Importance of substrate changes in the decrease of hepatic glucose cycling during insulin infusion and declining glycemia in the depancreatized dog

We wished to determine whether the elevated glucose cycling (GC) between glucose and glucose-6-phosphate (G<-->G6P) in diabetes can be reversed with acute insulin treatment. In six insulin-deprived, anesthetized, depancreatized dogs, insulin was infused for 6-9 h at a starting dose of 45-150 pmol.kg-1.min-1 to normalize plasma glucose from 23.9 +/- 1.4 to 5.0 +/- 0.4 mmol/l and gradually decreased to and maintained at a basal rate (1.7 +/- 1.0 pmol.kg-1.min-1) during the last 3 h. GC, measured with [2-3H]- and [6-3H]glucose, fell markedly from 15.3 +/- 2.7 and normalized at 1.3 +/- 0.6 mumol.kg-1.min-1 (P < 0.001). This occurred because total hepatic glucose output fell much more (from 41.2 +/- 3.1 to 11.6 +/- 1.2) than did glucose production (from 25.9 +/- 1.9 to 10.3 +/- 1.0 mumol.kg-1.min-1) (both P < 0.01). Freeze-clamped liver biopsies were taken at timed intervals for measurements of hepatic enzymes and substrates. The elevated hepatic hexose-6-phosphate levels decreased with insulin infusion (151 +/- 24 vs. 71 +/- 13 nmol/g, P < 0.01). Maximal activities of glucose-6-phosphatase (G6Pase) (from 17.6 +/- 0.8 to 19.6 +/- 2.6 U/g) and glucokinase (from 1.1 +/- 0.2 to 1.0 +/- 0.2 U/g) did not change. Insulin infusion resulted in a threefold increase (P < 0.05) in the activity of glycogen synthase (active form), but had no effect on hepatic glycogen content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Forearm substrate exchange during hyperinsulinaemic hypoglycaemia in normal man

To assess muscle substrate exchange during hypoglycaemia, 8 healthy young male subjects were studied twice during 2 h of hyperinsulinaemic euglycaemia followed by 4 h of (1) hypoglycaemia (plasma glucose < 2.8 mmol l-1), and (2) euglycaemia. Insulin was infused at a rate of 1.5 mU kg-1 min-1 throughout. When compared to euglycaemia, hypoglycaemia was associated with: (1) increment in circulating glucagon (65 +/- 8 vs 23 +/- 4 ng l-1, p < 0.05), growth hormone (19.9 +/- 3.6 vs 2.6 +/- 1.3 micrograms l-1, p < 0.05), adrenaline (410 +/- 88 vs 126 +/- 32 ng l-1, p < 0.05) and increased suppression of C-peptide (0.5 +/- 0.1 vs 1.0 +/- 0.1 micrograms l-1, p < 0.05) along with a modest lowering of insulin (103 +/- 10 vs 130 +/- 13 mU l-1, p < 0.05); (b) decrease in plasma glucose level (3.0 +/- 0.07 vs 5.0 +/- 0.12 mmol l-1, p < 0.05), forearm glucose uptake (0.21 +/- 0.09 vs 1.21 +/- 0.21 mmol l-1, p < 0.05) and requirement for exogenous glucose (5.6 +/- 1.1 vs 13.2 +/- 0.9 mg kg-1 min-1 p < 0.005) together with an impaired suppression of isotopically determined endogenous glucose production (0.34 +/- 0.5 vs -2.3 +/- 0.3 mg kg-1 min-1, p < 0.05); (3) exaggerated increase in blood lactate (1680 +/- 171 vs 1315 +/- 108 mumol l-1, p < 0.05) and a decrease in alanine (215 +/- 18 vs 262 +/- 19 mumol l-1, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies of lysophospholipids related to the hamster sperm acrosome reaction in vitro

1. One of the metabolic features of acquired immunodeficiency syndrome is increased tissue glucose uptake documented by euglycaemic-hyperinsulinaemic clamp studies, suggesting increased insulin sensitivity. However, these results may also be related to the confounding effect of increased non-insulin-mediated glucose uptake in acquired immunodeficiency syndrome, which will result in an erroneously presumed increased insulin sensitivity. To study the contribution of non-insulin-mediated glucose uptake to total tissue glucose uptake in acquired immunodeficiency syndrome, we conducted a hypoinsulinaemic clamp study in clinically stable human immunodeficiency virus-infected (Centers for Disease Control class IV) men (n = 7) and healthy subjects (n = 5). Glucose uptake was measured by a primed, continuous infusion of [3-3H]glucose in the postabsorptive state and during somatostatin-induced insulinopenia at euglycaemic (approximately 5.3 mmol/l) and hyperglycaemic (approximately 11 mmol/l) glucose concentrations. 2. Basal glucose concentration (patients, 5.2 +/- 0.1 mmol/l; control subjects, 5.3 +/- 0.1 mmol/l) and basal glucose tissue uptake (patients, 15.9 +/- 0.5 mumol min-1 kg-1 fat-free mass; control subjects, 15.2 +/- 0.4 mumol min-1 kg-1 fat-free mass) were not different between the two groups. 3. Euglycaemic glucose uptake during somatostatin infusion, reflecting non-insulin-mediated glucose uptake, decreased to 82 +/- 3% in patients and 78 +/- 2% in control subjects (not significant). Under hyperglycaemic (approximately 11 mmol/l) conditions with sustained insulinopenia, no differences in glucose uptake existed between the two groups (patients, 16.8 +/- 0.6 mumol min-1 kg-1 fat-free mass; control subjects, 16.1+/- 0.3 mumol min-1 kg-1 fat-free mass).(ABSTRACT TRUNCATED AT 250 WORDS)     

