Alanine Turnover Research Articles

Potential turnover differences of exogenous alanine in soils of typical forests in the Xiaoxing'an Mountains, China

Taking five typical forests (Betula platyphylla forest, Quercus mongolica forest, B. platyphylla + Pinus koraiensis + Acer mono mixed forest, P. koraiensis forest, and Larix olgensis forest) in Xiaoxing'an Mountains as test objects, we investigated the effects of forest types (broadleaved forest, mixed forest, and coniferous forest) and soil layers (0-10 cm, 10-20 cm, 20-30 cm) on the turnover of exogenous alanine. The results showed that the turnover of soil exogenous alanine varied across different forest types, with significant difference in time and profile. The turnover rate was the highest in the broadleaved forest, followed by the mixed forest, and the lowest in the coniferous forest, with the half-life being 2.6-4.2, 3.6-5.5, and 4.3-7.0 h, respectively. With increasing soil depth, the potential turnover rate of exogenous alanine decreased, the half-life became longer, and soil adsorption of alanine weakened. With the addition of exogenous alanine, the content of ammonium and nitrate significantly increased, with the former being increased by 83.8%-95.3%, 80.9%-94.6% and 73.7%-93.2%, and the latter being increased by 82.9%-94.7%, 82.3%-93.8% and 78.1%-92.5% in the broadleaved forest, mixed forest, and coniferous forest, respectively. The net ammoniation and nitrification rates increased sharply at first and then decreased slowly, which were both positive. Soil layer and forest type as well as their interaction significantly affected the turnover, half-life, ammoniation, and nitrification of exogenous alanine.

Regulation of hepatic mitochondrial oxidation by glucose-alanine cycling during starvation in humans.

In order to determine whether the glucose-alanine cycle regulates rates of hepatic mitochondrial oxidation in humans, we applied positional isotopomer NMR tracer analysis (PINTA) to assess rates of hepatic mitochondrial oxidation and pyruvate carboxylase flux in healthy volunteers following both an overnight (12 hours) and a 60-hour fast. Following the 60-hour fast, rates of endogenous glucose production and mitochondrial oxidation decreased, whereas rates of hepatic pyruvate carboxylase flux remained unchanged. These reductions were associated with reduced rates of alanine turnover, assessed by [3-13C]alanine, in a subgroup of participants under similar fasting conditions. In order to determine whether this reduction in alanine turnover was responsible for the reduced rates of hepatic mitochondrial oxidation, we infused unlabeled alanine into another subgroup of 60-hour fasted subjects to increase rates of alanine turnover, similar to what was measured after a 12-hour fast, and found that this perturbation increased rates of hepatic mitochondrial oxidation. Taken together, these studies demonstrate that 60 hours of starvation induce marked reductions in rates of hepatic mitochondrial oxidation, which in turn can be attributed to reduced rates of glucose-alanine cycling, and reveal a heretofore undescribed role for glucose-alanine in the regulation of hepatic mitochondrial oxidation in humans.

225-OR: Key Role for Glucose-Alanine Cycling in the Regulation of Hepatic Mitochondrial Oxidation during Starvation in Humans

We examined whether starvation alters rates of hepatic mitochondrial oxidation in humans by applying a novel 13C Positional Isotopomer NMR Tracer Analysis (PINTA) method to assess rates of hepatic mitochondrial oxidation in healthy volunteers (n=15) following an overnight (12h) and a 60h fast. A 3h intravenous infusion of [3-13C] lactate (4.3 μmol/Kg-min), [1,2,3,4,5,6,6-2H7] glucose (0.22 μmol/Kg-min), and [13C4]-β-hydroxybutyrate (BOHB) (0.01 mg/Kg-min) was administered and blood was collected for GC-MS, LC-MS/MS and 13C MRS PINTA analyses. Following the 60h fast rates of endogenous glucose production decreased by 27% (p=0.0002) and rates of hepatic mitochondrial oxidation decreased by 52% (p=0.0014) whereas rates of hepatic pyruvate carboxylase flux remained unchanged. To ascertain whether decreased rates of alanine turnover during starvation play a role in promoting decreased rates of hepatic mitochondrial oxidation we infused [3-13C] alanine in a subgroup (n=5) of subjects and found that 60h of fasting promoted a 28% reduction in alanine turnover (p=0.044 vs. 12h fast). In order to determine whether this reduction in alanine turnover was responsible for the reduced rates of hepatic mitochondrial oxidation we infused unlabeled alanine to a subgroup (n=9) of the 15 subjects in a repeat 60h fasting study to increase rates of alanine turnover to rates measured after 12h of fasting and found that this perturbation increased rates of hepatic mitochondrial oxidation by 63% (p=0.009 vs. 60h fast) to rates similar to the 12h fasting state (60h+ala: 232±21 vs. 12h: 295±44 μmol/min, p=0.303). Conclusion: These studies demonstrate that 60h of starvation in humans induces marked reductions in rates of hepatic mitochondrial oxidation, which in turn can be attributed to reduced rates of glucose-alanine cycling. Disclosure K. Petersen: Advisory Panel; Spouse/Partner; Aegerion Pharmaceuticals, AstraZeneca, AstraZeneca, Janssen Research & Development, Merck & Co., Inc., Novo Nordisk A/S. Consultant; Spouse/Partner; Gilead Sciences, Inc. Consultant; Self; Merck & Co., Inc. Consultant; Spouse/Partner; Nimbus Discoverey. Consultant; Self; Novo Nordisk A/S. S. Dufour: None. G. Cline: None. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research & Development, Merck & Co., Inc. Advisory Panel; Spouse/Partner; Merck & Co., Inc. Board Member; Self; Novo Nordisk A/S. Consultant; Self; Aegerion Pharmaceuticals, IMetabolic BioPharma Corporation, Longitude Capital, Nimbus Discovery, Inc., Staten Biotechnology B.V. Funding National Institutes of Health

