Anabolic effects of insulin and amino acids in promoting nitrogen accretion in postoperative patients

The present study evaluates the effect of insulin and amino acids on nitrogen balance in the immediate postoperative period in moderately stressed patients who have undergone major abdominal surgical operations. Patients were randomly assigned into two large groups (n = 16 each) and four subgroups (n = 8 each). Groups ICON and IINS received an infusion of total parenteral nutrition solution containing 0.25 g of nitrogen per kilogram per day with a calorie:nitrogen (C:N) ratio of 150:1. Groups IICON and IIINS received twice the load of nitrogen with a C:N ratio of 75:1. Groups IINS AND IIINS received an additional continuous infusion of insulin at a rate of 1.0 mU/kg per minute for 7 days. During the total parenteral nutrition period, the patients were kept NPO, and 24-hour urine output was collected for estimation of total nitrogen excretion and nitrogen balance. Net nitrogen excretion (grams per kilogram per day) averaged 0.143 +/- 0.06 in IINS and 0.23 +/- 0.08 in ICON (p < .05) and 0.178 +/- 0.6 in IIINS and 0.25 +/- 0.10 in IICON (p < .05). Nitrogen balance (grams per day) was positive in the four groups: +0.65 +/- 3.8 in IINS and +6.74 +/- 2.94 in ICON (p < .05), and +14.4 +/- 2.61 in IIINS and +11.63 +/- 6.44 in IICON (p = not significant). The average nitrogen incorporation (percent per day) was: 41.3 +/- 6.2 in IINS and 14.6 +/- 20.1 in ICON (p < .05), and 58.3 +/- 4.5 in IIINS and 38.7 +/- 26.2 in IICON (p = not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic hypercortisolemia on carbohydrate metabolism during insulin deficiency

This study was undertaken to further investigate the effect of acute selective insulin deficiency on glycogenolysis and gluconeogenesis occurring during chronic physiological hypercortisolemia in conscious overnight fasted dogs. After an 80-min tracer and dye equilibration period and a 40-min basal period, selective insulin deficiency was created during the 180-min experimental period by infusing somatostatin peripherally (0.8 micrograms.kg-1.min-1) with basal replacement of glucagon intraportally (0.65 ng.kg-1.min-1). In the cortisol group (n = 5), a continuous infusion of hydrocortisone (3.5 micrograms.kg-1.min-1) was begun 5 days before the experiment. In the saline group (n = 5), there was no infusion of cortisol. [3-3H]glucose, [U-14C]alanine, and indocyanine green dye were used to assess glucose production and gluconeogenesis using tracer and arteriovenous difference techniques. During selective insulin deficiency in the saline group, the arterial plasma glucose level (Glc) increased from 109 +/- 2 to 285 +/- 19 mg/dl; glucose production increased from 2.7 +/- 0.2 to 4.5 +/- 0.3 mg.kg-1.min-1. Gluconeogenic efficiency and conversion of alanine to glucose (Conv) increased by 300 +/- 55 and 356 +/- 67%. During selective insulin deficiency in the cortisol group, Glc increased from 117 +/- 3 to 373 +/- 50 mg/dl; glucose production increased from 3.3 +/- 0.5 to 6.9 +/- 0.7 mg.kg-1.min-1. Gluconeogenic efficiency and Conv increased by 268 +/- 41 and 393 +/- 75%, respectively. The maximal glycogenolytic rate increased significantly more in the cortisol group than in the saline group, accounting for the difference in glucose production. These results suggest that, even during chronic hypercortisolemia, acute insulin deficiency has more pronounced effects on glycogenolysis than gluconeogenesis.