Medical and health impact of complex emergencies: implications for the International Society of Nephrology Disaster Relief Task Force

The aim of the present study was to measure whole body glucose uptake (M) and oxidation rate by euglycaemic hyperinsulinaemic clamp and indirect calorimetry in 7 morbidly obese subjects (BMI > 40 kg/m2) at three time points: before bilio-pancreatic diversion (BPD) surgery (Ob); 3 months after surgery POI; and after reaching stable body weight, at least 2 years after surgery POII. A group of 7 control subjects (C), matched groupwise for sex, age and BMI with POII patients, was also studied. The M value at POI was significantly higher than at Ob (49.12 +/- 8.57 vs 18.14 +/- 8.57 mumol.kg-1.min-1). No statistical difference was observed between the POII and C groups. Similarly, glucose oxidation rate was significantly increased at POI with respect to Ob (24.2 +/- 7.23 vs 9.42 +/- 3.91 mumol.kg-1.min-1) and was not significantly different between POII and C. Basal levels of non-esterified fatty acids (NEFA) decreased significantly both from Ob to POI and from POI to POII (1517.1 +/- 223.9 vs 1039.6 +/- 283.4 vs 616.0 +/- 77.6 mumol.1(-1). The same applied to basal plasma triglycerides (2.07 +/- 0.77 vs 1.36 +/- 0.49 vs 0.80 +/- 0.19 g.1(-1). Weight decreased mainly in the late postoperative period (POI to POII 124.28 +/- 11.22 to 69.71 +/- 11.78, 83% of total decrement), rather than in the early postoperative period (Ob to POI 135.25 +/- 14.99 to 124.28 +/- 11.22 kg, 17% of total decrement). We also report the clinical case of a young woman of normal weight, who underwent BPD for chylomicronaemia (secondary to familial lipoprotein lipase deficiency), whose M value, plasma insulin and blood glucose levels were normalized upon normalization of serum NEFA and triglyceride levels as determined by the therapeutic lipid malabsorption. In conclusion, in obese diabetic patients lipid malabsorption induced by BPD causes a definite enhancement of insulin sensitivity and glucose tolerance. This improvement in metabolism is noticeable before the surgery has major effects on body weight. These observations suggest that lowered plasma lipids, rather than weight loss per se, are the cause of the reversibility of insulin resistance.     

The impact of metformin therapy on hepatic glucose production and skeletal muscle glycogen synthase activity in overweight type II diabetic patients

The effect of metformin therapy on glucose metabolism was examined in eight overweight newly presenting untreated type II diabetic patients (five males, three females). Patients were treated for 12 weeks with either metformin (850 mg x 3) or matching placebo using a double-blind crossover study design; patients were studied at presentation and at the end of each treatment period. Insulin action was assessed by measuring activation of skeletal muscle glycogen synthase (GS) before and during a 4-hour hyperinsulinemic euglycemic clamp (100 mU.kg-1 x h-1). Metformin therapy was associated with a significant decrease in fasting blood glucose (6.8 +/- 0.6 v 8.3 +/- 0.9 mmol.L-1, P < .01) and glycosylated hemoglobin ([HbA1] 7.7% +/- 0.4% v 8.5% +/- 0.5%, P < .01) levels. Fasting hepatic glucose production (HGP) was also significantly decreased following metformin therapy (1.98 +/- 0.13 v 2.41 +/- 0.20 mg.kg-1 x min-1, P < .02), whereas fasting insulin and C-peptide concentrations remained unaltered. The decrease in basal HGP correlated closely with the decrease in fasting blood glucose concentration (r = .92, P < .001). Insulin-stimulated glucose uptake was assessed using the hyperinsulinemic euglycemic clamp technique and was increased post-metformin (3.8 +/- 0.6 v 3.1 +/- 0.7 mg.kg-1 x min-1, P < .05). This was primarily the result of increased nonoxidative glucose metabolism (1.1 +/- 0.6 v 0.4 +/- 0.6 mg.kg-1 x min-1, P < .05); oxidative glucose metabolism did not change. Metformin had no measurable effect on insulin activation of skeletal muscle GS, the rate-limiting enzyme controlling muscle glucose storage.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hyperamylinemia is associated with hyperinsulinemia in the glucose-tolerant, insulin-resistant offspring of two Mexican-American non-insulin-dependent diabetic parents