P.1.g.079 - Effects of antipsychotics on serum metabolic parameters in rats perinatally treated with phencyclidine

The cirrhotic liver has been shown to be resistant to the actions of various glucoregulatory hormones. The objective of this study was to investigate the effects of epinephrine on hepatic glucose metabolism in cirrhotic patients. Thirteen cirrhotic and eight healthy subjects were studied. Hepatic glucose production and turnover of alanine and glycerol were measured using stable isotope technique before and during 70 and 150 minutes of epinephrine infusion (0.1 microgram/kg/min). beta-Adrenoreceptor binding sites and affinity in mononuclear leukocyte membranes also were determined. Hepatic glucose production and alanine turnover in normals significantly increased during epinephrine infusion, but did not change in cirrhotics. Glycerol turnover increased after 70 minutes of epinephrine infusion in both groups. Epinephrine induced a significant rise of high-affinity beta-adrenoreceptor binding sites in normals, yielding a significant correlation between hepatic glucose production and receptor density (r = .94, P < .0001). In cirrhotic patients, similar changes in the number of high-affinity beta- adrenoreceptors were observed, but no correlation with hepatic glucose production was detected. The cirrhotic liver did not respond normally to the stimulatory effect of epinephrine on hepatic glucose production. Because this blunted response was not related to changes of beta- adrenoreceptors, our findings suggest that epinephrine resistance in cirrhosis was caused by a postreceptor defect. (Hepatology 1996 Aug;24(2):330-6)

Amino acid turnover by bovine oocytes provides an index of oocyte developmental competence in vitro.

Amino acid profiling has been used to distinguish between human embryos of differing developmental competence. We sought to determine whether amino acid profiling could be used to distinguish between metaphase II (MII) bovine oocytes with different developmental capabilities in vitro. Amino acid turnover was assayed during the final 6 h of in vitro maturation prior to oocytes undergoing individual fertilization in vitro. Following insemination, zygotes were immobilized in groups of 16 on the base of a Petri dish using Cell-Tak tissue adhesive to enable the developmental progress of each to be tracked to the blastocyst stage. Spent droplets of in vitro maturation medium were analyzed by high performance liquid chromatography, which revealed glutamine, arginine, and asparagine were depleted in the greatest quantities. Incompetent MII oocytes that failed to cleave by 72 h postfertilization depleted significantly more glutamine from (P = 0.0006) and released more alanine (P = 0.0001) into the medium than oocytes that cleaved. When cutoff values were selected for the turnover of alanine, arginine, glutamine, leucine, and tryptophan and modeled to predict fertilization and cleavage potential, oocytes that did not exceed the cutoff values for ≥2 of these key amino acids were more likely to cleave. The sensitivity, specificity, accuracy, and positive predictive value of this model were 60.5%, 76.8%, 63.5%, and 92.0%, respectively. Significant differences (P ≤ 0.015) in the consumption/production of alanine and glutamine were also observed when comparing uncleaved oocytes with those that produced blastocysts. The data show that noninvasive amino acid profiling can be used to measure oocyte developmental competence.

