Hypersecretion of glucagon and gastrin in severely burnt patients

Role of Glucagon in Catabolism and Muscle Wasting of Critical Illness and Modulation by Nutrition

RATIONALE

Critical illness is hallmarked by muscle wasting and disturbances in glucose, lipid, and amino acid homeostasis. Circulating concentrations of glucagon, a catabolic hormone that affects these metabolic pathways, are elevated during critical illness. Insight in the nutritional regulation of glucagon and its metabolic role during critical illness is lacking.

OBJECTIVES

To evaluate whether macronutrient infusion can suppress plasma glucagon during critical illness and study the role of illness-induced glucagon abundance in the disturbed glucose, lipid, and amino acid homeostasis and in muscle wasting during critical illness.

METHODS

In human and mouse studies, we infused macronutrients and manipulated glucagon availability up and down to investigate its acute and chronic metabolic role during critical illness.

MEASUREMENTS AND MAIN RESULTS

In critically ill patients, infusing glucose with insulin did not lower glucagon, whereas parenteral nutrition containing amino acids increased glucagon. In critically ill mice, infusion of amino acids increased glucagon and up-regulated markers of hepatic amino acid catabolism without affecting muscle wasting. Immunoneutralizing glucagon in critically ill mice only transiently affected glucose and lipid metabolism, did not affect muscle wasting, but drastically suppressed markers of hepatic amino acid catabolism and reversed the illness-induced hypoaminoacidemia.

CONCLUSIONS

These data suggest that elevated glucagon availability during critical illness increases hepatic amino acid catabolism, explaining the illness-induced hypoaminoacidemia, without affecting muscle wasting and without a sustained impact on blood glucose. Furthermore, amino acid infusion likely results in a further breakdown of amino acids in the liver, mediated by increased glucagon, without preventing muscle wasting. Clinical trial registered with www.clinicaltrials.gov (NCT 00512122).

Unique roles of glucagon and glucagon-like peptides: Parallels in understanding the functions of adipokinetic hormones in stress responses in insects

Glucagon is conventionally regarded as a hormone, counter regulatory in function to insulin and plays a critical anti-hypoglycemic role by maintaining glucose homeostasis in both animals and humans. Glucagon performs this function by increasing hepatic glucose output to the blood by stimulating glycogenolysis and gluconeogenesis in response to starvation. Additionally it plays a homeostatic role by decreasing glycogenesis and glycolysis in tandem to try and maintain optimal glucose levels. To perform this action, it also increases energy expenditure which is contrary to what one would expect and has actions which are unique and not entirely in agreement with its role in protection from hypoglycemia. Interestingly, glucagon-like peptides (GLP-1 and GLP-2) from the major fragment of proglucagon (in non-mammalian vertebrates, as well as in mammals) may also modulate response to stress in addition to their other physiological actions. These unique modes of action occur in response to psychological, metabolic and other stress situations and mirror the role of adipokinetic hormones (AKHs) in insects which perform a similar function. The findings on the anti-stress roles of glucagon and glucagon-like peptides in mammalian and non-mammalian vertebrates may throw light on the multiple stress responsive mechanisms which operate in a concerted manner under regulation by AKH in insects thus functioning as a stress responsive hormone while also maintaining organismal homeostasis.

Minireview: Glucagon in stress and energy homeostasis

Glucagon is traditionally thought of as an antihypoglycemic hormone, for example in response to starvation. However, it actually increases energy expenditure and has other actions not in line with protection from hypoglycemia. Furthermore, it is often found to be elevated when glucose is also raised, for example in circumstances of psychological and metabolic stress. These findings seem more in keeping with glucagon having some role as a hormone enhancing the response to stress.

The relationship of plasma glucagon to the hyperglycaemia and hyperinsulinaemia of surgical operation

In a controlled metabolic study of 42patients undergoing abdominal surgery a significant increase in basal values of immunoreactive glucagon (IRG) was found 24 hours postoperatively. No correlation between the onset and duration of hyperglycaemia and the increase of IRG was observed. No increase in immunoreactive insulin (IRZ) was seen during operation, but there was a rise 24 hours postoperatively.