Several investigations have presented evidence that amylin inhibits insulin secretion and induces insulin resistance both in vitro and in vivo. However, basal and postmeal amylin concentrations proved similar in non-insulin-dependent diabetes mellitus (NIDDM) patients and controls. Since hyperglycemia may alter both amylin and insulin secretion, we examined basal and glucose-stimulated amylin secretion in eight glucose-tolerant, insulin-resistant Mexican-American subjects with both parents affected with NIDDM (offspring) and correlated the findings with the insulin sensitivity data acquired by an insulin clamp. Eight offspring and eight Mexican-Americans without any family history of diabetes (controls) underwent measurement of fat free mass (3H2O dilution method), 180-minutes, 75-g oral glucose tolerance test (OGTT), and 40-mU/m2, 180-minute euglycemic insulin clamp associated with 3H-glucose infusion and indirect calorimetry. Fasting amylin was significantly increased in offspring versus controls (11.5 +/- 1.4 v 7.0 +/- 0.8 pmol/L, P < .05). After glucose ingestion, both total (3,073 +/- 257 v 1,870 +/- 202 pmol.L-1.min-1, P < .01) and incremental (1,075 +/- 170 v 518 +/- 124 pmol.L-1.min-1, P < .05) areas under the curve (AUCs) of amylin concentration were significantly greater in offspring. The amylin to insulin molar ratio was similar in offspring and controls at all time points. Basal and postglucose insulin and C-peptide concentrations were significantly increased in the offspring. No correlation was found between fasting amylin, postglucose amylin AUC or IAUC, and any measured parameter of glucose metabolism during a euglycemic-hyperinsulinemic clamp (total glucose disposal, 7.21 +/- 0.73 v 11.03 +/- 0.54, P < .001; nonoxidative glucose disposal, 3.17 +/- 0.59 v 6.33 +/- 0.56, P < .002; glucose oxidation, 4.05 +/- 0.46 v 4.71 +/- 0.21, P = NS; hepatic glucose production, 0.29 +/- 0.16 v 0.01 +/- 0.11, P = NS; all mg.min-1.kg-1 fat-free mass, offspring v controls). In conclusion, these data do not support a causal role for amylin in the genesis of insulin resistance in NIDDM.     

Increased nonoxidative glucose metabolism in idiopathic reactive hypoglycemia

Idiopathic reactive hypoglycemia (IRH) is responsible for postprandial hypoglycemia. Normal insulin secretion and reduced response of glucagon to acute hypoglycemia, but mostly increased insulin sensitivity, represent the metabolic features of this syndrome- The present study has two aims: first, to investigate the fate of glucose utilization inside the cells to assess whether increased glucose disposal in IRH is due to the oxidative and/or nonoxidative pathway; and second, to evaluate glucagon response to prolonged insulin-induced hypoglycemia. In eight patients with IRH and eight normal (N) subjects, we performed two studies on different days: (1) 120-minute euglycemic-hyperinsulinemic (1.0 mU . kg-1 . min-1 regular human insulin) clamp associated with indirect calorimetry; and (2) 180-minute hypoglycemic (2.22 to 2.49 mmo/L achieved through 0.85 mU . kg-1 . min-1 intravenous [IV] regular human insulin) clamp. The results showed an increased insulin-mediated glucose uptake in IRH (9.10 +/- 0.19 v 6.78 +/- 0.18 mg kg-1 . min-1, P < .005). Glucose oxidation was similar in IRH subjects and controls both in basal conditions (1.39 +/- 0.16 v 1.42 +/- 0.15 mg . kg-1 . min-1 and during the clamp studies (2.57 +/- 0.21 v 2.78 +/- 0.26 mg . kg-1 . min-1. In contrast, nonoxidative glucose disposal was significantly higher in IRH than in N subjects (6.53 +/- 0.30 v 4.00 +/- 0.21 mg . kg-1 . min-1, P < .001). During insulinization, fat oxidation was reduced slightly more in IRH than in control subjects. During the hypoglycemic clamp, a significant (P < .01) increase in plasma glucagon concentrations was observed in normal subjects as compared with baseline, whereas no change occurred in IRH patients. In conclusion, in IRH: (1) increased insulin-mediated glucose disposal is due to the increase of nonoxidative glucose metabolism; and (2) glucagon secretion has been confirmed to be inadequate. The increase of insulin sensitivity associated with a deficiency in glucagon secretion can widely explain the occurrence of hypoglycemia in the late postprandial phase.     

