A B S T R A C T 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 -100 ,uU/ 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 < 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 ,umol/min kg of leg wt; P < 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) insulinmediated 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.

We investigated the effects of hyperinsulinemia and hyperglycemia on peripheral glucose uptake, hepatic glucose production, and splanchnic glucose uptake in man. Euglycemic and hyperglycemic clamp studies were carried out in 37 healthy subjects in combination with hepatic vein catheterization and [3H-3]glgcose infusion. In the basal state, hepatic glucose production ([3H-3]glucose) exceeded net splanchnic glucose output (catheter) in every subject (2.3 ± 0.04 versus 1.7 ± 0.07 mg/min · kg, P &lt; 0.001), indicating uptake of glucose by the splanchnic region at a rate of 0.6 ± 0.05 mg/ min · kg. In agreement with this estimate, [3H-3]glucose concentration was consistently lower in hepatic venous than in arterial blood, by 3.0 ± 0.2% (P &lt; 0.001). When plasma insulin levels were raised to 37 ± 2, 53 ± 2, 101 ± 2, 428 ± 37, and 1189 ± 14 μU/ml, with maintenance of euglycemia, total glucose uptake rose to 2.9 ± 0.4, 3.9 ± 1.0, 5.1 ± 0.4, 9.9 ±1.1, and 11.8 ± 1.3 mg/min · kg, respectively. The whole body glucose clearance rose significantly above baseline at each hyperinsulinemic plateau (P &lt; 0.05 or less). Hepatic glucose production fell by 68% (P &lt; 0.01) at the lowest hyperinsulinemic level, by 87% at insulin levels of 53 ± 2 μU/ml, and by over 95% with each higher insulin dose. Splanchnic glucose uptake was not significantly increased over basal values at any insulin concentration. When plasma glucose levels were raised to 137 ± 3 and 224 ± 2 mg/dl peripheral plasma insulin levels rose to 20 ± 4 and 55 ± 5 μU/ml, respectively. Total glucose uptake was enhanced (2.5 ± 0.4 and 5.3 ± 1.0 mg/min · kg, P &lt; 0.05 and P &lt; 0.01, respectively). Suppression of hepatic glucose production was &lt;90% at the lower hyperglycemic level, and virtually complete at the higher one. Splanchnic glucose uptake was not changed by mild hyperglycemia (0.5 ± 0.05 mg/min · kg), but rose significantly (1.3 ± 0.3 mg/ min · kg, P &lt; 0.01) with further hyperglycemia. The latter effect resulted primarily from increased glucose delivery to the splanchnic area, since the splanchnic glucose extraction ratio (4.0 ± 0.3%) was not different from baseline (3.0 ± 0.3%). When hyperglycemia (224 ± 1 mg/dl) was combined with a somatostatin infusion, thereby reducing plasma insulin from 15 ± 3 to 10 ± 1 μU/ml (P &lt; 0.01), both total glucose uptake (2.8 ± 0.03 mg/min · kg) and clearance (1.3 ± 0.01 mg/min · kg) were significantly (P &lt; 0.01) lower than in the hyperglycemic studies in which insulin secretion was not blocked. Hepatic glucose production, however, was effectively suppressed (by 74%, P &lt; 0.001), whereas splanchnic glucose uptake was only slightly increased above baseline. Replacement of insulin (via an exogenous infusion at a rate of 0.3 mU/min · kg) restored total glucose uptake, splanchnic glucose uptake, and suppression of hepatic glucose production to the levels seen with hyperglycemia without somatostatin. When hyperglycemia (216 ± 2 mg/dl) was combined with somatostatin and glucagon replacement (no insulin), hepatic glucose production was still suppressed by 47 ± 1% to 1.18 ± 0.01 mg/kg · min (P &lt; 0.001 versus hyperglycemia + SRIF without glucagon replacement). The results indicate that both hyperglycemia and hypoglucagonemia contribute to the decline in hepatic glucose production following somatostatin infusion. In conclusion, hyperinsulinemia alone stimulates glucose uptake by peripheral but not splanchnic tissues. The dose-response characteristics of stimulation of peripheral glucose uptake and inhibition of hepatic glucose production by insulin are very different, the half-maxima being ∼120 and ∼50 μU/ml, respectively. Hyperglycemia enhances glucose uptake by both peripheral and splanchnic tissues, but this action requires an intact endogenous insulin response. In contrast, hyperglycemia can suppress endogenous glucose production even in the presence of low insulin levels.

