Extraction Of Alanine Research Articles

Partition of Amino Acids in Aqueous Two-Phase Systems Comprising Hydrophilic Organic Solvents and Salts

An aqueous two-phase system (ATPS) comprising a hydrophilic organic solvent and inorganic salt is advantageous because of its high polarity, low viscosity, and low cost. In this work, nine amino acids were partitioned in an ATPS that comprised hydrophilic organic solvents (2-methyl-2-propanol, tetrahydrofuran, and 2-propanol) and salts (Na2SO4, K2HPO4, and (NH4)2SO4). Amino acids were successfully extracted using different combinations of solvents and salts. The distribution ratio of amino acids in the ATPS containing ammonium sulfate increased with an increase in their hydrophobicity, except for that of alanine. The specific extraction of alanine was observed because of its salting-out effect in ammonium sulfate solution. The sulfate salts of amino acids exhibited higher extractability than amphoteric amino acids.

The Metabolic Response to Infection With Wolbachia Implicates the Insulin/Insulin-Like-Growth Factor and Hypoxia Signaling Pathways in Drosophila melanogaster

The endosymbiotic bacteria, Wolbachia, are best known for their ability to manipulate insect-host reproduction systems that enhance their vertical transmission within host populations. Increasingly, Wolbachia have been shown to depend on their hosts' metabolism for survival and in turn provision metabolites to their host. Wolbachia depends completely on the host for iron and as such iron has been speculated to be a fundamental aspect of Wolbachia-host interplay. However, the mechanisms by which dietary iron levels, Wolbachia, and its host interact remain to be elucidated. To understand the metabolic dependence of Wolbachia on its host, the possibility of metabolic provisioning and extraction, and the interplay with available dietary iron, we have used NMR-based metabolomics and compared metabolite profiles of Wolbachia-infected and uninfected Drosophila melanogaster flies raised on varying levels of dietary iron. We observed marked metabolite differences in the affected metabolite pathways between Wolbachia-infected and uninfected Drosophila, which were dependent on the dietary iron levels. Excess iron led to lipid accumulation, whereas iron deficiency led to changes in carbohydrate levels. This represents a major metabolic shift triggered by alterations in iron levels. Lipids, some amino acids, carboxylic acids, and nucleosides were the major metabolites altered by infection. The metabolic response to infection showed a reprogramming of the mitochondrial metabolism in the host. Based on these observations, we developed a physiological model which postulates that the host's insulin/insulin-like-growth factor pathway is depressed and the hypoxia signaling pathway is activated upon Wolbachia infection. This reprogramming leads to predominantly non-oxidative metabolism in the host, whereas Wolbachia maintains oxidative metabolism. Our data also support earlier predictions of the extraction of alanine from the host while provisioning riboflavin and ATP to the host.

A molecular receptor selective for zwitterionic alanine.

A molecular receptor has been synthesized joining an aza-crown ether with a chiral chromane which mimics the oxyanion hole of the enzymes. With this receptor an apolar host-guest complex with zwitterionic alanine has been achieved through the formation of up to seven H-bonds. This complex allows the extraction of aqueous alanine to a chloroform phase, while other natural amino acids are poorly extracted or are not extracted at all. Due to the chiral nature of the receptor, enantioselective extraction from the aqueous alanine solution to a chloroform phase takes place. X-Ray analysis combined with anisotropic effects, NOE and CD studies revealed the absolute configuration of both strong and weak complexes. Modelling studies also support the proposed structures. The presence of an oxyanion-hole motif in this structure was corroborated by X-ray diffraction studies.

Altered alanine plasma levels despite normalized hepatic alanine extraction in the long-term course after liver transplantation.