Exogenous insulin reduces proteolysis and protein synthesis in extremely low birth weight infants

OBJECTIVE: To determine the effect of a continuous insulin infusion on protein and glucose metabolism in extremely low birth weight (ELBW) infants. STUDY DESIGN: We measured the rate of appearance (Ra) of the essential amino acids leucine and phenylalanine (reflecting proteolysis), utilization of phenylalanine for protein synthesis, and glucose Ra using stable isotope tracers during a basal infusion of glucose (6 mg/kg/min) and in response to a continuous infusion of insulin (0.05 U/kg/hr) by means of the euglycemic hyperinsulinemic clamp technique. Four clinically stable, euglycemic ELBW infants (26 +/- 0 weeks' gestation, 894 +/- 44 gm birth weight, 2.8 +/- 0.8 days of age) were studied. RESULTS: In response to a greater than tenfold increase in insulin concentration (from 7 +/- 2 to 79 +/- 13 microU/ml), there was a 20% decrease in leucine Ra (Basal: 272 +/- 27 mumol/kg/hr; Insulin: 226 +/- 29 mumol/kg/hr; p < 0.01) and in phenylalanine Ra (Basal: 91 +/- 5 mumol/kg/hr; Insulin: 72 +/- 2 mumol/kg/hr; p < 0.05). Use of phenylalanine for protein synthesis also decreased by a similar magnitude (Basal: 77 +/- 4 mumol/kg/hr; Insulin: 62 +/- 1 mumol/kg/hr; p < 0.05). Glucose utilization doubled (from 8 +/- 0.9 to 15.7 +/- 1.1 mg/kg/min; p = 0.0003) and plasma lactate concentrations tripled (from 2.1 +/- 0.5 to 5.7 +/- 1.0 mmol/L; p < 0.05) during the insulin infusion. CONCLUSIONS: During an infusion of glucose alone, pharmacologic concentrations of insulin in ELBW infants produced no net protein anabolic effect. Furthermore, euglycemic hyperinsulinemia was accompanied by development of significant metabolic acidosis.     

Insulin resistance in patients with a recent diagnosis of coronary artery disease

Insulin increases limb blood flow in a time- and dose-dependent manner. This effect can be blocked by inhibiting nitric oxide synthesis. These data raise the possibility that insulin resistance is associated with endothelial dysfunction. To examine whether endothelial function and insulin sensitivity are interrelated we quantitated in vivo insulin-stimulated rates of whole body and forearm glucose uptake at a physiological insulin concentration (euglycaemic hyperinsulinaemic clamp, 1 mU.kg-1.min-1 insulin infusion for 2 h) and on another occasion, in vivo endothelial function (blood flow response to intrabrachial infusions of sodium nitroprusside, acetylcholine, and N-monomethyl-L-arginine) in 30 normal male subjects. Subjects were divided into an insulin-resistant (IR) and an insulin-sensitive (IS) group based on the median rate of whole body glucose uptake (31 +/- 2 vs 48 +/- 1 mumol.kg-1.min-1, p < 0.001). The IR and IS groups were matched for age, but the IR group had a slightly higher body mass index, percentage of body fat and blood pressure compared to the IS group. The IR group also had diminished insulin-stimulated glucose extraction (p < 0.05) compared to the IS group, while basal and insulin-stimulated forearm blood flow rates were identical. There was no difference between the IR and IS groups in the forearm blood flow response to endothelium-dependent (acetylcholine and N-monomethyl-L-arginine) or -independent (sodium nitroprusside) vasoactive drugs. In conclusion, the ability of insulin to stimulate glucose uptake at physiological insulin concentrations and endothelium-dependent vasodilatation are distinct phenomena and do not necessarily coexist.     

Alterations in glucose metabolism in the elderly patient with diabetes

OBJECTIVE: To determine the alterations in glucose metabolism in elderly patients with NIDDM. RESEARCH DESIGN AND METHODS: We studied 9 healthy elderly control subjects (73 +/- 1 yr of age; body mass index 25.7 +/- 0.4 kg/m2) and 9 untreated elderly NIDDM patients (72 +/- 2 yr of age; BMI 25.9 +/- 0.5 kg/m2). Each subject underwent a 3-h oral glucose tolerance test (40 g/m2); a 2-h hyperglycemic glucose clamp study (glucose 5.4 mM above basal); and a 4-h euglycemic insulin clamp (40 mM.m2.min-1). Tritiated glucose methodology was used to measure glucose production and disposal rates during the euglycemic clamp. RESULTS: Patients with NIDDM had a higher fasting glucose (9.3 +/- 0.3 vs. 5.1 +/- 0.1 mM in control subjects vs. NIDDM patients, respectively, P < 0.001) and a greater area under the curve for glucose during the OGTT (16.0 +/- 0.6 vs. 6.7 +/- 0.3 mM in control subjects vs. NIDDM patients, respectively, P < 0.01) than the healthy control subjects. During the hyperglycemic clamp, patients with NIDDM had an absent first-phase insulin response (112 +/- 6 vs. 250 +/- 31 pM in control subjects vs. NIDDM patients, respectively, P < 0.01), and a blunted second-phase insulin response (159 +/- 11 vs. 337 +/- 46 pM in control subjects vs. NIDDM patients, respectively, P < 0.01). Before the euglycemic clamp, fasting insulin (99 +/- 5 vs. 111 +/- 10 pM in control subjects vs. NIDDM patients, respectively) and hepatic glucose production (11.8 +/- 0.7 vs. 11.5 +/- 0.5 mumol.kg-1-min-1 in control subjects vs. NIDDM patients, respectively) were similar. Steady-state (180-240 min) glucose disposal rates during the euglycemic clamp were slightly, but not significantly, higher in the normal control subjects (36.5 +/- 1.1 vs. 33.1 +/- 1.9 mumol.kg-1-min-1 in control subjects vs. NIDDM patients, respectively, NS). CONCLUSIONS: We conclude that NIDDM in nonobese elderly subjects is characterized by a marked impairment in insulin release. This may be attributable to the toxic effects of chronic hyperglycemia on the beta-cell. When compared with age-matched control subjects, the NIDDM patients showed no increase in fasting insulin or hepatic glucose production, and insulin resistance was mild.     

