Insulin regulation of renal glucose metabolism in conscious dogs.

Previous studies indicating that postabsorptive renal glucose production is negligible used the net balance technique, which cannot partition simultaneous renal glucose production and glucose uptake. 10 d after surgical placement of sampling catheters in the left renal vein and femoral artery and a nonobstructive infusion catheter in the left renal artery of dogs, systemic and renal glucose and glycerol kinetics were measured with peripheral infusions of [3-3H]glucose and [2-14C]glycerol. After baseline measurements, animals received a 2-h intrarenal infusion of either insulin (n = 6) or saline (n = 6). Left renal vein insulin concentration increased from 41 +/- 8 to 92 +/- 23 pmol/l (P < 0.05) in the insulin group, but there was no change in either arterial insulin, (approximately 50 pmol/l), glucose concentrations (approximately 5.4 mmol/l), or glucose appearance (approximately 18 mumol.kg-1.min-1). Left renal glucose uptake increased from 3.1 +/- 0.4 to 5.4 +/- 1.4 mumol.kg-1.min-1 (P < 0.01) while left renal glucose production decreased from 2.6 +/- 0.9 to 0.7 +/- 0.5 mumol.kg-1.min-1 (P < 0.01) during insulin infusion. Renal gluconeogenesis from glycerol decreased from 0.23 +/- 0.06 to 0.17 +/- 0.04 mumol.kg-1.min-1 (P < 0.05) during insulin infusion. These results indicate that renal glucose production and utilization account for approximately 30% of glucose turnover in postabsorptive dogs. Physiological hyperinsulinemia suppresses renal glucose production and stimulates renal glucose uptake by approximately 75%. We conclude that the kidney makes a major contribution to systemic glucose metabolism in the postabsorptive state.     

Glutamine: a major gluconeogenic precursor and vehicle for interorgan carbon transport in man.

To compare glutamine and alanine as gluconeogenic precursors, we simultaneously measured their systemic turnovers, clearances, and incorporation into plasma glucose, their skeletal muscle uptake and release, and the proportion of their appearance in plasma directly due to their release from protein in postabsorptive normal volunteers. We infused the volunteers with [U-14C] glutamine, [3-13C] alanine, [2H5] phenylalanine, and [6-3H] glucose to isotopic steady state and used the forearm balance technique. We found that glutamine appearance in plasma exceeded that of alanine (5.76 +/- 0.26 vs. 4.40 +/- 0.33 mumol.kg-1.min-1, P < 0.001), while alanine clearance exceeded glutamine clearance (14.7 +/- 1.3 vs. 9.3 +/- 0.8 ml.kg-1.min-1, P < 0.001). Glutamine appearance in plasma directly due to its release from protein was more than double that of alanine (2.45 +/- 0.25 vs. 1.16 +/- 0.12 mumol.kg-1.min-1, P < 0.001). Although overall carbon transfer to glucose from glutamine and alanine was comparable (3.53 +/- 0.24 vs 3.47 +/- 0.32 atoms.kg-1.min-1), nearly twice as much glucose carbon came from protein derived glutamine than alanine (1.48 +/- 0.15 vs 0.88 +/- 0.09 atoms.kg-1.min-1, P < 0.01). Finally, forearm muscle released more glutamine than alanine (0.88 +/- 0.05 vs 0.48 +/- 0.05 mumol.100 ml-1.min-1, P < 0.01). We conclude that in postabsorptive humans glutamine is quantitatively more important than alanine for transporting protein-derived carbon through plasma and adding these carbons to the glucose pool.     

Abnormal renal and hepatic glucose metabolism in type 2 diabetes mellitus.

Release of glucose by liver and kidney are both increased in diabetic animals. Although the overall release of glucose into the circulation is increased in humans with diabetes, excessive release of glucose by either their liver or kidney has not as yet been demonstrated. The present experiments were therefore undertaken to assess the relative contributions of hepatic and renal glucose release to the excessive glucose release found in type 2 diabetes. Using a combination of isotopic and balance techniques to determine total systemic glucose release and renal glucose release in postabsorptive type 2 diabetic subjects and age-weight-matched nondiabetic volunteers, their hepatic glucose release was then calculated as the difference between total systemic glucose release and renal glucose release. Renal glucose release was increased nearly 300% in diabetic subjects (321+/-36 vs. 125+/-15 micromol/min, P < 0.001). Hepatic glucose release was increased approximately 30% (P = 0.03), but increments in hepatic and renal glucose release were comparable (2.60+/-0.70 vs. 2.21+/-0.32, micromol.kg-1.min-1, respectively, P = 0.26). Renal glucose uptake was markedly increased in diabetic subjects (353+/-48 vs. 103+/-10 micromol/min, P < 0.001), resulting in net renal glucose uptake in the diabetic subjects (92+/-50 micromol/ min) versus a net output in the nondiabetic subjects (21+/-14 micromol/min, P = 0.043). Renal glucose uptake was inversely correlated with renal FFA uptake (r = -0.51, P < 0.01), which was reduced by approximately 60% in diabetic subjects (10. 9+/-2.7 vs. 27.0+/-3.3 micromol/min, P < 0.002). We conclude that in type 2 diabetes, both liver and kidney contribute to glucose overproduction and that renal glucose uptake is markedly increased. The latter may suppress renal FFA uptake via a glucose-fatty acid cycle and explain the accumulation of glycogen commonly found in the diabetic kidney.     