Nutritional and metabolic characterization of a thiamine-deficient rat model

The effects of a thiamine-deficient diet on plasma and tissue vitamin concentrations and on whole-body glucose metabolism were assessed. Male Sprague-Dawley rats (175 to 200 g body weight) fed a thiamine-deficient (TD) or nutritionally complete purified diet were used for plasma thiamine mononitrate and monophosphate and for red blood cell and tissue thiamine pyrophosphate (TPP) determinations weekly for up to 5 weeks. Additional rats were used for assessment of basal glucose kinetics by using a primed constant infusion of [3-3H]glucose. Plasma thiamine mononitrate levels decreased 60% at 1 week and were undetectable after 5 weeks on the diet. Plasma thiamine monophosphate decreased 80% after 1 week on the TD diet, and levels were undetectable after 4 weeks on the diet. Red blood cell TPP in the TD group decreased progressively with time: 54% at 1 week, 86% at 3 weeks, and 92% at 5 weeks. At 1 and 4 weeks, the decrease in tissue TPP was significant in the liver (65% and 89%, respectively), gut (52% and 94%, respectively), spleen (40% and 60%, respectively), and skeletal muscle (37% and 76%, respectively), with the brain (7% and 84%, respectively) showing the slowest initial rate of depletion. The TD diet did not alter plasma glucose concentrations, but it increased plasma lactate by 75% and plasma pyruvate by 50% to 75%. Rates of hepatic glucose production and peripheral glucose utilization were not different between the control and TD rats at 2 weeks, but they were 25% higher in the TD rats after 6 weeks on the diet.(ABSTRACT TRUNCATED AT 250 WORDS)

The opposing effects of insulin and hyperglycemia in modulating amino acid metabolism during a glucose tolerance test in lean and obese subjects

An intravenous glucose tolerance test (IVGTT) was administered in both lean (n = 9) and obese (n = 14) volunteers to ascertain the importance of the dynamic interactions between insulin and glucose on plasma concentrations of two amino acids known to be primarily used by skeletal muscle, namely leucine and isoleucine, and one amino acid, phenylalanine, which is primarily metabolized by the liver. After a 30-minute basal period, each subject received a bolus injection of glucose (0.3 g/kg IV) followed 20 minutes later by a bolus injection of tolbutamide (300 mg). Blood samples were drawn frequently for 180 minutes after the glucose infusion to determine plasma concentrations of glucose, insulin, leucine, isoleucine, and phenylalanine. Plasma glucose and insulin concentrations during the basal period were increased by 10% and 100%, respectively, in obese compared with lean individuals (P < .05), whereas phenylalanine, isoleucine, and leucine levels were similar between groups. During the IVGTT, plasma glucose level initially increased by twofold and slowly returned to basal level thereafter, whereas insulin level responded to glucose and tolbutamide infusions in a typical biphasic manner. Plasma leucine and isoleucine levels did not change from basal levels during the first 60 minutes of the IVGTT as hyperglycemic hyperinsulinemia prevailed in both groups. However, when plasma glucose had returned to near-basal levels, plasma leucine and isoleucine levels began to decrease, reaching a plateau of approximately 20% and 35% below basal, and plasma insulin level remained elevated in the lean and obese individuals, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Central NMDA enhances hepatic glucose output and non-insulin-mediated glucose uptake by a nonadrenergic mechanism

One of the hallmarks of the stress response is an increased rate of hepatic glucose production (HGP) which, in conjunction with the presence of insulin resistance, leads to hyperglycemia. Excitatory amino acids (EAA) within the brain mediate some of the cardiovascular responses to stress, but their role in the hormonal and metabolic alterations is poorly defined. The aim of the present study was to determine whether the intracerebroventricular (i.c.v.) injection of either N-methyl-D-aspartate (NMDA) or kainate would produce metabolic alterations comparable to those observed under stress conditions. An i.c.v. cannula and vascular catheters were placed in rats prior to the experiment. After an overnight fast, HGP and peripheral glucose utilization (GU) were assessed in conscious unrestrained rats using [3-3H]glucose. Arterial glucose levels were increased 34% by 15 min after the i.c.v. injection of NMDA (1 microgram) and remained elevated throughout the 3-h protocol. The hyperglycemia resulted from an early increase in HGP (84%) that exceeded a smaller elevation (66%) in GU. The increased glucose flux was associated with sustained insulinopenia (-30%), and elevated levels of corticosterone (40-100%) and epinephrine (75-216%). The hormonal and glucose metabolic responses were quantitatively similar, although of shorter duration, in rats injected with kainate (10 ng). Intravenous adrenergic blockade completely prevented the NMDA-induced hyperglycemia. Adrenergic blockade blunted the early rise in HGP, so that in this group the NMDA-induced increase in HGP was offset by a comparable elevation in GU.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential control of glucoregulatory hormone response and glucose metabolism by NMDA and kainate

