Decreased glucose oxidation during short-term starvation

Influence of intermittent fasting on autophagy in the liver

Studies have found that intermittent fasting (IF) can prevent diabetes, cancer, heart disease, and neuropathy, while in humans it has helped to alleviate metabolic syndrome, asthma, rheumatoid arthritis, Alzheimer's disease, and many other disorders. IF involves a series of coordinated metabolic and hormonal changes to maintain the organism's metabolic balance and cellular homeostasis. More importantly, IF can activate hepatic autophagy, which is important for maintaining cellular homeostasis and energy balance, quality control, cell and tissue remodeling, and defense against extracellular damage and pathogens. IF affects hepatic autophagy through multiple interacting pathways and molecular mechanisms, including adenosine monophosphate (AMP)-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), silent mating-type information regulatory 2 homolog-1 (SIRT1), peroxisomal proliferator-activated receptor alpha (PPARα) and farnesoid X receptor (FXR), as well as signaling pathways and molecular mechanisms such as glucagon and fibroblast growth factor 21 (FGF21). These pathways can stimulate the pro-inflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α), play a cytoprotective role, downregulate the expression of aging-related molecules, and prevent the development of steatosis-associated liver tumors. By influencing the metabolism of energy and oxygen radicals as well as cellular stress response systems, IF protects hepatocytes from genetic and environmental factors. By activating hepatic autophagy, IF has a potential role in treating a variety of liver diseases, including non-alcoholic fatty liver disease, drug-induced liver injury, viral hepatitis, hepatic fibrosis, and hepatocellular carcinoma. A better understanding of the effects of IF on liver autophagy may lead to new approaches for the prevention and treatment of liver disease.

Human magnetic sense is mediated by a light and magnetic field resonance-dependent mechanism

Numerous organisms use the Earth’s magnetic field as a sensory cue for migration, body alignment, or food search. Despite some contradictory reports, yet it is generally accepted that humans do not sense the geomagnetic field. Here, we demonstrate that a magnetic field resonance mechanism mediates light-dependent magnetic orientation in men, using a rotary chair experiment combined with a two-alternative forced choice paradigm. Two groups of subjects were classified with different magnetic orientation tendencies depending on the food context. Magnetic orientation of the subjects was sensitive to the wavelength of incident light and was critically dependent on blue light reaching the eyes. Importantly, it appears that a magnetic field resonance-dependent mechanism mediates these responses, as evidenced by disruption or augmentation of the ability to orient by radiofrequency magnetic fields at the Larmor frequency and the dependence of these effects on the angle between the radiofrequency and geomagnetic fields. Furthermore, inversion of the vertical component of the geomagnetic field revealed a non-canonical inclination compass effect on the magnetic orientation. These results establish the existence of a human magnetic sense and suggest an underlying quantum mechanical magnetoreception mechanism.

Physiological responses to acute fasting: implications for intermittent fasting programs

Intermittent fasting (IF) is a dietary strategy that involves alternating periods of abstention from calorie consumption with periods of ad libitum food intake. There is significant interest in the body of literature describing longitudinal adaptations to IF. Less attention has been given to the acute physiological responses that occur during the fasting durations that are commonly employed by IF practitioners. Thus, the purpose of this review was to examine the physiological responses - including alterations in substrate metabolism, systemic hormones, and autophagy - that occur throughout an acute fast. Literature searches were performed to locate relevant research describing physiological responses to acute fasting and short-term starvation. A single fast demonstrated the ability to alter glucose and lipid metabolism within the initial 24 hours, but variations in protein metabolism appeared to be minimal within this time frame. The ability of an acute fast to elicit significant increases in autophagy is still unknown. The information summarized in this review can be used to help contextualize existing research and better inform development of future IF interventions.

Fasting and Exercise in Oncology: Potential Synergism of Combined Interventions

Nutrition and exercise interventions are strongly recommended for most cancer patients; however, much debate exists about the best prescription. Combining fasting with exercise is relatively untouched within the oncology setting. Separately, fasting has demonstrated reductions in chemotherapy-related side effects and improved treatment tolerability and effectiveness. Emerging evidence suggests fasting may have a protective effect on healthy cells allowing chemotherapy to exclusively target cancer cells. Exercise is commonly recommended and attenuates treatment- and cancer-related adverse changes to body composition, quality of life, and physical function. Given their independent benefits, in combination, fasting and exercise may induce synergistic effects and further improve cancer-related outcomes. In this narrative review, we provide a critical appraisal of the current evidence of fasting and exercise as independent interventions in the cancer population and discuss the potential benefits and mechanisms of combined fasting and exercise on cardiometabolic, body composition, patient-reported outcomes, and cancer-related outcomes. Our findings suggest that within the non-cancer population combined fasting and exercise is a viable strategy to improve health-related outcomes, however, its safety and efficacy in the oncology setting remain unknown. Therefore, we also provide a discussion on potential safety issues and considerations for future research in the growing cancer population.

Optimal Replacement of Soybean Meal with Fermented Palm Kernel Meal as Protein Source in a Fish Meal-Soybean Meal-Based Diet of Sex Reversed Red Tilapia (Oreochromis niloticus × O. mossambicus)

Simple Summary

Replacement effects of soybean meal (SBM) with fermented palm kernel meal (FPKM) as a protein source was investigated in sex-reversed red tilapia. The two-month-old fish were fed fish meal-SBM-based diets with replacement by FPKM at 25% (25FPKM), 50% (50FPKM), 75% (75FPKM) and 100% (100FPKM) for 12 weeks, while an FPKM-free diet (0FPKM) was used as a control. Based on growth performance, feed utilization, digestive enzyme activities, flesh quality, carcass composition, hematological parameters and liver histoarchitecture, the 50% replacement level of SBM by FPKM support this alternative. Findings from the current study support the use of FPKM in aquafeed production, providing a low-cost diet for tilapia farming.

Abstract

The solid-state fermentation by effective microorganisms (containing photosynthetic bacteria, lactic acid bacteria, nitrogen-fixing bacteria, yeast and Bacillus sp.) improved the nutritive values of palm kernel meal (PKM). Increased crude protein (20.79%), nitrogen-free extract (40.07%) and gross energy (19.58%) were observed in fermented PKM (FPKM) relative to raw PKM while crude lipid (15.65%), crude fiber (36.45%) and ash (29.54%) were decreased. Replacement of soybean meal (SBM) with FPKM as a protein source was investigated for its effects in sex-reversed red tilapia (Oreochromis niloticus × O. mossambicus). The two-month-old fish (14.85 ± 0.28 g initial weight) were fed fish meal-SBM-based diets with replacement by FPKM at 25% (25FPKM), 50% (50FPKM), 75% (75FPKM) and 100% (100FPKM), while an FPKM-free diet (0FPKM) was used as a control. The five treatments, comprising triplicate cement ponds and forty fish each, were conducted in a recirculating system over 12 weeks. At the end of the feeding trial, fish fed the 50FPKM diet were superior in growth performance, while the feed utilization parameters were similar across all five treatments. Physiological adaptation of the protein-digesting (pepsin and trypsin) and lipid-digesting (lipase) enzymes was detected at all protein replacement levels (except for 25FPKM), as well as of the enzyme for cellulose digestion (cellulase), but not of the carbohydrate-digesting enzymes (amylase). Protein synthesis capacity in flesh was improved in fish fed the 50FPKM diet, while the quality of the main flesh proteins, actin and myosin, showed no significant differences across the five treatments. No differences in carcass composition and no negative effects on hematological parameters or liver histoarchitecture at the 50% replacement level of SBM by FPKM also support this alternative. Findings from the current study indicate the low-cost FPKM-containing diet for tilapia in comparison with control diet.