Quantification of gluconeogenesis in cirrhosis: response to glucagon

BACKGROUND & AIMS: Accelerated starvation and early recruitment of alternate fuels in cirrhosis have been attributed to reduced availability of hepatic glycogen. The aim of this study was to measure gluconeogenesis (as a marker of protein oxidation) in relation to total glucose production and glucagon-stimulated glycogenolysis. METHODS: Glucose and urea production, gluconeogenesis, and glycogenolysis were calculated using stable isotope methods before and during glucagon infusion (3 ng. kg-1. min-1) in 5 cirrhotic patients and 5 matched controls before and after glycogen repletion. RESULTS: In the basal state, cirrhotic patients had a normal rate of glucose production, but the contribution of gluconeogenesis was increased (74.3% +/- 4.1% vs. 55. 6% +/- 12.1%; P < 0.005). Glycogen repletion normalized the rate of gluconeogenesis. The glycemic response to glucagon (3 ng. kg-1. min-1) was blunted in cirrhotic patients because of a lower rate of glycogenolysis (0.63 +/- 0.23 vs. 1.22 +/- 0.23 mg. kg-1. min-1; P < 0.01) and was not affected by glycogen repletion. Despite increased gluconeogenesis, the simultaneously measured rate of urea synthesis was lower in cirrhotic patients (3.11 +/- 1.02 vs. 5.0 +/- 1.0 mg/kg; P < 0.05). CONCLUSIONS: These data show that in cirrhosis, glucose production is sustained by an increased rate of gluconeogenesis. The hepatic resistance to glucagon action is not caused by reduced glycogen stores.     

Insulin sensitivity in familial hypercholesterolemia

Insulin resistance is found in association with obesity, non-insulin-dependent diabetes mellitus, and essential hypertension, which are all risk factors for atherosclerotic cardiovascular disease. Furthermore, hyperinsulinemia has been reported in familial combined hyperlipoproteinemia and endogenous hypertriglyceridemia. Finally, relatively high serum triglyceride and low high-density lipoprotein (HDL) cholesterol concentrations invariably accompany hyperinsulinemia. Whether insulin sensitivity is affected by the isolated presence of high levels of serum low-density lipoprotein (LDL) cholesterol has not been clearly established. We studied 13 subjects with heterozygous familial hypercholesterolemia (FHC) and 15 normocholesterolemic subjects selected to be free of any other known cause of insulin resistance. Thus FHC patients and controls had normal body weight and fat distribution, glucose tolerance, blood pressure, and serum triglyceride and HDL cholesterol concentrations, but were completely separated on plasma LDL cholesterol concentrations (6.05 +/- 0.38 v 3.27 +/- 0.15 mmol/L, P < .0001). Fasting plasma levels of glucose, insulin, free fatty acids (FFA), and potassium and fasting rates of net carbohydrate and lipid oxidation were superimposable in the two study groups. During a 2-hour euglycemic (approximately 5 mmol/L) hyperinsulinemic (approximately 340 pmol/L) clamp, whole-body glucose disposal rates averaged 30.4 +/- 2.3 and 31.1 +/- 3.0 mumol.kg-1 x min-1 in FHC and control subjects, respectively (P = 0.88). The ability of exogenous hyperinsulinemia to stimulate carbohydrate oxidation and energy expenditure and suppress lipid oxidation and plasma FFA and potassium levels was equivalent in FHC and control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protein metabolism in human obesity: relationship with glucose and lipid metabolism and with visceral adipose tissue