Tissue sensitivity to insulin was examined in 36 control subjects and 19 insulin-dependent diabetics with diabetes of long-standing duration (mean = 10 ± 3 yr) employing the insulin clamp technique (A plasma insulin concentration -1 0 0 /xU/ml). Eleven of the diabetics (group I) were studied at their fasting hyperglycemic level (173 mg/dl); the remaining 8 diabetics (group II) were studied after lowering their plasma glucose concentration to euglycemic levels (90 mg/dl). Despite plasma glucose levels that were almost twice as great in the diabetics (group 1,173 versus 91 mg/dl, P < 0.001), insulin-mediated glucose metabolism, 4.77 ± 0.18 mg/kg min, was reduced by 32% versus controls, 7.03 ± 0.22 mg/kg min (P < 0.01). When the control subjects were restudied at plasma glucose levels (166 ± 2 mg/dl) that were comparable to those of the diabetics, insulin-mediated glucose metabolism was 12.14 ± 0.96 mg/kg min (P < 0.01). In diabetics studied at euglycemic levels (group II) insulin-mediated glucose metabolism, 3.39 ± 0.30 mg/kg min, was reduced even further. The metabolic clearance rate in the 19 diabetics, 3.31 ± 0.23 mg/kg min, was reduced by 58% compared with controls, 7.83 ± 0.25 (P < 0.001). These results emphasize the severe degree of insulin resistance that exists in the insulin-dependent diabetics.Basal hepatic glucose production in the diabetic group, 2.96 ± 0.24 mg/kg min, was 26% greater than in the controls, 2.35 ± 0.04 (P < 0.001). The fasting plasma glucose concentration displayed a strong positive correlation (r = 0.857, P < 0.001) with basal hepatic glucose production and was weakly and inversely correlated (r = -0.413, P = 0.07) with the basal glucose clearance. Following hyperinsulinemia, however, suppression of hepatic glucose production was -9 5 % in both diabetics and controls, suggesting that peripheral tissues are primarily responsible for the observed impairment in insulin-mediated glucose uptake.The present results indicate that impaired insulin action is a common feature of insulin-dependent diabetics, despite daily insulin requirements (35 ± 2 U/day) that would not clinically characterize them as being insulin resistant. DIABETES 37:795-801, September 1982.

A B S T R A C T Arterial concentrations and substrate exchange across the leg and splanchnic vascular beds were determined for glucose, lactate, pyruvate, glycerol, individual acidic and neutral amino acids, and free fatty acids (FFA) in six subjects at rest and during 4 h of exercise at approximately 30% of maximal oxygen uptake. FFA turnover and regional exchange were evaluated using "C-labeled oleic acid.The arterial glucose concentration was constant for the first 40 min of exercise, but fell progressively thereafter to levels 30% below basal. The arterial insulin level decreased continuously, while the arterial glucagon concentration had risen fivefold after 4 h of exercise. Uptake of glucose and FFA by the legs was markedly augmented during exercise, the increase in FFA uptake being a consequence of augmented arterial levels rather than increased fractional extraction. As exercise was continued beyond 40 min, the relative contribution of FFA to total oxygen metabolism rose progressively to 62%. In contrast, the contribution from glucose fell from 40% to 30% between 90 and 240 min. Leg output of alanine increased as exercise progressed.Splanchnic glucose production, which rose 100% above basal levels and remained so throughout exercise,