Optimal Feeding Frequency for Captive Hawksbill Sea Turtle (Eretmochelys imbricata)

Simple Summary

Head-starting programs of hatchlings before release of yearlings to natural habitat are an alternative approach for restoring the population of critically endangered sea turtles. Hawksbill sea turtle has been reared in captivity programs in several countries, while the feeding regimens have never been optimized. In the current study, the feeding frequency of hawksbill sea turtle was optimized in indoor experimental conditions. Two-month-old turtles were fed at different frequencies: one meal daily at 12.00 h, two meals daily at 08.00 and 12.00 h, two meals daily at 08.00 and 16.00 h, two meals daily at 12.00 and 16.00 h or three meals daily at 08.00, 12.00, and 16.00 h. At the end of an 8-week trial, two meals daily with long time interval (at 08.00 and 16.00 h) were optimal, based on assessment criteria of growth, feed utilization, digestive enzyme markers, available and unavailable nutrients present in the feces, hematological parameters, and carapace elemental composition. This finding could be directly used as a feeding guideline supporting the head-starting programs of this species.

Abstract

Hawksbill sea turtle (Eretmochelys imbricata) has been reared in head-starting captivity programs, while the feeding regimens have never been optimized. In the current study, the feeding frequency of hawksbill sea turtle was investigated in indoor experimental conditions. Two-month-old turtles (38.98 ± 0.02 g) were distributed to triplicates of five treatments containing three turtles each and they were fed at different frequencies: one meal daily at 12.00 h (1M12), two meals daily at 08.00 and 12.00 h (2M8–12), two meals daily at 08.00 and 16.00 h (2M8–16), two meals daily at 12.00 and 16.00 h (2M12–16), or three meals daily at 08.00, 12.00 and 16.00 h (3M8–12–16). At the end of an 8-week trial, growth performance (specific growth rate 2.39 ± 0.02% body weight day⁻¹) and feed consumption (feeding rate 2.00 ± 0.43 g day⁻¹) were highest for turtles fed 2M8–16, followed by 2M12–16 or 3M8–12–16 relative to the other treatments (p ˂ 0.05). These treatments had significantly higher trypsin specific activity and trypsin/chymotrypsin ratio, and vice versa for lipase specific activity and amylase/trypsin ratio, relative to the remaining treatments. These match well with the fecal thermal properties that indicate amounts of available and unavailable nutrients present in the feces. Hematological parameters and carapace elemental composition showed no negative effects to turtles in 2M8–16 treatment. Therefore, two meals daily with long time interval were optimal for feeding hawksbill sea turtle. Findings from the current study could be directly used as a feeding guideline supporting the head-starting programs of this species.

Optimal Background Color for Head-Starting Northern River Terrapins (Batagur baska Gray, 1831)

Simple Summary

Substrate color is an important physical condition affecting the lifestyle of reared animals. However, no prior data are available regarding northern river terrapins. In this study, the terrapins were reared in five types of colored tanks (transparent, green, red, blue, and black) for twelve weeks. Based on parameters assessing survival, growth, feed utilization, and health, the blue background is more suitable for rearing terrapins relative to other colored tanks. The findings from the current study could be applied to wall, pond, or aquaria decoration to support the head-starting programs of northern river terrapins before release to natural habitat, as well as in public displays, such as aquaria and zoos.

Abstract

Background color has significant effects on the lifestyles of various animal species. In this study, the effects of wall background color on growth, feed utilization, specific activity of gastric and pancreatic enzymes in fecal samples, fecal thermal properties, carapace elemental profile, and hematological parameters were investigated in northern river terrapin (Batagur baska Gray, 1831) in order to optimize the head-starting conditions. The terrapins (70.13 ± 0.04 g initial weight) were completely randomized into five types of colored tanks (transparent, green, red, blue, and black) and reared for twelve weeks. At the end of the experiment, tank color had no effect on survival and growth performance, but had significant effects on feeding rate, feed conversion ratio, and protein efficiency ratio (p < 0.05). Terrapins reared with black, red, or blue backgrounds had the highest feed utilization among the treatments. Among these three groups, analysis of specific activity of gastric and pancreatic enzymes in fecal samples and fecal thermal properties suggested improved digestive functionality in terrapins reared with a blue background relative to the other treatments. Carapace elemental composition and hematological parameters indicated no negative effects on health status of the terrapins reared with this optimal treatment. Findings from the current study support the head-starting program of northern river terrapins before release to natural habitats, and could also be applied in aquaria or zoos for public display.

Blue light-dependent human magnetoreception in geomagnetic food orientation

The Earth's geomagnetic field (GMF) is known to influence magnetoreceptive creatures, from bacteria to mammals as a sensory cue or a physiological modulator, despite it is largely thought that humans cannot sense the GMF. Here, we show that humans sense the GMF to orient their direction toward food in a self-rotatory chair experiment. Starved men, but not women, significantly oriented toward the ambient/modulated magnetic north or east, directions which had been previously food-associated, without any other helpful cues, including sight and sound. The orientation was reproduced under blue light but was abolished under a blindfold or a longer wavelength light (> 500 nm), indicating that blue light is necessary for magnetic orientation. Importantly, inversion of the vertical component of the GMF resulted in orientation toward the magnetic south and blood glucose levels resulting from food appeared to act as a motivator for sensing a magnetic field direction. The results demonstrate that male humans sense GMF in a blue light-dependent manner and suggest that the geomagnetic orientations are mediated by an inclination compass.

Minimal water volume for intensively producing male Siamese fighting fish (Betta splendens Regan, 1910)

Water volume is a key parameter affecting the individual rearing of male Siamese fighting fish (Betta splendens Regan, 1910). In this study, minimization of water volume was pursued by assessing growth, feed utilization, digestive enzyme activities, color coordinates, muscle quality, and carcass composition. One-month-old solid-red male fish (0.97 ± 0.01 g initial body weight) were distributed individually into glass aquaria with five alternative water volumes (100, 150, 200, 250, and 300 mL), comprising 15 fish per treatment (n = 15), over 8 weeks duration. No mortality of the reared fish was found during the study. Growth performance and feed utilization of the fish reared in 150 mL water were superior to the other treatments. The water volume significantly affected specific activities of the digestive enzymes (P ˂ 0.05), except for amylase, and no differences in enzyme activities were observed between fish reared in 150 and in 300 mL water. The preferred treatment maintained skin lightness (L*) and had the highest redness (a* and a*/b*) among the treatments. Protein synthesis (RNA concentration) and its turnover rate (RNA/protein ratio) and myosin and actin in muscle also benefited from this treatment. Carcass composition, in terms of moisture, crude protein, and crude ash, was maintained, but the amount of crude lipid fluctuated with water volume. Based on our experiments, the preferred minimal water volume for individual rearing of male Siamese fighting fish should be about 150 mL.

Safety and feasibility of fasting in combination with platinum-based chemotherapy

Background

Short-term starvation prior to chemotherapy administration protects mice against toxicity. We undertook dose-escalation of fasting prior to platinum-based chemotherapy to determine safety and feasibility in cancer patients.

Methods

3 cohorts fasted before chemotherapy for 24, 48 and 72 h (divided as 48 pre-chemo and 24 post-chemo) and recorded all calories consumed. Feasibility was defined as ≥ 3/6 subjects in each cohort consuming ≤ 200 kcal per 24 h during the fast period without excess toxicity. Oxidative stress was evaluated in leukocytes using the COMET assay. Insulin, glucose, ketones, insulin-like growth factor-1 (IGF-1) and IGF binding proteins (IGFBPs) were measured as biomarkers of the fasting state.

