The effect of hyperglycemia, hyperinsulinemia, and route of glucose administration on glucose oxidation and glucose storage

The separate effects of hyperinsulinemia, hyperglycemia, and the route of glucose administration on total glucose metabolism, glucose oxidation, and glucose storage were examined in 19 healthy young volunteers by employing the glucose clamp technique in combination with indirect calorimetry. Following 2 hr of euglycemic hyperinsulinemia (plasma insulin ～97μU/ml) created by intravenous insulin/glucose infusion, total glucose metabolism (6.08 ± 0.56 mg/kg. min), glucose oxidation ($\text{2.63 ± 0.26 mg}\text{0.26 mg kg · min}$), and glucose storage (3.46 ± 0.42 mg/kg · min) all increased 2 to 3-fold over basal rates. When additional hyperinsulinemia (163 ± 19 μU/ml) was created while maintaining euglycemia, total glucose metabolism (8.87 ± 0.69) and glucose storage (6.06 ± 0.51) both increased significantly (p < 0.005 and 0.02, respectively), but the rise in glucose oxidation (2.96 ± 0.17) was small and insignificant. During combined hyperglycemia (214 mg/dl) and hyperinsulinemia (217 μU/ml), total glucose metabolism (16.21 ± 0.58 mg/kg · min) and glucose storage (13.05 ± 0.57 mg/kg · min) both increased significantly (p < 0.001) compared to the euglycemic hyperinsulinemic conditions but glucose oxidation (3.04 ± 0.16 mg/kg · min) failed to increase further. These results indicate that the body's ability to oxidize glucose becomes saturated within the physiologic range of plasma insulin and glucose concentrations. With further increases in plasma glucose and insulin levels, the increase in glucose metabolism is primarily accounted for by an increase in glucose storage. The route of glucose administration, oral versus intravenous, had no effect on glucose oxidation. Under conditions of prolonged (6 hrs) euglycemic hyperinsulinemia, glucose oxidation was not significantly different whether the glucose was given intravenously (3.14 ± 0.11 mg/kg · min) or orally (3.63 ± 0.17). Similarly, under comparable conditios of hyperglycemic hyperinsulinemia, glucose oxidation was not different in subjects receiving intravenous (3.60 ± 0.28 mg/kg · min) and oral (4.03 ± 0.13) glucose. However, under conditions of hyperglycemic hyperinsulinemia both total body glucose metabolism (22.91 ± 0.42 versus 19.66 ± 1.10 mg/kg · min, p < 0.02) and glucose storage (18.76 ± 0.47 versus 15.95 ± 1.17, p < 0.02) were significantly greater during oral versus intravenous glucose. The site of the increased glucose storage observed with oral glucose could not be located since hepatic and femoral venous catheterization was not performed.     

Stimulatory effect of increased non-esterified fatty acid concentrations on proinsulin processing in healthy humans

Aims/hypothesis. To assess the effect of increased concentrations of non-esterified fatty acids (NEFA) on proinsulin processing in healthy humans.¶Methods. We did a hyperglycaemic clamp (130 min duration, 8 mmol/l glucose, with a 5-g arginine bolus at min 120) before and after a 5-h infusion of Intralipid/heparin in 14 healthy subjects. Of the subjects eight underwent a saline control experiment. The proinsulin : insulin (PI:I) ratio immediately after the arginine bolus (122.5 to 125 min) was considered to provide an estimate for the conversion of proinsulin to insulin in the beta cell.¶Results. Concentrations of NEFA were 757 ± 86 μmol/l and 1669 ± 134 μmol/l (p < 0.001) after the 5-h infusion of saline or Intralipid, respectively. Insulin secretion rates were no different between the Intralipid and saline infusions (p = 0.73). There was no statistically significant difference for either the proinsulin concentration or the PI:I ratio during glucose stimulation alone (0 to 120 min). In response to arginine, in contrast, proinsulin remained unchanged during the saline infusion (from 31 ± 6 to 29 ± 7 pmol/l, p = 0.50) but decreased during 5 h of lipid infusion from (21 ± 3 to 15 ± 2 pmol/l, p = 0.02). The PI:I ratio in response to the arginine bolus was higher during the saline infusion (2.0 ± 0.2 % vs 1.7 ± 0.2 %, p = 0.04) but decreased during the Intralipid infusion (from 1.6 ± 0.2 % to 1.2 ± 0.1 %, p = 0.04).¶Conclusion/interpretation. The statistically significantly lower PI:I ratio in response to arginine during experimentally increased concentrations of NEFA suggests that NEFA increase the conversion of proinsulin to insulin in humans in vivo. [Diabetologia (2000) 43: 1368–1373]     

The role of fractional glucose extraction in the regulation of splanchnic glucose metabolism in normal and diabetic man

