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PubMed1990

The effects of fasting on the quality of liver preservation by simple cold storage.

Although livers can be successfully preserved for 24 hr or more, often the transplanted livers have poor or no (primary nonfunction) function. The quality of the liver does not appear dependent upon the time of preservation but may be dependent upon the condition of the donor. In this study we have investigated the effects of fasting on the quality of livers for transplantation. Rabbits were fasted (48 hr) and livers preserved in the UW solution for 6-8 hr. Functions of the liver were analyzed by isolated perfusion for 2 hr. Also, pigs were fasted for 72 hr, livers preserved for 12 hr, and viability determined by orthotopic transplantation. Fasting depleted the liver glycogen by 85% but had no effect on ATP or glutathione concentrations. Rabbit livers from fasted animals produced similar amounts of bile, released similar concentrations of lactate dehydrogenase (LDH) and aspartate amino transaminase (AST) into the perfusate, maintained similar concentrations of ATP and glutathione in the tissue, and had a similar intracellular K:Na ratio after 24-hr preservation when compared to livers from fed animals. After 48-hr preservation, livers from fasted animals were less viable than livers from fed animals, including: reduced bile production (2.0 +/- 0.3 vs. 5.0 +/- 0.9 ml/2 hr, 100 g), greater release of LDH (3701 +/- 562 units vs. 1123 +/- 98 units) and AST, less ATP (0.326 +/- 74 vs. 0.802 +/- 160 nmol/g), less glutathione (0.303 +/- 13 vs. 0.933 +/- 137 nmol/g), and a lower K:Na ratio (1.5 +/- 0.9 vs. 7.4 +/- 0.6). Pigs receiving livers from fed animals preserved for 12 hr had better survival (5/6, 83%) than livers from fasted animals (3/6, 50%). The results show that the nutritional status of the donor can affect the outcome of liver preservation and transplantation. Increased injury in livers from fasted animals may be due to the loss of glycogen that may be an essential source of energy in the initial posttransplant period. In clinical liver transplantation the nutritional status of the donor may be an important factor in the initial function of the liver, and methods to increase the nutritional status of the donor may be important in increasing the quality of livers.

Adenosine Triphosphate↗
PubMed2004

Effects of effervescent ranitidine on gastric pH: comparison with almagate and placebo in fasting and postprandial conditions.

AIM: To compare the effect of effervescent ranitidine, almagate (magnesium carbonate-aluminium hydroxide) and placebo on gastric pH, in fasting and postprandial conditions. METHODS: Twelve healthy volunteers underwent a gastro-oesophageal pH monitoring on three different occasions after the administration of each of the following randomly allocated treatments: almagate, effervescent ranitidine and placebo. Treatment effects were assessed in fasting and postprandial conditions. Onset and duration of alkalinization, percentage of time with pH > 4 and median gastric pH after treatments were calculated in both periods. RESULTS: Onset of action of effervescent ranitidine was similar to almagate in fasting [median 1.2 min (IQR: 0.6-12.7) vs. 2.9 min (0.4-227.6)] and postprandial conditions [1.4 min (0.5-4.9) vs. 4.1 min (1.3-63.8)] and both were significantly faster than placebo [fasting 211.1 min (2.7-240); postprandial 240 min (175.6-240)]. The duration of action of effervescent ranitidine was statistically significant longer than almagate in fasting [235 min (105.2-239.4) vs. 19.4 min (6.7-38.8)] and postprandial conditions [171.8 min (133.2-239.5) vs. 61.3 min (44.7-91.9)]. Effervescent ranitidine was more effective than almagate in increasing the percentage of time with a pH > 4 both in fasting (73.9% vs. 7.3%) and postprandial (59.1% vs. 21.3%). CONCLUSIONS: Effervescent ranitidine shows an effect on gastric pH as fast as almagate but provides a duration of alkalinization longer than almagate, in both fasting and postprandial conditions.

Adult↗
PubMed1995

The effect of fasting on total serum bilirubin concentrations.