Results

The median age of our 20 subjects was 61, and 85 % were women. Feasibility criteria were met. Fasting-related toxicities were limited to ≤ grade 2, most commonly fatigue, headache, and dizziness. The COMET assay indicated reduced DNA damage in leukocytes from subjects who fasted for ≥48 h (p = 0.08). There was a non-significant trend toward less grade 3 or 4 neutropenia in the 48 and 72 h cohorts compared to 24 h cohort (p = 0.17). IGF-1 levels decreased by 30, 33 and 8 % in the 24, 48 and 72 h fasting cohorts respectively after the first fasting period.

Conclusion

Fasting for 72 h around chemotherapy administration is safe and feasible for cancer patients. Biomarkers such as IGF-1 may facilitate assessment of differences in chemotherapy toxicity in subgroups achieving the physiologic fasting state. An onging randomized trial is studying the effect of 72 h of fasting.

Trial registration

NCT00936364, registered propectively on July 9, 2009.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2370-6) contains supplementary material, which is available to authorized users.

The effects of 18-h fasting with low-carbohydrate diet preparation on suppressed physiological myocardial (18)F-fluorodeoxyglucose (FDG) uptake and possible minimal effects of unfractionated heparin use in patients with suspected cardiac involvement sarcoidosis

BACKGROUND

(18)F-fluorodeoxyglucose (FDG) PET plays an important role in the detection of cardiac involvement sarcoidosis (CS). However, diffuse left ventricle (LV) wall uptake sometimes makes it difficult to distinguish between positive uptake and physiological uptake. The aims of this study were to evaluate the effects of 18-h fasting with low-carbohydrate diet (LCD) vs a minimum of 6-h fasting preparations on diffuse LV FDG uptake and free fatty acid (FFA) levels in patients with suspected CS.

METHODS

Eighty-two patients with suspected CS were divided into 2 preparation protocols: one with a minimum 6-h fast without LCD preparation (group A, n = 58) and the other with a minimum 18-h fast with LCD preparation (group B, n = 24). All patients also received intravenous unfractionated heparin (UFH; 50 IU/kg) before the injection of FDG.

RESULTS

Group A showed a higher percentage of diffuse LV uptake than did group B (27.6 vs 0.0%, P = .0041). Group B showed higher FFA levels (1159.1  ±  393.0, 650.5  ±  310.9 μEq/L, P < .0001) than did group A. Patients with diffuse LV uptake (n = 16) showed lower FFA levels than did other patients (n = 66) (432.1  ±  296.1, 888.4  ±  381.4 μEq/L, P < .0001). UFH administration significantly increased FFAs in both groups, even in the patients with diffuse LV FDG uptake.

CONCLUSIONS

The 18-h fast with LCD preparation significantly reduced diffuse LV uptake and increased FFA levels. In particular, the FFA level was significantly lower in patients with LV diffuse uptake than in patients without LV diffuse uptake. Acutely increasing plasma FFA through the use of UFH may not have a significant role in reducing physiological LV FDG uptake.

Water-induced thermogenesis and fat oxidation: a reassessment

Background/Objectives:

Drinking large amounts of water is often recommended for weight control. Whether water intake stimulates energy and fat metabolism is, however, controversial with some studies reporting that drinking half a litre or more of water increases resting energy expenditure (REE) by 10–30% and decreases respiratory quotient (RQ), whereas others report no significant changes in REE or RQ. The aim here was to reassess the concept of water-induced thermogenesis and fat oxidation in humans, with particular focus on interindividual variability in REE and RQ responses, comparison with a time-control Sham drink, and on the potential impact of gender, body composition and abdominal adiposity.

Subjects/Methods:

REE and RQ were measured in healthy young adults (n=27; body mass index range: 18.5–33.9 kg m⁻²), by ventilated hood indirect calorimetry for at least 30 min before and 130 min after ingesting 500 ml of purified (distilled) water at 21–22 °C or after Sham drinking, in a randomized cross-over design. Body composition and abdominal fat were assessed by bioimpedance techniques.

Results:

Drinking 500 ml of distilled water led to marginal increases in REE (<3% above baseline), independently of gender, but which were not significantly different from Sham drinking. RQ was found to fall after the water drink, independently of gender, but it also diminished to a similar extent in response to sham drinking. Interindividual variability in REE and RQ responses was not associated with body fatness, central adiposity or fat-free mass.

Conclusions:

This study conducted in young men and women varying widely in adiposity, comparing the ingestion of distilled water to Sham drinking, suggests that ingestion of purified water per se does not result in the stimulation of thermogenesis or fat oxidation.

Effects of intermittent fasting on body composition and clinical health markers in humans

Intermittent fasting is a broad term that encompasses a variety of programs that manipulate the timing of eating occasions by utilizing short-term fasts in order to improve body composition and overall health. This review examines studies conducted on intermittent fasting programs to determine if they are effective at improving body composition and clinical health markers associated with disease. Intermittent fasting protocols can be grouped into alternate-day fasting, whole-day fasting, and time-restricted feeding. Alternate-day fasting trials of 3 to 12 weeks in duration appear to be effective at reducing body weight (≈3%-7%), body fat (≈3-5.5 kg), total cholesterol (≈10%-21%), and triglycerides (≈14%-42%) in normal-weight, overweight, and obese humans. Whole-day fasting trials lasting 12 to 24 weeks also reduce body weight (≈3%-9%) and body fat, and favorably improve blood lipids (≈5%-20% reduction in total cholesterol and ≈17%-50% reduction in triglycerides). Research on time-restricted feeding is limited, and clear conclusions cannot be made at present. Future studies should examine long-term effects of intermittent fasting and the potential synergistic effects of combining intermittent fasting with exercise.

Effects of postprandial starvation on mRNA expression of endocrine-, amino acid and peptide transporter-, and metabolic enzyme-related genes in zebrafish (Danio rerio)

The goal of this study was to systematically evaluate the molecular activities of endocrine-, amino acid and peptide transporters-, and metabolic enzyme-related genes in 35-day-old mixed-sex zebrafish (Danio rerio) after feeding . Zebrafish with initial body weights ranging from 9 to 11 mg were fasted for 384 h in a controlled indoor environment. Fish were sampled at 0, 3, 6, 12, 24, 48, 96, 192, and 384 h after fed. Overall, the present study results show that the regulatory mechanism that insulin-like growth factor I negative feedback regulated growth hormone is conserved in zebrafish, as it is in mammals, but that regulation of growth hormone receptors is highly intricate. Leptin and cholecystokinin are time-dependent negative feedback signals, and neuropeptide Y may be an important positive neuropeptide for food intake in zebrafish. The amino acid/carnitine transporters B(0,+) (ATB(0,+)) and broad neutral (0) amino acid transporter 1(B(0)AT1) mRNA levels measured in our study suggest that protein may be utilized during 24-96 h of fasting in zebrafish. Glutamine synthetase mRNA levels were downregulated, and glutamate dehydrogenase, alanine aminotransferase, aspartate transaminase, and trypsin mRNA levels were upregulated after longtime fasting in this study. The mRNA expression levels of fatty acid synthetase decreased significantly (P < 0.05), whereas those of lipoprotein lipase rapidly increased after 96 h of fasting. Fasting activated the expression of glucose synthesis genes when fasting for short periods of time; when fasting is prolonged, the mRNA levels of glucose breakdown enzymes and pentose phosphate shunt genes decreased.