Fasting hyperglycemia in the Goto-Kakizaki rat is dependent on corticosterone: a confounding variable in rodent models of type 2 diabetes

SUMMARYThe Goto-Kakizaki (GK) rat is an inbred model of type 2 diabetes (T2D); GK rats are lean but have hyperglycemia and increased gluconeogenesis. However, fasting hyperglycemia in other commonly used rodent models of T2D is associated with increased corticosterone, and thus the underlying mechanism for hyperglycemia differs significantly from T2D in humans. Information regarding corticosterone in the GK rat is not readily available. We studied 14- to 16-week-old GK rats in comparison with age-matched control Wistar-Kyoto (WK) rats. GK rats had lower body weights (WK: 343±10 g vs GK: 286±9 g, P<0.01), but higher plasma glucose concentrations (WK: 132±1.5 mg/dl vs GK: 210±11.7 mg/dl, P<0.01). This was associated with an ∼twofold increase in PEPCK1 expression (P<0.05). However, these findings were also associated with elevations in plasma corticosterone and urinary corticosterone excretion. Ketoconazole (KTZ) treatment in GK rats reduced plasma corticosterone, fasting glucose (GK: 218±15 mg/dl vs GK-KTZ: 135±19 mg/dl, P<0.01) and rates of glucose production [GK: 16.5±0.6 mg/(kg-minute) vs GK-KTZ: 12.2±0.9 mg/(kg-minute), P<0.01]. This was associated with an ∼40% reduction in hepatic PEPCK1 expression as well as a 20% reduction in alanine turnover. Thus, hypercorticosteronemia might contribute to the diabetic phenotype of GK rats and should be considered as a potential confounder in rodent models of T2D.

Improved methods of IVF quality control: murine ICM outgrowth and amino acid turnover versus human sperm survival assay and murine embryo assay

OBJECTIVE: To develop improved methods for IVF quality control using inner cell mass (ICM) outgrowth and amino acid analysis compared to human sperm assays and 2-cell murine embryo assay (MEA). DESIGN: Prospective, blinded, control trial. MATERIALS AND METHODS: Fresh donor sperm were prepared for a human sperm survival assay (HSSA). Sperm were exposed to 0, 16, 32 and 64 uM formaldehyde in G1 media (Vitrolife). Sperm motility and forward progression (grade) were assessed after 48 hours of culture. Two-cell murine embryo assay was performed with exposure to the same formaldehyde concentrations. Embryos were cultured in G1 media for 72 hours and transferred to MEM + 20% FCS for an additional 96 hours. The G1 media was collected at 72 hours post-thaw and 40 uL of conditioned media were analyzed using tandem mass spectrometry for amino acid concentrations. After 96 hours of extended culture the embryos were graded for ICM outgrowth. For each experiment 3 - 4 replicates were performed. Data were analyzed using ANOVA and student t-test. RESULTS: HSSA was able to identify sperm toxicity using grade when formaldehyde concentrations reached 32 uM, and motility index was able to identify toxicity at 64 uM (Table 1). Murine blastocyst rates were affected at 32 uM. ICM outgrowth and ICM grade were affected by 16 uM formaldehyde (Table 2). Of the amino acids present in G1 media, serine and alanine turnover were significantly affected by formaldehyde at 32 uM.Table 1Conventional QC methods0 uM16 uM32 uM64 uMHSSA Grade2.1 ± 0.21.7 ± 0.21.5 ± 0.4∗p< 0.05 compared to control.1.1 ± 0.2∗p< 0.05 compared to control.HSSA SMI0.98 ± 0.060.98 ± 0.060.93 ± 0.110.70 ± 0.19∗p< 0.05 compared to control.Blastocyst rate95.4 ± 6.490.2 ± 7.176.0 ± 12.9∗p< 0.05 compared to control.25.0 ± 17.3∗p< 0.05 compared to control.∗ p< 0.05 compared to control. Open table in a new tab Table 2Inner Cell Mass Outgrowth0 uM16 uM32 uM64 uMICM rate75.1 ± 6.756.5 ± 11.5∗p<0.05 compared to control.37.9 ± 6.3∗p<0.05 compared to control.0.0 ± 0.0∗p<0.05 compared to control.ICM grade1.78 ± 0.031.14 ± 0.17∗p<0.05 compared to control.1.10 ± 0.44∗p<0.05 compared to control.0.0 ± 0.0∗p<0.05 compared to control.∗ p<0.05 compared to control. Open table in a new tab CONCLUSIONS: This study demonstrates that ICM outgrowth is more sensitive for detecting formaldehyde than the standard MEA and HSSA. These preliminary results indicate that amino acid metabolism may also provide a more sensitive measure. While traditional methods such as sperm motility and MEA blastocyst rates have been sufficient to detect higher concentrations of toxins, further efforts should be made to improve quality control measures for IVF products.