Phenylalanine kinetics in human adipose tissue.

Very little is known about the regulation of protein metabolism in adipose tissue. In this study systemic, adipose tissue, and forearm phenylalanine kinetics were determined in healthy postabsorptive volunteers before and during a 2-h glucose infusion (7 mg.kg-1.min-1). [3H]Phenylalanine was infused and blood was sampled from a radial artery, a subcutaneous abdominal vein, and a deep forearm vein. Adipose tissue and forearm blood flow were measured with 133Xe and plethysmography, respectively, and body fat mass was determined by dual energy x-ray absorptiometry. During glucose infusion, glucose concentration increased from 86 +/- 2 to 228 +/- 13 mg/dl and insulin concentration increased from 6.6 +/- 0.6 to 35.0 +/- 3.9 mU/liter, both P < 0.001. Systemic phenylalanine appearance decreased from 40.3 +/- 1.9 to 37.0 +/- 1.6 mumol/min during glucose infusion (P < 0.05). Baseline whole body adipose tissue phenylalanine release (5.2 +/- 1.4 mumol/min) was approximately 12% of systemic phenylalanine appearance and decreased (P < 0.05) to 2.3 +/- 0.9 mumol/min during glucose infusion. In contrast, phenylalanine release from the forearm did not change during glucose infusion. These results indicate that adipose tissue is a small but significant contributor to systemic phenylalanine appearance. Phenylalanine release from adipose tissue like lipolysis, is relatively sensitive to hyperinsulinemia.     

Effects of L-arginine on systemic and renal haemodynamics in conscious dogs.

1. The effects of L-arginine on systemic and renal haemodynamics were investigated in conscious dogs. L-Arginine was administered intravenously at doses of 15 and 75 mumol min-1 kg-1 for 20 min. 2. Mean arterial blood pressure, heart rate and cardiac output were not changed significantly by L-arginine infusion. However, L-arginine infusion induced a significant elevation of renal blood flow from 50 +/- 3 to 94 +/- 12 ml/min (means +/- SEM, P less than 0.01). 3. Simultaneous infusion of NG-monomethyl-L-arginine (0.5 mumol min-1 kg-1) significantly inhibited the increase in renal blood flow produced by L-arginine (15 mumol min-1 kg-1) without significant changes in mean arterial blood pressure or heart rate. 4. Pretreatment with atropine completely inhibited the L-arginine-induced increase in renal blood flow, whereas pretreatment with indomethacin attenuated it (63 +/- 4 versus 82 +/- 10 ml/min, P less than 0.05). 5. A continuous infusion of L-arginine increased renal blood flow in the intact kidney (55 +/- 3 versus 85 +/- 9 ml/min, P less than 0.05), but not in the contralateral denervated kidney (58 +/- 3 versus 56 +/- 4 ml/min, P greater than 0.05). 6. These results suggest that intravenously administered L-arginine produces an elevation of renal blood flow, which may be mediated by facilitation of endogenous acetylcholine-induced release of endothelium-derived relaxing factor and vasodilatory prostaglandins.     