Does amifostine reduce metabolic rate? Effect of the drug on gas exchange and acute ventilatory hypoxic response in humans

Amifostine is added to chemoradiation regimens in the treatment of many cancers on the basis that, by reducing the metabolic rate, it protects normal cells from toxic effects of therapy. We tested this hypothesis by measuring the metabolic rate (by gas exchange) over 255 min in 6 healthy subjects, at two doses (500 mg and 1000 mg) of amifostine infused over 15 min at the start of the protocol. We also assessed the ventilatory response to six 1 min exposures to isocapnic hypoxia mid-protocol. There was no change in metabolic rate with amifostine as measured by oxygen uptake (p = 0.113). However in carbon dioxide output and respiratory quotient, we detected a small decline over time in control and drug protocols, consistent with a gradual change from carbohydrate to fat metabolism over the course of the relatively long study protocol. A novel result was that amifostine (1000 mg) increased the mean ± SD acute hypoxic ventilatory response from 12.4 ± 5.1 L/min to 20.3 ± 11.9 L/min (p = 0.045). In conclusion, any cellular protective effects of amifostine are unlikely due to metabolic effects. The stimulatory effect on hypoxic ventilatory responses may be due to increased levels of hypoxia inducible factor, either peripherally in the carotid body, or centrally in the brain.

Adaptive reciprocity of lipid and glucose metabolism in human short-term starvation

The human organism has tools to cope with metabolic challenges like starvation that are crucial for survival. Lipolysis, lipid oxidation, ketone body synthesis, tailored endogenous glucose production and uptake, and decreased glucose oxidation serve to protect against excessive erosion of protein mass, which is the predominant supplier of carbon chains for synthesis of newly formed glucose. The starvation response shows that the adaptation to energy deficit is very effective and coordinated with different adaptations in different organs. From an evolutionary perspective, this lipid-induced effect on glucose oxidation and uptake is very strong and may therefore help to understand why insulin resistance in obesity and type 2 diabetes mellitus is difficult to treat. The importance of reciprocity in lipid and glucose metabolism during human starvation should be taken into account when studying lipid and glucose metabolism in general and in pathophysiological conditions in particular.

Utilization of dietary glucose in the metabolic syndrome

This review is focused on the fate of dietary glucose under conditions of chronically high energy (largely fat) intake, evolving into the metabolic syndrome. We are adapted to carbohydrate-rich diets similar to those of our ancestors. Glucose is the main energy staple, but fats are our main energy reserves. Starvation drastically reduces glucose availability, forcing the body to shift to fatty acids as main energy substrate, sparing glucose and amino acids. We are not prepared for excess dietary energy, our main defenses being decreased food intake and increased energy expenditure, largely enhanced metabolic activity and thermogenesis. High lipid availability is a powerful factor decreasing glucose and amino acid oxidation. Present-day diets are often hyperenergetic, high on lipids, with abundant protein and limited amounts of starchy carbohydrates. Dietary lipids favor their metabolic processing, saving glucose, which additionally spares amino acids. The glucose excess elicits hyperinsulinemia, which may derive, in the end, into insulin resistance. The available systems of energy disposal could not cope with the excess of substrates, since they are geared for saving not for spendthrift, which results in an unbearable overload of the storage mechanisms. Adipose tissue is the last energy sink, it has to store the energy that cannot be used otherwise. However, adipose tissue growth also has limits, and the excess of energy induces inflammation, helped by the ineffective intervention of the immune system. However, even under this acute situation, the excess of glucose remains, favoring its final conversion to fat. The sum of inflammatory signals and deranged substrate handling induce most of the metabolic syndrome traits: insulin resistance, obesity, diabetes, liver steatosis, hyperlipidemia and their compounded combined effects. Thus, a maintained excess of energy in the diet may result in difficulties in the disposal of glucose, eliciting inflammation and the development of the metabolic syndrome.

Extended metabolic evaluation of suspected symptomatic hypoglycemia: the prolonged fast and beyond

The diagnostic evaluation of spontaneous hypoglycemia in adults is mainly directed at detecting an insulinoma. Its interpretation is troublesome in those patients who develop low venous plasma glucose levels with appropriate hypoinsulinemia during a prolonged supervised fast. In this study, we investigated in this group of patients whether abnormalities in intermediary metabolism (fatty acid oxidation and amino/organic acids) could be detected that might explain the hypoinsulinemic hypoglycemia. Ten patients with otherwise unexplained low venous plasma glucose levels (<3 mmol/L) during prolonged fasting were included in the study. The patients participated in an extended metabolic protocol based on stable isotope techniques after an overnight fast to explore abnormalities in endogenous glucose production and intermediary metabolism. Endogenous glucose production, glucoregulatory hormones, plasma acylcarnitines, gluconeogenic amino acids, and rates of fatty acid and carbohydrate oxidation after 16 and 22 hours of fasting were measured. Although during the prolonged fast all patients had low venous plasma glucose level, there were no hypoglycemic events during the extended metabolic protocol. No abnormalities in endogenous glucose production (compared with reference values obtained in young healthy volunteers), fatty acid oxidation, or amino acid/organic acids were found in this patient group. In a group of patients exhibiting low venous plasma glucose levels during prolonged fasting in whom insulinoma was excluded, we found no signs of metabolic disorders. Therefore, the observation of low plasma glucose values in this subgroup of patients probably does not warrant extensive metabolic evaluation.

Glucoregulation is more precise in women than in men during postexercise recovery

BACKGROUND

The regulation of glycemia is challenged in healthy men and women after exercise bouts of substantial energy expenditure.

OBJECTIVE

We determined rates of glucose appearance (Ra), disappearance (Rd), and metabolic clearance (MCR) before, during, and after isoenergetic moderate and hard-intensity exercise.

DESIGN

Ten men and 8 women received primed-continuous infusion of [6,6-(2)H(2)]glucose tracer to measure glucose kinetics. Participants were studied under 3 different conditions with diet unchanged between trials: 1) before, during, and 3 h after 90 min of exercise at 45% of peak oxygen consumption (VO(2)peak; E45); 2) before, during, and 3 h after 60 min of exercise at 65% VO(2)peak (E65), and 3) in a time-matched sedentary control trial.

RESULTS

In men and women, Ra, Rd, and MCR increased above the control trial during exercise and were higher in E65 than in E45 (P < 0.05). Average Ra, Rd, and MCR remained elevated above the control over 3 h of postexercise recovery in men after exercise in E45 and E65 (P < 0.05), and blood glucose concentrations were depressed below the control during recovery (P < 0.05). Glucose concentrations were not depressed in women during 3 h of postexercise recovery, and in contrast with that in men, average Ra and Rd did not remain significantly elevated during postexercise recovery in women, although MCR did remain elevated in E65 (P < 0.05).

CONCLUSIONS

After exercise bouts, women are better able to maintain glucose concentrations at sedentary control levels, thus not requiring the counter-regulation of glucose production that is seen in men and requiring less accentuation of lipid metabolism.

Metabolic and functional effects of glutamate intake in patients with chronic obstructive pulmonary disease (COPD)

BACKGROUND & AIMS

Patients with chronic obstructive pulmonary disease (COPD) often suffer from skeletal muscle weakness due to muscle wasting and altered muscle metabolism. Decreased muscle glutamate concentration in COPD is consistently reported and is associated with decreased muscle glutathione concentration and early lactic acidosis. We hypothesized that an increased availability of glutamate via glutamate ingestion increases muscle glutamate concentration leading to acute improvements in skeletal muscle energy metabolism and function.

METHODS

Two experiments were conducted. In experiment 1, in two groups of 6 male COPD patients (FEV(1): 44.8+/-3.4%pred) and 6 healthy controls, blood samples and muscle biopsies were taken at 0 and 80 min after repeated glutamate (30 mg/kg BW) or control ingestion (1.25 ml/kg BW), and after 20 min cycling at 50% peak workload. In experiment 2, in 10 COPD patients (FEV(1): 36.1+/-2.5%pred), the effect of the two drinks was tested on cycle endurance time and contractile quadriceps fatigue measured by magnetic stimulation before and after cycling at 75% peak workload.