The amino acid (AA) metabolism in cirrhosis is deranged, reflected by an altered plasma AA profile. Alanine is a unique AA with predominant production by muscle and the highest hepatic extraction rate. We studied circulating levels and hepatic alanine extraction in 52 patients with advanced cirrhosis, 16 stable patients more than 6 months after orthotopic liver transplant (OLT), and 50 controls. In addition, hepatic hemodynamics (portal pressure, hepatic blood flow, and splanchnic percent indocyanine green extraction) and parameters of hepatic metabolism (splanchnic oxygen uptake and splanchnic glucose production) were assessed. Circulating alanine levels decreased independently of the clinical stage in cirrhosis (262+/-15 micromol/L vs. 330+/-14 micromol/L in controls, P<0.001) and decreased even further after OLT (209+/-10 micromol/L, P<0.001). Hepatic alanine extraction decreased dependently on the clinical stage in cirrhosis (59+/-7 micromol/min) and was normalized after OLT (100+/-10 micromol/min, P<0.001), indicating that decreased plasma alanine levels in OLT patients are the result of changes in extrahepatic metabolism. Hepatic alanine extraction correlated with splanchnic oxygen uptake (r=0.64, P<0.001) and hepatic glucose production (r=0.65, P<0.001). These results demonstrate that significant alterations in muscular AA metabolism persist even in the clinically stable long-term course after OLT when the hepatic AA metabolism is normalized.

Hepatic response to increased exogenous supply of plasma amino acids by infusion into the mesenteric vein of Holstein-Friesian cows in late gestation.

The hepatic responses of late gestation, dry dairy cows to acute (6 h) infusions of an amino acid (AA) mixture (Synthamin; 0.0, 1.1, 2.2, 4.4, 8.8 and 17.6 mumol/min) into the mesenteric vein were determined. Neither blood flow nor O2 consumption across the portal-drained viscera (PDV) and liver was significantly altered by infusion. Similarly, there were no effects on net absorption, or hepatic removal, of acetate, propionate, butyrate or NH3. Glucose PDV appearance was unchanged but hepatic glucose production increased (P = 0.032) by 0.2 mumol/min per mumol/min of AA infused. Additional extraction of alanine, glycine (both infused) and glutamine (not infused) by the liver was sufficient to account for most of the extra C required for glucose synthesis. The N that would be liberated from these glucogenic AA would also account for a large proportion of the increase in urea-N produced in response to the AA infusion. This supports the concept of a correlation between gluconeogenesis and ureagenesis. Furthermore, the amide-N liberated from the extracted glutamine would contribute up to 0.17 of hepatic NH3 flux and assist in balancing N inputs into the carbamoyl phosphate and arginosuccinate entry points of the ornithine cycle. Rates of fractional extraction of the various AA by the liver were best fitted by linear equations, indicating that even at the highest rates of administration (approximately twice maximal physiological absorption) the transport systems were not saturated. Hepatic fractional extractions of infused essential AA were highest for methionine (0.83) and phenylalanine (0.87) with the lowest proportion removed observed for valine (0.25), leucine (0.30), lysine (0.31) and isoleucine (0.49). For the non-essential AA, the highest apparent fractional extractions were for glycine (0.73), arginine (0.79) and tyrosine (0.63) followed by alanine (0.54), proline (0.47) and serine (0.37). Hepatic removal of AA-N exceeded the increase in urea-N formation such that, at the highest rate of infusion, approximately 10 mmol/min of the extracted AA was apparently available for hepatic anabolism, more than is required to account for assumed increases in liver mass and export protein synthesis. Similarly, the amount of AA available for peripheral tissue protein gain, when assessed against phenylalanine supply as the limitation, would be the equivalent of a maximum of 0.5 g protein retained/min (6 mmol AA-N/min). This would provide sufficient AA for replenishment of peripheral (muscle) protein stores plus support of the placenta and fetus.

Extraction of alanine using emulsion liquid membranes featuring a cationic carrier

To recover alanine (Ala) from the secondary isoelectric-point crystallization other liquor of glutamic acid, a new separation method using an emulsion liquid membrane (ELM) process is studied. The membrane phase consists of D2EHPA (di-2-ethylhexyl phosphoric acid), Span 80 (sorbitan monooleate), and kerosene acting as carrier, surfactant. and diluent, respectively. The appropriate extraction conditions are obtained according to various affecting factors. The demulsification is investigated in a high electrostatic field. Further, a functional relation between demulsification rate and the relevant operating factors is established.

Hyperglucagonemia and hepatic glucose metabolism during infection in the conscious dog.