Differential roles of splanchnic and peripheral tissues in the pathogenesis of impaired glucose tolerance

To identify the mechanism(s) of the altered glucoregulatory response to a glucose load in subjects with impaired glucose tolerance, we selectively quantitated the components of net splanchnic glucose balance, i.e., splanchnic glucose uptake and hepatic glucose output, as well as peripheral glucose uptake, by combining [3-3H]glucose infusion with hepatic vein catheterization. After intravenous glucose infusion (6 mg X kg-1 X min-1 for 90 min), blood glucose rose to 172 +/- 7 mg/dl in controls and 232 +/- 13 mg/dl in subjects with impaired glucose tolerance (P less than 0.01). The response of plasma insulin did not differ significantly between the two groups (29 +/- 4 vs. 40 +/- 10 microU/ml at 90 min in control and in glucose intolerant subjects, respectively; P = NS). In both groups, glucose infusion caused the net splanchnic glucose balance to switch from the net output of the basal state to a net glucose uptake. However, this effect was more marked in subjects with impaired glucose tolerance than in control subjects (at 90 min: 2.83 +/- 0.53 vs. 1.60 +/- 0.18 mg X kg-1 X min-1, respectively: P less than 0.05). The different pattern of splanchnic glucose balance was entirely accounted for by a greater rise in splanchnic glucose uptake in the group of glucose intolerants , as the suppression of endogenous glucose output by the glucose load was practically complete in both groups. In contrast, glucose uptake by peripheral tissues increased considerably less in subjects with impaired glucose tolerance than in controls (2.2-2.6 vs 3.6-4.1 mg X kg-1 X min-1, respectively, between 60 and 90 min; P less than 0.01-0.001). Furthermore, a net splanchnic lactate uptake was present in the basal state, which was inhibited by the glucose load and switched to a comparable net lactate output in both groups. These results indicate that the mechanism responsible for the altered glucoregulation in subjects with impaired glucose tolerance resides entirely in the peripheral tissues whose ability to dispose of a glucose load is drastically reduced. On the other hand, no defect is detectable in any of the explored mechanisms regulating splanchnic glucose metabolism during the disposal of an exogenous glucose load.     

Insulin resistance and vasodilation in essential hypertension. Studies with adenosine.

Insulin-mediated vasodilation has been proposed as a determinant of in vivo insulin sensitivity. We tested whether sustained vasodilation with adenosine could overcome the muscle insulin resistance present in mildly overweight patients with essential hypertension. Using the forearm technique, we measured the response to a 40-min local intraarterial infusion of adenosine given under fasting conditions (n = 6) or superimposed on a euglycemic insulin clamp (n = 8). In the fasting state, adenosine-induced vasodilation (forearm blood flow from 2.6 +/- 0.6 to 6.0 +/- 1.2 ml min-1dl-1, P < 0.001) was associated with a 45% rise in muscle oxygen consumption (5.9 +/- 1.0 vs 8.6 +/- 1.7 mumol min-1dl-1, P < 0.05), and a doubling of forearm glucose uptake (0.47 +/- 0.15 to 1.01 +/- 0.28 mumol min-1dl-1, P < 0.05). The latter effect remained significant also when expressed as a ratio to concomitant oxygen balance (0.08 +/- 0.03 vs 0.13 +/- 0.04 mumol mumol-1, P < 0.05), whereas for all other metabolites (lactate, pyruvate, FFA, glycerol, citrate, and beta-hydroxybutyrate) this ratio remained unchanged. During euglycemic hyperinsulinemia, whole-body glucose disposal was stimulated (to 19 +/- 3 mumol min-1kg-1), but forearm blood flow did not increase significantly above baseline (2.9 +/- 0.2 vs 3.1 +/- 0.2 ml min-1dl-1, P = NS). Forearm oxygen balance increased (by 30%, P < 0.05) and forearm glucose uptake rose fourfold (from 0.5 to 2.3 mumol min-1dl-1, P < 0.05). Superimposing an adenosine infusion into one forearm resulted in a 100% increase in blood flow (from 2.9 +/- 0.2 to 6.1 +/- 0.9 ml min-1dl-1, P < 0.001); there was, however, no further stimulation of oxygen or glucose uptake compared with the control forearm. During the clamp, the ratio of glucose to oxygen uptake was similar in the control and in the infused forearms (0.27 +/- 0.11 and 0.23 +/- 0.09, respectively), and was not altered by adenosine (0.31 +/- 0.9 and 0.29 +/- 0.10). We conclude that in insulin-re15-76sistant patients with hypertension, adenosine-induced vasodilation recruits oxidative muscle tissues and exerts a modest, direct metabolic effect to promote muscle glucose uptake in the fasting state. Despite these effects, however, adenosine does not overcome muscle insulin resistance.     

The independent effect of ketone bodies on forearm glucose metabolism in normal man.

