Plasma free fatty acid concentration during hyperglycemic glucose clamp with and without somatostatin infusion in obese subjects with normal glucose tolerance

In the present study we evaluated the regulation of plasma free fatty acid (FFA) concentration by glucose and insulin in human obesity. To this purpose we measured plasma FFA concentration in normoglycemic, normoinsulinemic obese (n = 8) and nonobese (n = 8) healthy subjects during 240 min of exogenous hyperglycemia (hyperglycemic glucose clamp) in presence of both glucose-stimulated (0-120 min and 180-240 min) and somatostatin-inhibited (120-180 min) insulin secretion. We found that plasma FFA curves were roughly parallel in the 0-120 min period and FFA values of obese subjects were constantly higher throughout the experimental period. Moreover, the difference between the two groups was significant when individual data were expressed as a percent of fasting FFA value (P less than 0.0001 from 0 to 120 min). Plasma insulin levels were similar in the two groups during the entire study. The amount of glucose metabolized during the 80-120 min period was significantly lower in obese than in nonobese subjects (172 +/- 7 v. 341 +/- 11 mg/m2.min, P less than 0.01; means +/- s.e.). During the somatostatin period (120-180 min) plasma insulin was lowered close to basal values in both groups (116 +/- 15 and 109 +/- 11 pmol/l) and plasma FFA concentrations rose in a linear fashion. Our data suggest that suppression of plasma FFA concentrations by glucose and insulin is qualitatively similar in healthy nonobese and obese subjects, the latter having higher FFA values. Insulin action on FFA metabolism isn ot grossly impaired in obese subjects who are clearly insulin resistant as far as glucose metabolism is concerned.     

Lack of insulin inhibition on insulin secretion in non-diabetic morbidly obese patients.

OBJECTIVE: Insulin inhibition of insulin secretion has been described in normal lean subjects. In this study, we examined whether this phenomenon also occurs in the morbidly obese who often have severe peripheral insulin resistance. SUBJECTS: Twelve obese patients, normotolerant to glucose (8 F/4 M, body mass index (BMI)=54.8+/-2.5 kg/m(2), 39 y) and 16 lean control subjects (10 F/6 M, BMI=22.0+/-0.5 kg/m(2), 31 y). DESIGN AND MEASUREMENTS: An experimental study using various parameters, including an euglycemic hyperinsulinemic clamp (280 pmol/min/m(2) of body surface), an oral glucose tolerance test (OGTT), electrical bioimpedance and indirect calorimetry. RESULTS: The obese subjects were insulin resistant (M=19.8+/-1.6 vs 48.7+/-2.6 micromol/min kg FFM, P<0.0001) and hyperinsulinemic in the fasted state and after glucose ingestion. Fasting plasma C-peptide levels (obese 1425+/-131 pmol/l vs lean 550+/-63 pmol/l; P<0.0001) decreased less during the clamp in the obese groups (-16.9+/-6.9% vs -43.0+/-5.6% relative to fasting values; P=0.007). In the lean group, the C-peptide decrease during the clamp (percentage variation) was related to insulin sensitivity, M/FFM (r=0.56, P=0.03), even after adjustment for the clamp glucose variation. CONCLUSION: We conclude that, in lean subjects, insulin inhibits its own secretion, and this may be related to insulin sensibility. This response is blunted in morbidly obese patients and may have a role in the pathogenesis of fasting hyperinsulinemia in these patients.     