The chronic and acute roles of hyperglucagonemia in sustaining the increased glucose production observed in the conscious infected dog were examined. Three groups of dogs were studied: a sham group (SHAM; n = 10), an infected group (INFXN; n = 11), and a sham group in which the chronic (42-h) increase in glucagon observed in INFXN was simulated (SimGGN; n = 5). INFXN and SimGGN were studied in the presence of hyperglucagonemia. In addition, glucagon was selectively decreased for 180 min in INFXN by use of somatostatin with basal intraportal insulin replacement and in SimGGN by discontinuing the exogenous glucagon infusion. Tracer and arteriovenous difference techniques were used to assess hepatic glucose metabolism and gluconeogenesis. Whereas the rate of glucose appearance (Ra) was increased by 30% (3.3 +/- 0.1 vs. 2.5 +/- 0.1 mg.kg-1.min-1) in INFXN vs. SHAM, Ra did not increase in SimGGN (2.4 +/- 0.2 mg.kg-1.min-1). In addition, the 30% increase in net hepatic gluconeogenic precursor uptake seen in INFXN did not occur in SimGGN despite an augmented net hepatic alanine fractional extraction (0.62 +/- 0.03 vs. 0.47 +/- 0.05, SimGGN vs. INFXN). With acute removal of hyperglucagonemia, endogenous Ra decreased in SimGGN and INFXN by 1.0 +/- 0.2 and 1.4 +/- 0.3 mg.kg-1.min-1, respectively. Net hepatic alanine fractional extraction in INFXN, leading to a greater rise in arterial blood alanine levels. In summary, chronic hyperglucagonemia alone cannot explain the increase in Ra observed during an infection. The marked hyperglucagonemia seen during infection plays an essential role in sustaining normal net hepatic fractional alanine extraction to compensate for an impairment in glucagon-stimulated hepatic amino acid transport activation.

Altered coronary vasodilator reserve and metabolism in myocardium subtended by normal arteries in patients with coronary artery disease

Objectives. The aim of this study was to investigate coronary vasodilator reserve and metabolism in myocardium subtended by angiographically normal arteries remote from ischemia.Background. After infarction, structural and functional changes occur in remote myocardium often subtended by normal arteries. Whether changes occur in regions remote from ischemic but noninfarcted myocardium is unknown.Methods. Coronary vasodilator reserve was measured with positron emission tomography in 12 patients with single-vessel disease using intravenous dipyridamole (0.56 mg/kg for 4 min). In another 10 patients, simultaneous arterial/great cardiac vein catheterization was performed during atrial pacing to measure myocardial metabolism in regions subtended by diseased or normal arteries.Results. Basal myocardial blood flow in stenosis-related regions was comparable to that in remote regions but was lower after dipyridamole administration (1.73 ± 0.91 vs. 2.89 ± 0.93 ml/min per g, p < 0.01), giving coronary vasodilator reserve values of 1.80 ± 0.82 and 2.73 ± 0.89 (p < 0.01). In normal control subjects, basal myocardial blood flow was 0.92 ± 0.13 and 3.67 ±0.94 ml/min per g in the basal state and after dipyridamole (both p < 0.05 vs. values in remote regions), and coronary vasodilator reserve was 4.07 ± 0.98 (p < 0.01 vs. values in remote regions). During pacing there was net lactate release in diseased regions (−18 ± 27%, p < 0.05 vs. values in remote regions and control subjects) and extraction in remote regions (38 ± 17%) and in normal control subjects (26 ± 11%). Glucose and alanine extraction were increased in diseased (8 ± 6% and 6 ± 6%) and remote regions (6 ± 3% and 4 ± 3%), compared with values in normal control subjects (2 ± 3% and −1 ± 3%, both p < 0.05 vs. diseased and remote regions).Conclusions. Coronary vasodilator reserve is reduced and glucose and alanine metabolism is abnormal in regions subtended by normal arteries remote from ischemic but noninfarcted myocardium.