The aim of the present study was to elucidate the effect of kainate and N-methyl-D-aspartate (NMDA), two different excitatory amino acid (EAA) agonists, on glucoregulatory hormone production and whole body glucose metabolism. Rates of hepatic glucose production (HGP) and peripheral glucose utilization (GU) were assessed in overnight fasted, catheterized, conscious rats using [3-3H]glucose. At the highest dose of kainate examined (16 mg/kg), glucose levels increased 97% after 1 h; thereafter, glucose fell towards basal values but was still elevated 25% at the end of the 3 h experiment. This hyperglycemia resulted from a rapid increase in HGP that exceeded an increased rate of GU. Both HGP and GU were elevated 86% throughout the final 2 h of the experiment. NMDA induced changes in glucose flux that were qualitatively similar, yet of smaller magnitude and of shorter duration, than those produced by kainate. Kainate-induced increases in glucose metabolism were associated with an early transient hyperinsulinemia followed by a period of insulinopenia, and sustained increases in the plasma concentrations of glucagon, corticosterone, epinephrine and norepinephrine. In contrast, sustained increases in glucagon and catecholamines, as well as the late hypoinsulinemia were not detected in NMDA-treated rats. Adrenergic blockade attenuated the kainate- but not the NMDA-induced increase in glucose metabolism. These results indicate that EAA agonists that bind preferentially to different receptor subtypes produce qualitatively similar changes in glucose metabolism. Whereas the increased HGP in kainate-injected rats was associated with sustained elevations in glucagon, catecholamines and corticosterone, NMDA only transiently elevated circulating glucocorticoid levels, suggesting a different mechanism of action. These data, support the involvement of EAA in various aspects of glucoregulation.

The effects of acute hypercortisolemia on beta-hydroxybutyrate and glycerol metabolism during insulin deficiency

The present study was undertaken to determine whether an acute physiologic rise in plasma cortisol during selective insulin deficiency would have significant effects on glycerol and beta-hydroxybutyrate metabolism in conscious overnight-fasted dogs. Each experiment consisted of a two hour dye equilibration period, a 40 minute basal period, and a 3 hour experimental period. A continuous infusion of indocyanine green dye for blood flow estimation was initiated at the start of the equilibration period and continued throughout the experiment. In both of two protocols selective insulin deficiency was created during the experimental period by infusing somatostatin peripherally (0.8 microgram/kg-min) with basal replacement of glucagon intraportally (0.65 ng/kg-min). In the test protocol (CORTISOL, n = 5), 3.0 micrograms/kg-min of hydrocortisone was infused during the experimental period. In the control protocol (SALINE, n = 5), saline was infused. Net hepatic balances were determined using the (A-V) difference technique. During selective insulin deficiency alone (SALINE), the arterial blood glycerol level increased from 81 +/- 19 to 140 +/- 11 microM (p < 0.01) and net hepatic glycerol uptake (NHGlyU) tended to increase from 2.3 +/- 0.3 to 3.3 +/- 0.6 mumol/kg-min (0.05 < 0.1). The arterial plasma free fatty acid (FFA) level remained unchanged at 1041 +/- 35 microM. The arterial beta-hydroxybutyrate (BHOB) level increased slightly from 21 +/- 4 to 29 +/- 5 microM while net hepatic beta-hydroxybutyrate production (NHBP) remained unchanged (1.0 +/- 0.2 mumol/kg-min). During acute hypercortisolemia with selective insulin deficiency (CORTISOL), similar changes occurred in the arterial blood glycerol level and net hepatic glycerol uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Opiate-like substances in an invertebrate, an opiate receptor on invertebrate and human immunocytes, and a role in immunosuppression

The presence of morphine-like and codeine-like substances was demonstrated in the pedal ganglia, hemolymph, and mantle tissues of the mollusc Mytilus edulis. The pharmacological activities of the endogenous morphine-like material resemble those of authentic morphine. Both substances were found to counteract, in a dose-dependent manner, the stimulatory effect of tumor necrosis factor alpha or interleukin 1 alpha on human monocytes and Mytilus immunocytes, when added simultaneously to the incubation medium. The immunosuppressive effect of this opiate material expresses itself in a lowering of chemotactic activity, cellular velocity, and adherence. Codeine mimics the activity of authentic morphine, but only at much higher concentrations. Specific high-affinity receptor sites (mu 3) for morphine have been identified on human monocytes and Mytilus immunocytes. In Mytilus recovering from experimentally induced stress, the return of "altered" immunocytes to a more inactive state appears to be due to a significant rise in the content of morphine-like material in the pedal ganglia and hemolymph at this time. Thus, morphine may have a role in calming or terminating the state of immune alertness.