In order to express in equivalent terms seemingly divergent results obtained with isotopic tracer studies as compared to hepatic venous catheter studies on the role of the liver in the metabolism of oral glucose, our previously published studies using the hepatic venous catheter technique in normals and diabetics given intravenous and/or oral glucose were analyzed with respect to the splanchnic fractional extraction of glucose, total splanchnic glucose influx, and the proportion of total glucose metabolism accounted for by net splanchnic glucose uptake. In normal subjects during extreme hyperinsulinemia (plasma insulin, 500–1,200 μU/ml) induced by i.v. insulin while maintaining the blood glucose concentration at basal levels (insulin clamp), total glucose metabolism rose to 10.5 ± 0.9 mg/min · kg, while splanchnic fractional extraction of glucose was 4.2 ± 1.1%, and net splanchnic glucose uptake accounted for only 5 ± 2% of total glucose turnover. During hyperglycemic (blood glucose, 200 mg/dl) hyperinsulinemia induced by i.v. glucose, net splanchnic glucose uptake was twice that observed with euglycemic hyperinsulinemia, and the proportion of total glucose metabolism occurring in the splanchnic bed rose to 14 ± 4%. These increments were due entirely to a rise in splanchnic glucose influx since the fractional extraction (3.4 ± 0.5%) remained unchanged from that observed with euglycemic hyperinsulinemia. After oral glucose (100 g), splanchnic glucose influx was comparable to hyperglycemic hyperinsulinemia induced with i.v. glucose, but splanchnic fractional extraction rose to 13.1 ± 1.9% (p < 0.001 versus i.v. glucose), a value comparable to that observed with isotopic studies of oral glucose metabolism. Total glucose turnover was, however, 30% lower than after i.v. insulin (p < 0.01), so that net splanchnic glucose uptake accounted for 54 ± 5% of total glucose metabolism. In maturity-onset diabetics, after 100 g oral glucose splanchnic glucose influx was 69% greater than in controls (p < 0.001), but net splanchnic glucose uptake was 44% below controls (2.3 ± 0.5 versus 4.1 ± 0.5 mg/min · kg, p < 0.02). This reduction in glucose uptake could be accounted for by a splanchnic fractional extraction ratio (4.7 ± 1.4%) that was 64% lower than in controls given oral glucose (p < 0.001). It is concluded that: (1) in normal subjects, the ability of the splanchnic area to extract circulating glucose (as reflected by the splanchnic fractional extraction) is 2–3-fold greater after oral glucose than after intravenous glucose; (2) the rise in splanchnic fractional extraction to levels of 13% in association with only moderate increases in total glucose turnover fully accounts for the predominance of the splanchnic area in the metabolism of oral as compared to intravenous glucose; and (3) in maturity-onset diabetics, oral glucose fails to induce a rise in splanchnic fractional extraction of glucose comparable to that observed in normal subjects.     

Non-esterified fatty acids regulate lipid and glucose oxidation and glycogen synthesis in healthy man

Summary We examined the interrelationship of lipid and glucose metabolism in the basal state and during insulin stimulus in 19 healthy men (27±2 years, body mass index 23.6±0.6 kg/m²). In each subject, we performed a 4-h euglycaemic (5.3±0.1 mmol/l) hyperinsulinaemic (647±21 pmol/l) insulin clamp with indirect calorimetry in the basal state and during insulin infusion, and muscle biopsies before and at the end of the clamp. In the basal state, serum non-esterified fatty acid levels correlated directly with lipid oxidation (r =0.56, p<0.05) and indirectly with glucose oxidation (r = –0.80, p<0.001). Lipid and glucose oxidation rates were inversely related in the basal state (r = –0.47, p<0.05) and during insulin infusion (r = –0.65, p<0.01). Basal lipid oxidation and glycogen synthase total activity correlated inversely (r = –0.54, p<0.05). Lipid oxidation both in the basal state (r = –0.61, p<0.01) and during insulin infusion (r = –0.62, p<0.05) was inversely related to muscle glycogen content after the insulin clamp. Fasting plasma triglyceride concentration correlated directly to fasting insulin (r =0.55, p<0.05) and C-peptide (r =0.50, p<0.03) concentrations and inversely to non-oxidative glucose disposal rate at the end of clamp (r = –0.54, p<0.05). In conclusion: 1) Serum non-esterified fatty acid concentration enhances lipid and reduces glucose oxidation. 2) Lipid oxidation is inversely related to total glycogen synthase activity. 3) Lipid oxidation both in the basal state and during insulin stimulus correlates inversely with muscle glycogen content after insulin infusion. 4) Even in normotriglyceridaemic subjects, plasma triglycerides reduce insulin-stimulated non-oxidative glucose disposal. These data suggest that serum non-esterified fatty acids in physiologic concentrations have an important role in the regulation of lipid and glucose oxidation as well as glucose storage as glycogen. [Diabetologia (1994) 37: 202–209] Received: 2 June 1993 and in revised form: 27 August 1993     

Failure of insulin infusion during euglycemia to influence endogenous basal insulin secretion