Thirty-seven healthy volunteers, 19 of whom had consistently elevated total serum bilirubin (TSB) concentrations, took part in an open, randomised cross-over study to determine the effect of fasting on TSB concentrations. The study comprised of two treatments. During one treatment period volunteers ate a standard supper but fasted for 24 h thereafter. During the other treatment period volunteers ate a standard supper, snacks, breakfast and lunch. TSB concentrations were measured at regular intervals. In both the normal and high bilirubin groups, minimum TSB values were recorded 4 h after the supper. A 24 h fast more than doubled TSB concentration from baseline values in both the normal and high bilirubin groups. A clinically relevant rise in TSB took place after 12 h into the fasting period (TSB of 17.3 mumol l-1 in the fasted group vs 14.0 mumol l-1 in the non-fasted group). When designing a clinical trial, selecting volunteers, or judging the tolerance of a new drug, the rise in TSB caused by fasting must therefore be taken into account, particularly in trials where volunteers or patients fast before entering the study.

Adult↗
PubMed2005

Sex differences in the neuroendocrine response to short-term fasting in rhesus macaques.

When energy intake is restricted in mammals, there are neuroendocrine adjustments in the secretion of reproductive and metabolic hormones to reallocate energy for vital functions. In the present study, we investigated whether there were differences in the luteinising hormone (LH), growth hormone (GH) and cortisol responses to a 48-h fast in adult gonad-intact male and female rhesus macaques. In both male and female macaques, blood glucose levels were significantly lower in fasted than in control studies, and levels were higher in males than in females. Male rhesus monkeys had significantly lower (P < 0.01) mean serum LH levels after a 48-h fast than under fed conditions and this was attributable primarily to a decrease in the amount of LH released during each secretory episode. In fasted females, serum LH levels were significantly greater (P < 0.05) than during the fed conditions but no differences were found in pulse amplitude or in the number of pulses. Almost twice as many GH pulses were observed in both males and females during fasting but there was no difference in either mean serum GH levels or pulse amplitude between control and fasted studies. A typical diurnal profile in cortisol levels was observed in both sexes and both experimental conditions. Under control conditions, male macaques released less cortisol than females, and although fasting increased mean cortisol levels in both males and females, only the males shown a significant rise over levels observed in control studies. The changes in plasma LH and cortisol levels in fasted rhesus macaques are similar to those observed in humans and suggest that gonadotrophin and corticotrophin secretion are more resistant to short-term energy deprivation in female than in male primates.

Animals↗
PubMed2005

Prevalence of undiagnosed Type 2 diabetes and impaired fasting glucose in older British men and women.

AIM: To estimate the prevalence of undiagnosed diabetes and impaired fasting glucose in older British men and women, using the 1999 World Health Organization (WHO) thresholds based on fasting glucose measurements. METHODS: Participants in the British Regional Heart Study and the British Women's Heart and Health Study were selected from one socially representative general practice in 24 British towns. Included in this analysis were 3736 men and 3642 women aged 60-79 years (predominantly white), who provided a single fasting blood sample at a clinical examination between 1998 and 2001, and who had no previous diagnosis of diabetes. RESULTS: Two hundred and eleven men (5.7%) and 190 women (5.2%) had a fasting blood glucose level consistent with the WHO threshold for a diagnosis of diabetes (> or = 7.0 mmol/l), whilst a further 667 men (17.9%) and 642 women (17.6%) had impaired fasting glucose levels (6.1 < or = 7 mmol/l). When analyses were restricted to subjects who had fasted for at least 8 h, and whose blood sample was taken before 12.00 h, the predicted prevalence of undiagnosed diabetes (based on two separate measurements) was 6.7% in men and 6.0% in women. The predicted prevalence of impaired fasting glucose (based on two separate measurements) was approximately 20% in both sexes. CONCLUSIONS: More than one-fifth of older white British men and women have either undiagnosed diabetes or impaired fasting glucose according to new WHO criteria. Strategies for the primary and secondary prevention of Type 2 diabetes among older individuals are urgently needed.