Granulocyte colony-stimulating factor prevents ethanol-induced impairment in host defense in septic rats

Ethanol is a potent immunosuppressive agent that impairs neutrophil effector function. The purpose of this study was to determine whether granulocyte colony-stimulating factor (G-CSF), a cytokine that increases neutrophil number and functional activity, could prevent the ethanol-induced impairment of antibacterial host defense. Rats were injected with human recombinant G-CSF for 2 days. Eight hr after the last injection of G-CSF, animals were infused with ethanol (or saline) for 1 hr before the subcutaneous injection of live Escherichia coli. The infusion of alcohol was continued after the bacterial challenge and produced blood alcohol levels of 275-300 mg/dl. In control animals, the injection of E. coli resulted in a marked leukopenia. There was an influx of leukocytes into the subcutaneous space where the bacteria were injected, and neutrophil accumulation in tissues adjacent to the focus of infection (i.e., dorsal skin and muscle). Based on myeloperoxidase activity, there was no detectable accumulation of neutrophils in other soft tissues. In acutely intoxicated rats, leukocyte migration to the inflammatory site was impaired, and the number of viable bacteria isolated from the subcutaneous pocket was markedly increased. G-CSF prevented the sepsis-induced leukopenia, increased the influx of neutrophils in to the infection site, reduced the number of bacteria in the subcutaneous lavage fluid, and decreased the incidence of bacteremia in ethanol-treated rats when compared with rats not receiving G-CSF. These results demonstrate that G-CSF is a potent immunomodulator that stimulates neutrophil recruitment selectively to the site of infection and that can be used to ameliorate the ethanol-induced impairment in bacterial host defense.

Acute hyperglycemia enhances proteolysis in normal man

The influence of hyperinsulinemic-hyperglycemia on protein and carbohydrate homeostasis was assessed using L-[1-13C]-leucine and [3-3H]glucose combined with open-circuit indirect calorimetry. After a 30-min basal period, healthy human volunteers were subjected to two sequential experimental periods (150 min each) during which insulin was continuously infused at a rate to elicit maximal effects (10.0 mU.kg-1 x min-1, resulting in 220-fold basal levels) in conjunction with an infusion of L-amino acids to maintain euleucinemia. Plasma glucose was maintained near basal (94 +/- 2 mg/dl) during period I and at twofold basal (191 +/- 4 mg/dl) during period II. The endogenous rate of leucine appearance (index of proteolysis in mumol.kg-1 x h-1) dropped by 80% from basal during period I (P < 0.01) but only by 44% during period II. Although hyperglycemia stimulated the rate of proteolysis threefold (18.0 +/- 10.2 to 49.8 +/- 7.2, P < 0.001), neither leucine oxidation nor nonoxidative leucine rate of disappearance (an estimate of protein synthesis) was altered. During both glycemic conditions, the rates of hepatic glucose production were completely suppressed, and this was accompanied by 3- and 11-fold increases in the estimated rates of protein and carbohydrate oxidation, respectively, and an 80% decrease in the rate of lipid oxidation. The estimated rate of glucose storage was increased fourfold during period I and by an additional 2.3-fold (to approximately 10-fold basal) in period II. The present study demonstrates that, during hyperinsulinemia, acute elevations of plasma glucose to two times basal levels result in a marked stimulation of whole body proteolysis during hyperinsulinemia.

Role of IL-1 alpha in central nervous system immunomodulation of glucoregulation

Hyperglycemia is a hallmark of the stress response, and has been largely attributed to elevated plasma levels of catabolic hormones. Recently, various cytokines have been shown to be endogenously produced within the brain and may represent an important component of the central regulation of this metabolic response. Therefore, the aim of the present study was to determine whether the intracerebroventricular (i.c.v.) injection of one such peptide, interleukin (IL)-1, can produce hormonal and metabolic alterations comparable to those observed under stress conditions. An i.c.v. cannula and vascular catheters were placed in rats prior to the experiment. Whole body glucose flux was assessed in overnight fasted conscious unrestrained rats using [3-3H]glucose. A mild hyperglycemia was elicited 20 min after the i.c.v. injection of IL-1 alpha (human recombinant, 100 ng) that was not detected in control rats. Glucose levels gradually increased and were 26% higher than control values during the last hour of the 3 h experimental period. The hyperglycemia resulted from a 44% increase in the rate of hepatic glucose output (HGO), which preceded a proportional rise in peripheral glucose utilization. No increase in metabolic clearance rate was observed, suggesting that the increased glucose uptake was the result of mass action. The increased glucose flux was associated with a transient hyperinsulinemia (+95%), and sustained elevations in the arterial concentrations of glucagon (56%) and corticosterone (175%). In contrast, glucose flux was not altered by intravenous administration of the same dose of IL-1 alpha, or i.c.v. injection of IL-1 beta, or heat-inactivated IL-1 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal and metabolic effects of neuroglucopenia

