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Although a reduction in both energy expenditure and protein turnover has been demonstrated in starved volunteers, few metabolic data are available for patients in whom malnutrition is due to nonneoplastic gastrointestinal diseases. Chronically malnourished, unstressed adult patients with nonneoplastic gastrointestinal diseases (body mass index, 15.8 +/- 2.5 kg/m2, n = 13) and healthy control subjects (n = 10) were studied in the postabsorptive state using indirect calorimetry, as well as substrate fluxes of L[1-13C]leucine, L-[2-15N]glutamine (seven patients and six controls), and D[6,6-2H2]glucose (seven patients and eight controls). Resting energy expenditure (REE) expressed in kilocalories per 24 hours was significantly lower in patients than in controls; REE expressed per unit of fat-free mass (FFM) was not significantly different in both groups. Whole-body leucine turnover, oxidation, and nonoxidative disposal rates, based on either 13C-leucine or 13C-alpha-ketoisocaproic acid (KIC) enrichments, and glucose turnover rate were not significantly different between malnourished patients and controls. Moreover, glutamine turnover was increased by 28% in malnourished patients as compared with normal volunteers (429.8 +/- 86.8 v 334.9 +/- 15.9 mumol/kg/h, P = .02). These results suggest that hypometabolic adaptation, although previously documented in starved volunteers, is not operative during states of chronic malnutrition due to gastrointestinal disease. The increase in glutamine turnover rate might represent an adaptative mechanism to malnutrition for preservation of visceral mass or function.

Insulin resistance is present in patients suffering from lipoatrophic syndromes long before the onset of diabetes mellitus. Thus, the decreased peripheral glucose disposal may not be the only mechanism of hyperglycaemia. The kinetic parameters of glucose homeostasis were evaluated in six young females aged 15, 16, 18, 19 and 24 years with generalized lipoatrophy; one patient was studied both at 12 and 15 years. Insulin resistance was evaluated in vivo by the hyperinsulinaemic euglycaemic clamp (3-4 insulin infusion rates from 1 to 100 mU/kg.min). All patients showed a rightward shift of the dose-response curve, indicating decreased insulin sensitivity. In two patients, maximal glucose disposal was moderately decreased, while in five patients it was dramatically reduced (3.6-6.9 mg/kg.min). Fasting plasma glucose was variable (4.3-18.3 mmol/l) and did not correlate with peripheral glucose disposal rates. Hepatic glucose production, measured by infusion of [6,6-2H] glucose, varied from 1.7 to 8.3 mg/kg.min and was significantly correlated with fasting plasma glucose. The overproduction of glucose despite basal hyperinsulinism suggested hepatic insulin resistance, which was confirmed by the abnormal response to constant unlabelled glucose infusion (2 mg/kg.min) in five patients. In conclusion, impaired glucose tolerance seems to develop in generalized lipoatrophy with aggravated peripheral insulin resistance. The present data show that fasting hyperglycaemia is mainly the consequence of increased hepatic glucose production.

Intraperitoneal infusion of insulin should be more physiological than intravenous insulin since part of the insulin is directed toward the portal vein, which allows the liver to retain its major role in glucose homeostasis. The regulation of hepatic glucose production during the intraperitoneal and intravenous infusions of insulin were compared in eight Type 1 (insulin-dependent), C-peptide-deficient diabetic patients. Primed, continuous infusions of [6,6-2H]glucose were given in the postabsorptive state and during continuous infusion of unlabelled glucose at 1.5 and 4 mg/kg.min, while normoglycaemia was maintained by closed-loop intraperitoneal and intravenous insulin delivery. During all three periods, plasma glucose concentrations remained near normal (variations 3.8-6.1%). The insulin infusion rates required for normal plasma glucose concentrations were essentially the same for the intravenous and intraperitoneal routes in all cases, although the variations were greater with intraperitoneal insulin. Plasma free-insulin levels were only slightly, non-significantly lower with intraperitoneal infusion than with intravenous infusion. Hepatic glucose production was significantly lower with intraperitoneal insulin during all three conditions: basal: 1.71 +/- 0.14, i.p. vs 2.37 +/- 0.26 mg/kg.min, i.v.; 1.5 mg/kg.min glucose infusion: 0.49 +/- 0.23, i.p. vs 0.88 +/- 0.18 mg/kg.min, i.v.; 4 mg/kg.min glucose infusion: 0.31 +/- 0.10, i.p. vs 0.56 +/- 0.12 mg/kg.min, i.v.. These results, obtained with steady-state conditions for plasma glucose, isotopic plasma glucose enrichments and unlabelled glucose infusion rates, suggest that better control of hepatic glucose production leading to normoglycaemia was achieved with the intraperitoneal infusion.