RESULTS

Glutamate ingestion increased plasma (p<0.01) but not muscle glutamate concentration. Muscle total and reduced glutathione and plasma lactate concentration were not affected by glutamate ingestion. Glutamate ingestion did not influence contractile muscle fatigue and endurance time.

CONCLUSION

Continuous oral glutamate ingestion for 80 min did not lead to an acute effect on skeletal muscle substrate metabolism and muscle performance in COPD patients and in age-matched healthy controls.

Effects of fasting and carbohydrate consumption on voluntary resting apnea duration

Breath holding is normally terminated due to the urge to breathe, mainly caused by the increasing carbon dioxide level. It was recently shown that a combination of 18 h of carbohydrate-free diet and prolonged exercise prior to breath holding lowered the respiratory exchange ratio (RER) and end-expiratory PO(2 )at maximal breath-hold break-point (MBP). Current hypothesis: fasting will result in longer breath-hold duration than will fasting followed by carbohydrate intake. It was also hypothesized that breath-holds during carbohydrate supplementation would be ended at a higher alveolar PO(2). Ten male non-divers performed multiple breath-holds either to the first diaphragmatic contraction (PBP), or to MBP. The breath-holds were performed during normal diet (control; C), twice during fasting (F14 h, F18 h), followed by post fasting carbohydrate consumption (PFCC) and a repetition of the breath-hold testing 1-2 h after ingestion of carbohydrates. Duration, RER, end-tidal PO(2) and PCO(2), SaO(2) and blood glucose were determined. RER and blood glucose increased after PFCC compared with fasting and control conditions (P < 0.001). PBP breath-hold duration increased from 129 +/- 34 s at C to 148 +/- 33 s at F18 h, and was reduced during PFCC to 122 +/- 30 s (P < 0.001). End-tidal PO(2) was higher at PFCC compared to F18 h (10.4 +/- 1.2 vs. 9.5 +/- 1.2 kPa at PBP, P < 0.05). Similar trends in breath-hold duration and physiology were seen in breath-holds that were terminated at MBP. Dietary restriction can affect breath-hold duration. The lower O(2) level at breakpoint during fasting suggests that breath holding may be less safe during fasting; the increased risk may be mitigated by ingestion of carbohydrates before breath holding.

Dynamics of starvation in humans

A differential equation model describing the dynamics of stored energy in the form of fat mass, lean body mass and ketone body mass during prolonged starvation is developed. The parameters of the model are estimated using available data for 7 days into starvation. A simulation of energy stores for a normal individual with body mass index between 19 and 24 and an obese individual with body mass index over 30 are calculated. The length of time the obese subject can survive during prolonged starvation is estimated using the model.

Best Practice Methods to Apply to Measurement of Resting Metabolic Rate in Adults: A Systematic Review

Several factors may alter apparent resting metabolic rate (RMR) during measurement with indirect calorimetry. Likewise, numerous indirect calorimetry measurement protocols have been developed over the years, and the methodology employed could influence test results. As part of a larger project to determine the role of indirect calorimetry in clinical practice, a systematic review of the literature was undertaken to determine the ideal subject condition and test methodology for obtaining reliable measurement of RMR with indirect calorimetry. Food, ethanol, caffeine, and nicotine affect RMR for a variable number of hours after consumption; therefore, intake of these items must be controlled before measurement. Activities of daily living increase metabolic rate, but a short rest (< or =20 minutes) before testing is sufficient for the effect to dissipate. Moderate or vigorous physical activity has a longer carryover effect and therefore must be controlled in the hours before a measurement of RMR is attempted. Limited data were found regarding ideal ambient conditions for RMR testing. Measurement duration of 10 minutes with the first 5 minutes deleted and the remaining 5 minutes having a coefficient of variation <10% gave accurate readings of RMR. Individuals preparing for RMR measurement via indirect calorimetry should refrain from eating, consuming ethanol and nicotine, smoking, and engaging in physical activity for varying times before measurement. The test site should be physically comfortable and the individual should have 10 to 20 minutes to rest before measurement commences. A 10-minute test duration with the first 5 minutes discarded and the remaining 5 minutes having a coefficient of variation of <10% will give an accurate measure of RMR.

Effect of interleukin 1alpha and interleukin 2 over glucose metabolism in isolated uterus of restricted diet rats. Influence of NO and COX-2

A 25-day dietary restriction (50% of the normal diet) produce a fall in the production of 14CO2 from 14C-glucose in rats isolated uteri. The addition of 10 or 20 ngml(-1) interleukin 1alpha (IL-1alpha) or interleukin 2(IL-2) to the Krebs-Ringer bicarbonate solution medium stimulates glucose metabolism in uteri from underfed rats. Such concentrations are not effective in control rats. The addition of Nomega-nitro-L arginine methyl ester--an inhibitor of both the constitutive and inducible forms of nitric oxide synthase (NOS)--and of aminoguadinine--a preferential inhibitor of the inducible form of NOS--block such stimulation. In other experiments, the addition to the medium of arginine-a substrate for the formation of nitric oxide-increases interleukin stimulation of glucose metabolism, which is blocked by NOS inhibitor. At the same time, NS-398--a selective inhibitor of inducible cyclooxygenase (COX)--eliminates the interleukin metabolism stimulation. We conclude that IL-1alpha and IL-2 produce an increase of glucose metabolism in uteri isolated from underfed rats. Nitric oxide produced by the inducible form of NOS mediates the interleukins-induced glucose metabolism stimulation with the participation of inducible COX.

Dietary fat content alters insulin-mediated glucose metabolism in healthy men

BACKGROUND

A high dietary fat intake is involved in the pathogenesis of insulin resistance.

OBJECTIVE

The aim was to compare the effect of different amounts of dietary fat on hepatic and peripheral insulin sensitivity.

DESIGN

Six healthy men were studied on 3 occasions after consuming for 11 d diets with identical energy and protein contents but different percentages of energy as fat and carbohydrate as follows: 0% and 85% [low-fat, high-carbohydrate (LFHC) diet], 41% and 44% [intermediate-fat, intermediate-carbohydrate (IFIC) diet], and 83% and 2% [high-fat, low-carbohydrate (HFLC) diet]. Insulin sensitivity was quantified by using a hyperinsulinemic euglycemic clamp (plasma insulin concentration: approximately 190 pmol/L).

RESULTS

During hyperinsulinemia, endogenous glucose production was higher after the HFLC diet (2.5 +/- 0.3 micromol x kg(-1) x min(-1); P < 0.05) than after the IFIC and LFHC diets (1.7 +/- 0.3 and 1.2 +/- 0.4 micromol x kg(-1) x min(-1), respectively). The ratio of dietary fat to carbohydrate had no unequivocal effects on insulin-stimulated glucose uptake. In contrast, insulin-stimulated, nonoxidative glucose disposal tended to increase in relation to an increase in the ratio of fat to carbohydrate, from 14.8 +/- 5.1 to 20.6 +/- 1.9 to 26.2 +/- 2.9 micromol x kg(-1) x min(-1) (P < 0.074 between the 3 diets). Insulin-stimulated glucose oxidation was significantly lower after the HFLC diet than after the IFIC and LFHC diets: 1.7 +/- 0.8 compared with 13.4 +/- 2.1 and 19.0 +/- 2.1 micromol x kg(-1) x min(-1), respectively (P < 0.05). During the clamp study, plasma fatty acid concentrations were higher after the HFLC diet than after the IFIC and LFHC diets: 0.22 +/- 0.02 compared with 0.07 +/- 0.01 and 0.05 +/- 0.01 mmol/L, respectively (P < 0.05).

CONCLUSION

A high-fat, low-carbohydrate intake reduces the ability of insulin to suppress endogenous glucose production and alters the relation between oxidative and nonoxidative glucose disposal in a way that favors storage of glucose.