Despite some evidence of self-regulation of insulin secretion, it is unclear whether endogenous insulin influences insulin secretion independently of blood glucose. The aim of the present study was to examine this question in humans. Seven healthy fasting men were given two-hour porcine insulin infusions (40 mU/min) with and without maintenance of euglycemia (glucose clamp). Intravenous glucose required to maintain basal blood glucose levels (4.2 ± 0.1 mmole/liter) during insulin infusion was 34.3 ± 3.0 gm with a mean rate of 273 ± 29 mg/min in the second hour of insulin infusion. During the glucose clamp, mean C-peptide levels were not significantly altered from fasting levels of 1.91 ± 0.24 ng/ml, but when blood glucose levels fell by approximately 1 mmole/liter, C-peptide fell to 0.37 ± 0.07 ng/ml. Plateau insulin levels were significantly higher during euglycemia than during mild hypoglycemia (53.2 ± 5.6 mU/liter versus 38.5 ± 3.6 mU/liter, P < 0.01). Plasma nonesterified fatty acids were suppressed equally in the two studies. However, a rise in plasma glucagon seen during mild hypoglycemia was absent when euglycemia was maintained. We conclude that insulin self-regulation (either direct or neurally mediated) is not physiologically important in the basal state in normal humans and that the blood glucose-insulin feedback loop dominates in the short-term control of basal insulin secretion.     

Evidence for a physiologic role of pancreatic glucagon in human glucose homeostasis: Studies with somatostatin

To study the role of glucagon in human glucose homeostasis, experimental glucagon deficiency was produced by infusing somatostatin (i.v. 250 μg bolus, followed by infusion of 500 μg/hr) in six normal subjects and in two hypophysectomized patients—an insulin-dependent diabetic and a nondiabetic. In normal subjects, somatostatin lowered plasma glucagon from a mean (± SE) basal level of 85 ± 15 to 33 ± 10 pg/ml, p < 0.001. Concurrently, plasma glucose fell from $\text{90 ± 2 to 73 ± 3 mg}\text{100 ml}$, p < 0.001. Serum insulin and growth hormone fell slightly during somatostatin infusion, while plasma free fatty acids rose. In both hypophysectomized patients, somatostatin lowered plasma glucagon and glucose levels. In all subjects, after stopping somatostatin infusions, plasma glucagon and glucose returned promptly to control values, while serum growth hormone did not change. In additional in vitro studies, somatostatin (1 μg/ml) had no effect on muscle glucose uptake. Since it is known that somatostatin has no direct effect on hepatic glucose production, these results suggest that the fall in plasma glucose during somatostatin infusion resulted from inhibition of glucagon secretion, thus providing evidence that this hormone plays a physiologic role in the maintenance of fasting euglycemia in man.     

Effect of steroid-therapy on insulin sensitivity in insulin-dependent diabetic patients after kidney transplantation

Little information is available on glucose and energy metabolism in insulin-dependent diabetes mellitus (IDDM) patients receiving immunosuppression after kidney transplantation. We therefore measured insulin sensitivity (euglycemic insulin clamp in combination with indirect calorimetry and infusion of tritiated glucose) in (a) eight steroid-treated IDDM patients after kidney transplantation, (b) ten IDDM patients without nephropathy, (c) ten nondiabetic patients after kidney transplantation, and (d) ten healthy control subjects. Hepatic glucose production was enhanced in both steroid-treated transplanted IDDM patients [4.8 ± 0.6 mg/kg lean body mass (LBM)·min] and IDDM patients without complications (3.8 ± 0.2 mg/kg LBM·min) compared with nondiabetic renal graft recipients and with healthy controls (2.8 ± 0.2 and 2.7 ± 0.1 mg/kg LBM·min; p < 0.01). Insulin-stimulated glucose disposal was reduced in transplanted and non-transplanted IDDM patients and nondiabetic transplanted patients versus healthy controls (6.6 ± 0.8, 5.7 ± 0.7, and 7.5 ± 0.6 versus 9.3 ± 0.6 mg/kg LBM·min; p < 0.05). This reduction was mainly due to an impairment in nonoxidative glucose metabolism, i.e., glycogen synthesis (3.1 ± 0.6, 2.7 ± 0.4, and 3.3 ± 0.5 versus 5.0 ± 0.5 mg/kg LBM·min; p < 0.05 versus healthy controls). It is concluded that IDDM patients without nephropathy show both hepatic and peripheral insulin resistance. In IDDM patients a further increase of insulin resistance caused by treatment with corticosteroids can be corrected by increased insulin doses. However, nondiabetic steroid-treated renal graft recipients show insulin resistance comparable to IDDM patients.     

Effect of a 3-day fast on glucose storage and oxidation in obese hyperinsulinemic diabetics