Consequences of missense mutations for dimerization and turnover of alanine:glyoxylate aminotransferase: Study of a spectrum of mutations

Alanine:glyoxylate aminotransferase (AGT) is a liver peroxisomal enzyme, deficiency of which results in primary hyperoxaluria type 1 (PH1). More than 65 PH1-related mutations are now documented in the AGT gene ( AGXT), of which about 50% are missense. We have generated a spectrum of 15 missense changes including the most common PH1 mutation, G170R, and expressed them on the appropriate background of the major or minor allele, in an Escherichia coli overexpression system and in a rabbit reticulocyte transcription/translation system. We have investigated their effects on enzyme activity, dimerization, aggregation, and turnover. The effect of pyridoxal phosphate (PLP) on dimerization and stability was also investigated. Although all 15 mutant AGTs were expressed as intact proteins in E. coli, only three: G41R and G41V on the major allele, and the common mutation G170R, resulted in significant amounts of enzymatic activity. Dimerization failure was a frequent observation (13/15) except for G41V and D183N. Dimerization was poor with S187F but was substantially improved with PLP. Proteasome-mediated protein degradation was observed for all the mutations except G41R on the major allele, G41V, D183N, G170R, and S218L. Increases in the stability of the mutant enzymes in the presence of PLP were small; however, G41R on the minor allele showed a direct relationship between its half life and the concentration of PLP. The minor allele AGT product and many of the mutants were subject to a limited non-proteasomal proteolytic cleavage when ATP was depleted.

Amino acid kinetics during the anhepatic phase of liver transplantation.

Alanine and glutamine are interorgan nitrogen/carbon carriers for ureagenesis and gluconeogenesis, which are mainly but not necessarily only hepatic. The liver is central to alanine and glutamine metabolism, but most organs can produce and use them. We studied amino acid kinetics after liver removal to depict initial events of liver failure and to provide a model to study extrahepatic gluconeogenesis and nitrogen disposal in humans. We measured amino acid kinetics with [5,5,5-(2)H(3)]leucine and [3-(13)C]alanine or [1,2-(13)C(2)]glutamine tracers in 21 subjects during and after the anhepatic phase of liver transplantation: 12 were at 7 months posttransplantation, and 7 were healthy control subjects. Anhepatic leucine kinetics, including proteolysis, was unchanged. Alanine plasma and whole-body contents increased 3x and 2x, with a halved metabolic clearance and a doubled production, 2% greater than disposal. Free whole-body glutamine decreased 25% but increased 50% in plasma. Glutamine clearance was halved, and the production decreased by 25%, still 2% greater than disposal. Liver replacement decreased alanine and glutamine concentrations, leaving leucine unchanged. Liver removal caused doubled alanine fluxes, minor changes in glutamine, and no changes in leucine. The initial events after liver removal are an accumulation of three-carbon compounds, an acceleration of alanine turnover, and limited nitrogen storage in alanine and glutamine.

Effects of ATP infusion on glucose turnover and gluconeogenesis in patients with advanced non-small-cell lung cancer

Cancer cachexia is associated with elevated lipolysis, proteolysis and gluconeogenesis. ATP infusion has been found to significantly inhibit loss of body weight, fat mass and fat-free mass in patients with advanced lung cancer. The present study was aimed at exploring the effects of ATP on whole-body glucose turnover, alanine turnover and gluconeogenesis from alanine. Twelve patients with advanced non-small-cell lung cancer (NSCLC) were studied 1 week before and during 22-24 h of continuous ATP infusion. After an overnight fast, turnover rates of glucose and alanine, and gluconeogenesis from alanine, were determined using primed constant infusions of ¿6, 6-(2)H(2)ğlucose and ¿3-(13)Călanine. Thirteen NSCLC patients and eleven healthy subjects were studied as control groups without ATP infusion. During high-dose ATP infusion (75 microg.min(-1).kg(-1)), glucose turnover was 0.62+/-0.07 mmol.h(-1).kg(-1), compared with 0. 44+/-0.13 mmol.h(-1).kg(-1) at baseline (P=0.04). For gluconeogenesis a similar, but non-significant, trend was observed ¿baseline, 0.30+/-0.16 mmol.h(-1).kg(-1); during ATP, 0.37+/-0.13 mmol.h(-1).kg(-1) (P=0.08). At lower ATP doses (37-50 microg. min(-1).kg(-1)) these effects were not detected. The relative increase in glucose turnover during ATP infusion compared with baseline showed a significant correlation with the ATP dose (r=0.58, P=0.02). No change in alanine turnover was observed at any ATP dose. The results of this study indicate an increase in glucose turnover during high-dose ATP infusion compared with baseline levels. During high-dose ATP infusion, glucose turnover was similar to that during low-dose ATP infusion and to that in control NSCLC patients. Between ATP infusions, however, glucose turnover in patients treated with high-dose ATP was significantly lower than that in the low-dose and control NSCLC patients (P=0.04 and P=0.03 respectively), and similar to that in healthy subjects. This would suggest that repeated high-dose ATP infusions may inhibit glucose turnover between infusion periods.