A method is described for measuring glutamine (GLN) and alpha-ketoglutarate (KG) concentration and specific activity (SA) using high-performance liquid chromatography (HPLC). Plasma GLN and KG are separated on miniature ion-exchange columns. KG is derivatized with O-phenylene diamine, the derivative is extracted in ethyl acetate, dried, and dissolved in pH 7 phosphate buffer. The isolated GLN is enzymatically converted to KG and analysed as such. Derivatized samples are stable for weeks at -20 degrees C. Samples are injected onto a reversed-phase HPLC column. Absolute standards are injected to determine the nmol content of unknown samples. alpha-Ketoadipate and [3H]-glutamine are used as internal standards to quantitate KG and GLN concentrations, respectively. Collection of the entire peak of interest permits determination of the radioactivity in the GLN and KG peaks; this together with the determination of the nanomoles injected permits the calculation of the SA. Typical precision is 3.5 and 4.6% for GLN and KG concentrations and 5.3 and 3.3% for GLN and KG SA, respectively. Analysis time is ca. 7 min. Using this method, the turnover rate of GLN carbon was determined during a 5-h infusion of L-[U-14C]glutamine in a human subject.

Glutamine is the most copious aminoacid in the body where it plays fundamental physiological roles. Its is a precursor of hepatic ureagenesis and renal ammoniagenesis; it acts as cellular fuel in tissues with fast turnover (intestine, skin, immune system) and is a potential regulator of protein synthesis. The sites of production (muscle) and utilization of glutamine have been established by multiple catheterization, while 15N-labelled tracers have made it possible to quantify its role as main inter-organ nitrogen carrier, to determine the origin of nitrogen used in its synthesis and to demonstrate in vivo the utilization of glutamine in the human bowel.

Glutamine and leucine kinetics were measured using stable isotopes in five enterectomized patients (residual small bowel, 80 +/- 25 cm [mean +/- SE]) who were in a near normal nutritional status at distance from surgery. While parameters of leucine metabolism were normal, rates of whole body glutamine utilization were reduced by 20% in the patients. The data suggest that the small intestine plays a prominent role in glutamine utilization in vivo in humans.

Insulin resistance was explored in vivo and in vitro in 3 lipoatrophic diabetic girls (12, 15 and 19 years old = L1, L2 and L3). Patients L1 and L2 were explored with fasting hyperglycaemia (9 mmol/l); patient L3 was normoglycaemic. All had abnormal OGTT with marked hyperinsulinemia. Their basal glucose productions, measured by [6,6(-2)H] glucose constant infusion, were 3.3, 2.6 and 3.4 mg kg-1 min-1, respectively; they did not correlate with fasting plasma glucose. Glucose production in response to a 2 mg kg-1 min- unlabeled glucose infusion, was normally suppressed in L2, but was incompletely suppressed (by 1.5 mg kg-1 min-1) in L1 and L3. The dose-response curve during hyperinsulinemic euglycaemic clamp at 1, 2 and 10 mU kg-1 min-1 insulin infusion was shifted to the right in all three patients. However the maximal glucose disposal rates were close to normal (9 and 9 mg kg-1 min-1) in L1 and L3, while it remained very low (3.6 mg kg-1 min-1 at 10 mU kg-1 min-1 insulin infusion) in L2. The endogenous insulin secretion (plasma C-peptide) was also incompletely suppressed during insulin infusion. Thus, the in vivo insulin resistance of lipoatrophic diabetes concerns not only glucose disposal but also hepatic glucose output and insulin secretion; in addition, the alterations of glucose metabolism were not the same in all subjects. The in vitro studies showed no pre-receptor defect (anti-insulin antibodies, insulin receptor antibodies). Insulin binding to erythrocytes and cultured fibroblasts was normal.(ABSTRACT TRUNCATED AT 250 WORDS)