Defective amplification of the late phase insulin response to glucose by GIP in obese Type II diabetic patients

AIMS/HYPOTHESIS: Glucagon-like-peptide-1 (GLP-1) is strongly insulinotropic in patients with Type II (non-insulin-dependent) diabetes mellitus, whereas glucose-dependent insulinotropic polypeptide (GIP) is less effective. Our investigation evaluated "early" (protocol 1) - and "late phase" (protocol 2) insulin and C-peptide responses to GLP-1 and GIP stimulation in patients with Type II diabetes. METHODS: Protocol 1: eight Type II diabetic patients and eight matched healthy subjects received i.v. bolus injections of GLP-1(2.5 nmol) or GIP(7.5 nmol) concomitant with an increase of plasma glucose to 15 mmol/l. Protocol 2: eight Type II diabetic patients underwent a hyperglycaemic clamp (15 mmol/l) with infusion (per kg body weight/min) of either: 1 pmol GLP-1 (7-36) amide (n=8), 4 pmol GIP (n=8), 16 pmol GIP (n=4) or no incretin hormone (n=5). For comparison, six matched healthy subjects were examined. RESULTS: Protocol 1: Type II diabetic patients were characterised by a decreased "early phase" response to both stimuli, but their relative response to GIP versus GLP-1 stimulation was exactly the same as in healthy subjects [insulin (C-peptide): patients 59+/-9% (74+/-6%) and healthy subjects 62+/-5% (71+/-9%)]. Protocol 2, "Early phase" (0-20 min) insulin response to glucose was delayed and reduced in the patients, but enhanced slightly and similarly by GIP and GLP-1. GLP-1 augmented the "late phase" (20-120 min) insulin secretion to levels similar to those observed in healthy subjects. In contrast, the "late phase" responses to both doses of GIP were not different from those obtained with glucose alone. Accordingly, glucose infusion rates required to maintain the hyperglycaemic clamp in the "late phase" period (20-120 min) were similar with glucose alone and glucose plus GIP, whereas a doubling of the infusion rate was required during GLP-1 stimulation. CONCLUSION/INTERPRETATION: Lack of GIP amplification of the late phase insulin response to glucose, which contrasts markedly to the normalising effect of GLP-1, could be a key defect in insulin secretion in Type II diabetic patients.     

Insulin and glucagon secretion are suppressed equally during both hyper- and euglycemia by moderate hyperinsulinemia in patients with diabetes mellitus

Hyper- and euglycemic clamp studies were performed in patients with noninsulin-dependent diabetes mellitus to examine the effects of exogenous insulin administration on insulin and glucagon secretion. Plasma glucose was kept at the fasting level [mean, 10.0 +/- 0.2 (+/- SE) mmol/L; hyperglycemic clamp], and graded doses of insulin (1, 3, and 10 mU/kg.min, each for 50 min) were infused. The plasma C-peptide level gradually decreased from 523 +/- 66 to 291 +/- 43 pmol/L (n = 13; P less than 0.005) by the end of the hyperglycemic clamp study. After 90 min of equilibration with euglycemia (5.4 +/- 0.1 mmol/L; euglycemic clamp), the same insulin infusion protocol caused a similar decrease in the plasma C-peptide level. With the same glucose clamp protocol, physiological hyperinsulinemia for 150 min (676 +/- 40 pmol/L), obtained by the infusion of 2 mU/kg.min insulin, caused suppression of the plasma C-peptide level from 536 +/- 119 to 273 +/- 65 pmol/L during hyperglycemia and from 268 +/- 41 to 151 +/- 23 pmol/L during euglycemia (n = 9; P less than 0.005 in each clamp). Plasma glucagon was suppressed to a similar degree in both glycemic states. These results demonstrate that 1) insulin secretion in non-insulin-dependent diabetes mellitus is suppressed by high physiological doses of exogenous insulin in both the hyper- and euglycemic states, the degree of inhibition being independent of the plasma glucose level; and 2) glucagon secretion is also inhibited by such doses of exogenous insulin.     