It is controversial whether metabolic disorders of human obesity include protein metabolism. Even less information is available concerning the effect of fat distribution on protein metabolism. Therefore, a comprehensive evaluation of glucose, lipid, and protein metabolism was performed in 11 obese nondiabetic and 9 normal women whose body composition and regional fat distribution were determined. [1-14C]Leucine and [3-3H]glucose were infused in the postabsorptive state and during an euglycemic hyperinsulinemic (35-40 microU/mL) clamp combined with indirect calorimetry for assessment of leucine flux, oxidation, and nonoxidative disposal, glucose turnover and oxidation, and lipid oxidation. Fat-free mass (FFM) was estimated by a bolus of 3H2O. Subcutaneous abdominal and visceral adipose tissues were determined by nuclear magnetic resonance imaging. During the clamp, obese women had lower glucose turnover (4.51 +/- 0.41 vs. 6.63 +/- 0.40 mg/min.kg FFM; P < 0.05), with a defect in both oxidation (3.27 +/- 0.22 vs. 3.89 +/- 0.21) and nonoxidative disposal (1.24 +/- 0.27 vs. 2.74 +/- 0.41; P < 0.005), whereas lipid oxidation was higher during the clamp (0.49 +/- 0.15 vs. 0.17 +/- 0.09 mg/min.kg FFM). There was no difference in leucine flux (basal, 2.23 +/- 0.17 vs. 2.30 +/- 0.29; clamp, 2.06 +/- 0.19 vs. 2.10 +/- 0.24 mumol/min.kg FFM), oxidation (basal, 0.37 +/- 0.04 vs. 0.36 +/- 0.05; clamp, 0.34 +/- 0.04 vs. 0.39 +/- 0.06) and nonoxidative leucine disposal (basal, 1.86 +/- 0.17 vs. 1.94 +/- 0.26; clamp, 1.72 +/- 0.20 vs. 1.71 +/- 0.19) in the two groups. In obese women, basal leucine oxidation was directly related with glucose oxidation and inversely to lipid oxidation (both P < 0.05), whereas visceral adipose tissue was inversely related to leucine flux both in the basal state and during the clamp (P < 0.05). In conclusion, in human obesity, 1) rates of protein metabolism in the basal state and in the range of insulin concentrations encountered after a meal are normal; 2) protein oxidation is positively related to glucose oxidation and negatively related to lipid oxidation; and 3) visceral adipose tissue is inversely related to all parameters of protein metabolism.     

Total intravenous anaesthesia with sufentanil-midazolam for major abdominal surgery

Haemodynamic and endocrine stress responses were compared during total intravenous anaesthesia with sufentanil and midazolam or fentanyl and midazolam in patients undergoing elective major abdominal surgery. Twenty-two ASA I and II patients were allocated randomly to receive sufentanil (induction 1.5 micrograms kg-1 plus infusion 1.5 micrograms kg-1 h-1) or fentanyl (induction 10 micrograms kg-1 plus infusion 10 micrograms kg-1 h-1) supplemented with 0.15 microgram kg-1 sufentanil or 1 microgram kg-1 fentanyl as necessary. Midazolam was infused to obtain plasma concentrations of 500-600 ng ml-1. Ventilation was with oxygen-enriched air. The opioid infusion was reduced post-operatively by half and benzodiazepine effects were reversed by titration with flumazenil. Mean arterial pressure, heart rate and cardiac index decreased in both groups after induction (cardiac index: sufentanil 4.94 +/- 0.45 to 2.99 +/- 0.18 litre min-1; fentanyl 4.97 +/- 0.45 to 3.71 +/- 0.36 litre min-1), but all returned to baseline during surgery. With sufentanil; mean arterial pressure was lower throughout the study period, and heart rate was lower intra-operatively. Oxygen uptake decreased in both groups after induction (sufentanil 289 +/- 29 to 184 +/- 21 ml min-1; fentanyl 318 +/- 32 to 216 +/- 32 ml min-1) and remained low with sufentanil until flumazenil was given. Adrenaline concentrations increased in both groups but there was no intergroup difference. The median noradrenaline concentration was lower intra-operatively with sufentanil (0.47 nmol litre-1 (range 0.06-6.77)) than with fentanyl (0.73 nmol litre-1 (0.07-4.58)). Cortisol, glucose and lactate concentrations increased in both groups. Bradycardia occurred in four patients with sufentanil and in three with fentanyl. There were two cases of marked thoracic rigidity with sufentanil and one with fentanyl.     

