythrocytes antioxidant enyzme (superoxide dismutase) and blood glutathione peroxidase.

Adult↗

PubMed2004

Usefulness of fasting 18F-FDG PET in identification of cardiac sarcoidosis.

UNLABELLED: Cardiac PET using (18)F-FDG under fasting conditions (fasting (18)F-FDG PET) is a promising technique for identification of cardiac sarcoidosis and assessment of disease activity. The aim of this study was to investigate the usefulness of fasting (18)F-FDG PET in detecting inflammatory lesions of cardiac sarcoidosis from a pathophysiologic standpoint. METHODS: Twenty-two patients with systemic sarcoidosis were classified into 2 groups of 11 each according to the presence or absence of sarcoid heart disease. Cardiac sarcoidosis was diagnosed according to the Japanese Ministry of Health and Welfare guidelines for diagnosing cardiac sarcoidosis with the exception of scintigraphic criteria. Nuclear cardiac imaging with fasting (18)F-FDG PET, (99m)Tc-methoxyisobutylisonitrile ((99m)Tc-MIBI) SPECT, and (67)Ga scintigraphy were performed in all patients. PET and SPECT images were divided into 13 myocardial segments and the standardized uptake value (SUV) of (18)F-FDG was calculated and defect scores (DS) for (99m)Tc-MIBI uptake were assessed for each segment. The total SUV (T-SUV) and total DS (TDS) were calculated as the sum of measurements for all 13 segments, and the diagnostic accuracy of fasting (18)F-FDG PET was compared with that of the other nuclear imaging modalities. In addition, pathophysiologic relationships between inflammatory activity and myocardial damage were examined by segmental comparative study using the SUV and DS. RESULTS: In patients with cardiac sarcoidosis, fasting (18)F-FDG PET revealed a higher frequency of abnormal myocardial segments than (99m)Tc-MIBI SPECT (mean number of abnormal segments per patient: 6.6 +/- 3.0 vs. 3.0 +/- 3.2 [mean +/- SD], P < 0.05). The sensitivity of fasting (18)F-FDG PET in detecting cardiac sarcoidosis was 100%, significantly higher than that of (99m)Tc-MIBI SPECT (63.6%) or (67)Ga scintigraphy (36.3%). The accuracy of fasting (18)F-FDG PET was significantly higher than (67)Ga scintigraphy. The T-SUV demonstrated a good linear correlation with serum angiotensin-converting enzyme levels (r = 0.83, P < 0.01), and the TDS showed a significant negative correlation with the left ventricular ejection fraction (r = -0.82, P < 0.01). In abnormal myocardial segments on the nuclear scan, the SUV showed a significant negative correlation with the DS (r = -0.63, P < 0.0001). CONCLUSION: This study suggests that fasting (18)F-FDG PET can detect the early stage of cardiac sarcoidosis, in which fewer perfusion abnormalities and high inflammatory activity are noted, before advanced myocardial impairment.

Adult↗

PubMed2005

Effects of anesthetic agents and fasting duration on 18F-FDG biodistribution and insulin levels in tumor-bearing mice.