Influence of insulin on the metabolism of glucose in uteri isolated from ovariectomized and non ovariectomized underfed rats

The effects of insulin on the metabolism of U14C-glucose in uteri isolated from ovariectomized and non-ovariectomized rats receiving a restricted diet (50% of the normal food intake) for 25 days, were studied. As a result of food restriction, the production of 14CO2 diminishes in intact rats, while results are reversed in ovariectomized ones. Various concentrations of insulin were added to the medium, but only 0.50 IU. ml(-1)was effective in increasing glucose metabolism in intact rats receiving a restricted diet; neither underfed castrated animals nor control ones receiving a normal diet, reacted to this concentration. The increase of 14CO2 produced by insulin is not affected by acetyl salicylic acid. Insulin does not alter the effect of underfeeding over arachidonic acid metabolism. On the contrary, the increase in glucose metabolism was blocked by N(G)methyl-L-arginine or by hemoglobin, increased with the addition of L arginine and is not affected by acetyl salicylic acid. Hemoglobin and L-arginine show no effects without insulin. We can conclude that the stimulating effect of insulin on glucose metabolism in uteri isolated from intact rats subjected to dietary restriction, is nitric oxide dependent.

Biologic responses to IFN-alpha administration in humans

Although interferon-alpha (IFN-alpha) was discovered over 40 years ago, it was many years before it was registered as a therapeutic agent. Because of its unique qualities, it has been registered for both antiviral and antitumor indications. In addition to its therapeutic effects in viral diseases and cancer, IFN-alpha interferes with several important physiologic systems. It interacts with the immune system and affects several neuroendocrine and metabolic circuits. The specific mechanisms by which IFN-alpha exerts its therapeutic effects are complex, and it is very difficult to tie the biologic actions of IFN-alpha to specific clinical effects.

Effects of morphine and naloxone on glucose metabolism in uterine strips from ovariectomized and non-ovariectomized restricted diet rats

The effect of underfeeding over glucose metabolism in uteri isolated from ovariectomized and non-ovariectomized rats subjected to a restricted diet for 25 days (50% of the normal food intake), was studied. Underfeeding decreases (14)CO(2) formation from U(14) C-glucose in intact animal uteri. While in ovariectomized rats (25 days), the effect is the opposite. The addition of morphine 10(-6) M to the medium does not affect rats fed ad libitum. However, (14)CO(2) levels increase significantly in intact animals receiving a restricted diet. In ovariectomized rats morphine does not show any activity, regardless of the type of diet rats were subjected to. None of the rat groups seems to be sensitive to naloxone 10(-6) M. The s.c. injection of morphine (4 mg.kg (-1)) increases glucose metabolism only in intact rats provided with a restricted diet, while naloxone (2.5 mg.kg (-1) ) produces a decrease of ( 14)CO(2) in ovariectomized underfed animals. To conclude, morphine either 'in vivo' or 'in vitro' is active only in uteri from intact rats subjected to underfeeding. Naloxone produces a decrease in (14)CO(2) production, particularly when it is s.c. injected to ovariectomized rats undergoing a dietary restriction. Since the uterus does not react to naloxone, the effect of the opiod blocker may be the result of endogenous opioids originated in other tissues.

Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine

BACKGROUND

The effects of food restriction on energy metabolism have been under investigation for more than a century. Data obtained are conflicting and research has failed to provide conclusive results.

OBJECTIVE

The objective of this study was to test the hypothesis that in lean subjects under normal living conditions, short-term starvation leads to an increase in serum concentrations of catecholamines and thus to an increase in resting energy expenditure.

DESIGN

Resting energy expenditure, measured by indirect calorimetry, and hormone and substrate concentrations were measured in 11 healthy, lean subjects on days 1, 2, 3, and 4 of an 84-h starvation period.

RESULTS

Resting energy expenditure increased significantly from 3.97 +/- 0.9 kJ/min on day 1 to 4.53 +/- 0.9 kJ/min on day 3 (P < 0.05). The increase in resting energy expenditure was associated with an increase in the norepinephrine concentration from 1716. +/- 574 pmol/L on day 1 to 3728 +/- 1636 pmol/L on day 4 (P < 0.05). Serum glucose decreased from 4.9 +/- 0.5 to 3.5 +/- 0.5 mmol/L (P < 0.05), whereas insulin did not change significantly.

CONCLUSIONS

Resting energy expenditure increases in early starvation, accompanied by an increase in plasma norepinephrine. This increase in norepinephrine seems to be due to a decline in serum glucose and may be the initial signal for metabolic changes in early starvation.

Effects of inhibitors of nitric oxide synthase on isolated uteri of fasting rats

The effects of inhibitors of nitric oxide synthase on the glucose metabolism of uteri isolated from 4-day underfed rats were studied. In control rats receiving normal feeding, the addition of indomethacin (5 x 10(-6) M); acetyl salicylic acid (10(-4) M); 400 microM of N(G)methyl-L-arginine, (L-NMMA) or 400 microM of sodium nitroprusside (SNP), does not modify the production of 14CO2 from U14C-glucose. On the contrary, in fasted rat uteri, indomethacin increases glucose oxidation significantly, while acetyl salicylic acid does not alter it. Also, the addition of L-NMMA has no effect. In another group of experiments, in the preparations containing indomethacin of uteri isolated from underfed rats, the addition of L-NMMA significantly changes the effect of indomethacin. Another inhibitor of nitric oxide synthase, N(omega)nitro-L-arginine methyl ester (L-NAME), or hemoglobin (2 microg ml(-1)) a nitric oxide scavenger have the same effects while N(omega)nitro arginine-D-methyl ester (D-NAME) does not. However (SNP), a nitric oxide donor, does not alter the production of 14CO2 in uteri isolated from fasted rats. These results show that in underfed rats, indomethacin increases glucose oxidation independently from its inhibiting effect on cyclooxygenase. Specific inhibitors of nitric oxide synthase can reverse this effect.

Short-term hypocaloric nutrition but not bed rest decrease insulin sensitivity and IGF-I bioavailability in healthy subjects: the importance of glucagon

Hyperinsulinemic, normoglycemic clamps were performed before and after 24 h of either hypocaloric nutrition or bed rest in healthy subjects. Decreased insulin sensitivity and insulin-like growth factor-I (IGF-I) bioavalibility, as measured by the serum IGF-I/insulin-like growth factor binding protein-1 (IGFBP-1) ratio, was found after fasting, whereas no metabolic changes were found after bed rest. Glucagon seems to be a key regulator of IGFBP-1 after brief hypocaloric nutrition. Hypocaloric nutrition and immobilization may add to the catabolic response to surgery and other trauma. Presently, six healthy subjects were studied before and after a 24-h period of hypocaloric nutrition (200 kcal/24 h, fast) or immobilization (bed rest) using the hyperinsulinemic (0.8 mU.kg-1.min-1), normoglycemic (4.5 mmol/L) clamp, indirect calorimetry, and circulating levels of substrates and hormones. After fast, body weight decreased (P < 0.05), and nitrogen balance was negative (-10 +/- 1 g urea nitrogen/24 h). Basal levels of free fatty acids, glucagon, and IGFBP-1 increased (P < 0.05), whereas c-peptide levels and the IGF-I/IGFBP-1 ratio decreased (P < 0.05). However, no change was found in basal levels of IGF-1 or substrate oxidation. Furthermore, changes (%) in basal levels of glucagon after fast correlated to IGFBP-1 (r = 1.0, P < 0.05), whereas the suppressibility of IGFBP-1 by insulin was maintained at normal levels. During clamps, glucose infusion rates (GIR) decreased after fast (-43 +/- 13%, mean +/- SEM, P < 0.001). Although not significantly, clamp levels of fat oxidation tended to increase and glucose oxidation tended to decrease. Levels of IGFBP-1 during clamps were higher as compared with the control clamp (P < 0.05). No adverse metabolic changes were seen after bed rest, and no change in GIR during clamps were seen as compared with the control measurement (0 +/- 14%). After brief hypocaloric nutrition, insulin sensitivity is reduced, whereas IGF-I bioavalibility is reduced by an increase in levels of IGFBP-1. Glucagon seems to contribute to the increase in IGFBP-1 during these conditions.