Aged↗
PubMedDate not supplied

Fasting in labor: relic or requirement.

OBJECTIVE: To evaluate the scientific literature on restrictions of eating and drinking during labor. DATA SOURCES: Computerized searches in MEDLINE and CINAHL, as well as historical articles, texts, and references cited in published works. Key words used in the searches included anesthesia in labor, childbirth, eating and drinking, epidural, fasting, fasting in labor, fasting and pregnancy, gastric aspiration, gastric emptying, intrapartum, intravenous fluids, i.v.s in labor, ketonuria, ketonuria in labor, parturition, pregnancy, and stomach contents in labor. STUDY SELECTION: Articles from indexed journals, excluding single-person case studies. DATA EXTRACTION: Data were extracted and organized under the following headings: historical review, effects of fasting on labor, research on maternal mortality/morbidity from aspiration, research on gastric emptying in labor, intravenous hydration in labor, and implications for nursing research. DATA SYNTHESIS: Research does not support restricting food and fluids in labor to prevent gastric aspiration. Restricting oral intake during labor has unexpected negative outcomes. CONCLUSIONS: Little is known about the differences in labor progress, birth outcomes, and neonatal status between mothers who consume food and/or fluids during labor and women who fast during labor. Research also is needed on the effects of epidural opioids on gastric emptying, nutritional requirements during labor, and the physiologic implications of fasting during labor. Fasting during labor is a tradition that continues with no evidence of improved outcomes for mother or newborn. Many facilities (especially birth centers) do not restrict eating and drinking. Across the United States, most hospitals restrict intake, usually to ice chips and sips of clear liquids. Anesthesia studies have focused on gastric emptying, measured by various techniques, presuming that delayed gastric emptying predisposes women to aspiration. Narcotic analgesia delays gastric emptying, but results are conflicting on the effect of normal labor and of epidural anesthesia on gastric emptying. The effect of fasting in labor on the fetus and newborn and on the course of labor has not been studied adequately. Only one study evaluated the probable risk of maternal aspiration mortality, which is approximately 7 in 10 million births.

Fasting↗
PubMedDate not supplied

Actual versus instructed fasting times and associated discomforts in women having scheduled cesarean birth.

OBJECTIVES: To measure actual and instructed preoperative fasting durations in women undergoing scheduled cesarean birth, to compare these times with national guidelines for healthy patients undergoing elective procedures, and to describe discomforts associated with preoperative fasting. DESIGN: One group, nonexperimental, comparative, descriptive. SETTING: Nonprofit private medical center in Texas with 6,000 births/year. PATIENTS: Convenience sample of 51 hospitalized postpartum women. INTERVENTIONS: Participants were interviewed an average of 44 hours after their cesarean birth, and their medical records were reviewed for fasting information. MAIN OUTCOME MEASURES: Duration of actual and instructed fasting, comparison with national guidelines, and ratings of thirst and hunger. RESULTS: The participants fasted from liquids and solids an average of 11 and 13 hours, respectively. Both actual and instructed fasting durations were significantly longer than national guidelines. Most participants (70%) were instructed to be nulla per os after midnight whether they were to have a.m. or p.m. surgery. Thirst and hunger scores averaged 5 and 4, respectively, on a 0-10 scale. CONCLUSION: Patients having scheduled cesarean birth fast for unnecessarily long periods. Nurses should be knowledgeable about evidence-based preoperative fasting practices and collaborate with physicians to implement them.

Attitude to Health↗
PubMed1985

Effects of fasting and refeeding on the activity of hepatic glucose-6-phosphatase in rats.