The effects of hyperinsulinemia, hyperglycemia, and the route of glucose administration on total glucose utilization and on net splanchnic glucose exchange were studied in 20 normal volunteers with the hepatic venous catheter technique. Euglycemic hyperinsulinemia [induced by a priming plus continuous infusion of insulin resulting in plasma insulin levels of ,units (international)/ml and a variable glucose infusion] caused a 5-to 6-fold increase above basal in total glucose turnover. However, net splanchnic glucose uptake (0.5 ± 0.2 mg/kg per min) accounted for only 4-5% of total glucose utilization. When hyperglycemia (223 + .1 mg/dl) was induced in addition to hyperinsulinemia by the intravenous infusion of glucose, splanchnic glucose uptake increased 100% to 1.0-1.1 mg/kg per min but was still responsible for only 10-14% of total glucose utilization. In other studies hyperglycemia (223 + 2 mg/dl) was maintained constant by a variable intravenous infusion of glucose for 4 hr and oral glucose (1.2 gm/kg) was administered at 1 hr. After the oral glucose, net splanchnic glucose uptake increased to values 6-fold higher than with intravenous glucose despite unchanged plasma glucose levels and plasma insulin concentrations well below those observed in the studies with euglycemic hyperinsulinemia. The results indicate that hyperinsulinemia or hyperglycemia induced by intravenous infusion of glucose or insulin causes minimal net uptake of glucose by the splanchnic bed despite marked stimulation of total glucose turnover. In contrast, administration of glucose by the oral route has a marked stimulatory effect on net splanchnic glucose uptake. These findings suggest that orally consumed glucose causes the release of a gastrointestinal factor that enhances insulin-mediated glucose uptake by the liver.The liver has long been recognized to play a central role in blood glucose homeostasis (1)(2)(3)(4). However, the factors that regulate hepatic glucose uptake still remain controversial. The pioneering studies of Soskin and Levine (5) suggested that hyperglycemia per se was responsible for the switch of the liver from a glucose-producing to a glucose-assimilating organ. However, subsequent in vivo studies by Madison (3) and Felig and Wahren (2, 4) indicated that this switch is dependent upon the presence of hyperinsulinemia. More recently Bergman (6) has reemphasized the importance of hyperglycemia in the regulation of hepatic glucose uptake and has suggested that concommitant hyperinsulinemia enhances its effect. What role, if any, the route of glucose administration (i.e., oral versus intravenous) has in determining hepatic glucose uptake has not been established. The present study was consequently undertaken to evaluate the relative effects of hyperglycemia, hyperinsulinemia, and the route of glucose administration on net splanchnic glucose uptake. Euglycemic Hyperinsulinemia. The effect on splanchnic glucose balance of hyperinsulinemia at a basal plasma glucose concentration was determined by the "insulin cla...

A B S T R A C T Insulin binding to monocytes and insulin action in vivo was examined in 14 obese subjects during the postabsorptive state and after starvation and refeeding. Tissue sensitivity to insulin was evaluated with the euglycemic insulin clamp technique. The plasma insulin concentration is acutely raised and maintained 100 ,uU/ml above the fasting level, and plasma glucose is held constant by a variable glucose infusion. The amount of glucose infused is a measure of tissue sensitivity to insulin and averaged 285+15 mg/m2 per min in controls compared to 136±13 mg/ m2 per min in obese subjects (P < 0.001). 1251-Insulin binding to monocytes averaged 8.3±0.4% in controls vs. 4.6±0.5% in obese subjects (P < 0.001). Insulin binding and insulin action were highly correlated in both control (r = 0.86, P < 0.001) and obese (r = 0.94, P < 0.001) groups. Studies employing tritiated glucose to measure glucose production indicated hepatic as well as extrahepatic resistance to insulin in obesity.After 3 and 14 days of starvation, insulin sensitivity in obese subjects decreased to 69±4 and 71±7 mg/M2 per min, respectively, whereas 125I-insulin binding increased to 8.8±0.7 and 9.0±0.4%. In contrast to the basal state, there was no correlation between insulin binding and insulin action. After refeeding, tissue sensitivity increased to 168±14 mg/M2 per min (P < 0.001) whereas insulin binding fell to 5.0±0.3%.We conclude that (a) in the postabsorptive state insulin binding to monocytes provides an index of in vivo insulin action in nonobese and obese subjects and, (b) during starvation and refeeding, insulin binding and insulin action changes in opposite directions sugDr. Soman is the recipient of a Research and Development