Differential effects of enzyme supplementation therapy on manifestations of type 1 Gaucher disease

BACKGROUND

In type 1 Gaucher disease (GD), the accumulation of glucocerebroside in macrophages, caused by deficient activity of glucocerebrosidase, results in a variety of disease manifestations. In addition to the characteristic features of hepatosplenomegaly, cytopenia, and bone abnormalities, resting energy expenditure (REE) and glucose production are increased. In this study the effects of enzyme supplementation therapy on metabolic parameters in relation to other disease manifestations in type 1 GD patients are investigated.

PATIENTS AND METHODS

In 12 adult type 1 GD patients, measurements of REE (by indirect calorimetry), liver and spleen volume (by spiral computerized axial tomography [CT]) and hemoglobin and platelet count were obtained before and after 6 months of alglucerase therapy (15 U/kg per month). In 7 of the 12 patients hepatic glucose production was measured by infusing 3-3H glucose. For comparison, REE and glucose metabolism were studied in 7 weight- and age-matched healthy subjects.

RESULTS

REE and glucose production were increased in GD patients as compared with controls (REE: 29.8 kcal/kg/24 h +/- 3.6 and 23.1 +/- 2.3 kcal/kg/24 h, respectively, P < 0.05; glucose production: 14.00 mumol/kg/min +/- 0.51 and 10.77 mumol/kg/min +/- 0.26, respectively, P < 0.03). There were no differences in plasma glucose concentrations. Whereas the elevated REE decreased after 6 months of alglucerase therapy from 129% to 120% of predicted values (P < 0.01), the increase in hepatic glucose production did not change. An increase in weight occurred after 6 months of treatment (1.7 +/- 0.8 kg, P < 0.001), which was accounted for by an increase in fat mass of 1.6 +/- 1.5 kg (P < 0.02). Hemoglobin levels increased from 11.2 mg/dL to 12.1 mg/dL (P = 0.05) and platelet counts rose from 84 x 10(9)/L to 113 x 10(9)/L (P < 0.05). Although liver and spleen volumes decreased by approximately 10% and approximately 20%, respectively, there was no correlation between the decrease in organ volumes and the decrease in REE.

CONCLUSIONS

Treatment with alglucerase improves hypermetabolism and organomegaly in GD, whereas the increase in glucose production persists. Therefore, the dose-response effects of alglucerase are variable for the different manifestations of type 1 GD.

Altered muscle energy metabolism in post-absorptive patients with chronic renal failure

Skeletal muscle biopsies were performed on 12 healthy sedentary subjects and on 22 non-dyalized chronic renal failure patients (CRF) on a free diet and after overnight fasting. Parathormone, glucagon and insulin were determined at the same time of biopsies. CRF patients showed significantly low ATP and creatine phosphate levels. Regarding enzyme activities, a high hexokinase Vmax was found, while the pyruvate kinase activity was lower than in the control group. For the tricarboxylic acid cycle, citrate synthase, succinate dehydrogenase and malate dehydrogenase activities were higher; total NADH cytochrome c reductase activity was also high, while cytochrome oxidase activity was slightly lower. Both alanine aminotransferase and aspartate aminotransferase activities were considerably high in comparison with the control group. In conclusion, our study revealed a hypermetabolic TCA cycle, but impaired oxidative phosphorylation, which partly explained the reduced ATP concentration. Excessive protein intake and hormonal derangements may play a role in these metabolic changes.

Modulation of glucose production by indomethacin and pentoxifylline in healthy humans

Indomethacin, an inhibitor of prostaglandin synthesis that modulates cytokine production, increases hepatic glucose output (HGO) in humans. However, prostaglandins stimulate glucose production in vitro. To investigate the mechanism of HGO stimulation by indomethacin, we compared the effect of pentoxifylline, an inhibitor of cytokine production, versus saline (study 1, n = 6) and of indomethacin versus the combination of indomethacin and pentoxifylline (study 2, n = 5) on basal HGO. HGO was measured by primed, continuous infusion of 3-3H-glucose. In study 1, pentoxifylline infusion resulted in an immediate, transient decrease of HGO of approximately 50% (from 12.9 +/- 0.4 to 6.0 +/- 1.7 micromol/kg/min after 15 minutes, P < .03 v control). There were no differences in concentrations of glucoregulatory hormones between the two experiments. In study 2, after indomethacin administration, HGO increased transiently by approximately 84% (from 9.7 +/- 0.7 at baseline to 16.7 +/- 2.4 micromol/kg/min after 135 minutes, P < .05). However, pentoxifylline did not affect the increase in HGO induced by indomethacin. There were no differences in concentrations of glucoregulatory hormones between the two experiments. Therefore, indomethacin stimulates HGO by mechanisms unrelated to glucoregulatory hormones, prostaglandins, or cytokines.

Endocrinologic and metabolic effects of interleukin-6 in humans

Interleukin-6 (IL-6) is one of the major circulating cytokines in catabolic states. To investigate its endocrinologic and metabolic actions in vivo, we studied eight patients with metastatic renal cell cancer two times, once during infusion of saline (control) and once during a 4-h infusion of 150 micrograms recombinant human IL-6 (rhIL-6). Rates of appearance (Ra) of glucose and free fatty acids (FFA) in plasma were measured by using the isotope dilution method. Energy expenditure and substrate oxidation were determined by indirect calorimetry. rhIL-6 induced increases in plasma norepinephrine (+261 +/- 97%, P < 0.001), cortisol (+210 +/- 48%, P < 0.001), and glucagon (+70 +/- 18%, P < 0.001), in resting energy expenditure (+25 +/- 2%, P < 0.001 vs. control), and in plasma FFA concentration (+60 +/- 30%, P < 0.001), FFA Ra (+105 +/- 18%, P < 0.001), and fat oxidation (+38 +/- 16%, P < 0.001). Glucose Ra increased by 20 +/- 5% (P < 0.01) during rhIL-6 infusion with a concomitant increase in the metabolic clearance rate of glucose. In conclusion, our data demonstrate that rhIL-6 induces many of the endocrinologic and metabolic changes found in catabolic states and thus may mediate some of the metabolic effects previously ascribed to other cytokines.

Sex differences in the adaptation of glucose metabolism to short-term fasting: effects of oral contraceptives

The adaptation to long-term starvation is different in men and women. To evaluate whether there are also sex differences during short-term fasting (< 24 hours), we studied glucose metabolism after 16 and again after 22 hours of starvation in healthy subjects: six men, six women in both the follicular and luteal phases of their menstrual cycle, and six women on oral contraceptives ([OCC] day 12 of cycle). Glucose oxidation was measured by indirect calorimetry, and hepatic glucose output by infusion of 3-3H-glucose. There were no differences in hepatic glucose output between men and women during short-term fasting. The basal (16 hours) plasma glucose concentration was lower in women on OCC than in men (P < .05). Prolongation of the postabsorptive state induced a similar decline in plasma glucose concentrations in all groups. Basal (16 hours) glucose oxidation was lower in women on OCC than in men (P < .05). Prolongation of the postabsorptive state by 6 hours caused a significant decrease in glucose oxidation only in men. After 22 hours of fasting, glucose oxidation was lower in women on OCC than in women with normal menstrual cycles. In conclusion, the metabolic adaptation to the postabsorptive state (< 24 hours of fasting) is regulated differently in women on OCC as compared with women with normal menstrual cycles and men. These differences preclude inclusion of women on OCC in studies of glucose metabolism in the postabsorptive state.