Weight loss and elevated gluconeogenesis from alanine in lung cancer patients

The role of gluconeogenesis from protein in the pathogenesis of weight loss in lung cancer is unclear. Our aim was to study gluconeogenesis from alanine in lung cancer patients and to analyze its relation to the degree of weight loss. In this cross-sectional study, we used primed-constant infusions of [6,6-(2)H(2)]-D-glucose and [3-(13)C]-L-alanine to assess whole-body glucose and alanine turnover and gluconeogenesis from alanine in weight-losing (WL, n = 9) and weight-stable (WS, n = 10) lung cancer patients and healthy control (n = 15) subjects. Energy intake and plasma alanine concentrations did not differ significantly among the subject groups. Mean (+/-SEM) whole-body glucose production was significantly higher in WL than in WS and control subjects (0.74 +/- 0.06 compared with 0.55 +/- 0.04 and 0.51 +/- 0.04 mmol*kg(-)(1)*h(-)(1), respectively, P < 0.01). Alanine turnover was significantly elevated in WL compared with WS and control subjects (0.57 +/- 0.04 compared with 0.42 +/- 0.05 and 0.40 +/- 0.03 mmol*kg(-)(1)*h(-)(1), respectively, P < 0.01). Gluconeogenesis from alanine was significantly higher in WL than in WS and control subjects (0.47 +/- 0.04 compared with 0.31 +/- 0.04 and 0.29 +/- 0.04 mmol*kg(-)(1)*h(-)(1), respectively, P < 0.01). The degree of weight loss was positively correlated with glucose and alanine turnover and with gluconeogenesis from alanine (r = 0.45 for all, P < 0.01). Aberrant glucose and alanine metabolism occurred in WL lung cancer patients. These changes were related to the degree of weight loss and not to the presence of lung cancer per se.

Glucagon-like peptide-1 has no insulin-like effects in insulin-dependent diabetic dogs maintained normoglycemic and normoinsulinemic

A pharmacological concentration of glucagon-like peptide-1 (GLP-1) in the insulin-deficient state clearly decreases the blood glucose level. Therefore, this study was designed to evaluate a putatively relevant effect of the gastrointestinal peptide as an adjuvant to insulin replacement therapy. GLP-1 (GLP-1(7–36) amide 10 pmol · kg −1 · min −1) was infused intravenously over 8 hours in nine fasting, C-peptide-negative diabetic dogs. The animals were under normoglycemic control by glucose-controlled insulin infusion (GCII) during the night before and during GLP-1 administration. During the paired control tests, the animals received saline infusion instead of GLP-1. In addition to the insulin infusion rates required to maintain normoglycemia, hormones, metabolites, and the turnover rates for glucose (6- 3H-glucose), alanine (U- 14C-alanine), and urea ( 15N 2-urea) were measured during the final 2 hours of GLP-1 administration. Circulating plasma GLP-1 levels increased from 3 ± 1 to 17 ± 7 pmol/L. There was no significant difference in the insulin infusion rate between the experimental and control groups (0.43 ± 0.05 v 0.40 ± 0.05 mU · kg −1 · h −1, average over the entire interval). Glycemia was maintained at a practically identical level (4.9 ± 0.3 v 4.8 ± 0.4 mmol/L). Also, the concentration of plasma insulin—which was not hyperinsulinemic—and pancreatic glucagon remained unaltered. We found no appreciable effect of GLP-1 on glucose production and metabolic clearance, alanine turnover and the formation of glucose from alanine (1.8 ± 0.2 v 1.4 ± 0.2 μmol · kg −1 · min −1), or the urea production rate as a measure of overall amino acid catabolism (4.1 ± 0.4 v 4.1 ± 0.4 μmol · kg −1 · min −1). Thus, no conclusive adjuvant effect of GLP-1 was ascertained in insulin-treated diabetic dogs under normoglycemic control.