The infusion of arginine was accompanied by a rise in IRG both pre- and postoperatively, but despite the high values obtained there was no accompanying further increase in basal plasma glucose in the postoperative situation. The pre- and postoperative IRI responses were similar. Our evidence suggests that glucagon is not a primary mediator of the stress response, or of the hyperglycaemia of surgical operation in these patients.

Decreased cerebral glucose utilization in rats during the ebb phase of thermal injury

OBJECTIVE

Thermal injury is associated with the development of encephalopathy. The mechanism(s) for the development of this condition have not been established. In the present study, the effects of thermal injury were determined on rat brain glucose utilization (Rg), using 2-[18F]fluoro-2-deoxy-D-glucose (18FDG).

DESIGN

Four types of studies were performed. In one group of rats, the effect of thermal injury on total rat brain glucose utilization (Rg) was determined at 6 hours, 24 hours, and 3 weeks after injury. The brains of thermally injured rats were also assayed for hexokinase and glucose-6-phosphatase activities, since these enzyme activities are responsible for the phosphorylation and dephosphorylation of the 18FDG. We also measured total body oxygen consumption in the thermally injured rats. We wanted to compare the changes produced by thermal injury on rat brain glucose utilization (Rg) with the effects produced by compounds known to modify energy metabolism and/or rat brain glucose utilization (Rg). For that reason, in a second group of rats, an inflammatory state was produced by lipopolysaccharide injection, and rat brain glucose utilization (Rg) was determined. In the third group of rats, overall metabolism in rats was reduced by pentobarbital injection, followed by hypothermia, and rat brain glucose utilization (Rg) was determined. In the fourth group of rats, overall metabolism in rats was stimulated by 2,4-dinitrophenol injection, and rat brain glucose utilization (Rg) was determined.

MATERIALS AND METHODS

Glucose utilization (Rg) by the brains of these treated rats was determined using 18FDG. Oxygen consumption in vivo, as well as glucose-6-phosphatase and hexokinase activity in vitro, were measured by standard procedures.

MEASUREMENTS AND MAIN RESULTS

Glucose utilization (Rg) by rat brain was significantly reduced (p < 0.01) at 6 and 24 hours after injury, but returned to normal values 3 weeks after injury. These reductions were associated with decreases in rat brain hexokinase activity, increases in rat brain glucose-6-phosphatase activity, and decreased oxygen consumption by rats in vivo. Pentobarbital injection followed by hypothermia reduced rat brain glucose utilization (Rg) (p < 0.01), while 2,4-dinitrophenol treatment elevated rat brain glucose utilization (Rg) (p < 0.01). In contrast, LPS treatment had no effect on rat brain glucose utilization (Rg).

CONCLUSIONS

These data indicate that thermal injury decreases glucose utilization (Rg) in rat brain during the hypometabolic phase. This effect can be explained, at least in part, by alterations in hexokinase and glucose-6-phosphatase activities, as well as reductions in oxygen consumption. Thus, the changes in brain glucose utilization (Rg) appear to be associated with the ebb phase of the thermal injury. The present results observed in burned rats may provide evidence to explain the encephalopathy observed in burned patients.

The role of glucagon in the control of protein and amino acid metabolism in vivo

The relative contribution of hyperglucagonemia to the mechanisms of nitrogen loss during catabolic states has not been clearly established. The present study examines the independent effect of physiologic elevations of plasma glucagon on whole-body protein kinetics, as well as on net amino acid balance across the liver and gastrointestinal tract tissues, in conscious 18-hour-fasted dogs (n = 7). Each study consisted of a 120-minute equilibration period, a 30-minute basal period, and a 150-minute experimental period. Leucine kinetics were measured using L-[1-14C]leucine. Pancreatic hormones were maintained by infusing intravenous somatostatin (0.8 micrograms/kg.min), intraportal insulin (275 microU/kg.min), and intraportal glucagon (0.65 ng/kg.min basally and 2.5 experimentally). Dextrose was infused to maintain plasma glucose constant (14.1 +/- 0.3 mumol/L), thereby providing a consistent metabolic steady state for the study of protein and amino acid metabolism. In the experimental period, plasma glucagon was fourfold basal levels (112 +/- 10 v 32 +/- 6 pg/mL), whereas plasma insulin remained stable (mean, 10 +/- 1 microU/mL). Hepatic glucose production was increased 30%, but leucine rates of appearance ([Ra] proteolysis), oxidative disappearance (Rd), and nonoxidative Rd (protein synthesis) were not altered during the experimental period. Furthermore, the net release of amino acids by the gastrointestinal tract was not increased by glucagon. However, uptake and extraction of amino acids by the liver were increased, resulting in a 17% decrease in total plasma amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Randomised double blind trial of somatostatin in the treatment of massive upper gastrointestinal haemorrhage