Glucose disposal was measured for a 3-hr period after a 100-g oral glucose load by means of a new adaptation of continuous indirect calorimetry in 6 obese hyperinsulinemic diabetics and 5 nonobese normal subjects who served as the control. While total glucose oxidized during the 3-hr test was not significantly lower in the obese diabetic group (31 ± 3 g) than in the control group (37 ± 3 g), a marked impairment of net glucose storage was observed in the former group (26 ± 7 g) in comparison to the control group (64 ± 3 g; p < 0.001). This marked decrease in net glucose storage suggests that a limited capacity for glucose storage might play a major role in glucose intolerance in these cases of obese hyperinsulinemic diabetes. In the obese diabetic group, after a 3-day fast supplemented with protein, the plasma glucose values dropped significantly both in the fasting state and in response to the glucose load. This was accompanied by a marked improvement of glucose storage (52 ± 9 versus 26 ± 7 g before the fast; p < 0.001), a decrease in glucose urinary loss (5 ± 1 g versus 14 ± 4 g prior to fast), but a marked impairment in glucose oxidation (13 ± 1 g versus 31 ± 3 g before fast; p < 0.001). In the control group, a moderate impairment of glucose tolerance was observed, probably related to the important decrease in glucose oxidation (12 ± 3 g versus 37 ± 3 g prior to fast), in spite of the increase in glucose storage (82 ± 4 g versus 64 ± 3 g prior to fast). These observations suggest that glucose intolerance observed in obese hyperinsulinemic diabetics in the postabsorptive state might result at least in part from deficiency in net glucose storage capacity. The marked lowering of the plasma glucose tolerance curve in the same subjects after a 3-day period of fast is probably a consequence of the overall effect of a decrease in the glucose pool and an increase in net glucose storage in spite of a decrease in glucose oxidation and in urinary glucose loss. It does not exclude, however, other factors, such as changes in tissue insulin sensitivity.     

Sympathetic nerve activity and insulin sensitivity in normotensive offspring of hypertensive parents

Insulin resistance and elevated sympathetic nerve activity (SNA) are observed in young borderline hypertensive humans. A positive family history of hypertension (FH) is a strong risk factor for developing hypertension. To assess whether insulin resistance and increased sympathetic tone precede the onset of hypertension, we studied 17 young adults with and 17 without a documented family history of hypertension. Subjects were matched for age (33 ± 0.4 years in FH positive and 32 ± 0.5 years in FH negative; mean ± SE) and body mass index (BMI, 25 ± 1 kg/m² in both FH positive and FH negative subjects). We measured blood pressure (BP), heart rate (HR), muscle sympathetic nerve activity (MSNA, microneurography), forearm blood flow, and insulin sensitivity (total glucose uptake determined by an euglycemic/hyperinsulinemic clamp using stable isotope tracer infusion), and calculated forearm vascular resistance (FVR). Mean BP and HR were similar in both groups (86 ± 3 mm Hg and 61 ± 2 beats/min, and 85 ± 2 mm Hg and 62 ± 2 beats/min, respectively, in FH positive and negative respectively, P = ns). Baseline MSNA (24 ± 3 bursts/min in FH positive v 20 ± 3 bursts/min in FH negative, P = ns) and total glucose uptake [0.104 ± 0.014 mg/(kg × min × μU insulin/mL) in FH positive v 0.095 ± 0.014 mg/(kg × min × μU insulin/mL) in FH negative, P = ns] did not differ between the groups. Sympathetic and vascular responses to insulin were also similar in both groups. The increase in MSNA was 10 ± 2 bursts/min in FH positive and 10 ± 1 bursts/min in FH negative, P = ns. Thus, age- and weight-matched offspring with and without a FH of hypertension did not vary in MSNA or insulin sensitivity. These findings suggest that in the abscence of obesity and high arterial pressure, a FH of hypertension may not be accompanied by decreased insulin sensitivity or increased MSNA.     

Neonatal de-afferentation of capsaicin-sensitive sensory nerves increases in vivo insulin sensitivity in conscious adult rats

Summary Sensory neuropeptides, released from the peripheral nervous system, might modulate glucose homeostasis by antagonizing insulin action. The effects of de-afferentation of functional small diameter unmyelinated C-fibres (sensory nerves) on in vivo insulin-mediated intracellular glucose metabolism were investigated by using euglycaemic insulin (6 and 18 mU/kg.min) clamps with [3-³H]-glucose infusion in 24 adult rats, treated neonatally with either capsaicin (CAP) (50 mg/kg) or vehicle (CON). Following the clamp, skeletal muscle groups, liver and adipose tissue were freeze-clamped. At plasma insulin levels of approximately 90 mU/l, CAP-rats showed a 21 % increase in whole body glucose uptake compared with CON (24.4 ± 1.6 vs 20.1 ± 0.8 mg/kg · min, p < 0.02), which was paralleled by a 20 % increase in whole body glycolysis (12.6 ± 0.8 vs 10.5 ± 0.5 mg/kg.min p < 0.05) (concentration of ³H₂O in plasma). Whole body skeletal muscle glycogenesis was increased by 80 % in CAP-rats (5.7 ± 0.7 vs 3.1 ± 0.7 mg/kg · min, p < 0.05) with increased muscle glycogen synthase activity. Whole body (muscle, liver and adipose tissue combined) de novo lipogenesis also was increased in CAP-rats compared with CON (0.69 ± 0.10 vs 0.44 ± 0.06 mg/kg · min, p < 0.05) (incorporation of [3-³H]-glucose counts into glycogen or fat). Hepatic glucose production was lower in CAP-rats compared with CON (0.6 ± 0.6 vs 2.1 ± 0.7 mg/kg · min, p < 0.05). Plasma glucagon, corticosterone, epinephrine and norepinephrine levels were reduced in CAP-rats: 43 ± 2 compared with 70 ± 6 pg/ml, 855 ± 55 compared with 1131 ± 138 nmol/l, 513 ± 136 compared with 1048 ± 164 pmol/l and 928 ± 142 compared with 1472 ± 331 pmol/l, respectively, p < 0.05. At plasma insulin levels of approximately 400 mU/l, CAP-rats showed no differences in peripheral and hepatic insulin action compared with CON. We conclude that the removae of endogenous sensory neuropeptides, by de-afferentation of capsaicin-sensitive sensory nerves, increases in vivo insulin sensitivity, but not responsiveness: 1) primarily through an increased sensitivity of skeletal muscle glycogen synthesis to insulin; 2) through a reduction in the levels of counter-regulatory hormones, thereby creating a milieu which favours overall in vivo insulin sensitivity with respect to glucose uptake, glucose production, glycolysis, glycogenesis and lipogenesis. [Diabetologia (1998) 41: 813–820] Received: 10 November 1997 and in revised form 4 March 1998     