We examined the role of central neuroglucopenia, induced by intracerebroventricular (i.c.v.) administration of 2-deoxyglucose (2-DG), on glucose and amino acid kinetics in conscious dogs. Group 1 received i.c.v. 2-DG at 2.5 mg.kg-1 x min-1 for 15 min. Group 2 received an equal intravenous (i.v.) amount of 2-DG. In the i.c.v. group, plasma glucose levels rose from 106 +/- 4 mg/dl to a peak of 204 +/- 12 mg/dl by 90 min. Blood lactate increased from 689 +/- 1 to 2,812 +/- 5 mumol/l and blood alanine not change from basal (256 +/- 41 mumol/l). The rate of hepatic glucose production, determined isotopically, was increased 2-fold over basal (P < 0.01). Significant increases (P < 0.001) over basal were also noted in plasma epinephrine, norepinephrine, insulin, glucagon and cortisol. Leucine rate of appearance (Ra) showed a 30% decrease from basal to 2.4 +/- 0.05 mumol.kg-1 x min-1 (P < 0.01). In group 2 plasma glucose levels were not altered but plasma cortisol and glucagon showed a modest transient increase above basal (P < 0.05). No significant changes were noted in amino acid kinetics. These findings suggest that periventricular neuroglucopenia, in the absence of peripheral glucose deprivation, is accompanied by hyperglycemia secondary to enhanced hepatic glucose production with decreased glucose utilization and by increased hepatic uptake of gluconeogenic precursors. These, however, were not accompanied by increased whole body proteolysis as was previously seen with generalized glucopenia resulting from insulin-induced hypoglycemia.

Removal of glycylglutamine from plasma by individual tissues: mechanism and impact on amino acid fluxes in postabsorption and starvation

A possible source of glutamine, for inclusion in the parenteral solutions, is glycylglutamine. The aim of this article is to review briefly the information on metabolism of glycylglutamine when administered intravenously. The fact that there is efficient utilization of intravenously infused glycylglutamine was evident with very little excretion in the urine. Although all the tissues examined, except brain, participated in the removal of glycylglutamine from plasma, kidney predominated in this regard. This may be related to the presence of carrier-mediated systems for cellular uptake of glycylglutamine in the kidney and the lack of them in other tissues. Starvation did not alter the metabolic clearance of glycylglutamine, although it reduced the removal by the kidney. Renal metabolism of glycylglutamine resulted in the release of constituent amino acids that were largely utilized by the liver in the postabsorptive state and by skeletal muscle in starvation. This alteration was accompanied by a selective inhibition of muscle release of amino acids that are substrates for enhanced hepatic gluconeogenesis and renal ammoniagenesis in starvation. Because there was no change either in plasma glucose level or ammonia excretion during the infusion of glycylglutamine in starved human subjects, apparently the amino acid residues of glycylglutamine fulfilled the substrate needs for these functions. These results provide a metabolic basis for further investigations of the possible nutritional benefit of including glycylglutamine in parenteral nutrition.

Effects of chronic elevation in plasma cortisol on hepatic carbohydrate metabolism