The activities of glucose-6-phosphate hydrolase and glucose-6-phosphate translocase were determined in rats fasted for 1-3 days and in animals fasted for one day and then either refed with mixed pellet or given oral or intraperitoneal glucose. The assay was based on the colorimetric measurement of the released inorganic phosphate. Fasting over 24 h significantly increased both the translocase and the hydrolase activity of glucose-6-phosphatase. These parameters showed a further increase when rats were fasted for another 24 h. In animals fasted for 24 h and then refed with standardized pellet diet, a progressive fall of enzyme activity was noticed. However, even 72 h of refeeding did not lead to complete normalization. Glucose given orally or intraperitoneally also suppressed the enzyme activity, although the effect was somewhat delayed. As expected, in fasting rats glucose and insulin levels were significantly decreased. Normoglycaemia was established after just 24 h, regardless of refeeding with pellets or with glucose. The former group exhibited hyper- and the latter hypo-insulinaemic pattern. We speculate that augmented activity of hepatic glucose-6-phosphatase during fasting stimulates the metabolism of glucose through the glucose cycle and is thereby at least partially responsible for insulin resistance accompanying the fasting state.

Administration, Oral↗
PubMed2001

Three days fast in sportsmen decreases physical work capacity but not strength or perception-reaction time.

This study investigates, in young nonobese healthy athletes, the consequences of a 3-day fast coupled, or not, to enhanced physical activity. Eight male subjects, aged 21+/-2 years, fasted for 3 days on two separate occasions, 4 weeks apart. On the first occasion, subjects continued their daily training activities. On the second occasion, a daily physical exercise program was added to these activities. Subjects were evaluated before and after 24 hours and 72 hours of fasting. Evaluation consisted of body composition, basal respiratory exchange ratio, plasma metabolic parameters, perception-reaction time (both simple and discriminant), hand grip strength, and physical work capacity at 170 beats per minute (PWC170). Fasting determined significant reductions in body weight, body fat, and muscle mass. These reductions were not affected by enhanced physical activity. Basal respiratory exchange ratio decreased with fasting but was not influenced by increased training activities. Fasting determined a significant decrease in blood glucose levels, while plasma proteins, urea, uric acid, and free fatty acids increased. Perception-reaction time and hand grip strength were unmodified during fasting. By contrast, PWC170 was significantly and progressively reduced during fasting, and this decrease was not reversed by an increase in training activities.

Adult↗
PubMed1999

Effect of fasting on temporal variation in the nephrotoxicity of amphotericin B in rats.

Evidence for temporal variation in the nephrotoxicity of amphotericin B was recently reported in experimental animals. The role of food in these variations was determined by studying the effect of a short fasting period on the temporal variation in the renal toxicity of amphotericin B. Twenty-eight normally fed and 28 fasted female Sprague-Dawley rats were used. Food was available ad libitum to the fed rats, while the fasted animals were fasted 12 h before and 24 h after amphotericin B injection to minimize stress for the animals. Water was available ad libitum to both groups of rats, which were maintained on a 14-h light, 10-h dark regimen (light on at 0600 h). Renal toxicity was determined by comparing the levels of excretion of renal enzyme and the serum creatinine and blood urea nitrogen (BUN) levels at the time of the maximal (0700 h) or the minimal (1900 h) nephrotoxicity after the intraperitoneal administration of a single dose of dextrose (5%; control group) or amphotericin B (50 mg/kg of body weight; treated group) to the rats. The nephrotoxicities obtained after amphotericin B administration at both times of day were compared to the nephrotoxicities observed for time-matched controls. In fed animals, the 24-h urinary excretion of N-acetyl-beta-D-glucosaminidase and beta-galactosidase was significantly higher when amphotericin B was injected at 0700 and 1900 h. The excretion of these two enzymes was reduced significantly (P < 0.05) in fasting rats, and this effect was larger at 0700 h (P < 0.05) than at 1900 h. The serum creatinine level was also significantly higher (P < 0.05) in fed animals treated at 0700 h than in fed animals treated at 1900 h. Fasting reduced significantly (P < 0.05) the increase in the serum creatinine level, and this effect was larger in the animals treated at 0700 h. Similar data were obtained for BUN levels. Amphotericin B accumulation was significantly higher (P < 0.05) in the renal cortexes of fed rats than in those of fasted animals, but there was no difference according to the time of injection. These results demonstrated that fasting reduces the nephrotoxicity of amphotericin B and that food availability is of crucial importance in the temporal variation in the renal toxicity of amphotericin B in rats.