UNLABELLED: Small-animal PET has opened the way for imaging (18)F-FDG uptake in murine tumor models, but the need for anesthesia raises concern over its potential influence on (18)F-FDG kinetics. We thus investigated such effects on cultured cells and on tumor-bearing mice after short- and long-term fasting. METHODS: Lewis lung carcinoma (LLC) cells and cardiomyoblasts were treated for 2 h with a 100 micromol/L concentration of xylazine, ketamine, xylazine plus ketamine (Xy/Ke), or pentobarbital and were measured for (18)F-FDG uptake. LLC tumor-bearing C57BL6 mice that had been kept fasting for either 4 or 20 h were injected with Xy/Ke, pentobarbital, or saline and were administered 1.8 MBq of (18)F-FDG 15 min later. Biodistribution studies and plasma glucose and insulin assays were performed 45 min after injection. Separate anesthetized and control mice underwent (18)F-FDG PET. RESULTS: (18)F-FDG uptake in LLC cells was unaffected by anesthetic agents, whereas xylazine and ketamine caused a small increase of uptake in cardiomyoblasts. In mice kept fasting 4 h, Xy/Ke induced a marked elevation of (18)F-FDG activity (percentage injected dose [%ID]) in blood (6.8 +/- 0.9%ID/g vs. 1.1 +/- 0.6%ID/g) and kidneys while decreasing myocardial uptake (2.3 +/- 1.3%ID/g vs. 4.7 +/- 1.8%ID/g). Target-to-blood ratios were significantly reduced. Pentobarbital caused a moderate increase in blood activity (2.5 +/- 0.8%ID/g), decreased myocardial uptake (2.8 +/- 0.5%ID/g), and reduced target-to-blood ratios. PET images of mice kept fasting 4 h were consistent with the biodistribution data. Insulin levels were lower with Xy/Ke and higher with pentobarbital. In mice kept fasting 20 h, Xy/Ke and pentobarbital increased blood (18)F-FDG activity (5.5 +/- 2.2 and 4.9 +/- 0.9%ID/g vs. 2.4 +/- 0.3%ID/g) and reduced target-to-blood ratios, but these changes were substantially attenuated, compared with those in mice kept fasting 4 h. In addition, insulin levels were low and unaffected by anesthesia. CONCLUSION: Xy/Ke anesthesia markedly elevates blood (18)F-FDG activity and reduces tumor uptake ratios through inhibition of insulin release in mice kept fasting 4 h, whereas pentobarbital induces a similar but less severe response through insulin resistance. These metabolic effects, however, are substantially attenuated after 20 h of fasting. Hence both the choice of anesthetic and the duration of fasting have important effects on (18)F-FDG kinetics and PET images of tumor-bearing mice and should be considered when such studies are performed.

Anesthetics↗

PubMedDate not supplied

Does the circadian pattern for acute cardiac events presentation vary with fasting?

BACKGROUND: Over one billion Muslims fast worldwide during the month of Ramadan. The impact of fasting on circadian presentation with acute cardiac events is unknown. AIM: To determine if fasting has any effect on the circadian presentation of acute cardiac events. SETTING AND DESIGN: A prospective study in a general hospital. MATERIALS AND METHODS: Patients with acute coronary events were divided into two groups based on the history of fasting. Information about age, gender, cardiovascular risk factor profiles and outcome was collected. The relationship of time of presentation of initial symptoms with fasting was evaluated using Student's t-test, Mann-Whitney U-test and chi2 analysis. RESULTS: Of the 1019 patients hospitalized during the study period, 162 were fasting. Although, fasting patients were more likely to present to the emergency department in the time periods 5-6 AM (10.5% vs 6.3%) and 11 PM (11.1% vs 7.1%) and were less likely to present in the time periods 1-2 PM (3.7% vs 7.2%) and 5-6 PM (3.7% vs 7.0%); these differences were not statistically significant. Fasting patients were less likely to have their symptoms start between 5 and 8 AM (11.1% vs 19.4%) and more likely to have symptoms between 5 and 6 PM (11.1% vs 6.0%) and 3 and 4 AM (11.1% vs 6.9%). These differences for time of initial symptoms were statistically significant (P=0.002). CONCLUSION: Exogenous factors associated with fasting, namely, the changes in food intake and/or sleep timings, affect the circadian rhythm and influence the timing of presentation of acute coronary events.

Angina, Unstable↗

PubMed1990

Fasting decreases apolipoprotein B mRNA editing and the secretion of small molecular weight apoB by rat hepatocytes: evidence that the total amount of apoB secreted is regulated post-transcriptionally.

Two different molecular weight forms of apoB are produced from a common initial transcript via editing of a Gln codon (CAA) to a stop codon (UAA), leading to a truncated translation product (apo BS) that consists of the amino terminal half of the larger form (apoBL). Previous studies have shown that fasting coordinately decreases lipogenesis and the secretion of very low density lipoprotein (VLDL) lipids and apoBS. Secretion of the apoBL is unaffected by fasting. We studied whether editing of apoB RNA is repressed by fasting, thus accounting for the selective decreased secretion of apoBS. Column chromatography of [35S]methionine-labeled lipoproteins secreted by hepatocytes from fed rats showed that essentially all of apoBL is secreted in the VLDL fraction, whereas a significant amount (15%) of apoBS is secreted associated as lipoproteins eluting in the HDL fractions. Fasting decreased the relative amount of apoBS that eluted in the VLDL fractions and increased the amount secreted in the HDL fractions. Consistent with previous results, hepatocytes from fasted rats show a selective twofold decrease in apoBS secretion. Fasting did not affect the relative abundance of apoB RNA, determined by slot blot hybridization assays using two different 32P-labeled cDNA probes coding either for both molecular weight forms or for only the large molecular weight form. However, quantitative of the editing of apoB RNA showed that fasting caused a 60% decrease in the amount of apoB RNA possessing the stop codon. These data show that the editing of apoB RNA is sensitive to metabolic state (i.e., fasting) resulting in a selective decrease in the secretion of apoBS. However, since the total secretion of apoB was decreased by fasting, while apoB mRNA levels remained constant, additional (post-transcriptional) mechanisms play a role in regulating apoB secretion.