Ketone bodies and non-esterified fatty acids (NEFA) inhibit insulin stimulated glucose uptake in muscle in-vitro. In man the infusion of ketone bodies lowers plasma NEFA levels thus confounding the interpretation of individual effects. The aim of this study was to examine the effect of ketone bodies on insulin mediated forearm glucose metabolism independent of the changes in the plasma NEFA levels. Seven healthy men received sodium 3-hydroxybutyrate (15 mumol kg-1 min-1) or sodium bicarbonate (control) for 240 min. Heparin (0.2 U kg-1 min-1) and insulin (0.01 U kg-1 h-1) were infused for 90 min (pre-clamp), followed by insulin alone (0.025 U kg-1 h-1) and euglycaemia was maintained (clamp). Plasma NEFA levels and rates of forearm NEFA uptake (+23 +/- 14 and +49 +/- 21 [mean +/- SEM] nmol 100 ml forearm [FA]-1 min-1) were comparable during the pre-clamp periods, and were suppressed equally during hyperinsulinaemia. Sodium 3-hydroxybutyrate infusion raised the blood ketone body levels from 70 +/- 4 mumol/l to a plateau of 450 +/- 30 mumol/l, while control levels declined from baseline (ketone body vs control; P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the time courses of insulin and the portal signal on hepatic glucose and glycogen metabolism in the conscious dog.

To investigate the temporal response of the liver to insulin and portal glucose delivery, somatostatin was infused into four groups of 42-h-fasted, conscious dogs (n = 6/group), basal insulin and glucagon were replaced intraportally, and hyperglycemia was created via a peripheral glucose infusion for 90 min (period 1). This was followed by a 240-min experimental period (period 2) in which hyperglycemia was matched to period 1 and either no changes were made (CON), a fourfold rise in insulin was created (INS), a portion of the glucose (22.4 mumol.kg-1.min-1) was infused via the portal vein (Po), or a fourfold rise in insulin was created in combination with portal glucose infusion (INSPo). Arterial insulin levels were similar in all groups during period 1 (approximately 45 pM) and were 45 +/- 9, 154 +/- 20, 43 +/- 7, and 128 +/- 14 pM during period 2 in CON, INS, Po, and INSPo, respectively. The hepatic glucose load was similar between periods and among groups (approximately 278 mumol.kg-1.min-1). Net hepatic glucose output was similar among groups during period 1 (approximately 0.1 mumol.kg-1.min-1) and did not change significantly in CON during period 2. In INS net hepatic glucose uptake (NHGU; mumol.kg-1.min-1) was -3.8 +/- 3.3 at 15 min of period 2 and did not reach a maximum (-15.9 +/- 6.6) until 90 min. In contrast, NHGU reached a maximum of -13.0 +/- 3.7 in Po after only 15 min of period 2. In INSPo, NHGU reached a maximum (-23.6 +/- 3.5) at 60 min. Liver glycogen accumulation during period 2 was 21 +/- 10, 84 +/- 17, 65 +/- 16, and 134 +/- 17 mumol/gram in CON, INS, Po, and INSPo, respectively. The increment (period 1 to period 2) in the active form of liver glycogen synthase was 0.7 +/- 0.4, 6.5 +/- 1.2, 2.8 +/- 1.0, and 8.5 +/- 1.3% in CON, INS, Po, and INSPo, respectively. Thus, in contrast to insulin, the portal signal rapidly activates NHGU. In addition, the portal signal independent of a rise in insulin, can cause glycogen accumulation in the liver.     

Effect of alpha-ketoglutarate infusions on organ balances of glutamine and glutamate in anaesthetized dogs in the catabolic state.

1. The salt complex of L-(+)-ornithine and alpha-ketoglutarate (2-oxoglutarate) has recently been proposed for the treatment of patients in the catabolic state. As yet, it is unclear which of the two substrates (ornithine or alpha-ketoglutarate) is responsible for the anticatabolic effect. We infused alpha-ketoglutarate into anaesthetized post-operative dogs in order to investigate whether infusion of alpha-ketoglutarate affects the flux of glutamine and glutamate between skeletal muscle and the splanchnic bed. We used three infusion rates: 3, 10 and 20 mumol min-1 kg-1. A steady state of alpha-ketoglutarate concentration in arterial whole-blood was attained only when the infusion rate was 3 mumol min-1 kg-1. 2. Arterial whole-blood concentrations of alpha-ketoglutarate were 8.8 +/- 1.2 mumol/l in the basal period and rose to 208 +/- 41, 344 +/- 61 and 1418 +/- 315 mumol/l after 60 min infusions of alpha-ketoglutarate at 3, 10 and 20 mumol min-1 kg-1, respectively. 3. alpha-Ketoglutarate uptake was measured in skeletal muscle, liver, gut and kidneys in the basal period and during the infusion of alpha-ketoglutarate. The net uptake of infused alpha-ketoglutarate was highest in the skeletal muscle, followed by kidneys, liver and gut. 4. The alpha-ketoglutarate load increased the muscular tissue content of alpha-ketoglutarate from 49.5 +/- 5 to 142 +/- 15 nmol/g of dry substance (P less than 0.001), but did not alter the muscular glutamate or glutamine contents.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanism of increased gluconeogenesis in noninsulin-dependent diabetes mellitus. Role of alterations in systemic, hepatic, and muscle lactate and alanine metabolism.