Acetylglucosaminidase↗
PubMed2004

Effect of leptin administration versus re-feeding on hypothalamic neuropeptide gene expression in fasted male rats.

Adipocytes are the primary source of circulating leptin. Leptin inhibits eating, increases metabolism, and stimulates the reproductive axis. Numerous hypothalamic neuropeptides have been implicated in leptin's behavioral and neuroendocrine effects, including neuropeptide Y (NPY) and cocaine- and amphetamine-regulated transcript (CART). The aim of this study was to investigate the physiological relevance of leptin's signaling of nutritional status by comparing the effects of leptin with the effects of re-feeding on fasting-induced changes in the expression of the long form of the leptin receptor (Ob-Rb), NPY, and CART. Adult male rats were fasted for 48 h and treated with either intracerebroventricular (i.c.v.) or subcutaneous (s.c.) leptin throughout the fast, or fed ad libitum for 24 h after terminating the fast. Expression of NPY, Ob-Rb, and CART mRNA in the arcuate nucleus (ARC) was determined by in situ hybridization histochemistry and compared with vehicle-treated fed or fasted controls. Fasting increased NPY and Ob-Rb expression and decreased CART expression in the ARC. Leptin (regardless of route) and re-feeding were equally effective in normalizing CART mRNA expression. A similar trend was observed with Ob-Rb expression. In contrast, neither re-feeding nor s.c. leptin reversed the increased expression of NPY that was induced by fasting. Only i.c.v. leptin was effective in this regard. Our results indicate leptin and re-feeding are equally effective in normalizing fasting-induced changes in CART and Ob-Rb expression, but less effective in normalizing NPY expression. These results suggest that leptin is the primary nutritional signal regulating CART and Ob-Rb expression in the ARC, and highlight potential differences between CART and NPY neuron sensitivity to leptin signaling.

Animals↗
PubMed1981

The normal fasting and postprandial diisopropyl-IDA Tc 99m hepatobiliary study.

Diisopropyl-IDA Tc 99m imaging studies were performed in 11 normal subjects in both the fasting and postprandial states. In 5- to 60-minute analog images obtained in both fasting and postprandial studies, the cardiac blood pool was almost never seen, renal pelvic radioactivity was commonly seen, the extrahepatic biliary tract was always seen, and the left hepatic duct was always more prominent than the right hepatic duct. The biliary tract was visualized by ten minutes in nine of 11 fasting studies and 10 of 11 postprandial studies. The gallbladder was visualized in all eleven fasting studies, but in only four postprandial studies. The gallbladder was visualized in all eleven fasting studies, but in only four postprandial studies (p less than 0.05). The zero- to sixty-minute digital data indicated a greater hepatocyte clearance, an earlier time of peak parenchymal radioactivity, and a faster parenchymal washout in the postprandial studies compared with fasting studies (p less than 0.05). Approximately nine percent of the injected dose was recovered in the urine during the first three hours in fasting and postprandial studies. The normal diisopropyl-IDA Tc 99m study in the fasting and postprandial states is defined; significant differences exist between the two states.

Adult↗
PubMed2006

Extracellular signal-regulated kinase pathway is differentially involved in beta-agonist-induced hypertrophy in slow and fast muscles.