Action Profile of the Rapid Acting Insulin Analogue: Human Insulin B28Asp

The time-action profile of the human insulin analogue B28Asp, which displays faster absorption rates from subcutaneous tissue compared to soluble human insulin, was studied under euglycaemic glucose clamp conditions (blood glucose 5.0 mmol l^?1) in 14 healthy male volunteers. Subcutaneous injection of 0.15 U kg^?1 body weight (range 9.5–14.3 U) of the insulin analogue or soluble human insulin resulted in half-maximal glucose infusion rates (after subtraction of mean baseline glucose infusion rates) that were reached significantly earlier after injection of B28Asp (45 ± 11 (SD) min) as compared to human insulin (58 ± 25 min, p < 0.05). Forty-five and 60 min after injection of human insulin, glucose infusion rates had increased by 3.4 ± 1.8 and 4.8 ± 2.3 mg min^?1 kg^?1 above baseline glucose infusion rates, reflecting 30 ± 15 and 42 ± 17% of maximal action of 10.6 ± 2.7 mg min^?1 kg^?1. Following the injection of B28Asp, glucose infusion rates increased by 6.3 ± 2.7 after 45 min and by 7.9 ± 2.8 mg min^?1 kg^?1 after 60 min above baseline glucose infusion rates, reflecting 64 ± 28% and 81 ± 26% of maximal action of human soluble insulin (p < 0.001). Peak glucose infusion rates after injection of B28Asp were significantly higher and were reached earlier than after subcutaneous injection of soluble human insulin (p < 0.05 and p < 0.001). The human insulin analogue B28Asp showed a significantly faster onset of action as compared to soluble human insulin.     

Sex and insulin sensitivity

To analyze whether enhanced adiposity in females as compared with males is associated with a decreased sensitivity to insulin, a group of healthy normal weight females (n = 13, age 21 ± 1 years) and males (n = 11, age 23 ± 1 year, mean ± SEM) was studied. In each subject, body composition (% fat and % muscle), maximal aerobic power (V_O2 max) and whole body insulin-mediated glucose metabolism were measured. The group of women had a higher percentage of fat to total body weight (P < 0.001) and a lower percentage of muscle (P < 0.001) than the group of men. The higher percentage of fat in women compared with males was due to enhanced peripheral fat accumulation in the arm and thigh regions. V_O2 max levels were comparable in both groups (48 ± 1 mL/kg/min for women, 53 ± 2 mL/kg/min for men, P = NS). The rate of glucose metabolism (M) was comparable in women (8.78 ± 0.74 mg/kg/min), and men (8.31 ± 0.89 mg/kg/min) when expressed per kilogram of total body weight, but when expressed per kilogram of muscle tissue (M_m), it was 45% higher in women (29.4 ± 2.4 mg/kg/min) than in men (20.2 ± 1.6 mg/kg/min, P < 0.005). Partial correlation analysis indicated that the percentage of fat was inversely related to M and M_m in both women (P < 0.05) and men (P < 0.05), but not to percentage of muscle or V_O2 max. Conclusions: (1) Insulin-mediated glucose disposal is inversely related to adiposity in normal weight healthy males and females. (2) Women and men utilize equal amounts of glucose despite a higher adiposity in females. (3) Since muscle tissue utilizes most of intravenously administered glucose, this result indicates enhanced glucose uptake by muscle tissue in females compared with males. (4) Elevated glucose uptake by muscle in women may provide a mechanism by which women are protected against excessive hyperglycemia despite their smaller amount of glucose-consuming tissue.     