To assess the mechanisms responsible for increased gluconeogenesis in noninsulin-dependent diabetes mellitus (NIDDM), we infused [3-14C]lactate, [3-13C]alanine, and [6-3H]glucose in 10 postabsorptive NIDDM subjects and in 9 age- and weight-matched nondiabetic volunteers and measured systemic appearance of alanine and lactate, their release from forearm tissues, and their conversion into plasma glucose (corrected for Krebs cycle carbon exchange). Systemic appearance of lactate and alanine were both significantly greater in diabetic subjects (18.2 +/- 0.9 and 5.8 +/- 0.4 mumol/kg/min, respectively) than in the nondiabetic volunteers (12.6 +/- 0.7 and 4.2 +/- 0.3 mumol/kg/min, respectively, P less than 0.001 and P less than 0.01). Conversions of lactate and alanine to glucose were also both significantly greater in NIDDM subjects (8.6 +/- 0.5 and 2.4 +/- 0.1 mumole/kg/min, respectively) than in nondiabetic volunteers (4.2 +/- 0.4 and 1.8 +/- 0.1 mumol/kg/min, respectively, P less than 0.001 and P less than 0.025). The proportion of systemic alanine appearance converted to glucose was not increased in NIDDM subjects (42.7 +/- 1.9 vs. 44.2 +/- 2.9% in nondiabetic volunteers), whereas the proportion of systemic lactate appearance converted to glucose was increased in NIDDM subjects (48.3 +/- 3.8 vs. 34.2 +/- 3.8% in nondiabetic volunteers, P less than 0.025); the latter increased hepatic efficiency accounted for approximately 40% of the increased lactate conversion to glucose. Neither forearm nor total body muscle lactate and alanine release was significantly different in NIDDM and nondiabetic volunteers. Therefore, we conclude that increased substrate delivery to the liver and increased efficiency of intrahepatic substrate conversion to glucose are both important factors for the increased gluconeogenesis of NIDDM and that tissues other than muscle are responsible for the increased delivery of gluconeogenic precursors to the liver.     

Alanine and glutamine release from the human forearm: effects of glucose administration

The effect of glucose infusion alone (175 mg/kg bolus dose followed by 4 mg min-1 kg-1 for 70 min) and in combination with forearm exercise on the exchange of glucose, alanine, glutamine and other metabolites and amino acids across forearm muscle was studied in six healthy individuals after an overnight fast. Arterial and deep venous blood was sampled and a mercury strain gauge plethysmograph was used to measure forearm blood flow. Total body energy expenditure and net glucose and fat oxidation were assessed by indirect calorimetry. The infusion of glucose increased the mean arterial blood glucose concentration from 4.95 +/- 0.19 (SEM) to a plateau of 9.6-9.9 mmol/l (P less than 0.01). The arterial blood concentrations of alanine and glutamine were not significantly altered but that of lactate increased from 0.50 +/- 0.02 to 0.65 +/- 0.05 mmol/l (P less than 0.02) and that of pyruvate increased from 46 +/- 5 to 72 +/- 6 mumol/l (P less than 0.01). In the resting state glucose administration did not significantly affect the lactate/pyruvate ratio in arterial or venous blood. Arterial plasma insulin concentration increased four-fold and total ketone body concentration decreased two- to three-fold. After glucose administration, alanine release was suppressed (in all subjects) from a mean value of 153 +/- 22 to 57 +/- 16 nmol min-1 100 ml-1 of forearm (P less than 0.02) whereas that of glutamine was not significantly affected (160 +/- 30 to 143 +/- 29 nmol min-1 100 ml-1 of forearm). Lactate release, like that of alanine, decreased, whereas pyruvate was slowly released in the basal state and was taken up during glucose administration (P less than 0.01). These changes were associated with a decrease in the uptake of total ketone bodies to one-fifth to one-tenth of that in the basal state. The net amino acid balance across the forearm muscle bed was negative throughout the study but decreased from a mean value of -567 in the basal state to -300 nmol min-1 100 ml-1 of forearm after glucose administration for 60 min. This was predominantly due to decreased release of effluxing amino acids, particularly alanine.(ABSTRACT TRUNCATED AT 400 WORDS)     

Simultaneous measurements of lactate turnover rate and umbilical lactate uptake in the fetal lamb.