Blood Glucose Lowering and Glucagonostatic Effects of Glucagon-Like Peptide I in Insulin-Deprived Diabetic Dogs

To establish potential effects of glucagon-like peptide I (GLP-I) on blood glucose control in insulin-deficient states, GLP-I [GLP-I(7-36) amide; 10 pmol x kg(-1) x min(-1)] was infused intravenously in six fasting, canine C-peptide-negative, chronically diabetic dogs for 8 h. Blood samples were saved for the analysis of hormones, metabolites, and turnover rates of glucose (6-(3)H-glucose), alanine (U-(14)C-alanine), and urea ((15)N(2)-urea) starting 22 h after the last subcutaneous dose of exogenous insulin. Circulating plasma GLP-I levels rose under infusion from 2.9 +/- 0.8 to 41.4 +/- 10.1 pmol/l. This was efficient to significantly reduce the preexisting diabetic hyperglucagonemia. Since in the utilized model functioning pancreatic beta-cells are lacking, GLP-I had no insulinogenic effect. Compared with control experiments in the same animals receiving saline infusion, glycemia dropped from 20.8 +/- 1.9 to 16.2 +/- 1.0 mmol/l (P < 0.05). This was in parallel to the infusion of GLP-I and was most likely caused by a decrease of elevated glucose production since overall glucose turnover decreased with no alteration in glucose metabolic clearance. Alanine turnover was significantly reduced, obviously reflecting a decline in alanine production in relation to changed muscle glucose uptake under conditions of lower glycemia and overall glucose turnover. There was, however, neither an effect of GLP-I on alanine conversion into circulating glucose nor an effect on urea production rate, indicating unchanged gluconeogenesis from amino acid precursors. We conclude that the blood glucose-lowering effect of GLP-I in an animal model of insulinopenia was shown to be due to a reduction in hepatic glucose output, possibly secondary to reduction in glucagon concentrations leading to decreased glycogenolysis. Whether GLP-I might be therapeutically useful in clinical insulin-deficient diabetes needs to be verified.

Effects of epinephrine on glucose metabolism in patients with alcoholic cirrhosis.

The cirrhotic liver has been shown to be resistant to the actions of various glucoregulatory hormones. The objective of this study was to investigate the effects of epinephrine on hepatic glucose metabolism in cirrhotic patients. Thirteen cirrhotic and eight healthy subjects were studied. Hepatic glucose production and turnover of alanine and glycerol were measured using stable isotope technique before and during 70 and 150 minutes of epinephrine infusion (0.1 microgram/kg/min). beta-Adrenoreceptor binding sites and affinity in mononuclear leukocyte membranes also were determined. Hepatic glucose production and alanine turnover in normals significantly increased during epinephrine infusion, but did not change in cirrhotics. Glycerol turnover increased after 70 minutes of epinephrine infusion in both groups. Epinephrine induced a significant rise of high-affinity beta-adrenoreceptor binding sites in normals, yielding a significant correlation between hepatic glucose production and receptor density (r = .94, P < .0001). In cirrhotic patients, similar changes in the number of high-affinity beta- adrenoreceptors were observed, but no correlation with hepatic glucose production was detected. The cirrhotic liver did not respond normally to the stimulatory effect of epinephrine on hepatic glucose production. Because this blunted response was not related to changes of beta- adrenoreceptors, our findings suggest that epinephrine resistance in cirrhosis was caused by a postreceptor defect. (Hepatology 1996 Aug;24(2):330-6)

Effects of Epinephrine on Glucose Metabolism in Patients With Alcoholic Cirrhosis

The cirrhotic liver has been shown to be resistant to the actions of various glucoregulatory hormones. The objective of this study was to investigate the effects of epinephrine on hepatic glucose metabolism in cirrhotic patients. Thirteen cirrhotic and eight healthy subjects were studied. Hepatic glucose production and turnover of alanine and glycerol were measured using stable isotope technique before and during 70 and 150 minutes of epinephrine infusion (0.1 microgram/kg/min). β–Adrenoreceptor binding sites and affinity in mononuclear leukocyte membranes also were determined. Hepatic glucose production and alanine turnover in normals significantly increased during epinephrine infusion, but did not change in cirrhotics. Glycerol turnover increased after 70 minutes of epinephrine infusion in both groups. Epinephrine induced a significant rise of high–affinity β–adrenoreceptor binding sites in normals, yielding a significant correlation between hepatic glucose production and receptor density (r = .94, P &lt; .0001). In cirrhotic patients, similar changes in the number of high–affinity β– adrenoreceptors were observed, but no correlation with hepatic glucose production was detected. The cirrhotic liver did not respond normally to the stimulatory effect of epinephrine on hepatic glucose production. Because this blunted response was not related to changes of β– adrenoreceptors, our findings suggest that epinephrine resistance in cirrhosis was caused by a postreceptor defect.