Time–action Profile of Inhaled Insulin

We compared the pharmacodynamics of insulin after inhalation of 99 U microcrystalline solid insulin and subcutaneous injection of 10 U regular insulin and intravenous injection of 5 U regular insulin. The time–action profiles of the three insulin administrations were studied in 11 healthy volunteers using the euglycaemic glucose clamp technique. The insulins were administered to each volunteer on three separate occasions in random order. Onset of action, assessed as glucose infusion rate, after insulin inhalation was substantially more rapid than after subcutaneous injection and half-maximal action was reached earlier (31 ± 17 vs 54 ± 12 min; p < 0.001). Maximal metabolic response was reached earlier after insulin inhalation in comparison to subcutaneous injection (108 ± 49 vs 147 ± 53 min; p < 0.001). The maximal glucose infusion rate after inhalation of insulin was lower than after subcutaneous insulin injection (6.2 ± 2.4 vs 9.1 ± 2.5 mg kg⁻¹ min⁻¹; p < 0.001). The glucose infusion rates in the first 60 min after inhalation were significantly greater than after insulin injection (area under the glucose infusion rate curve: 0.23 ± 0.12 vs 0.13 ± 0.08 g kg⁻¹ 60 min⁻¹; p < 0.001). However, the total metabolic effect after inhalation was significantly lower than after insulin injection (1.44 ± 0.68 vs 1.90 ± 0.47 g kg⁻¹ 360 min⁻¹; p < 0.001). Relative effectiveness of inhaled insulin calculated with regard to the data from the intravenous insulin application was 9.5 ± 4.1 % and of the subcutaneous insulin application was 7.6 ± 2.9 %. With its rapid onset of action, inhaled insulin might have potential for clinical use. © 1997 by John Wiley & Sons, Ltd.     

Opposite effects of short- and long-term fatty acid infusion on insulin secretion in healthy subjects

Summary Our study investigates short- and long-term effects of infusion of non-esterified fatty acids (NEFA) on insulin secretion in healthy subjects. Twelve healthy individuals underwent a 24-h Intralipid (10% triglyceride emulsion) infusion at a rate of 0.4 ml/min with a simultaneous infusion of heparin (a bolus of 200 U followed by 0.2 U/min per kg body weight). After an overnight fast (baseline), at 6 and at 24 h of Intralipid infusion and 24 h after Intralipid discontinuation (recovery test), all subjects underwent an intravenous glucose tolerance test (iv-GTT) (25 g of glucose/min). Intralipid infusion caused a threefold rise in plasma NEFA concentrations with no difference between the 6- and the 24-h concentrations. Compared to baseline acute insulin response (AIR) (AIR=63±8 mU/l), short-term (6-h) Intralipid infusion was associated with a significant increase in AIR (86±12 mU/l p<0.01); in contrast, long-term (24-h) Intralipid delivery was associated with inhibition of AIR (31±5 mU/l) compared to baseline (p<0.001) and to the 6-h (p<0.03) triglyceride emulsion infusion. Intralipid infusion was associated with a progressive and significant decline in respiratory quotient (RQ). A positive correlation between changes in fasting plasma NEFA concentrations and AIR at the 6-h infusion (r=0.89 p<0.001) was found. In contrast, at the end of the Intralipid infusion period, changes in plasma NEFA concentrations and AIR were negatively correlated (r=–0.87 p<0.001). The recovery test showed that fasting plasma NEFA concentrations, RQ and AIR had returned to baseline values. In the control study (n=8) 0.9% NaCl infusion did not mimick the effect of Intralipid. In conclusion, our study demonstrates that short- and long-term exposures of beta cells to high plasma NEFA concentrations have opposite effects on glucose-induced insulin secretion.Abbreviations NEFA Non-esterified fatty acids - ivGTT intravenous glucose tolerance test - AIR acute insulin response - NIDDM non-insulin-dependent diabetes mellitus     

Insulin resistance characterizes glucose uptake in skeletal muscle but not in the heart in NIDDM

Summary Skeletal muscle insulin resistance and coronary heart disease (CHD) often precede non-insulin-dependent diabetes mellitus (NIDDM). A recent study showed the myocardium of patients with CHD to be insulin resistant, independent of blood flow. We determined whether myocardial insulin resistance is a feature of NIDDM patients with no CHD. Skeletal muscle and myocardial glucose uptake were determined in 10 patients with NIDDM and 9 age- and weight-matched normal men of similar age and body mass index men using [¹⁸F]-2-fluoro-2-deoxy-d-glucose and positron emission tomography under normoglycaemic hyperinsulinaemic conditions. Whole body glucose uptake, as determined by the euglycaemic clamp technique, was significantly lower in the patients with NIDDM (35 ± 3 μmol/kg body weight · min) than the normal subjects (45 ± 3 μmol/kg body weight · min, p < 0.02). Insulin-stimulated femoral muscle glucose uptake was significantly lower in the patients with NIDDM (71 ± 6 μmol/kg muscle · min) than in the normal subjects (96 ± 5 μmol/kg muscle · min, p < 0.01). Whole body glucose uptake was correlated with femoral muscle glucose uptake in the entire group (r = 0.76, p < 0.001), in patients with NIDDM and in normal subjects. Rates of insulin-stimulated myocardial glucose uptake were comparable between the patients with NIDDM (814 ± 76 μmol/kg muscle · min) and the normal subjects (731 ± 63 μmol/kg muscle · min, p > 0.4). Whole body or femoral muscle, and myocardial glucose uptake were not correlated in all subjects, patients with NIDDM or normal subjects. We conclude that insulin resistance of the myocardium is not a feature of uncomplicated NIDDM. [Diabetologia (1998) 41: 555-559] Received: 8 August 1997 and in revised form: 6 December 1997     