Relationship between fatty acid delivery and fatty acid oxidation during strenuous exercise

To evaluate the extent to which decreased plasma free fatty acid (FFA) concentration contributes to the relatively low rates of fat oxidation during high-intensity exercise, we studied FFA metabolism in six endurance-trained cyclists during 20-30 min of exercise [85% of maximal O2 uptake (VO2max)]. They were studied on two occasions: once during a control trial when plasma FFA concentration is normally low and again when plasma FFA concentration was maintained between 1 and 2 mM by intravenous infusion of lipid (Intralipid) and heparin. During the 20-30 min of exercise, fat and carbohydrate oxidation were measured by indirect calorimetry, and the rates of appearance (Ra) of plasma FFA and glucose were determined by the constant infusion of [6,6-2H2]glucose and [2H2]palmitate. Lipid-heparin infusion did not influence the Ra or rate of disappearance of glucose. During exercise in the control trial, Ra FFA failed to increase above resting levels (11.0 +/- 1.2 and 12.4 +/- 1.7 mumol.kg-1.min-1 for rest and exercise, respectively) and plasma FFA concentration dropped from a resting value of 0.53 +/- 0.08 to 0.29 +/- 0.02 mM. The restoration of plasma FFA concentration resulted in a 27% increase in total fat oxidation (26.7 +/- 2.6 vs. 34.0 +/- 4.4 mumol.kg-1.min-1, P < 0.05) with a concomitant reduction in carbohydrate oxidation, apparently due to a 15% (P < 0.05) reduction in muscle glycogen utilization. However, the elevation of plasma FFA concentration during exercise at 85% VO2max only partially restored fat oxidation compared with the levels observed during exercise at 65% VO2max. These findings indicate that fat oxidation is normally impaired during exercise at 85% VO2max because of the failure of FFA mobilization to increase above resting levels, but this explains only part of the decline in fat oxidation when exercise intensity is increased from 65 to 85% VO2max.     

Release, oxidation, and reesterification of fatty acids from infused triglycerides: effect of heparin

We have investigated the effects of heparin on rates of fatty acid (FA) release, oxidation, and reesterification from intravenously (IV) infused triglycerides (TGs) during euglycemic (4.7 mmol.L-1) hyperinsulinemia (approximately 450 pmol.L-1). Four healthy men (aged 31 +/- 3 years; body mass index, 26.1 +/- 0.9 kg/m2) received i.v. TGs (1.02 mmol TG.kg-1.4 h-1), four other men (aged 24.3 +/- 2.8 years: body mass index, 24.7 +/- 1.7 kg/m2) received TGs plus heparin (200-U bolus followed by 0.4 U.kg-1.min-1), and nine men and one woman (aged 28.8 +/- 2.3 years; body mass index, 23.1 +/- 0.9 kg/m2) received saline (controls). Heparin increased lipolysis from infused TGs (to 1.0 +/- 0.1 from 0.3 +/- 0.1 mmol.kg-1.4 h-1, P < .01), increased plasma free fatty acids ([FFA] to 737 +/- 32 from 597 +/- 136 mumol.L-1, P < .05). and increased FA reesterification (to 0.84 +/- 0>14 from 0.18 +/- 0.12 mmol.kg-1.4 h-1, P < .02), but had no effect o n FA oxidation (0.13 +/- 0.02 v 0.12 +/- 0.04 mmol.kg-4 h-1) or net energy gain (167 +/- 42 v 243 +/- 79 kJ.4 h-1). In summary, addition of heparin (1) increased lipolysis (to approximately 98% from approximately 29%) and reesterification (to approximately 82% from approximately 17%) of infused TG, but had no significant effects on fat oxidation (approximately 12%) and net energy gain. We conclude that heparin accelerated removal of infused lipid from the blood and its deposition into endogenous fat depots. Since the doses of heparin and insulin used in this study were higher than those generally used in total parenteral nutrition protocols, our results may not be strictly applicable to the usual clinical situation.     

Free fatty acid metabolism in aerobically fit individuals

The impact of aerobic fitness level on the production and disposal of serum free fatty acids was investigated in 26 normal young volunteers. The fitness level was ascertained by history and confirmed by determination of maximal aerobic capacity. Energy expenditure and substrate oxidation at rest were measured with indirect calorimetry. Free fatty acid turnover was measured with an infusion of [14C]palmitic acid. All tests were done > or = 48 h after the last bout of exercise. The sedentary (SED) volunteers had higher rates of systemic delivery of fatty acids than aerobically fit (FIT) individuals (532 +/- 53.4 vs. 353 +/- 62.3 mumol/min; P = 0.05). This difference was accentuated when the values were normalized to fat-free mass (9.2 +/- 0.8 and 5.9 +/- 0.98 mumol.kg-1.min-1 for SED and FIT, respectively). Fatty acid oxidation was similar between FIT and SED volunteers in absolute numbers (209 +/- 25 vs. 202 +/- 21 mumol/min, respectively; NS) as well as when normalized to fat-free mass (3.8 +/- 0.9 vs. 3.6 +/- 1.4 mumol.kg-1.min-1, respectively; NS). In contrast, the nonoxidative disposal of serum fatty acids was higher in SED (330 +/- 46.1 mumol/min) than in FIT individuals (144 +/- 52 mumol/min; P = 0.026). Thus, the ratio of nonoxidative to oxidative disposal rates of fatty acids was higher in SED than in FIT individuals (1.65 +/- 0.29 vs. 0.75 +/- 0.17; P = 0.021). The data support the hypothesis that high aerobic fitness level is associated with a low rate of systemic delivery of fatty acids at rest. Nevertheless, subjects with high aerobic fitness levels have fat oxidation at the same rate as unfit individuals.     