The molecular mechanisms controlling beta-adrenergic receptor agonist (BA)-induced skeletal muscle hypertrophy are not well known. We presently report that BA exerts a distinct muscle- and muscle fiber type-specific hypertrophy. Moreover, we have shown that pharmacologically or genetically attenuating extracellular signal-regulated kinase (ERK) signaling in muscle fibers resulted in decreases (P < 0.05) in fast but not slow fiber type-specific reporter gene expressions in response to BA exposure in vitro and in vivo. Consistent with these data, forced expression of MAPK phosphatase 1, a nuclear protein that dephosphorylates ERK1/2, in fast-twitch skeletal muscle ablated (P < 0.05) the hypertrophic effects of BA feeding (clenbuterol, 20 parts per million in water) in vivo. Further analysis has shown that BA-induced phosphorylation and activation of ERK occurred to a greater (P < 0.05) extent in fast myofibers than in slow myofibers. Analysis of the basal level of ERK activity in slow and fast muscles revealed that ERK1/2 is activated to a greater extent in fast- than in slow-twitch muscles. These data indicate that ERK signaling is differentially involved in BA-induced hypertrophy in slow and fast skeletal muscles, suggesting that the increased abundance of phospho-ERK1/2 and ERK activity found in fast-twitch myofibers, compared with their slow-twitch counterparts, may account, at least in part, for the fiber type-specific hypertrophy induced by BA stimulation. These data suggest that fast myofibers are pivotal in the adaptation of muscle to environmental cues and that the mechanism underlying this change is partially mediated by the MAPK signaling cascade.

Adrenergic beta-Agonists↗
PubMed1983

Cerebral metabolism of amino acids and glucose in fed and fasted sheep.

Net cerebral uptake from or release into whole blood of oxygen, carbon dioxide, glucose, amino acids, lactate, pyruvate, ketone bodies, and acetate was estimated in fed, 3-day-fasted, and 6-day-fasted sheep. The respiratory quotient was similar in all three groups of sheep (approximately 0.95). Glucose uptake (35 mumol X min-1 X 100 g-1) was maintained during fasting, and about 94% of the cerebral oxygen consumption could have been accounted for by glucose oxidation in all sheep. A cerebral uptake of the branched-chain amino acids (leucine, isoleucine, and valine) and proline also was observed with a concomitant production of glutamine and asparagine. The brains of fed and 3-day-fasted sheep were in nitrogen balance, but a small net release of nitrogen occurred in 6-day-fasted sheep (2 mumol N. min-1 X 100 g-1). A small amount of pyruvate was always released (1.4 mumol X min-1 X 100 g-1) into the blood, whereas lactate was released (6 mumol X min-1 X 100 g-1) only in 6-day-fasted sheep. Ketone body and acetate utilization always was negligible when compared with that for glucose. The total cerebral nonglucose carbon release found for 6-day-fasted sheep was equivalent to 23% of the glucose carbon taken up, although only 8% could have been derived directly from glucose. Thus, metabolism by the ovine brain seems resistant to prolonged periods of hypoglycemia with only small adaptations occurring after a 6-day fast.

Amino Acids↗
PubMed1985

Insulin action during fasting and refeeding in rat determined by euglycemic clamp.

To further characterize the role of insulin in glucose metabolism during fasting and refeeding, euglycemic-hyperinsulinemic clamps were performed in control, 3 day-fasted, and 3 day-fasted then 3 day-refed rats. Glucose production and utilization were measured by using [3-3H]glucose. In control and refed rats, hepatic glucose production was totally suppressed at insulin concentration higher than 500 microU/ml; by contrast, during fasting, hepatic glucose production was not suppressed even at insulin concentration tenfold higher. Maximal increment of glucose utilization was lower in fasted than in control rats. Three days of refeeding restored almost entirely normal responses to insulin for glucose utilization. Blood glucose concentration was clamped at a different level in fasted and in control and refed rats; however, increment in glucose clearance in response to insulin was lower in fasted rats than in the two other groups. Thus fasting produces a state of insulin unresponsiveness both at the hepatic and peripheral levels, normal responsiveness being restored after 3 days of refeeding.

Animals↗
PubMed1987

Fasting-mediated alteration studies in insulin action on lipolysis and lipogenesis in obese women.