Infusion of long-chain or medium-chain triglycerides inhibits peripheral glucose metabolism in men

To investigate whether increased availability of lipids affects glucose metabolism in healthy postabsorptive men when lipid and glucose are infused in amounts used in parenteral nutrition, we infused glucose (4 mg/kg.min-1) for 6 hours and clamped plasma glucose at basal level during the first 3 hours. After 3 hours, either long-chain triglycerides (LCTs) (0.07 g/kg.h-1) (n = 7) or a mixture of LCTs and medium-chain triglycerides (MCTs) (MCTs/LCTs, 50/50%, 0.07 g/kg.h-1) (n = 7) was administered, and the infusion rates of glucose and insulin were unchanged compared with the first 3 hours. In a control study, glucose was infused for a period of 6 hours without the lipid infusion (n = 5). After 6 hours, the plasma glucose concentration and glucose tissue uptake were not affected by LCT or MCT/LCT infusion. Nonetheless, glucose oxidation decreased in the LCT group (from 6.42 +/- 1.04 to 2.31 +/- 0.85 mumol/kg.min-1, p < .001) and in the MCT/LCT group (from 7.62 +/- 1.50 to 5.50 +/- 0.76 mumol/kg.min-1, p < .01) but not in the control group. Concentrations of the glucoregulatory hormones were not different among the three groups. In conclusion, MCTs/LCTs administered concomitantly with glucose infusion, in amounts similar to those used in total parenteral nutrition, inhibit glucose oxidation without affecting glucose tissue uptake, just as LCTs do.

Progressive alterations in lipid and glucose metabolism during short-term fasting in young adult men

Stable isotope tracers and indirect calorimetry were used to evaluate the progressive alterations in lipid and glucose metabolism after 12, 18, 24, 30, 42, 54, and 72 h of fasting in six healthy male volunteers. The rates of appearance (Ra) of glycerol and palmitic acid in plasma doubled from 2.08 +/- 0.22 and 1.63 +/- 0.20 mumol.kg-1 x min-1, respectively, after 12 h to 4.36 +/- 0.36 and 3.26 +/- 0.40 mumol.kg-1 x min-1, respectively, after 72 h of fasting (P < 0.01). Of the total increase in lipid kinetics, 60% occurred between 12 and 24 h of fasting; the greatest interval change occurred between 18 and 24 h of fasting. Glucose Ra and plasma concentration decreased by approximately 25% between 12 h (11.0 +/- 0.4 mumol.kg-1 x min-1 and 5.58 +/- 0.08 mmol/l, respectively) and 72 h (8.3 +/- 0.3 mumol.kg-1 x min-1 and 4.14 +/- 0.10 mmol/l, respectively) of fasting (P < 0.01), but no statistically significant changes occurred between 18 and 24 h of fasting. Plasma insulin decreased by approximately 50% between 12 h (64.6 +/- 12.9 pmol/l) and 72 h (30.1 +/- 7.9 pmol/l) of fasting (P < 0.001). Of the total decline in plasma insulin, 70% occurred within the first 24 h of fasting. These results demonstrate that the mobilization of adipose tissue triglycerides increases markedly between 18 and 24 h of fasting in young adult men. The early alterations in lipid metabolism are associated with a decline in circulating insulin but do not seem to be regulated by changes in glucose kinetics or plasma glucose concentrations.

Tumor necrosis factor mimics the metabolic response to acute infection in healthy humans

To evaluate the role of tumor necrosis factor (TNF) in the initiation of the metabolic response to acute infection, we performed a crossover saline-controlled study in six healthy postabsorptive men, investigating the metabolic effects of a bolus intravenous injection of recombinant human TNF (50 micrograms/m2). TNF induced a transient stress hormone response, associated with an early and sustained rise in plasma glucose concentrations (percentage increase at 2 h 23 +/- 7; P less than 0.05). Glucose turnover, measured 7.5 h postinjection, was 10 +/- 3% higher after TNF administration (P less than 0.05). Plasma free fatty acids (FFA) and glycerol concentrations increased transiently after TNF injection, peaking after 4 h (percentage increase 363 +/- 83 and 67 +/- 14, respectively; both P less than 0.05). FFA turnover, determined 6.5 h postinjection, increased in five subjects to a variable extent (percentage increase 126 +/- 55; P less than 0.05). Finally, resting energy expenditure showed a transient rise after TNF injection (34 +/- 2% at 4 h; P less than 0.05). We conclude that intravenous TNF reproduces many of the metabolic changes observed in septicemia, suggesting that TNF may be an initiating factor in the development of the metabolic response to acute infection.

Insulin sensitivity and insulin clearance in human immunodeficiency virus-infected men

To test whether clinically stable human immunodeficiency virus (HIV) infection, like other infections, is associated with insulin resistance and increased insulin clearance, we measured the sensitivity to insulin and insulin clearance using the euglycemic insulin clamp technique in 10 clinically stable outpatients with symptomatic HIV infection (Centers for Disease Control [CDC] group IV) and 10 healthy controls. During administration of 0.8 and 4 mU insulin.kg-1.min-1, HIV-infected men had 40% (P less than .02) and 83% (P less than .01) higher rates of insulin clearance when compared with healthy controls. Despite significantly lower steady-state insulin concentrations (42 +/- 2 v 52 +/- 4 microU/mL, P less than .05, and 255 +/- 17 v 392 +/- 14 microU/mL, P less than .001, patients v controls), patients and controls had similar total glucose uptake (7.99 +/- 0.81 v 7.92 +/- 0.44 mg.kg-1.min-1 and 14.00 +/- 0.81 v 13.65 +/- 0.65 mg.kg-1.min-1, patients v controls). In the postabsorptive state, no differences were found between patients and controls in insulin levels (7 +/- 1 microU/mL in both) and endogenous glucose production (2.52 +/- 0.07 and 2.24 +/- 0.17 mg.kg-1.min-1, respectively), but plasma glucose levels in the patients (5.02 +/- 0.15 mmol/L) were significantly lower when compared with controls (5.46 +/- 0.14 mmol/L, P less than .05). The results indicate that HIV-infected men have increased rates of insulin clearance and increased sensitivity of peripheral tissues to insulin, which makes HIV infection unique with regard to glucose and insulin metabolism.

Glucose and fat metabolism during short-term starvation in cirrhosis

To evaluate the metabolic consequences of short-term (i.e., less than 24 hours) starvation, glucose and fat metabolism were studied in eight healthy subjects and in eight patients with stable cirrhosis after 16-hour and again after 22-hour starvation by 3-[3H]glucose and [14C]palmitate turnover and by indirect calorimetry. Although patients and controls showed significant increases in free fatty acid concentration (respectively, 48% +/- 12% and 53% +/- 17%) and turnover (55% +/- 14% and 71% +/- 21%) during short-term starvation, the values after 16- and after 22-hour starvation were higher in cirrhosis. Fat oxidation was enhanced in the patients, but did not increase during fasting in contrast to controls (increase 19% +/- 17%, P less than 0.05). Net glucose oxidation was decreased in postabsorptive cirrhotics (P less than 0.05). Although postabsorptive glucose turnover was not different from controls, starvation induced a greater decrease in glucose turnover in the patients (25% +/- 3% vs. 10% +/- 3%, P less than 0.05). This was not reflected in plasma glucose concentrations. In conclusion, the effects of starvation on glucose and fat metabolism are enhanced in cirrhosis; fasting hypoglycemia is prevented by decreased use of glucose. It remains to be established whether these changes are merely explained by defective liver function, per se.