Glutamine and Alanine Metabolism in NIDDM

Gluconeogenesis is increased in NIDDM. We therefore examined the metabolism of glutamine and alanine, the most important gluconeogenic amino acids, in 14 postabsorptive NIDDM subjects and 18 nondiabetic volunteers using a combination of isotopic ([6-3H]glucose (20 microCi, 0.2 microCi/min), [U-14C]glutamine (20 microCi, 0.2 microCi/min), [3-13C]alanine (99% 13C, 2 mmol, 20 micromol/min), [ring-2H5]phenylalanine (99% 2H, 2 micromol/kg, 0.03 micromol x kg(-1) x min(-1)), and limb balance techniques. Alanine turnover (4.54 +/- 0.24 vs. 5.64 +/- 0.33 micromol x kg(-1) x min(-1)), de novo synthesis (3.00 +/- 0.25 vs. 4.01 +/- 0.33 micromol x kg(-1) x min(-1)), and conversion to glucose (1.02 +/- 0.09 vs. 1.56 +/- 0.17 micromol x kg(-1) x min(-1)) were increased in NIDDM subjects (all P < 0.01), while its forearm release (0.45 +/- 0.04 vs. 0.39 +/- 0.04 micromol x kg(-1) x min(-1)) was unaltered. Although glutamine turnover (4.81 +/- 0.23 vs. 4.40 +/- 0.31 micromol x kg(-1) x min(-1)) was unaltered in NIDDM, its conversion to glucose (0.57 +/- 0.04 vs. 1.08 +/- 0.10 micromol x kg(-1) x min(-1)) and to alanine (0.10 +/- 0.01 vs. 0.34 +/- 0.04 micromol x kg(-1) x min(-1)) (both P = 0.001) was increased while its oxidation (2.84 +/- 0.27 vs. 1.84 +/- 0.15 micromol x kg(-1) x min(-1), P = 0.03) and forearm release (0.77 +/- 0.05 vs. 0.62 +/- 0.09 micromol x kg(-1) x min(-1), P < 0.008) were both reduced. Our results thus demonstrate that there are substantial alterations of glutamine and alanine metabolism in NIDDM. Conversion of both amino acids to glucose and the proportion of their turnover used for gluconeogenesis are increased; release of both amino acids from tissues other than skeletal muscle seems to be increased. Finally, the reduction in glutamine oxidation, possibly the result of competition with glucose and free fatty acids as fuels, makes more glutamine available for gluconeogenesis without a change in its turnover.

Plasma disposal rate and hepatic alanine metabolism in pregnant and nonpregnant rabbits.

To better define the glucose-alanine relationship and hepatic alanine metabolism during pregnancy, glucose and alanine turnover rates (TR) and simultaneous hepatic alanine uptake were determined in nine term pregnant (P) and 12 nonpregnant (NP) rabbits who had undergone chronic catheterization of both the systemic and hepatic circulations. [U-14C3]Alanine and [3-3H1]glucose were used as tracers. Whole animal [U-14C3]alanine TR was significantly greater in P than in NP animals (42.7 +/- 1.7 versus 31.9 +/- 1.8 mumol.min-1, respectively, p < 0.001). However, there was no difference when the alanine TR was compared on a weight-specific basis (11.3 +/- 0.6 versus 9.6 +/- 0.6 mumol.min-1.kg-1). The glucose TR was higher in P compared with NP rabbits on both an absolute (122.3 +/- 6.2 versus 79.8 +/- 5.8 mumol.min-1, p < 0.001) and a weight-specific basis (32.9 +/- 1.4 versus 24.0 +/- 1.9 mumol.min-1.kg-1, p < 0.005). Although the fraction of plasma glucose derived from plasma alanine in the whole animal was similar in P and NP animals (16.7% +/- 1.4 versus 13.9 +/- 0.7%, respectively), the absolute amount of plasma glucose derived from plasma alanine was greater in P rabbits (20.8 +/- 1.8 versus 11.2 +/- 1.2 mumol.min-1, p < 0.0005). In addition, the percentage of plasma alanine being converted to plasma glucose was greater in P than in NP animals (48.1 +/- 2.6 versus 34.6 +/- 2.0%, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose-alanine relationship in diabetes in human pregnancy