Impact of chronic stress hormone infusion on hepatic carbohydrate metabolism in the conscious dog

The effects of chronic administration of counterregulatory hormones on hepatic glycogenolysis and gluconeogenesis were investigated. We studied 14 20-h fasted conscious dogs prior to (day 0) and after a 70-h stress hormone (SHI, n = 7) or saline (n = 7) infusion (day 3). Glucose production and gluconeogenesis were assessed using tracer and arteriovenous difference techniques. SHI increased plasma glucagon, cortisol, epinephrine, and norepinephrine levels approximately fivefold. SHI increased the arterial plasma glucose and insulin concentrations (110 +/- 2 to 204 +/- 19 mg/dl and 13 +/- 2 to 36 +/- 3 microU/ml on day 3). Tracer-determined glucose appearance and net hepatic glucose output were increased 80 and 60%, respectively. Net hepatic lactate uptake and fractional extraction were increased by 11.2 +/- 3.8 and 0.51 +/- 0.18 mumol.kg-1 x min-1, respectively, as was net hepatic glycerol uptake (1.0 +/- 0.6 mumol.kg-1 x min-1). Net hepatic fractional alanine extraction was also increased by 0.37 +/- 0.03 mumol.kg-1 x min-1; however, net hepatic alanine uptake was not altered. The efficiency of alanine conversion to glucose almost doubled (0.33 +/- 0.05 to 0.59 +/- 0.09). Renal glucose production was also increased, accounting for 33% of the increase in glucose turnover. This increase was paralleled by an increase in renal gluconeogenic precursor uptake. In conclusion, SHI created marked hyperglycemia and hyperinsulinemia and elevated glucose production from both the liver and the kidney, with gluconeogenesis accounting for approximately 70% of the response.

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 μg · 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. When plasma cortisol levels were increased and the pancreatic hormones were allowed to change (CORT), there was a transient but significant decrease in plasma insulin levels, while plasma glucagon levels remained unchanged. There was no change in the concentration, production (R a), or clearance of glucose. However, gluconeogenic conversion of alanine increased 190% ± 59%, gluconeogenic efficiency increased 57% ± 43%, NHAO increased 75% ± 25%, and hepatic alanine fractional extraction increased 48% ± 6%. These changes were all statistically significant by the first 90 minutes of hydrocortisone infusion. In addition, there was a tendency for both net hepatic production of lactate and net hepatic uptake of glycerol to be elevated compared with the other two groups. These results suggest that an acute physiologic increase in plasma cortisol level can increase the gluconeogenic conversion of alanine to glucose by increasing both NHAU and hepatic fractional extraction of alanine. This increase in plasma cortisol level may also be associated with a transient decrease in plasma insulin level that may further promote gluconeogenesis.

Importance of basal glucagon in maintaining hepatic glucose production during a prolonged fast in conscious dogs.

We undertook studies in conscious dogs to assess the role of basal glucagon in stimulating glucose production after a 7-day fast. Two protocols consisting of a 40-min basal period (-40 to 0 min), and a 180-min test period (0-180 min) were used. During the test period of the first protocol (hormone replacement; n = 4), somatostatin was infused (0.8 micrograms.kg-1.min-1) along with basal intraportal replacement amounts of insulin and glucagon, whereas in the second protocol (glucagon deficiency; n = 5), somatostatin plus insulin alone were infused. Glucose production and gluconeogenesis were measured using tracer and arteriovenous difference techniques. Plasma insulin levels were similar during the test period in both protocols (6 +/- 1 microU/ml). The plasma immunoreactive glucagon level in the control protocol averaged 50 +/- 8 pg/ml, whereas in the glucagon-deficiency protocol the level fell from 50 +/- 8 to 29 +/- 8 pg/ml (P less than 0.05). The plasma glucose level and the rate of glucose production were unchanged during bihormonal replacement. During glucagon deficiency the plasma glucose level was held constant at 100 +/- 4 mg/dl by glucose infusion. Tracer-determined endogenous glucose production fell from 1.8 +/- 0.1 to 1.0 +/- 0.1 mg.kg-1.min-1 by 30 min (P less than 0.05). After 3 h of glucagon deficiency, gluconeogenic conversion of alanine to glucagon was reduced 40% and the hepatic fractional extraction of alanine was reduced by 45%. The efficiency of the gluconeogenic process within the liver was not altered by glucagon deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic glutamine metabolism in the septic rat.