The effects of fasting on insulin-induced antilipolysis and lipogenesis were investigated in vitro in isolated human fat cells of 11 obese females. Glycerol release and lipogenesis were determined simultaneously in the same test tube and related to methylglucose transport and specific insulin binding. Insulin binding and sensitivity and the responsiveness (maximum effect) of insulin-induced antilipolysis were enhanced by fasting. The latter was strongly correlated with an enhancement in the lipolysis rate. The effects of fasting on antilipolysis were not dependent on the glucose concentration, unlike insulin-stimulated lipogenesis. At 1 mumol/l of glucose, where hexose transport is rate limiting, sensitivity and responsiveness of insulin-induced lipogenesis were inhibited by fasting. Similar results were obtained with methylglucose transport. At 1-10 mmol/l of glucose, where hexose metabolism is rate limiting, insulin stimulated lipogenesis before fasting but was totally ineffective after fasting. In conclusion, fasting induces multiple alterations in insulin action on lipolysis and lipogenesis in adipocytes. Antilipolysis is enhanced because of stimulation at the receptor and postreceptor levels, which may be associated with an enhanced rate of lipolysis. Fasting inhibits the lipogenic effect of insulin due to postreceptor changes involving both transport and metabolism of glucose, making lipogenesis unresponsive to insulin at physiological glucose concentrations.

Adipose Tissue↗
PubMed1989

Effect of short- and long-term beta-adrenergic blockade on lipolysis during fasting in humans.

Stable isotope tracers and indirect calorimetry were used to evaluate the importance of beta-adrenergic stimulation of lipolysis and triglyceride-fatty acid cycling during fasting in healthy human volunteers. Each subject was studied after 12 and 84 h of fasting both with and without propranolol infusion (protocol 1) and when oral propranolol treatment was given throughout fasting (protocol 2). In protocol 1, the rates of appearance of glycerol and palmitic acid increased from 3.04 +/- 0.19 and 1.78 +/- 0.17 mumol.kg lean body mass-1.min-1, respectively, after 12 h of fasting to 5.28 +/- 0.31 and 3.47 +/- 0.15 mumol.kg lean body mass-1.min-1, respectively, after 84 h of fasting (P less than 0.005). The rate of triglyceride-fatty acid cycling increased from 97 +/- 8 to 169 +/- 5 mumol/min (P less than 0.005). Intravenous propranolol infusion decreased the rate of lipolysis after both 12 and 84 h of fasting, but the magnitude of the antilipolytic effect was much greater after 84 h (P less than 0.005). In protocol 2, the rate of lipolysis and triglyceride-fatty acid cycling was still increased by fasting despite beta-adrenergic blockade with oral propranolol. This study demonstrates that beta-adrenergic stimulation contributes to the mobilization of fat during fasting. However, other mechanism(s) can increase lipolysis and triglyceride-fatty acid cycling when beta-adrenergic receptors are continuously blocked.

Adult↗
PubMed1989

Hepatic glycogen in humans. I. Direct formation after oral and intravenous glucose or after a 24-h fast.

The formation of hepatic glycogen by the direct pathway is assessed in humans 1) after a 12-h fast and oral loading (100 g) or 2) intravenous infusion (90 g) and 3) after a 24-h fast and the same oral glucose load. The methodology used is based on the double tracer method. [3-3H]glucose is infused at a constant rate for the determination of the metabolic clearance of glucose. [1-14C]glucose is administered with the glucose load. One hour after absorption or the intravenous glucose infusion is terminated, a glucagon infusion is initiated to mobilize the glycogen labeled with [1-14C]glucose and formed during the absorptive period. At this time a third tracer, [6-3H]glucose, is administered to measure glucose clearance. It was found that after the 12-h fast and oral glucose loading 7.2 +/- 1.1 g of hepatic glycogen appears to be formed directly from glucose compared with 8.4 +/- 1.0 g after the same load and a 24-h fast and 8.5 +/- 0.4 g after a 12-h fast and an equivalent intravenous glucose infusion. When the amount of label ([14C]glucose) mobilized that was not corrected for metabolic recycling was calculated, the data suggested that the amount of glycogen formed by gluconeogenic pathways was probably at least equal to that formed by direct uptake. It was also approximately 60% greater after a 24-h fast. It can be concluded that the amount of hepatic glycogen formed directly from glucose during glucose loading is not significantly altered by the route of entry or the extension of the fasting period to 24 h. The data suggest, however, that gluconeogenetic formation of glycogen increases with fasting.

Adult↗