Animals↗

PubMed1990

[Insulin and thyroxine levels in dairy cows during lactation and after a 9-day fast].

The aim of the study was to observe the effect of longer fasting of dairy cows during lactation on the insulin and thyroxine levels in blood serum. The test was performed at the Research Institute of Animal Production, Nitra. The blood samples for determination of the hormone levels were collected in the morning from the vena jugularis of four fasted 4-5-year-old dairy cows of the Black Pied breed during lactation with an average daily performance of 16.91. The blood was collected on the first, fifth, sixth, seventh, eight and ninth day (fasting) and then on the fifteenth and twenty first day of the test (feeding). The insulin level in the blood serum of fasted dairy cows was more or less balanced till the seventh day of fasting, and ranged from 4.33 to 4.91 microU.ml-1. On the last two days of fasting, the insulin level increased up to 7.11 microU.ml-1 on the 9th day of fasting. The insulin level was significantly higher during feeding than during starvation. The thyroxine level was statistically significantly lower in fasted dairy cows. Increasing insulin level at the last two collections of the fasting period was probably closely connected with the shifting of the endocrine balance from dominant position of insulin to the dominance of the growth hormone and glucocorticoids. A comparatively high effect on the increase of the insulin level was exerted during that time also by the increasing amounts of non-esterifed fatty acids. Starvation significantly reduced the levels of the studied hormones in dairy cows during lactation.

Animals↗

PubMed1989

Acute effects of fever, fasting and aspirin on infant rat gastric mucosa.

Clinical experience shows that young children with gastrointestinal bleeding have frequently had some preceding febrile illness for which aspirin was administered. Febrile young children often have poor food or liquid intake, or have been in a fasting state because of diarrhea, vomiting or anorexia. The objective of this study was to determine the acute effects of fever, fasting and oral aspirin administration on the gastrointestinal mucosa. One hundred and sixty-eight infant rats, from 21 to 28 days of age and weighting from 70 to 120 g were studied. Random assignment was made to eight groups (Grs): Control (Gr I); aspirin administration only (Gr II); fasting only (Gr III); fever only (Gr IV); aspirin and fever (Gr V); fasting and fever (Gr VI); aspirin and fasting (Gr VII); and aspirin, fever and fasting (Gr VIII). Aspirin was given orally in a single daily dose of 200 mg/kg for two days. Fever was induced by an intraperitoneal injection of 0.6 ml salmonella vaccine. Fasting time lasted from 40 to 48 hours (8 hours prior to the beginning of the experiment to the end of study). The severity of the gastric bleeding was estimated by scoring the number of petechiae and the percentage of the hemorrhagic erosion area from grade 0 to 3. Results showed that rats in Grs VII and VIII had significantly more severe grades of petechiae and hemorrhage than the other groups. These were the groups where the risk factors of fasting and aspirin administration coexisted. In addition to fasting, Gr VIII had fever, but this group did not show more gastric mucosal damage than Gr VII showed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Secretion and uptake of nascent hepatic very low density lipoprotein by perfused livers from fed and fasted rats.