Lactic acid represents a major exogenous nutrient for the developing fetal lamb in utero. Our study was undertaken (a) to quantitate the net consumption of lactate by the fetus, (b) to quantitate the net lactate production and metabolism by the placenta, and (c) to compare the net fetal lactate consumption with fetal lactate use, measured simultaneously with radioactive tracers. 14 pregnant sheep were prepared with catheters in the maternal femoral artery and uterine vein and in the fetal aorta and umbilical vein. By simultaneous application of the Fick principle to the uterine and umbilical circulations, placental glucose consumption and placental lactate production were rapid, averaging 39.8 +/- 5.1 and 11.8 +/- 0.7 mg.min-1. Net lactate umbilical uptake averaged 1.95 +/- 0.16 mg-1.kg.min-1. During infusion of L-[14C(U)]lactate, fetal lactate turnover was much more rapid, averaging 6.5 +/- 0.8 mg.kg-1.min-1, and lactate utilization within the anatomic fetus was 5.9 +/- 0.7 mg.kg-1.min-1. During infusion of tracer glucose, endogenous fetal lactate production from glucose and nonglucose substrates averaged 3.0 and 1.5 mg.kg-1.min-1, respectively. The present studies have quantitated under well oxygenated, steady-state conditions, the rapid placental metabolism and production of lactate, the net fetal consumption of lactate, and the rapid endogenous fetal lactate production from glucose and nonglucose substrates.     

Kidney, splanchnic, and leg protein turnover in humans. Insight from leucine and phenylalanine kinetics.

The rate of kidney protein turnover in humans is not known. To this aim, we have measured kidney protein synthesis and degradation in postabsorptive humans using the arterio-venous catheterization technique combined with 14C-leucine, 15N-leucine, and 3H-phenylalanine tracer infusions. These measurements were compared with those obtained across the splanchnic bed, the legs (approximately muscle) and in the whole body. In the kidneys, protein balance was negative, as the rate of leucine release from protein degradation (16.8 +/- 5.1 mumol/min.1.73 m2) was greater (P < 0.02) than its uptake into protein synthesis (11.6 +/- 5.1 mumol/min. 1.73 m2). Splanchnic net protein balance was approximately 0 since leucine from protein degradation (32.1 +/- 9.9 mumol/min. 1.73 m2) and leucine into protein synthesis (30.8 +/- 11.5 mumol/min. 1.73 m2) were not different. In the legs, degradation exceeded synthesis (27.4 +/- 6.6 vs. 20.3 +/- 6.5 mumol/min. 1.73 m2, P < 0.02). The kidneys extracted alpha-ketoisocaproic acid, accounting for approximately 70% of net splanchnic alpha-ketoisocaproic acid release. The contributions by the kidneys to whole-body leucine rate of appearance, utilization for protein synthesis, and oxidation were approximately 11%, approximately 10%, and approximately 26%, respectively; those by the splanchnic area approximately 22%, approximately 27%, and approximately 18%; those from estimated total skeletal muscle approximately 37%, approximately 34%, and approximately 48%. Estimated fractional protein synthetic rates were approximately 42%/d in the kidneys, approximately 12% in the splanchnic area, and approximately 1.5% in muscle. This study reports the first estimates of kidney protein synthesis and degradation in humans, also in comparison with those measured in the splanchnic area, the legs, and the whole-body.     

Insulin sensitivity and secretion in healthy elderly human subjects with ''abnormal'' glucose tolerance

Glucose tolerance deteriorates dramatically with advancing age. It is not known whether the underlying pathophysiology is different in older subjects. We employed a two step hyperinsulinaemic euglycaemic glucose clamp with [6(14)C] glucose infusion to compare peripheral and hepatic insulin sensitivity in eight elderly (EAGT) with eight young (YAGT) subjects with abnormal (matched) glucose tolerance and nine elderly subjects with normal glucose tolerance (ENGT). There was no difference in basal HGO (EAGT 14.5 +/- 0.9, YAGT 15.3 +/- 1.1 mumol kg-1 min-1). Glucose turnover was similar in both groups at step 1 (EAGT 13.2 +/- 0.8, YAGT 13.4 +/- 0.8 mumol kg-1 min-1) and step 2 (EAGT 25.1 +/- 3.1, YAGT 27.2 +/- 2.7 mumol kg-1 min-1). HGO was lower in the EAGT subjects at step 1 (2.3 +/- 0.4 vs. 4.3 +/- 0.6 mumol kg-1 min-1 P = 0.01). Incremental serum insulin response to oral glucose was comparable (EAGT 66.8 +/- 11.6 YAGT 57.8 +/- 12.2 mU l-1.h). Compared to the ENGT group the EAGT group was insulin resistant with a lower MCR of glucose at step 1 (2.03 +/- 0.28 vs. 3.23 +/- 0.44 ml kg-1 min-1 P = 0.04) and at step 2 (6.18 +/- 0.83 vs. 9.64 +/- 0.38 ml kg-1 min-1 P = 0.004) and had a lower early insulin response (AUC 0-30 min 5.9 +/- 1.1 vs. 9.8 +/- 1.4 mU l-1.h P = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)     