In order to evaluate the effect of somatostatin in the treatment of massive upper gastrointestinal bleeding a randomised double blind trial of 95 patients has been undertaken during a 28 months period. Patients with oesophageal varices have been excluded as well as patients with diabetes. All patients were endoscoped within eight hours of admission to the hospital, whereupon the source of bleeding and types of stigmata were assessed. Forty six patients, chosen at random, were given a 72 hour infusion of somatostatin, while the remaining 49 patients received infusion of placebo. The two groups were well matched for sex, age, and source of bleeding. On the day after admission, an additional endoscopy was performed at which eight patients in the somatostatin group and 16 in the placebo group were found to have a persistent bleeding. A total of five patients in the somatostatin group and 14 in the placebo group underwent surgery (Fisher's exact test, 2-tail, p = 0.04). Rebleeding occurred in six patients in the somatostatin group, of whom five experienced rebleeding after completion of the somatostatin treatment. In the placebo group, rebleeding occurred in five patients, of whom four rebled on the day after admission. The need for blood transfusions and the mortality rate did not differ significantly between the two groups. No toxic side effects were found as a result of the infusion of somatostatin. In this study, somatostatin reduced the number of patients needing surgery with massive upper gastrointestinal bleeding.

Mechanism of prevention of postburn hypermetabolism and catabolism by early enteral feeding

This study was performed to investigate the mechanism whereby immediate enteral feeding after burn injury reduces postburn hypermetabolism and hypercatabolism. Fifty-seven burned guinea pigs (30% TBSA) were divided into three groups: A (N = 19), given 175 kcal/kg/day beginning 2 hours after burn; B (N = 20), given 175 kcal/kg/day with an initial 72-hour adaptation period; and C (N = 18), given 200 kcal/kg/day with the same adaptation period as B. Resting metabolic expenditure (RME) on PBD 13 was lowest in group A (109% of preburn level), compared with group B (144%, p less than 0.001) and group C (137%, p less than 0.01). On PBD 1, group A had the greatest jejunal mucosal weight and thickness (p less than 0.001), and mucosal weight had negative correlations with plasma cortisol (r = 0.829, p less than 0.001) and glucagon (r = 0.888, p less than 0.001). Two weeks after burn, urinary vanillyl mandelic acid (VMA) excretion, plasma cortisol, and glucagon were lowest in group A (p less than 0.05 to p less than 0.01). These hormones also significantly correlated with RME (p less than 0.01 to p less than 0.001). These findings suggest that immediate postburn enteral feeding can prevent hypermetabolism via preservation of gut mucosal integrity and prevention of excessive secretion of catabolic hormones.

Burn encephalopathy in children

Among 287 children with burns treated over a recent two-year period, 13 (5%) showed evidence of encephalopathy. The major clinical symptoms were an altered sensorium and seizures. The majority of symptoms began later than 48 hours after the burn and were accompanied by multiple metabolic aberrations including hypocalcemia. Three children had a relapsing course, and 1 had temporarily enlarged cerebral ventricles. Eleven children improved to normal. In the majority of instances, burn encephalopathy probably reflects central nervous system dysfunction resulting from complex metabolic, hematological, and hemodynamic abnormalities rather than from a single metabolic abnormality.