Compared to glibenclamide, repaglinide treatment results in a more rapid fall in glucose level and beta-cell secretion after glucose stimulation

BACKGROUND: The more rapid onset of action and the shorter half-life of repaglinide may reduce the post-load glucose excursion and limit sustained insulin secretion compared to sulphonylurea (SU) derivatives. METHODS: We studied 12 patients with type 2 diabetes (age 62 +/- 2 years, BMI 28.3 +/- 1.3 kg m(-2), HbA1c 6.7 +/- 0.2%) on SU monotherapy at submaximal dose. Patients were treated for 3 weeks with repaglinide or glibenclamide in a randomized, crossover trial. At the end of each treatment period, patients underwent a 60-min hyperglycaemic clamp (glucose 12 mmol L(-1)) followed by 4-h observation (60-300 min) with frequent blood sampling for determination of glucose, insulin, proinsulin and C-peptide levels. Before the clamp (5 min for repaglinide, 30 min for glibenclamide), patients ingested their usual morning drug dose. RESULTS: After the end of the hyperglycaemic clamp, mean plasma glucose fell to a level of 5 mmol L(-1) after approximately 150 min with repaglinide, and after approximately 190 min with glibenclamide. While initially quite similar, in the period from 240 to 300 min, insulin, proinsulin and C-peptide levels were lower during repaglinide treatment (insulin 133 +/- 20 vs 153 +/- 25 pmol L(-1) (P < 0.05), proinsulin 14 +/- 3 vs 19 +/- 4 pmol L(-1) (P = 0.06) and C-peptide 0.81 +/- 0.19 vs 1.14 +/- 0.18 nmol L(-1) (P = 0.05) for repaglinide vs glibenclamide, respectively). CONCLUSIONS: Following glucose stimulation, plasma glucose levels, and insulin concentration decrease more rapidly after repaglinide treatment than after glibenclamide. Proinsulin and C-peptide secretion tended to fall more rapidly as well. These findings are consistent with a more rapid onset and shorter duration of beta-cell stimulation associated with repaglinide.     

Characteristics of insulin resistance in Turner syndrome

The characteristics of insulin resistance, in Turner syndrome are still unclear. For this purpose in 4 patients with Turner syndrome and in 8 control females we performed an euglycaemic hyperinsulinemic glucose clamp at the following insulin infusion rates (50 and 100 mU/Kg x h), each period lasting 120 min. A simultaneous infusion of D-3-H-glucose allowed us to determine in basal conditions and during the clamp hepatic glucose output and glucose disappearance rate (Rd). In basal conditions plasma glucose (4.8 +/- 0.1 vs 4.6 +/- 0.2 mmol/1 p = NS) and plasma glucagon (102 +/- 7.5 vs 112 +/- 11.3 ng/l p = NS) were similar in both groups despite higher plasma insulin (19 +/- 1.8 vs 7 +/- 2.2 mU/l p less than 0.05) and C-peptide (1.0 less than 0.1 vs 0.8 +/- 0.06 pmol/l p less than 0.05) levels in patients with Turner syndrome. In the last 60 min of the lower insulin infusion rate glucose infusion rate (4.1 +/- 0.3 vs 2.9 +/- 0.4 mg/Kg x min p less than 0.05) and glucose disappearance rate (3.89 +/- 0.12 vs 2.63 +/- 0.11 mg/Kg x min p less than 0.01) were significantly reduced in patients with Turner. On the contrary hepatic glucose output was similarly suppressed in both groups of subjects. Doubling the insulin infusion rate, we obtained similar results in patients and controls respectively. So we conclude that in Turner syndrome the insulin resistance state is mainly due to a muscular receptor defect.     

Effect of sulphonylurea on glucose-stimulated insulin secretion in healthy and non-insulin dependent diabetic subjects: a dose-response study