Livers from fed or 24-hr fasted male rats were perfused in a recycling system. VLDL labeled with [1-14C]oleate (95% in triglyceride), produced in separate perfusions of livers from fed rats, was added to the medium as a pulse. Uptake of VLDL 14C-labeled triglyceride by livers from fasted rats was less than that from fed rats regardless of addition of oleate. During the interval in which radioactive triglyceride was taken up, the mass of triglyceride in the medium increased, indicative of the synthesis and net secretion of triglycerides. The rates of secretion of VLDL and uptake of VLDL were both more rapid in livers from fed rats in comparison to those from fasted animals. It was calculated that about 50% of the triglyceride synthesized and secreted by the liver was taken back by livers from fed rats. The VLDL from livers of fasted rats did not contain any apoE detectable by SDS gel electrophoresis or by radioimmunoassay when no fatty acid or 166 mumol of oleic acid was infused. In contrast, apoE comprised 6% of the VLDL apoprotein derived from perfusion of livers from fed animals in the absence of added fatty acid, and 20% when the fed livers were infused with 166 mumol of oleic acid. However, the net output (accumulation) of apoE by fasted liver was only two-thirds that from fed livers. When lipoprotein-free rat plasma containing apoE (4 mg/dl) was used in place of bovine serum albumin, the VLDL secreted by livers from either fed or fasted rats contained apoE and was taken up to a similar extent by such livers. These data suggested that the apoE of the d greater than 1.21 g/ml fraction was transferred to newly secreted VLDL which then stimulated uptake of the VLDL by livers from fasted rats. With further stimulation of secretion of VLDL triglyceride by infusion of 332 mumol of oleic acid/hr, the percent of apoE in the VLDL secreted by livers from fasted rats increased to 20%, which was similar to that of the VLDL produced by livers from fed rats when either 166 or 332 mumol/hr was infused. These data suggest a relationship between rates of hepatic secretion of VLDL (TG) and apoE, and the association of apoE with the secreted VLDL. During fasting, reduced secretion of both VLDL and apoE resulted in a VLDL particle that was considerably diminished in content of apoE and, therefore, that would be taken up by the liver at a reduced rate, in comparison to that observed in the fed animal.

Animals↗

PubMed1984

Fasting reduces the responses of the rat vas deferens to sympathomimetics.

The effect of fasting, L-DOPA pretreatment and high glucose medium on the response of the rat vas deferens to sympathomimetics was studied in vitro. The contractile responses of the rat isolated vas deferens were reduced by fasting, the effect being significant after 24-hr fast with noradrenaline and tyramine, after a 48-hr fast with dopamine, and after a 72-hr fast with methoxamine. Treatment with L-DOPA for 7 days before sacrifice abolished the effect of a 24-hr fast in reducing responses to noradrenaline and tyramine, and the response to methoxamine after a 72-hr fast was enhanced. Doubling the concentration of glucose in the solution bathing the isolated vas deferens from rats fasted for 24 hr increased the responses to noradrenaline and tyramine. It is concluded that fasting reduces the responses of the rat vas deferens to sympathomimetics whilst L-DOPA pretreatment and high glucose restore and/or enhance the responses.

Animals↗

PubMed1983

The effect of neonatal head-irradiation and subsequent fasting on the mechanisms of catch-up growth.

The heads of 2 day old male and female rats were X-irradiated with 600 rad. Non-irradiated littermates served as controls. At 40 days of age groups of irradiated and non-irradiated rats were subjected to a 48 hour fast. Non-fasted groups of irradiated and non-irradiated rats were fed ad lib. and were used for comparative studies. Growth of body weight and tail length was recorded at intervals through 70 days of age. At sacrifice, pituitary weight, tibial length, and tibial epiphyseal width were also determined. The results confirm earlier findings that whole head irradiation produces reduced growth of body weight and of tail length which remains uncompensated by catch-up growth. After fasting and then refeeding normal catch-up growth acceleration occurred in both male and female irradiated and nonirradiated animals. The fasted non-irradiated animals caught up to the non-irradiated control rat size for both body weight and tail length. Similarly, the fasted irradiated rats caught up to the irradiated, non-fasted rat size, but did not catch up to the size of the non-irradiated controls. Pituitary weight and tibial length were significantly reduced in irradiated males and females. At sacrifice, no significant difference existed between the fasted and non-fasted subgroups. The tibial epiphyseal growth plate was not narrowed in irradiated rats; fasted rats had increased epiphyseal width during recovery in only one group. We conclude that the catch-up growth control is intact in the head-irradiated stunted rat. The findings suggest that the mechanism which recognizes normal body size (set-point for body size) and which determines the limit of catch-up growth acceleration is reset for a smaller body size by the head-irradiation.

Animals↗

PubMed1981

Effects of total fasting in obese women. IV. Response of serum triiodothyronine (T3) and reverse triiodothyronine (rT3) to administered T3.