This study was undertaken to investigate the effects of chronic physiological elevations in plasma cortisol on glycogenolysis and gluconeogenesis in conscious, overnight-fasted dogs. Experiments consisted of an 80-min tracer and dye equilibration period and a 40-min sampling period. Infusions of D-[3-3H]glucose, L-[U-14C]alanine, and indocyanine green dye were used to assess glucose production (Ra) and gluconeogenesis using tracer and arteriovenous (a-v) difference techniques. In the cortisol group, (n = 10), a continuous infusion of hydrocortisone (3.5 micrograms.kg-1 x min-1) was begun 5 days before the experiment and continued throughout the sampling period. In the saline group (n = 10), there was no infusion of cortisol. The fivefold elevation in plasma cortisol increased plasma insulin from 12 +/- 2 to 19 +/- 2 microU/ml. Glucose Ra was elevated in the cortisol group (3.5 +/- 0.2 vs. 2.8 +/- 0.2 mg.kg-1 x min-1) but net hepatic glucose output was markedly diminished (1.2 +/- 0.4 vs. 2.7 +/- 0.3 mg.kg-1 x min-1). Gluconeogenic conversion of alanine to glucose was increased slightly by cortisol (0.60 +/- 0.13 to 0.99 +/- 0.12 mumol.kg-1 x min-1), but the gluconeogenic efficiency of the liver was unchanged. Cortisol increased hepatic glycogen content evident at the end of the study greater than twofold (76.4 +/- 7.9 vs. 30.0 +/- 4.7 g/liver). These results suggest that cortisol 1) promotes glucose cycling through glycogen, 2) greatly inhibits nonhepatic glucose utilization, 3) increases hepatic gluconeogenesis in vivo primarily through enhanced substrate delivery to the liver, and 4) raises plasma insulin levels, which restrains intrahepatic gluconeogenesis.

The effects of acute elevations in plasma cortisol levels on alanine metabolism in the conscious dog

The present study was undertaken to determine whether an acute physiological increase in plasma cortisol level had significant effects on alanine metabolism and gluconeogenesis within 3 hours in conscious, overnight-fasted dogs. Each experiment consisted of an 80-minute tracer and dye equilibration period, a 40-minute basal period, and a 3-hour experimental period. A primed, continuous infusion of [3-3H]glucose and continuous infusions of [U-14C]alanine and indocyanine green dye were initiated at the start of the equilibration period and continued throughout the experiment. Dogs were studied with (1) a hydrocortisone infusion ([CORT] 3.0 micrograms.kg-1.min-1, n = 5), (2) hydrocortisone infused as in CORT, but with pancreatic hormones clamped using somatostatin and basal intraportal replacement of insulin and glucagon (CLAMP+CORT, n = 5), or (3) saline infusion during a pancreatic clamp (CLAMP, n = 5). Glucose production and gluconeogenesis were determined using tracer and arteriovenous difference techniques. During CLAMP, all parameters were stable except for a modest 67% +/- 6% increase in gluconeogenic conversion of alanine to glucose and a 53% +/- 26% increase in gluconeogenic efficiency. When plasma cortisol levels were increased fourfold during CLAMP+CORT, there was no change in the concentration, production, or clearance of glucose. Gluconeogenic conversion of alanine to glucose increased 10% +/- 34% and gluconeogenic efficiency increased 65% +/- 43%, while net hepatic alanine uptake (NHAU) increased 60% +/- 19% and hepatic fractional extraction of alanine increased 38% +/- 12%. Cortisol did not cause an increase in the arterial glycerol level or net hepatic glycerol uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of the central nervous system in modulating glucose and protein metabolism during insulin-induced hypoglycemia

We previously established that insulin-induced hypoglycemia is associated with enhanced proteolysis with the GI tract being the major contributor to this response. In the present study we examined whether brain hypoglycemia modulates the changes in amino acid and glucose kinetics during insulin-induced hypoglycemia. Studies were performed in 24 h faster conscious dogs chronically fitted with catheters in the femoral artery, portal vein, hepatic vein, femoral vein and in both carotid and vertebral arteries, and that were also fitted with permanent tracheostomies. Following a 30 min basal period insulin was infused i.v. at 300 mU/kg.h to achieve systemic hypoglycemia averaging 42 +/- 2 mg/dl. In group I (n = 6) both central and systemic (global) hypoglycemia was allowed to develop. The rate of net hepatic glucose output (NHGO) increased by 50% above basal. Plasma leucine increased from 120 +/- 12 mumol/l basally to 154 +/- 30 mumol/l during the last hour of hypoglycemia. The rate of leucine appearance into the plasma compartment (R(a)) increased from 154 +/- 30 to 200 +/- 36 mumol/kg.h and its rate of oxidation increased from 22 +/- 5 to 51 +/- 8 mumol/kg.h, while its non-oxidative rate of disposal (141 +/- 12 mumol/kg.h) did not change. Net leucine balance across the gut was neutral (6 +/- 5 mumol/kg.h) and switched to net output of 96 +/- 24 mumol/kg.h. In group II (n = 5) 10% dextrose in water was infused into both carotid and vertebral arteries to prevent profound CNS glucopenia. This was associated with a drop in NHGO.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between aerobic fitness level and daily energy expenditure in weight-stable humans