1. The hepatic metabolism of glutamine, alanine, ammonia, urea, glutathione and glucose was studied in rats made septic by caecal ligation and puncture and was compared with that in rats that had undergone sham operation (laparotomy). 2. Sepsis resulted in increases in the plasma activities of gamma-glutamyltransferase (P less than 0.001), alanine aminotransferase (P less than 0.001) and aspartate aminotransferase (P less than 0.001), the serum total and direct bilirubin concentrations (P less than 0.001), and the blood lactate (P less than 0.01), glutamine (P less than 0.05), alanine (P less than 0.001) and urea (P less than 0.05) concentrations, but produced decreases in the blood ketone body (P less than 0.001) and glutathione (P less than 0.05) concentrations and in the plasma cholesterol concentration (P less than 0.05). These changes were associated with marked negative nitrogen balance in septic rats. 3. Sepsis increased total hepatic blood flow (by 22.7%) together with hepatic arterial flow (by 25.8%) and portal venous flow (by 18.7%). Sepsis resulted in marked increases in the net rates of hepatic extraction of glutamine (by 164%), alanine (by 138%) and ammonia (by 259%) with concomitant increases in the net rates of hepatic release of glutamate (by 105%), glutathione (by 87.5%), glucose (by 70.1%) and urea (by 100.4%). 4. Sepsis increased the activities of liver carbamoylphosphate synthase (by 16.4%), ornithine transcarbamylase (by 29.8%), argininosuccinate synthase (by 28.1%) and arginase (by 33.8%). 5. Septic rats exhibited marked increases in hepatic protein (by 46.0%), RNA (by 43.4%) and DNA (by 37.7%) contents. These changes were accompanied by marked increases in the activity of thymidine kinase (by 35.9%).(ABSTRACT TRUNCATED AT 250 WORDS)

Electrotransport of alanine through ion-exchange membranes

The extraction of alanine by electrodialysis was studied taking into consideration the competition of protons or hydroxyl ions in the membrane transport process. The diffusion and electrodiffusion of alanine from solutions (1 M) were examined at different pH varying from 1.4 to 11, by measuring, under different current densities in the range 0–30 mA-cm 2, the alanine fluxes through an anion exchange membrane as well through a cation exchange membrane. The best value of the acid pH for extraction of alanine into the cationic form is around 2.1. At lower pH the competition of protons is too strong. For extraction of alanine into the anionic form the best value of the basic pH is 11 where the current efficiency is near 100%. In the electrotransport of alanine, concentration polarization and water splitting in the anion exchange membrane have an influence on the alanine extraction rate.

Renal cortical intermediary metabolism in the recovery phase of postischemic acute renal failure in the dog.

Renal metabolism has been studied in eight dogs before and 48 hr after a 60-min period of renal ischemia induced by clamping the left renal artery with the simultaneous removal of the right kidney, and in 12 sham-operated animals. The study involved the measurement of renal uptake and production of lactate, glutamine, glutamate, alanine, ammonium, and oxygen, and the measurement of the tissue concentrations of ATP, glutamine, lactate, alpha-ketoglutarate, aspartate, and alanine in the renal cortex. Two days after a temporary renal ischemia, the remaining kidney showed a 22% decrease in glomerular filtration rate (GFR) and a 25% decrease in renal plasma flow. Fractional sodium and potassium excretions were similar to those of control dogs. Renal production or extraction of glutamine, glutamate, alanine, ammonium, and oxygen (all expressed by 100 ml of GFR) was not significantly different in basal conditions or 2 days after ischemia, but lactate extraction was reduced in postischemic kidneys (-101 +/- 29 vs -204 +/- 38 mumol/100 ml GFR in control dogs). The cortical concentrations of glutamine and glutamate were lower in postischemic than in control kidneys. No differences were found in cortical concentration of alpha-ketoglutarate, aspartate, lactate, pyruvate, or ATP, but total nucleotides and inorganic phosphate were decreased in postischemic kidneys. It is concluded that in the recovery phase of the ischemia, a decreased lactate uptake is the main metabolic change, and total ATP production is adapted to the decrease of GFR and sodium reabsorption.