A novel mechanism of glipizide sulfonylurea action: decreased metabolic clearance rate of insulin

To examine whether sulfonylureas inhibit the metabolic clearance rate (MCR) of insulin, 19 healthy young subjects participated in two experiments. In the first protocol (n=10), a 3-h oral glucose load was performed with and without 2 mg of glipizide given 30 min before glucose ingestion. The total insulin response was 60% greater with than without glipizide (5.9±0.6 vs 3.7±0.5 μU/ml;P<0.001). However, the total C-peptide responses were virtually identical (4.7±0.5 vs 4.8±0.4 nmol/l) in both studies. In the second protocol (n=9), the MCR of insulin was measured during 4-h euglycemic insulin clamps performed with and without glipizide. In the study with glipizide, the subjects ingested 5 mg of glipizide at 120 min. The steady-state plasma insulin concentration during the 4th h, i.e., 1–2 h after glipizide ingestion, was significantly higher than during the 2nd h, i.e., before glipizide ingestion (99±22 vs 78±17 μU/ml;P<0.01). In addition, glucose uptake during the 4th h was greater (8.0±1.6 vs 6.4±1.5 mg/kg·min) and the MCR of insulin was reduced (503±126 vs 621±176 ml/m²·min;P<0.01). We conclude that glipizide augments plasma insulin levels both by enhancing its secretion and by decreasing the MCR of insulin.     

Nature and biologic activity of “extrapancreatic glucagon”: Studies in pancreatectomized cats

After total pancreatectomy concentrations of circulating immunoreactive glucagon (IRG) were elevated (255 ± 37 pg/ml, mean ± SEM; n = 20) in comparison to unoperated cats (119 ± 27 pg/ml). Plasma glucagon concentrations were determined in an assay regarded as specific for pancreatic glucagon. The nature of this extrapancreatic IRG was further examined in the following studies. Arginine (0.45 gm/kg i.v.) caused a marked elevation of IRG in normal animals but did not cause a consistent elevation of IRG in 6 pancreatectomized cats. Whereas somatostatin (20 μg/kg/hr i.v. for 1 hr) in 10 pancreatectomized cats caused a reduction in IRG from 195 ± 45 to 64 ± 22 pg/ml (p < 0.02), blood glucose did not change. Moreover, insulin (0.22 U/kg/hr i.v. for 1 hr) failed to reduce blood glucose levels in 6 pancreatectomized cats despite a fall in IRG from 269 ± 87 to 150 ± 62 pg/ml (p < 0.05). Glucagon (4 ng/kg/min i.v. for 1 hr) given during the second hour of somatostatin infusion failed to raise blood glucose in 7 untreated pancreatectomized cats. However, when euglycemia was achieved by prolonged insulin therapy in 2 pancreatectomized animals, extrapancreatic IRG became completely suppressed and a hyperglycemic response to exogenous glucagon was restored. Although extrapancreatic IRG appeared identical to pancreatic glucagon by immunoassay, Sephadex G50 chromatography of plasma from 4 pancreatectomized animals showed that 40%–90% of the IRG was of approximately 9000–10,000 molecular weight. Only 10%–60% was of molecular weight corresponding to pancreatic glucagon, i.e., 3500. This contrasted with normal cats, in whom more than 90% of IRG was of molecular weight 3500. The excessive secretion of extrapancreatic IRG is probably related to insulin deficiency since it is reversed by prolonged insulin therapy. The circulating material is heterogeneous and would correspond in molecular size to pancreatic glucagon and a larger molecular weight glucagon precursor. The lack of a consistent response to arginine and predominance of 9000–10,000 molecular weight material could be due to chronic hyperstimulation of true A cells situated in the upper gastrointestinal tract or other extrapancreatic sites; on the other hand, these results could suggest that the cell of origin of extrapancreatic IRG is distinct from the A cell. A major role for extrapancreatic glucagon in the hyperglycemia of diabetes is not evident in these studies, though hepatic glycogen depletion and a reduced rate of peripheral glucose utilization in the operated animals may have reduced the impact on blood glucose levels of changes in IRG. It is possible that extrapancreatic IRG contributes to the poor response to exogenous insulin and glucagon seen in untreated pancreatectomized animals.     