A B S T R A C T To evaluate the role of hyperketonemia in the hypoalaninemia and decreased protein catabolism of prolonged starvation, Na DL-P-hydroxybutyrate was administered as a primed continuous 3-6-h infusion in nonobese subjects and in obese subjects in the postabsorptive state and after 3 days and 3-51 wk of starvation. An additional obese group received 12-h ketone infusions on 2 consecutive days after 5-10 wk of fasting.The ketone infusion in nonobese and obese subjects studied in the postabsorptive state resulted in total blood ketone acid levels of 1.1-1.2 mM, a 5-15 mg/100 ml decrease in plasma glucose, and unchanged levels of insulin, glucagon, lactate, and pyruvate. Plasma alanine fell by 21% (P <0.001) in 3 h. In contrast, other amino acids were stable or varied by less than 10%. Infusions lasting 6 h reduced plasma alanine by 37%, reaching levels comparable to those observed in prolonged starvation. Equimolar infusions of NaCl and/or administration of NaHCOs failed to alter plasma alanine levels.During prolonged fasting, plasma alanine, which had fallen by 40% below prefast levels, fell an additional 30% in response to the ketone infusion. In association with repeated prolonged (12 h) infusions in subjects fasted 5-10 wk, urinary nitrogen excretion fell by 30%, returning to base line after cessation of the infusions and paralleling the changes in plasma alanine. Ketone infusions resulted in two-to fourfold greater increments in blood ketone acids in fasted as compared to postabsorptive subjects.It is concluded that increased blood ketone acid levels induced by infusions of Na DL-P-hydroxybutyrate result in hypoalaninemia and in nitrogen conservation in starvation. These data suggest that hyperketonemia may be a contributory factor in the decreased availability of circulating alanine and reduction in protein catabolism characteristic of prolonged fasting. INTRODUCTIONIn fasting man survival is dependent upon the conservation of body protein stores as well as the continuous supply of energy-yielding fuels for brain metabolism (1). The need for gluconeogenesis and concomitantly the rate of protein breakdown progressively decline in prolonged starvation as ketone acids replace glucose as the major fuel consumed by the brain (2). The diminution in hepatic gluconeogenesis in prolonged fasting is mediated by a reduction in circulating glucogenic amino acids, particularly alanine, and a decrease in the outflow of these amino acids from muscle (3, 4). After a prolonged fast, plasma alanine decreases to a greater extent than that of all other amino acids, while splanchnic uptake and peripheral release of alanine are reduced to less than 50% of postabsorptive levels (3, 4).

A B S T R A C T Arterial concentrations and splanchnic exchange of glucose, lactate, pyruvate, glycerol, free fatty acids, and individual acidic and neutral amino acids were determined in obese and nonobese control subjects in the basal state and during a 45 min infusion of glucose. Glucose was administered to the controls at a rate (2 mg/kg/min; 144±4 mg/min) known to inhihit splanchnic glucose output without influencing peripheral glucose utilization. The obese subjects received glucose at two dose levels (75 and 150 mg/min) which simulated either the rise in insulin or the inhibition in splanchnic glucose production observed in the controls.In the basal state splanchnic glucose production did not differ significantly between obese and control subjects. However splanchnic uptake of lactate, glycerol, alanine, free fatty acids, and oxygen was 50-160% greater in obese subjects. Splanchnic uptake of glucose precursors could account for 33% of hepatic glucose output in the obese group as compared to 19% in controls. The increase in alanine and lactate uptake was due in part, to a 50% increase in splanchnic fractional extraction.Administration of glucose to the control subjects 144±4 mg/min) resulted in a 50-60% increment in arterial insulin and a 75% reduction in splanchnic glucose output. In the obese group, infusion of glucose at a rate of 75 mg/min resulted in an equivalent rise in arterial insulin, but was accompanied by a less than 40% inhibition in splanchnic glucose output. Glucose infusion at a rate of 150 mg/min in the obese resulted in a 75% reduction in splanchnic glucose output which was equivalent to that observed in controls, but was accom- It is concluded that in obesity (a) despite basal hyperinsulinemia, splanchnic uptake of glucose precursors is increased, the relative contribution to total glucose release attributable to gluconeogenesis being 70% higher than in controls; (b) infusion of glucose at rates causing equivalent increases in arterial insulin induces a smaller inhibition in splanchnic glucose output than inl controls; (c) infusion of glucose at rates causing comparable inhibition in splanchnic glucose output is accompanied by a disproportionately greater increase in endogenous insulin than in controls. These data are compatible with hepatic resistance to insulin in obesity. INTRODUCTION Obesity has been characterized by a variety of abnormalities in carbohydrate and insulin metabolism. Augmented insulin secretion (1, 2), decreased responsiveness of fat and muscle tissue to insulin (3, 4), and an increased incidence of diabetes (5) have been well documented. Despite these clear indications of altered carbohydrate homeostasis, the contribution of the liver to these metabolic changes has not been established. Specifically, direct observations of glucose production and uptake of precursor substrates by the splanchnic bed have not been previously reported in obese subjects. Furthermore the effect of obesity on hepatic responsiveness to increments in endogenous insulin has not been determin...