Serum levels of T4, T3, rT3, RT3U and TSH were estimated in 12 obese women in the course of a 14-day fasting. Seven of these patients were treated with T3 in a daily dose of 60--80 micrograms. Fasting led to a small increase of serum T4, while fasting combined with T3 administration was accompanied by a small decrease of serum T4. Serum T3 decreased in the course of the first 2 days of fasting to 40--50% of initial values and remained at this low level up to the 15th day of fasting. In the T3 treated group a prompt increase of serum T3 was recorded (+80%), followed by a steady decrease, reaching the control values on day 15, in spite of a continuous T3 administration. Serum rT3 in the untreated fasting group steadily increased up to the 12th day (+43%) and then dropped below the control value (-28%). In the treated group after a non-significant increase (+22%), a decrease of serum rT3 was also observed (-42%). Fasting was accompanied by a tendency to increased serum RT3U values, in the T3 treated group no change occurred. TSH in the untreated fasting women remained practically unchanged while T3 administration was accompanied by a tendency to a transient decrease. The heart rate showed a non-significant tendency to increase in the T3 treated group and the last week of fasting was also accompanied in several patients by a larger weight loss. These results suggest that in addition to an enhanced synthesis of rT3 to the detriment of a decreased production of T3 from T4, an increased catabolism of administered T3 and of endogenous rT3 is involved in a strict calorie restriction. An abortive T3-TRH-TSH feed-back may also operate in these conditions.

Adult↗

PubMed1981

Erythropoietin production in fasted rats. Effects of thyroid hormones and glucose supplementation.

The effect of T3 replacement and glucose supplementation on erythropoietin production was investigated in fasted hypoxic rats. It was found that 48 hr of fasting significantly reduced the circulating levels of thyroid hormones and the production of renal and extrarenal erythropoietin in response to hypoxia. These effects of fasting were completely abolished when the animals had free access to 25% glucose solution as drinking water, despite their lack of protein intake. Replacement doses of T3 (0.5 micrograms/100 gm per day) restored erythropoietin production in the fasted animals but also increased the response of the fed controls. To avoid the effect of endogenous T3, the experiments were repeated in thyroidectomized rats. Erythropoietin production in athyroid rats was found to be markedly decreased, with values equivalent to those found in normal fasted animals, and were not affected by fasting or glucose supplementation. Replacement doses of T3 increased erythropoietin production in all three groups, but the fasted animals needed five times as much T3 to obtain a response similar to that observed in the fed group. Glucose supplementation enhanced the effect of T3 in the fasted animals but did not completely restore it. These results indicate that caloric deprivation is primarily responsible for the decreased erythropoietin production induced by fasting and that this effect is probably mediated by both a decreased level of T3 and a decreased responsiveness to it.

Acid-Base Equilibrium↗

PubMed1994

Investigation of the mechanism of glycogen rebound in the liver of 72-hour fasted rats.

We have investigated the mechanism of the rebound of glycogen stores in the liver of 72-h fasted rats. The liver of 72- and 96-h fasted rats contains significant amounts of glycogen (about 5 mg/g, wet weight) as compared to the liver of 24- and 48-h fasted rats, which contains less than 2 mg of glycogen/g of liver, wet weight. Rebound of glycogen does not involve glycogen synthase activation or glycogen phosphorylase inhibition. It could be dependent on the concentration of the precursor substrate of glycogenesis, i.e. glucose 6-phosphate (Glc-6-P), which is higher by about 45% in the liver of 72- and 96-h fasted rats than in the liver of 48-h fasted rats. The 72-h increase of Glc-6-P compared with the 48-h values could not be explained either by late modifications of the total activities of glucokinase, hexokinases, Glc-6-P dehydrogenase, and glucose-6-phosphatase (Glc-6-Pase) or by changes in plasma glucose and insulin/glucagon ratio. In agreement with the fact that total glucose output tends to decrease upon prolonged fasting, the increase of Glc-6-P concentration in the liver of 72-h fasted rats suggests the involvement of a metabolite inhibition of Glc-6-Pase. The increase of the alpha-ketoglutarate concentration in the 72- and 96-h fasted liver with regard to the 48-h fasted liver (about three times) might account for such an inhibition since we show here that Glc-6-Pase is inhibited in vitro in the presence of relevant concentrations of alpha-ketoglutarate, Glc-6-P, and Mg2+ ions.

Animals↗