50 g fructose and 50 g glucose loads, naturally 13C labelled, were orally administered in random order to six healthy subjects submitted to 90 mn exercise at VO2 max/2 on a treadmill. 13CO2/12CO2 variations in the expired air were followed before and after exercise for a total of 240 min. On the whole, fructose appeared to be as good a fuel as glucose during exercise even if slight but significant differences in kinetics were observed: the delta 13C peak values at 90 min were significantly lower with fructose. Between 90 and 240 min, delta 13C remained higher but not significantly with 13C-fructose than with 13C-glucose. During exercise, plasma glucose and insulin levels were significantly lower (p less than 0.05 and p less than 0.01) after fructose than after glucose. We conclude that fructose can be readily used during exercise by healthy subjects.

Glutamine's role as an energetic fuel has been extensively studied in the past using 14C- and 3H-labeled tracers in cultured human cells. Yet another prominent role of glutamine, that of a nitrogen shuttle, cannot be approached without an N-tracer. We therefore used 15N-labeled glutamine and glutamate to address the following questions: 1) is it possible to study the exchangeable pools of intracellular free glutamine and glutamate nitrogen with stable isotope methods? and 2) to what extent is intracellular glutamine pool regulated by extracellular glutamine? We observed that: 1) intracellular [15N]-glutamine enrichment reached a plateau at 80% within 20 min of incubation in a buffer containing 0.7 mM pure 15N-glutamine and no glutamate; in contrast, intracellular 15N-glutamate enrichment rose only to 40% after 4 hours of incubation in a buffer containing 0.5 mM pure 15N-glutamate and no glutamine; 2) the cell-free glutamine content was tightly dependent on extracellular glutamine level, while the cell-free glutamate remained steady irrespective of the extracellular glutamate level; 3) the cells took up glutamine and glutamate against a concentration gradient; the rate of glutamine uptake accounted for 90% of the cell glutamine turnover rate; and 4) when cells were confronted with a glutamine-free medium, only one fourth of intracellular glutamine was derived from the exchangeable glutamate. We conclude that: 1) The size and turnover rate of the intracellular pool of free glutamine nitrogen are measureable using stable isotope methodology; 2) glutamine uptake from the extracellular medium accounts for most of glutamine turnover rate in cultured fibroblasts; and 3) intracellular free glutamate is divided up between several pools in cultured human fibroblasts.

Although glycosuria is important in the control of diabetes in children, few studies clearly show its significance as compared to glycemia. The aim of the present study was therefore to determine the two parameters that control glucose presence in urine, i.e. glucose glomerular filtration rate (GFR) and tubular reabsorption (JrG). GFR was measured by using a 110 min polyfructosan perfusion in 96 diabetic children and adolescents. The results are as follows: 1) In this population there is a significant correlation (p less than 0.01) between the quantity of glucose in urine and mean glycemia during the test; 2) polyfructosan clearance that reflects GFR in diabetic children without renal complication is 2.11 +/- 0.04 ml/s 1.73 m2, or 126 +/- 2.4 ml/min 1.73 m2 (mean +/- SEM); it is higher than in the reference values already published; 3) JrG is correlated with glucose filtered load (p less than 0.01), GFR (p less than 0.01) and sodium reabsorption (p less than 0.01). The ratio JrG/GFR could be substituted for the classical concept of "renal threshold", as it can be easily measured and may help in interpreting glycosuria in some diabetic children. To conclude, in IDD children, the parameters controlling glycosuria may be studied by a simple method. The clinical value of such renal exploration has still to be determined.