We have previously reported a decrease in gluconeogenesis from alanine in normal pregnant women at term gestation as compared with nonpregnant women. In the present study, the effect of diabetes on alanine metabolism was examined in five gestationally diabetic (GDM) women and seven women with type I (insulin-dependent) diabetes (IDDM) during the third trimester of pregnancy. The hemoglobin A 1c (HbA 1c) concentrations in all subjects were within normal range, indicating good metabolic control. After an overnight fast, each subject was infused simultaneously with l-[2,3, 13C 2]alanine and d-[6,6, 2H 2]glucose tracers as prime constant rate infusion. Plasma alanine and glucose isotopic enrichments were measured by gas chromatography-mass spectrometry. Alanine and glucose turnover rates were quantified by trace dilution. In five subjects, the contribution of alanine carbon to CO 2 was quantified by respiratory calorimetry and by measurement of 13C enrichment of expired CO 2. Data from 15 previously reported normal pregnant subjects were used for comparison. The rate of alanine turnover was similar in the GDM and IDDM subjects and was not different from the normal subjects (GDM, 4.6 ± 1.9; IDDM, 5.4 ± 2.5; normals, 4.4 ± 0.8 μmol/kg · min, mean ± SD). The rate of glucose turnover was significantly reduced ( P < .05) in IDDM as compared with GDM and normal subjects (IDDM, 8.1 ± 0.8; GDM, 11.5 ± 3.5; normals, 12.2 ± 2.2 μmol/kg · min). The contribution of alanine C to glucose C and expired CO 2 was similar in the three groups. These data demonstrate that rigorous metabolic control results in normal glucose and alanine metabolism in diabetic pregnancy during fasting. It is speculated that the observed perinatal morbidity in pregnant women with diabetes may be related to metabolic decompensation during feeding.

The effect of a high protein diet on leucine and alanine turnover in acid maltase deficiency.

Leucine and alanine production rate was measured in 5 patients with acid maltase deficiency in the postabsorptive state, following 6 months on a normal diet with placebo and 6 months on an isocaloric high protein diet (16-22% protein). Whole body leucine production rate, a measure of protein degradation, expressed in terms of lean body mass was significantly greater than in five control subjects. Following the high protein diet, leucine production rate was decreased in four of the five patients but this was not statistically significant. Alanine production rate expressed in terms of lean body mass was significantly greater than in control subjects. After the high protein diet, alanine production rate and concentration were significantly decreased (p less than 0.05). There were no significant improvements in any of the clinically relevant variables measured in these patients. It is possible that a larger increase in protein intake over a longer time period may have a clinical effect.

Alterations of fasting glucose and fat metabolism in intrauterine growth-retarded newborn dogs.

Maternal nutritional deprivation resulted in reduced fetal weight at term gestation (251 +/- 7 vs. 277 +/- 7 g, P less than 0.01) in newborn dogs. Growth-retarded pups developed lower blood glucose levels after 3, 6, and 9 h of neonatal fasting, reduced plasma levels of free fatty acids (FFA) at 9 and 24 h, and lower ketone bodies at 24 h compared with age-matched newborn control pups. Systemic rates of palmitate and alanine turnover were not affected, but systemic glucose turnover was reduced for 3-9 h after birth. The rate of alanine incorporation into glucose from 3 to 9 h was also reduced in growth-retarded pups compared with timed controls. Paradoxically, the rate of incorporation of palmitate into triglycerides was augmented in the smaller growth-retarded pups. Hepatic glycogen content was reduced at every time in the study among growth-retarded pups, whereas the rates of glycogenolysis between birth and 24 h were equivalent in the two pup groups. In contrast, hepatic triglyceride levels were augmented throughout the study in pups with growth retardation. Maternal starvation and lower glucose levels resulted in a lower hepatic energy charge, and augmented cytoplasmic and mitochondrial NAD-to-NADH ratios in intrauterine growth-retarded pups. These data suggest that intrauterine growth retardation in dogs results in fasting neonatal hypoglycemia that is due in part to reduced systemic glucose production. We speculate that reduced rates of gluconeogenesis from alanine and reduced oxidation of alternate fuels such as FFA contribute to hypoglycemia. FFA recycling to triglyceride synthesis rather than oxidative pathways may contribute to the observed reduction of circulating glucose levels.