Alanylglutamine reduces muscle loss of alanine and glutamine in post-operative anaesthetized dogs

1. The present study examined the effect of an infusion of the dipeptide alanylglutamine or of the corresponding amino acids alanine and glutamine in equimolar amounts (10 mumol min-1 kg-1) on the canine hindlimb exchange of alanine and glutamine in the post-operative anaesthetized dog. In contrast to glutamine, the dipeptide alanylglutamine is stable in aqueous solution and therefore would be a suitable substrate for parenteral nutrition. 2. The infusion of alanylglutamine increased (a) the arterial concentration of alanylglutamine to a plateau level (120 +/- 9.5 mumol/l, mean +/- SEM) 20 min after start of the infusion, (b) the mean arterial alanine concentration from 761 +/- 42 to a plateau of 1500-1700 mumol/l (P greater than 0.01) and (c) the arterial glutamine concentration from 407 +/- 51 to a plateau of 1050-1500 mumol/l (P greater than 0.01). Alanine and glutamine levels were slightly higher (14% and 26%, respectively, NS) in the group receiving the equimolar amount of alanine and glutamine. 3. Infusion of alanylglutamine for 1 h abolished the net efflux of glutamine (from -0.80 +/- 0.1 to -0.03 +/- 0.2 mumol min-1 kg-1; P greater than 0.05) and invoked a net influx of alanine (from -0.50 +/- 0.19 to +0.27 +/- 0.14 mumol min-1 kg-1; P greater than 0.01). These changes were similar to those achieved when the two amino acids were infused. 4. This study demonstrates that during short-term administration of alanylglutamine or of the corresponding amino acids the nitrogen release from the hindlimb of the anaesthetized post-operative dog via alanine and glutamine is reduced.     

Incomplete suppression of hepatic glucose production in non-insulin dependent diabetes mellitus measured with [6,6-2H2]glucose enriched glucose infusion during hyperinsulinaemic euglycaemic clamps

We have minimized methodological errors in the isotope dilution technique by using stable isotope, [6,6-2H2]glucose, thus avoiding the problem of contamination of tritiated glucose tracers and, by maintaining a constant plasma tracer enrichment have reduced error due to mixing transients. Using these modifications we have calculated hepatic glucose production in 20 patients with non-insulin-dependent diabetes mellitus during low (1 mU kg-1 min-1) and high (8 mU kg-1 min-1) dose insulin infusions. Mean fasting hepatic glucose production was 14.2 +/- 0.8 mumol kg-1 min-1. This suppressed by only 68% to 4.6 +/- 0.8 mumol kg-1 min-1 during the low-dose insulin infusion (plasma insulin 0.85 +/- 0.05 nmol l-1) and did not suppress further during the high-dose insulin infusion (plasma insulin 14.55 +/- 0.83 nmol l-1). Hepatic glucose production was significantly higher than zero throughout the study. Thus, we have found that minimization of known errors in the isotope dilution technique results in physiologically plausible and significantly positive values for hepatic glucose production indicating that the liver is resistant to insulin in patients with non-insulin-dependent diabetes mellitus.     

Loss of hepatic autoregulation after carbohydrate overfeeding in normal man.