Intramuscular triglyceride content is increased in IDDM

Summary Increased lipid oxidation is related to insulin resistance. Some of the enhanced lipid utilization may be derived from intramuscular sources. We studied muscle triglyceride (mTG) concentration and its relationship to insulin sensitivity in 10 healthy men (age 29 ± 2 years, BMI 23.3 ± 0.6 kg/m²) and 17 men with insulin-dependent diabetes mellitus (IDDM) (age 30 ± 2 years, BMI 22.8 ± 0.5 kg/m², diabetes duration 14 ± 2 years, HbA_{1 c} 7.7 ± 0.3 %, insulin dose 48 ± 3 U/day). Insulin sensitivity was measured with a 4 h euglycaemic (5 mmol/l) hyperinsulinaemic (1.5 mU or 9 pmol · kg^–1· min^–1) clamp accompanied by indirect calorimetry before and at the end of the insulin infusion. A percutaneous biopsy was performed from m. vastus lateralis for the determination of mTG. At baseline the IDDM patients had higher glucose (10.2 ± 0.9 vs 5.6 ± 0.1 mmol/l, p < 0.001), insulin (40.3 ± 3.2 vs 23.2 ± 4.2 pmol/l, p < 0.01), HDL cholesterol (1.28 ± 0.06 vs 1.04 ± 0.03 mmol/l, p < 0.01) and mTG (32.9 ± 4.6 vs 13.6 ± 2.7 mmol/kg dry weight, p < 0.01) concentrations than the healthy men, respectively. The IDDM patients had lower insulin stimulated whole body total (–25 %, p < 0.001), oxidative (–18 %, p < 0.01) and non-oxidative glucose disposal rates (–43 %, p < 0.001), whereas lipid oxidation rate was higher in the basal state ( + 44 %, p < 0.01) and during hyperinsulinaemia ( + 283 %, p < 0.05). mTG concentrations did not change significantly during the clamp or correlate with insulin stimulated glucose disposal. In healthy men mTG correlated positively with lipid oxidation rate at the end of hyperinsulinaemia (r = 0.75, p < 0.05). In conclusion: 1) IDDM is associated with increased intramuscular TG content. 2) mTG content does not correlate with insulin sensitivity in healthy subjects or patients with IDDM. [Diabetologia (1998) 41: 111–115] Received: 12 June 1997 and in revised form: 8 September 1997     

Insulin secretion and cellular glucose metabolism after prolonged low-grade intralipid infusion in young men

We examined the simultaneous effects of a 24-h low-grade Intralipid infusion on peripheral glucose disposal, intracellular glucose partitioning and insulin secretion rates in twenty young men, by 2-step hyperinsulinemic euglycemic clamp [low insulin clamp (LI), 10 mU/m(2) x min; high insulin clamp (HI), 40 mU/m(2) x min], 3-(3)H-glucose, indirect calorimetry, and iv glucose tolerance test. Free fatty acid concentrations were similar during basal steady state but 3.7- to 13-fold higher during clamps. P-glucagon increased and the insulin/glucagon ratio decreased at both LI and HI during Intralipid infusion. At LI, glucose oxidation decreased by 10%, whereas glucose disposal, glycolytic flux, glucose storage, and glucose production were not significantly altered. At HI, glucose disposal, and glucose oxidation decreased by 12% and 24%, respectively, during Intralipid infusion. Glycolytic flux, glucose storage, and glucose production were unchanged. Insulin secretion rates increased in response to Intralipid infusion, but disposition indices (DI = insulin action.insulin secretion) were unchanged. In conclusion, a 24-h low-grade Intralipid infusion caused insulin resistance in the oxidative (but not in the nonoxidative) glucose metabolism in young healthy men. Moreover, insulin hypersecretion perfectly countered the free-fatty acid-induced insulin resistance. Future studies are needed to determine the role of a prolonged moderate lipid load in subjects at increased risk of developing diabetes.     

Determinants of postabsorptive endogenous glucose output in non-diabetic subjects

Aim/hypothesis. To gain insight into the physiologic determinants of postabsorptive endogenous glucose output (EGO) in humans.¶Methods. We analysed the data of 344 non-diabetic subjects (212 men and 132 women) with a wide range of age (18–85 years) and body mass index (15–55 kg/m²) who participated in the European Group for the Study of Insulin Resistance (EGIR) project. Whole-body endogenous glucose output was measured by tracer ([³H]glucose) dilution at steady-state, peripheral insulin sensitivity (Ñ glucose clearance/Ñ insulin) was measured by the euglycaemic insulin (7 pmol × min^–1× kg^–1) clamp technique.¶Results. Whole-body endogenous glucose output showed a large variability (mean = 768 ± 202 μmol · min^–1, range 209–1512) and was strongly related to lean body mass (r = 0.63, p < 0.0001). This association entirely explained the endogenous glucose output being higher in men than in women (827 ± 189 vs 674 × 187 μmol × min^–1, p < 0.0001), its relation to body mass (+ 10 ± 2 per unit of body mass index, p < 0.0001) and its trend to decline with age (–1.1 ± 0.7 μmol · min^–1 per year, p = 0.10). Although inversely related to one another (r = –0.41, p < 0.0001), peripheral insulin sensitivity and fasting plasma insulin were both independently associated with endogenous glucose output in an inverse fashion (with partial r's of 0.19 and 0.21, respectively, after adjusting for lean body mass and centre, p < 0.0001 for both).¶Conclusion/interpretation. Among non-diabetic subjects in the postabsorptive condition, total body endogenous glucose output variability is wide and is largely explained by the amount of lean mass; this, in turn, explains differences in total endogenous glucose output due to sex, obesity and age. Independently of the amount of lean mass, peripheral insulin resistance is associated with a higher endogenous glucose output independently of fasting plasma insulin concentration, suggesting coupled regulation of insulin action in peripheral tissues and the liver. [Diabetologia (2000) 43: 1266–1272]