Coronary hemodynamics and myocardial metabolism in patients with syndrome X: Response to pacing stress

Coronary hemodynamics, myocardial metabolism and left ventricular function at rest and after incremental atrial pacing were evaluated in 12 patients with stress-induced angina and ST segment depression, angiographically normal coronary arteries and no evidence of spasm, generally labeled as syndrome X, and in 10 normal subjects.At baseline study, great cardiac vein flow was comparable in patients and control subjects. During pacing, an equivalent ratepressure product was reached in the two groups, but the slope of the relation between rate-pressure product and great cardiac vein flow was significantly less steep in patients than in normal subjects (0.0027 vs. 0.0054 ml/mm Hg · beat, p < 0.001). Nevertheless, the left ventricular ejection fraction was comparable in both groups at rest (66 ± 6% vs. 71 ± 7%, p = NS) and during pacing (71 ± 7% vs. 66 ± 5%, p = NS).At baseline study, myocardial glucose extraction was more efficient in patients with syndrome X (p < 0.05), but net myocardial exchange of pyruvate and alanine was, respectively, smaller and greater than in control subjects. Lactate was extracted to a similar extent in the two groups and in no instance was net lactate release observed during pacing or recovery. During pacing and recovery, patients with syndrome X showed net pyruvate release, unlike the control subjects in whom net pyruvate exchange was positive. In addition, patients with syndrome X continued to show net myocardial extraction of alanine during pacing and recovery, whereas normal subjects produced alanine throughout the study.Myocardial carbohydrate oxidation increased significantly during maximal pacing in normal subjects but not in patients, in whom it always remained below (p < 0.01) the concurrent rate of myocardial uptake of carbohydrate equivalents (glucose, lactate, pyruvate, alanine). Myocardial energy expenditure was significantly lower in patients than in control subjects at maximal rate-pressure product levels (p < 0.01).The metabolic pattern in patients with syndrome X therefore is not consistent with classic ischemia, although differences in the net exchange of circulating substrates (glucose, pyruvate, alanine) can be demonstrated. Thus, in patients with syndrome X, the symptoms, electrocardiographs signs and impairment in the increase in great cardiac vein flow during pacing coexist with preserved global and regional left ventricular function and myocardial energy efficiency.

Effects of insulin on glucagon-stimulated glucose production in the conscious dog

The relative importance of insulin and glucagon as primary regulators of glucose metabolism in vivo was assessed in 18-hour fasted conscious dogs. Glucose turnover was determined using [3- 3H]glucose and gluconeogenesis was assessed using tracer ([ 14C]alanine) and A-V difference techniques during a 40-minute control period and a 3-hour period during which various hormonal perturbations were brought about. During the infusion of somatostatin and basal intraportal replacement amounts of insulin and glucagon for the entire study, the plasma glucose concentration (109 ± 5 mg/dL), glucose production (3.24 ± 0.30 mg/kg/min), and glucose utilization (3.17 ± 0.32 mg/kg/min) remained unchanged. When the glucagon infusion rate was increased fourfold at the end of the control period, the plasma glucose level increased from 107 ± 4 to 225 ± 23 mg/dL by 1 hour and remained elevated. Glucose production increased from 3.14 ± 0.29 to 7.66 ± 0.51 mg/kg/min by 15 minutes and decreased to 4.23 ± 0.35 mg/kg/min by 3 hours. Glucose utilization rose from a basal value of 3.20 ± 0.26 to 5.46 ± 0.27 mg/kg/min by 3 hours. When a fourfold increase in the insulin infusion rate was brought about at the end of the control period, glucose production decreased from 2.83 ± 0.20 to 1.16 ± 0.57 mg/kg/min by 1 hour, after which it increased slightly (1.62 ± 0.81 mg/kg/min). Glucose utilization increased from 2.92 ± 0.30 to 8.12 ± 1.12 mg/kg/min by 3 hours. Euglycemia was maintained by glucose infusion. Concomitant fourfold increases in the insulin and glucagon infusion rates caused glucose production to fall from 3.03 ± 0.23 to 0.76 ± 0.39 mg/kg/min by 1 hour and to remain similarly suppressed for 3 hours. Glucose utilization rose from 2.95 ± 0.20 to 8.44 ± 0.87 mg/kg/min and euglycemia was again maintained by glucose infusion. Gluconeogenic conversion increased (67 ± 12%) in the studies in which insulin and glucagon were kept at basal values, but the level, fractional extraction, and hepatic uptake of alanine did not change significantly. The selective increase in glucagon caused gluconeogenic conversion (169% ± 42%), hepatic fractional alanine extraction (0.32 ± 0.05 to 0.66 ± 0.10), and hepatic alanine uptake (2.96 ± 0.45 to 4.54 ± 0.43 μmol/kg/min) to increase, while the alanine level decreased (387 ± 40 to 272 ± 48 μmol/L). The selective increase in insulin was associated with an increase in gluconeogenic conversion (40% ± 25%) similar to that apparent in the control group, no change in the fractional extraction or uptake of alanine by the liver, and a small fall in alanine level (337 ± 33 to 249 ± 55 μmol/L). Concomitant increases in both insulin and glucagon left gluconeogenic conversion unchanged (26% ± 21%), but increased the fractional extraction of alanine by the liver (0.39 ± 0.05 to 0.64 ± 0.03). Hepatic alanine uptake did not change, but a decrease in the alanine level (353 ± 40 to 174 ± 16 μmol/L) was observed. These studies indicate that in the overnight fasted conscious dog, insulin is a potent inhibitor of the stimulatory effects of glucagon on hepatic glycogenolysis and gluconeogenesis. However, insulin is unable to limit alanine uptake by suppression of hepatic fractional extraction, instead it prevents increased alanine uptake by limiting the net release of alanine from extrahepatic tissues.