To determine the effect of increased glycogen stores on hepatic carbohydrate metabolism, 15 nondiabetic volunteers were studied before and after 4 d of progressive overfeeding. Glucose production and gluconeogenesis were assessed with [2-3H] glucose and [6-14C] glucose (Study I, n = 6) or [3-3H] glucose and [U-14C]-alanine (Study II, n = 9) and substrate oxidation was determined by indirect calorimetry. Overfeeding was associated with significant (P < 0.01) increases in plasma glucose (4.97 +/- 0.10 to 5.09 +/- 0.11 mmol/liter), insulin (18.8 +/- 1.5 to 46.6 +/- 10.0 pmol/liter) and carbohydrate oxidation (4.7 +/- 1.4 to 18.0 +/- 1.5 mumol.kg-1.min-1) and a decrease in lipid oxidation (1.2 +/- 0.2 to 0.3 +/- 0.1 mumol.kg-1.min-1). Hepatic glucose output (HGO) increased in Study I (10.2 +/- 0.5 to 13.1 +/- 0.9 mumol.kg-1.min-1, P < 0.01) and Study II (11.17 +/- 0.67 to 13.33 +/- 0.83 mumol.kg-1.min-1, P < 0.01), and gluconeogenesis decreased (57.6 +/- 6.4 to 33.4 +/- 4.9 mumol/min, P < 0.01), indicating an increase in glycogenolysis. The increase in glycogenolysis was only partly compensated by an increase in glucose cycle activity (2.2 +/- 0.2 to 3.4 +/- 0.4 mumol.kg-1.min-1, P < 0.01) and the fall in gluconeogenesis, thus resulting in increased HGO. The suppression of gluconeogenesis despite increased lactate and alanine (glycerol was decreased) was associated with decreased free fatty acid (FFA) oxidation and negligible FFA enhanced gluconeogenesis. These studies suggest that increased liver glycogen stores alone can overwhelm normal intrahepatic mechanisms regulating carbohydrate metabolism resulting in increased HGO in nondiabetic man.     

Insulin resistance in uremia.

Tissue sensitivity to insulin was examined with the euglycemic insulin clamp technique in 17 chronically uremic and 36 control subjects. The plasma insulin concentration was raised by approximately 100 microU/ml and the plasma glucose concentration was maintained at the basal level with a variable glucose infusion. Under these steady-state conditions of euglycemia, the glucose infusion rate is a measure of the amount of glucose taken up by the entire body. In uremic subjects insulin-mediated glucose metabolism was reduced by 47% compared with controls (3.71 +/- 0.20 vs. 7.38 +/- 0.26 mg/kg . min; P less than 0.001). Basal hepatic glucose production (measured with [3H]-3-glucose) was normal in uremic subjects (2.17 +/- 0.04 mg/kg . min) and suppressed normally by 94 +/- 2% following insulin administration. In six uremic and six control subjects, net splanchnic glucose balance was also measured directly by the hepatic venous catheterization technique. In the postabsorptive state splanchnic glucose production was similar in uremics (1.57 +/- 0.03 mg/kg . min) and controls (1.79 +/- 0.20 mg/kg . min). After 90 min of sustained hyperinsulinemia, splanchnic glucose balance reverted to a net uptake which was similar in uremics (0.42 +/- 0.11 mg/kg . min) and controls (0.53 +/- 0.12 mg/kg . min). In contrast, glucose uptake by the leg was reduced by 60% in the uremic group (21 +/- 1 vs. 52 +/- 8 mumol/min . kg of leg wt; P less than 0.005) and this decrease closely paralleled the decrease in total glucose metabolism by the entire body. These results indicate that: (a) suppression of hepatic glucose production by physiologic hyperinsulinemia is not impaired by uremia, (b) insulin-mediated glucose uptake by the liver is normal in uremic subjects, and (c) tissue insensitivity to insulin is the primary cause of insulin resistance in uremia.     

Influence of body fat distribution on free fatty acid metabolism in obesity.

In order to determine whether differences in body fat distribution result in specific abnormalities of free fatty acid (FFA) metabolism, palmitate turnover, a measure of systemic adipose tissue lipolysis, was measured in 10 women with upper body obesity, 9 women with lower body obesity, and 8 nonobese women under overnight postabsorptive (basal), epinephrine stimulated and insulin suppressed conditions. Results: Upper body obese women had greater (P less than 0.005) basal palmitate turnover than lower body obese or nonobese women (2.8 +/- 0.2 vs. 2.1 +/- 0.2 vs. 1.8 +/- 0.2 mumol.kg lean body mass (LBM)-1.min-1, respectively), but a reduced (P less than 0.05) net lipolytic response to epinephrine (59 +/- 7 vs. 79 +/- 5 vs. 81 +/- 7 mumol palmitate/kg LBM, respectively). Both types of obesity were associated with impaired suppression of FFA turnover in response to euglycemic hyperinsulinemia compared to nonobese women (P less than 0.005). These specific differences in FFA metabolism may reflect adipocyte heterogeneity, which may in turn affect the metabolic aberrations associated with different types of obesity. These findings emphasize the need to characterize obese subjects before studies.