The relationship between exercise and energy expenditure is unclear, with some suggestions that exercise leads to increased energy expenditure over and beyond the increase due to the exercise itself. In this cross-sectional study, we examined the relationships among aerobic fitness level, body composition, and total daily energy expenditure in 78 subjects. Daily energy expenditure (determined in a whole room calorimeter) was significantly correlated with both fat-free mass (FFM) and aerobic fitness (estimated from maximum aerobic capacity or VO2max). However, multiple-regression analysis demonstrated that, after accounting for FFM, VO2max did not explain a significant amount of the remaining variation in energy expenditure. In addition, the relationship between resting metabolic rate and both FFM and VO2max was evaluated using data from 214 weight-stable subjects analyzed retrospectively. The results were identical with the results obtained from the 78 subjects in that VO2max did not have effects independent of FFM on energy expenditure. We conclude that aerobic fitness does not have a direct effect on energy expenditure. However, it may have effects that are mediated through body composition, since in both populations studied here, VO2max was positively correlated with FFM and negatively correlated with adiposity.

Role of leucine and other amino acids in regulating protein metabolism in vivo

The present study examines the independent effects of amino acids and leucine in modulating insulin's effect on leucine kinetics in 24-h fasted conscious dogs during an experimental period where insulin was infused at 600 mU.kg-1.h-1. Group I (n = 7) received saline, group II (n = 10) received sequential infusions of L-leucine at 0, 1, 3, and 1 mumol.kg-1.min-1 each lasting for 90 min, and group III (n = 6) received L-amino acids with doses of L-leucine matching those of group II. Plasma leucine (mumol/l) was 120 +/- 5 basally and 135 +/- 23 and 129 +/- 12 during the infusion of 3.0 mumol.kg-1.min-1 in groups II and III compared with 40 +/- 3 in group I. Leucine rate of appearance (mumol.kg-1.min-1) was 3.5 +/- 0.3 during the basal period and was suppressed 80% in both groups II and III as compared with 40% in group I (P less than 0.01). Leucine oxidation (basal = 0.7 +/- 0.15 mumol.kg-1.min-1) dropped 20% in group I but increased to threefold basal in group II and twofold in group III (P less than 0.05). Nonoxidative rate of disposal (basal = 2.6 +/- 0.2 mumol.kg-1.min-1) dropped 25% in group I and 55% in group II but did not change in group III. These data show that, in addition to insulin, amino acids and particularly leucine cause a marked suppression of proteolysis. Availability of all amino acids to prevent hypoaminoacidemia is necessary to sustain basal rates of protein synthesis. The infusion of leucine alone resulted in significant stimulation of leucine oxidation.

Short-term effects of dietary-fat ingestion on energy expenditure and nutrient balance

Joule for joule, dietary fat may promote obesity more than protein or carbohydrate. In this study we determined whether the addition of 50 g dietary fat to a standard breakfast would increase energy expenditure or fat oxidation during the immediate 6-h postprandial period or over the ensuing 18 h. We also determined whether subjects with a high level of aerobic physical fitness would show a greater increase in fat oxidation after the ingestion of the extra fat than would less fit subjects. Adding fat did not increase fat oxidation or energy expenditure either during the immediate 6-h postprandial period or over the following 18 h. This was true regardless of the subject's fitness level. Acutely, dietary fat ingested in excess of its usual rate of oxidation appears to be stored in the body. Being physically fit does not appear to provide an advantage in avoiding short-term storage of excess dietary fat.

Nutrient balance and energy expenditure during ad libitum feeding of high-fat and high-carbohydrate diets in humans

To study the influence of diet composition on regulation of body weight, we fed 21 weight-stable subjects (11 lean, 10 obese) high-carbohydrate (HC) and high-fat (HF) diets for 1 wk each. Although diet composition was fixed, total energy intake was unrestricted. Subjects had a higher energy intake on the HF (11,039 +/- 2700 kJ/d) than on the HC (10,672 +/- 2617 kJ/d) diet (P less than 0.05), but energy expenditure was not different between diets. On day 7 of the HC diet, carbohydrate (CHO) oxidation was significantly related to CHO intake with the slope of the regression line 0.99, suggesting that overall CHO balance was near zero. However, the slope of the regression line was greater for obese than for lean subjects. On day 7 of the HF diet, fat oxidation was significantly related to fat intake but the slope of the line was 0.50, suggesting that overall fat balance was positive. However, this relationship was due entirely to lean subjects, with obese subjects showing no relationship between fat intake and oxidation.