Metabolic profiles of thermal trauma

The study was designed to establish where significant correlations exist in a variety of metabolic substrates and hormone mediators in patients sustaining thermal injury. The factors studied were insulin, human growth hormone, cortisol, glucagon, free fatty acid, triglyceride and glucose. Incorporated into this design was an evaluation of the impact of quantitated severity of injury upon these correlations. In patients sustaining a low severity of injury (Probability of death (p = 2.2 to 33.9) there appeared a loss of glucose regulation in conjunction with insulin resistance without significant interplay of other factors studied. In contrast, patients sustaining high severity injury (p = 46.9 to 100) evidenced correlations between glucagon and glucose (negative), cortisol and free fatty acid indicating a significant role of hyperglucagonemia in these patients. A discriminant function analysis was employed to incorporate all significant variables into a probability model. Only insulin, glucose and glucagon appeared in the optimal classification equation.

Influence of increasing carbohydrate intake on glucose kinetics in injured patients

The metabolic and hormonal effect of glucose loads, ranging from 125 to 504 g/70 kg/day, were studied in severely injured patients. There was little or no correlation of glucose intake with nitrogen balance, plasma glucose, fatty acid concentrations, or epinephrine excretion. Increased norepinephrine excretion correlated with and may have resulted from increased glucose intake. Serum glucagon concentrations averaged 320 pg/ml and were not depressed by glucose intake. Insulin concentrations rose with glucose intake but were low for the level of plasma glucose. Glucose oxidation and non-oxidative metabolism, including glycogen deposition, correlated well with glucose intake. Gluconeogenesis from alanine was much higher than normal but was completely suppressed at very high intakes. The data imply that cycling of glucose, with glycerol, glycogen, or both, increased with increasing glucose intake.

Change of glucagon reacting to 30 K antibody in totally depancreatized dogs

Total pancreatectomy was performed in dogs; and arginine test was conducted at the first, second and third weeks after surgery, and measurement was made of blood glucose, glucagon and insulin on a time-course basis for a comparative study with normal dogs. 1) After total pancreatectomy, glucagon reacting to 30 K antibody decreased once but increased with the lapse of time when no insulin was administered. 2) In the arginine test, glucagon showed a biphasic reaction in normal dogs, but a monophasic reaction in totally depancreatized dogs. This reaction declined three weeks after surgery. 3) When blood samples were taken from the pancreaticoduodenal vein, the left-gastroepiploic and mesenteric veins, during and after arginine was infused for 30 minutes. Glucagon in the pancreaticoduodenal vein increased markedly, but there were no such prominent changes in the left-gastroepiploic or mesenteric veins, Meanwhile, the level of glucagon in the left-gastroepiploic vein increased remarkably in dogs one week after total pancreatectomy.

Glucagon infusion in normal man: effects on 3-methylhistidine excretion and plasma amino acids

In order to assess the role of glucagon in human protein metabolism and to examine its action as a "catabolic" hormone, studies were conducted in two normal male subjects over an 8-day period. After minimum and stable urinary nitrogen excretion had been produced by the continuous nasogastric administration of carbohydrate (720 g/day) for 8 consecutive days, a continuous intravenous infusion of glucagon (1.0 mg/24 hr) was superimposed on days 7 and 8. Excretion of total nitrogen (N) and urea-N increased significantly (p less than 0.05). Excretion of 3-methylhistidine was unaltered, suggesting that the source of the N losses produced by glucagon did not derive from increased muscle proteolysis. Although striking hypoaminoacidemia was produced, the reductions of extracellular amino acids alone could not account for all of the extra urea excreted. These data suggest that hyperglucagonemia in normal man induces mild nitrogen losses by stimulation of hepatic ureogenesis from free intracellular amino acid pools and not by increased rates of muscle protein breakdown.

Plasma glucagon levels in haemorrhagic shock

Eleven healthy dogs were subjected to haemorrhagic shock for 90 min. after which shed blood was reinfused. Detailed studies were made of cardiopulmonary function. Samples of blood were taken at frequent intervals for the measurement of glucagon, insulin and glucose. Three dogs had samples taken for catecholamine levels. The glucagon level rose during haemorrhagic shock but there was no relationship between this rise and the change in cardiorespiratory measurement, but there was a relationship between the plasma glucagon level, the blood glucose and the catecholamine level. It is suggested that the release of glucagon in haemorrhagic shock is mediated by sympathetic stimulation of the alpha cell and that the rise in glucagon is in part responsible for the hyperglycaemia which is found in shock.