Counterregulation by epinephrine and glucagon during insulin-induced hypoglycemia in the conscious dog

We assessed the combined role of epinephrine and glucagon in regulating gluconeogenic precursor metabolism during insulin-induced hypoglycemia in the overnight-fasted, adrenalectomized, conscious dog. In paired studies (n = 5), insulin was infused intraportally at 5 mU.kg-1.min-1 for 3 h. Epinephrine was infused at a basal rate (B-EPI) or variable rate to simulate the normal epinephrine response to hypoglycemia (H-EPI), whereas in both groups the hypoglycemia-induced rise in cortisol was simulated by cortisol infusion. Plasma glucose fell to approximately 42 mg/dl in both groups. Glucagon failed to rise in B-EPI, but increased normally in H-EPI. Hepatic glucose release fell in B-EPI but increased in H-EPI. In B-EPI, the normal rise in lactate levels and net hepatic lactate uptake was prevented. Alanine and glycerol metabolism were similar in both groups. Since glucagon plays little role in regulating gluconeogenic precursor metabolism during 3 h of insulin-induced hypoglycemia, epinephrine must be responsible for increasing lactate release from muscle, but is minimally involved in the lipolytic response. In conclusion, a normal rise in epinephrine appears to be required to elicit an increase in glucagon during insulin-induced hypoglycemia in the dog. During insulin-induced hypoglycemia, epinephrine plays a major role in maintaining an elevated rate of glucose production, probably via muscle lactate release and hepatic lactate uptake.     

Effects of glucose load on brain extracellular lactate concentration in conscious rats using a microdialysis technique

Changes in the brain lactate concentration in cerebral extracellular fluid (ECF) during intravenous infusion of glucose and local administration of glucose were investigated in adult, conscious, unrestrained rats, with a microdialysis probe in the posterior hippocampus. The rats were infused intravenously with either 25% sucrose solution or 25% glucose solution at a rate of 16.6 microliters.min-1.100 g-1 for three hours. The blood glucose concentration reached 17.0 +/- 2.6 mM at the end of the glucose infusion, and brain ECF glucose showed a parallel change with the blood glucose concentration and increased to 2.37 +/- 0.30 mM. However, blood and brain ECF glucose concentrations did not change in animals infused with the sucrose solution. On the other hand, the blood lactate concentration in the glucose-infused group also increased from 0.93 +/- 0.18 mM to 2.85 +/- 0.39 mM at the end of the glucose infusion, which was significantly higher than that measured in the sucrose-infused group. The blood lactate level in the glucose-infused group returned to the basal level by the end of the experiment. Brain ECF lactate concentrations increased from 1.21 +/- 0.06 mM to 1.69 +/- 0.11 mM in glucose-infused animals, but did not change in the sucrose-infused animals. The brain ECF lactate concentration showed a positive correlation with the brain ECF glucose concentration in glucose-infused animals. Another group of rats was administered glucose locally for 90 min after substitution of artificial cerebrospinal fluid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics of insulin action in vivo. Identification of rate-limiting steps

To examine the kinetic steps in insulin's in vivo action, we have assessed the temporal relationship between arterial insulin, interstitial insulin, glucose disposal rate (GDR), and insulin receptor kinase (IRK) activity in muscle and between portal insulin, hepatic glucose production (HGP), and IRK activity in liver. Interstitial insulin, as measured by lymph-insulin concentration (muscle only), and IRK activity were used as independent methods to determine the arrival of insulin at its tissue site of action. Euglycemic clamps were conducted in seven mongrel dogs and consisted of an activation phase with a venous insulin infusion (7.2 nmol.kg-1.min-1, 100 min) and a deactivation phase. Liver and muscle biopsies were taken to assess IRK activity. Arterial, portal, and lymph insulin rose to 636 +/- 12, 558 +/- 18, and 402 +/- 24 pmol/l, respectively. GDR increased from 13.9 +/- 0.6 to 41.7 +/- 2.8, and HGP declined from 14.4 +/- 0.6 to 1.1 +/- 0.6 mumol.kg-1.min-1. Muscle and liver IRK activity increased significantly from 5.9 +/- 0.9 to 14.6 +/- 0.6 and 5.5 +/- 0.7 to 23.7 +/- 1.9 fmol P/fmol insulin receptor (IR), respectively. The time to half-maximum response (t1/2a) for stimulation of GDR (19.8 +/- 4.8 min) and suppression of HGP (21.5 +/- 3.7 min) were similar. The t1/2a for stimulation of GDR, muscle IRK, and rise in lymph insulin were not significantly different from one another and were all markedly greater than that for the approach to steady state of arterial insulin (2.3 +/- 1.2 min, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)