Effect of hyperglucagonemia on hepatic glycogenolysis and gluconeogenesis after a prolonged fast

The aim of this study was to determine if glucagon can stimulate hepatic glucose production in prolonged fasted (7 days) animals. Two protocols were used; in one ("hormone replacement"; n = 4), intraportal basal replacement amounts of insulin and glucagon were given during a somatostatin infusion, whereas, in the other ("glucagon excess"; n = 5) basal insulin was given along with somatostatin and excess glucagon. Plasma insulin levels were similar and constant throughout both protocols (6 +/- 1 microU/ml). The plasma glucagon was basal in the hormone-replacement protocol (49 +/- 9 pg/ml) but rose from 46 +/- 7 to 448 +/- 35 pg/ml (P less than 0.05) in the other protocol. Plasma glucose levels and the rates of glucose production were unchanged during hormone replacement but rose from 100 +/- 5 to 199 +/- 28 mg/dl and from 1.5 +/- 0.1 to a peak of 5.6 +/- 0.2 mg.kg-1.min-1 at 15 min (P less than 0.05) and an eventual plateau of 2.7 +/- 0.2 mg.kg-1.min-1 (P less than 0.05) in response to glucagon excess. Because of the sluggish increase in gluconeogenic parameters, the early marked rise in glucose production was attributable to increased glycogenolysis. Eventually, however, the gluconeogenic rate rose, with net hepatic uptake of alanine increasing 50% and fractional alanine extraction doubling. Gluconeogenic efficiency and conversion increased in response to glucagon excess by 0.30 +/- 0.05 and 159 +/- 48%, respectively, although it should be noted that these parameters rose 0.15 +/- 0.06 and 150 +/- 49% in the hormone-replacement protocol. In conclusion, even after a prolonged fast physiological glucagon can cause hyperglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucagon is a primary controller of hepatic glycogenolysis and gluconeogenesis during muscular work.