Short-term regulation of insulin-mediated glucose utilization in four-day fasted human volunteers: role of amino acid availability

Glucose homeostasis in men fasted for 84 h was assessed using isotopes, indirect calorimetry and forearm balance techniques during a basal period and three sequential hyperinsulinaemic euglycaemic clamps each lasting for 150 min. Two protocols (n = 12 in each) were used: subjects were either allowed to develop hypoaminoacidaemia or received a commercial solution of L-amino acids while maintaining near-basal plasma leucine levels. Insulin infusions resulted in 3-, 35- and 650-fold increases in plasma insulin levels in both protocols. The infusion of amino acids produced a rightward shift in the dose-response curve of insulin's effect on suppressing hepatic glucose production, indicating decreased sensitivity in addition to blunting of the maximal responsiveness. Total body glucose rate of disappearance was progressively increased with escalating insulin doses, but was 22% lower at the intermediate and highest insulin doses in the group that was infused with amino acids (3.44 +/- 0.53 vs 4.82 +/- 0.71 and 7.72 +/- 1.01 vs 10.36 +/- 1.08 mg.kg-1.min-1, respectively; p less than 0.05). Forearm balance data confirmed the isotopic data, since amino acid infusions blunted the insulin-mediated increase in net forearm glucose utilization (by 50-83%). Furthermore, the infusion of amino acids resulted in marked reductions in the rate of carbohydrate oxidation and storage as assessed by indirect calorimetry. The data indicate that the amino acid-mediated suppression of glucose utilization and carbohydrate oxidation is exerted on the responsive component of insulin action.

Different roles of IL-1 and TNF on hemodynamics and interorgan amino acid metabolism in awake dogs

The present study examines the effects of interleukin 1 (IL-1) and tumor necrosis factor (TNF) on various hemodynamic parameters and interorgan fluxes of amino acids, glucose, and lactate in chronically catheterized awake dogs. The dogs received 5 micrograms.kg-1.h-1 of either human recombinant IL-1 beta or TNF intravenously for 2 h. Hemodynamic parameters and substrate fluxes across the gut and liver were determined during and 2 h after discontinuation of the cytokine infusions. Substrate fluxes were calculated by blood flows and arteriovenous differences. Both IL-1 and TNF enhanced the uptake of alanine, uptake of lactate, and output of glucose by the liver. These changes were associated with elevated arterial levels of alanine and lactate while arterial levels of glucose decreased. Uptake of glutamine by the liver was reduced by either IL-1 or TNF infusions. The effects of IL-1 and TNF on the hemodynamic parameters and on gut amino acid metabolism varied with the cytokine infused. IL-1 produced hyperdynamic state, increased splanchnic blood flow, and enhanced glutamine uptake by the gut. TNF infusion did not cause a hyperdynamic state, nor did it alter the gut handling of amino acids. We conclude that IL-1 and TNF exert distinct different effects on the systemic and hemodynamic parameters and on interorgan balances of amino acids, glucose, and lactate across the gut and the liver.

Rapid measurement of leucine-specific activity in biological fluids by ion-exchange chromatography and post-column ninhydrin detection

Commonly used methods for the measurement of leucine-specific activity use either high-performance liquid chromatography (HPLC) and pre-column derivatization or conventional ion-exchange chromatography. These are time-consuming, labor-intensive, relatively costly procedures, requiring high concentrations of radioactivity for accuracy. The present paper describes a method for the measurement of plasma leucine-specific activity using HPLC equipment, a large-bore ion-exchange column and post-column ninhydrin detection. With this method, determination of leucine concentration and leucine radioactivity was found to be linear (r2 greater than 0.999) over physiological ranges for both standards and deproteinized plasma. The intra- and inter-assay coefficients of variation for leucine concentrations were 1.4 and 2.7%, respectively. The intra- and inter-assay coefficients of variation for leucine-specific activities were 1.5 and 1.9%, respectively. The automated method is relatively fast (injection to injection time approximately 45 min), economical and capable of accurately assessing relatively small amounts of radioactivity.