The current artificial pancreases, which are not wearable, are mainly used for physiological research. However, they may also become useful tools for clinical or therapeutic investigations in diabetes mellitus. This is clearly demonstrated by our own experience of the Biostator in 300 young diabetics. The steady state regulation of plasma glucose offers a wide range of possible investigations: clinical, such as measuring insulin activity in states of insulin resistance, urinary excretion of glucose and renal threshold; therapeutic, like evaluating the hypoglycemic activity of commercial insulins, or alternative routes of insulin administration, such as the peritoneum; physiopathological, for better evaluation of metabolic alterations in diabetes by measuring the turnover of various substrates. Experience of the artificial pancreas also appears to be crucial for a better handling of the many problems involved in the design of future wearable or implantable devices.

Oral rehydration therapy of diarrhea is based upon the promoting effect of glucose on sodium absorption. This ionic transport could be further enhanced by the addition of glutamine, an amino acid which is also the major energy source for the enterocyte. The aim of this in vitro study was to assess glutamine intestinal transport and to evaluate ionic movements associated with this transport. Strips of ileal epithelium from rabbits at weaning were mounted in Ussing chambers. Both sides of the epithelium were bathed with Ringer solution supplemented, after a basal period, with 2, 5, 10 or 25 mM glutamine. Unidirectional transepithelial fluxes of glutamine were measured with 3H and 14C tracers. Short circuit current, reflecting ionic transport, and potential difference were continuously monitored. Glucose 9 mM was later added to both sides. An apparent bidirectionnal transepithelial transport of glutamine was observed. The net result was a dose-dependent absorption (1.8 +/- 0.3 mumoles/h. cm2 at 25 mM). Glutamine induced a significant (p less than 0.01) dose-dependent saturable increase of short-circuit current and potential difference; the epithelial conductance was not modified. The addition of glucose did not significantly modify glutamine transport but caused and additional increase of short-circuit current. These results suggest that glutamine is actively transported by the ileal epithelium and stimulates ionic transport, suggesting Na+ absorption. The mechanism of this stimulation may differ from that of glucose, as the effects were additive. The present data provide support to the clinical evaluation of glutamine-supplemented rehydration solutions in the treatment of diarrhea.

Dynamic aspects of whole body glucose metabolism were assessed in ten young adult insulin-dependent (type I) diabetic men. Using a primed, continuous intravenous infusion of [6,6-2H]glucose and [U-13C]glucose, endogenous production, tissue uptake, carbon recycling, and oxidation of glucose were measured in the postabsorptive state. These studies were undertaken after blood glucose had been maintained overnight at 5.9 +/- 0.4 mmol/L (n = 10), and on another night at 10.5 +/- 0.4 mmol/L (n = 4) or 15.2 +/- 0.6 mmol/L (n = 6). In the normoglycemic state, endogenous glucose production averaged 2.15 +/- 0.13 mg x kg-1 x min-1. This value, as well as the rate of glucose carbon recycling (0.16 +/- 0.04 mg x kg-1 x min-1) and glucose oxidation (1.52 +/- 0.16 mg x kg-1 x min-1) are comparable to those found in nondiabetic controls. In the hyperglycemic states at 10 or 15 mmol/L, endogenous glucose production was increased by 11% (P less than .01) and 60% (P less than .01) compared to the normoglycemic states, respectively. Glucose carbon recycling contributed only a small percentage to this variation in glucose production (15% at the 15 mmol/L glucose level). This suggests that if gluconeogenesis participates in the increased glucose output, it is not dependent on a greater systemic supply of three-carbon precursors. The increased rate of glucose production in the hyperglycemic state was quantitatively offset by a rise in urinary glucose excretion. Glucose tissue uptake, as well as glucose oxidation, did not vary between normoglycemic and hyperglycemic states.(ABSTRACT TRUNCATED AT 250 WORDS)