The effects of the exercise-induced rise in glucagon were studied during 2.5 h of treadmill exercise in 18-h fasted dogs. Five dogs were studied during paired experiments in which pancreatic hormones were clamped at basal levels during a control period (using somatostatin and intraportal hormone replacement), then altered during exercise to stimulate the normal exercise-induced fall in insulin, while glucagon was 1) increased to mimic its normal exercise-induced rise (SG) and 2) maintained at a basal level (BG). Six additional dogs were studied as described with saline infusion alone (C). Gluconeogenesis (GNG) and glucose production (Ra) were measured using tracers [( 3-3H]glucose and [U-14C]alanine) and arteriovenous differences. Glucose fell slightly during exercise in C and was infused in SG and BG so as to mimic the response in C. Glucagon rose from 60 +/- 3 and 74 +/- 5 pg/ml to 118 +/- 14 and 122 +/- 17 pg/ml with exercise in C and SG and was unchanged from basal in BG (67 +/- 6 pg/ml). In C, SG, and BG, insulin fell during exercise by 5 +/- 1, 6 +/- 1, and 6 +/- 1 microU/ml. Ra rose from 3.3 +/- 0.2 and 3.0 +/- 0.2 mg.kg-1.min-1 to 8.6 +/- 0.8 and 9.5 +/- 1.5 mg.kg-1.min-1 with exercise in C and SG, but from only 3.0 +/- 0.2 to 5.5 +/- 0.8 mg.kg-1.min-1 in BG. GNG increased by 248 +/- 38 and 183 +/- 75% with exercise in C and SG but by only 56 +/- 21% in BG. Intrahepatic gluconeogenic efficiency was also enhanced by the rise in glucagon increasing by 338 +/- 55 and 198 +/- 52% in C and SG but by only 54 +/- 46% in BG. The rise in hepatic fractional alanine extraction was 0.38 +/- 0.04 and 0.33 +/- 0.04 during exercise in C and SG and only 0.08 +/- 0.06 in BG. Ra was increased beyond that which could be explained by effects on GNG alone, hence hepatic glycogenolysis must have also been enhanced by the rise in glucagon. In conclusion, in the dog, the exercise-induced rise in glucagon 1) controls approximately 65% of the increase in Ra, 2) increases hepatic glycogenolysis and GNG, and 3) enhances GNG by stimulating precursor extraction by the liver and precursor conversion to glucose within the liver.

Influence of peripheral arterial occlusive disease on muscular metabolism. Part 2: Changes in pyruvate, alanine, and urea concentration in femoral blood.

The metabolites pyruvate, alanine and urea were determined under resting conditions in blood from the femoral artery, femoral vein and cubital vein of 23 patients with stage II, 10 patients and 20 diabetics with stage IV PAOD as well as 19 healthy volunteers. Measurements were also carried out immediately and 20 min after ergometric calf exercise in the patients with stage II PAOD and the controls. In both patient groups with stage IV PAOD, there were lower arterial and venous alanine levels and higher urea concentrations at rest than in patients with adequate resting circulation, which is evidence for increased hepatic alanine extraction. After exercise, a significantly higher increase in the arteriovenous difference of pyruvate concentration was to be found in the patient group with stage II PAOD than in the control group. Moreover, there was a significant increase in femoral venous concentration and a rise in the arteriovenous difference of alanine, indicating muscular release, only in the PAOD patients and not in the volunteers in spite of a three times higher exercise load. The exercise-induced rise in femoral venous alanine correlated closely with those of pyruvate and ammonia. Alanine formation fulfills the function of a non-toxic carrier of muscularly produced amino groups and represents in PAOD a compensating mechanism that delays the limitation of muscular contractility. Alanine determination, especially in association with an exercise test, appears to be suitable for assessing the extent of anaerobic energy production in muscles of limbs affected by PAOD.

Splanchnic metabolism of amino acids in healthy subjects: Effect of 60 hours of fasting

Brief starvation is accompanied by decreased circulating levels of most amino acids, which has been attributed to an increased splanchnic uptake of amino acids, primarily alanine, for gluconeogenesis. However, quantitative data on splanchnic exchange of amino acids and gluconeogenic precursors is lacking. Consequently, arterial concentrations and splanchnic exchange of whole blood amino acids, ketone bodies, glucose, and gluconeogenic precursors were measured in 16 prolonged fasted (60 to 64 hours) and 15 overnight fasted (12 to 14 hours) healthy, nonobese subjects. After the 60-hour fast net splanchnic glucose production decreased by 41% to 0.31 ± 0.02 μmol/L ( P < .001), whereas the splanchnic uptake of gluconeogenic precursors increased and could account for the total glucose output. Net splanchnic uptake of taurine, threonine, serine, glycine, lysine, histidine, and arginine rose significantly in response to fasting ( P < .05 to .01) due to increased splanchnic fractional extraction. Although the splanchnic fractional extraction of alanine was augmented by 40% ( P < .001), net splanchnic uptake was not influenced by fasting. Total net splanchnic uptake of amino acids increased by 68%, from 231 ± 44 μmol/min in the postabsorptive state to 388 ± 63 μmol/min (mean ± SEM) ( P < .05) in the 60-hour fasted state. However, only one half of this rise was accounted for by gluconeogenic amino acids.