The effect of a rapid-acting sulphonylurea, glipizide, on the dose-response relationship between the -cell response (insulin and C-peptide secretion) and the ambient plasma glucose concentration was examined in 12 healthy and 6 non-insulin-dependent diabetic subjects. The subjects participated in two sets of experiments which were performed in random order: (A) four hyperglycaemic clamp studies, during which the plasma glucose concentration was raised for 120 min by 1 (only in healthy subjects), 3, 7, and 17 mmol/l; and (B) the same four hyperglycaemic clamp studies preceded by ingestion of 5 mg glipizide. All subjects participated in a further study, in which glipizide was ingested and the plasma glucose concentration was maintained at the basal level. In control subjects in the absence of glipizide, the firstphase plasma insulin response (0–10 min) increased progressively with increasing plasma glucose concentration up to 10 mmol/l, above which it tended to plateau. Glipizide augmented the first-phase insulin response without changing the slope of the regression line relating plasma insulin to glucose concentrations. The second-phase plasma insulin response (20–120 min) increased linearly with increasing hyperglycaemia (r=0.997). Glipizide alone increased the plasma insulin response by 180 pmol/l. A similar increase in plasma insulin response following glipizide was observed at each hyperglycaemic step, indicating that glipizide did not affect the sensitivity of the -cell to glucose. First-phase insulin secretion was reduced in the type 2 (non-insulin-dependent) diabetic patients, and was not influenced by glipizide. The dose-response curve relating second-phase insulin secretion to the ambient plasma glucose concentration was significantly (P<0.001) flatter in the diabetic patients than in the control subjects. Glipizide alone increased the plasma insulin response by 60 pmol/l without changing the slope of the dose-response curve. It is concluded that, in both type 2 diabetic patients and healthy subjects: (A) sulphonylurea augments glucose-stimulated second-phase insulin secretion without changing the sensitivity of the -cell to glucose; (B) first-phase insulin secretion is reduced in non-insulin-dependent diabetic patients with fasting hyperglycaemia and is not influenced by sulphonylurea.     

Lack of effect of a physiological elevation of plasma non-esterified fatty acid levels on insulin secretion

Elevated plasma non-esterified fatty acid (NEFA) levels in obese subjects may contribute to their higher insulin secretory rates by direct effects on the islet B-cells. This may involve short-term metabolic effects, or long-term effects on islet B-cell mass, which is characteristically increased in obesity. We examined the effects of elevating plasma NEFA levels for 5.5 to 7 h on insulin secretion after an overnight fast and during a 90 min 12 mmol/l hyperglycemic clamp in 9 normal women (40.1 +/- 9.5 years [mean +/- SD]; BMI: 25.2 +/- 3.72 kg/m(2) ). Subjects were studied twice. In one study plasma NEFA levels were increased approximately 2-fold by infusion of 20% Intralipid (60 ml/h) and heparin (900 U/h) for 5.5 h before and throughout the glucose clamp. Elevated NEFA levels were associated with a small increase in fasting plasma glucose (5.0 +/- 0.1 vs 4.7 +/- 0.1 mmol/l, P <0.05) and C-peptide levels (0.54 +/- 0.09 vs 0.41 +/- 0.06 nmol/l, P <0.05). The increase in fasting insulin levels did not, however, reach statistical significance (9.0 +/- 2.5 vs 5.3 +/- 1.4 mU/l, NS). During the glucose clamp, plasma NEFA levels were suppressed to very low levels in the saline control study. Although plasma NEFA levels also fell in the lipid/heparin study, they remained significantly higher than on the control day, and somewhat higher than might be expected postprandially in obese subjects. During the glucose clamps, plasma glucose, insulin, and C-peptide profiles were similar on the two study days. No difference in either first or second phase insulin secretion was observed between the two studies. In conclusion, our findings do not support the idea that the exaggerated insulin secretion in obesity is mediated by short-term effects of plasma NEFA levels on islet B-cell metabolism, independent of plasma glucose levels.     

Altered metabolic and hormonal responses to epinephrine and beta-endorphin in human obesity

Catecholamines and endogenous opioid peptides are released in response to stress. Exogenous infusions of epinephrine and beta-endorphin (both in doses of 15, 50, and 80 ng/kg.min sequentially, each dose lasting 30 min) were used to mimic short term stress in both normal weight (body mass index, less than 25 kg/m2) and obese (body mass index, greater than 30 kg/m2) subjects. Fasting plasma insulin, C-peptide, and beta-endorphin concentrations were significantly higher in the obese than in the normal subjects (P less than 0.01-0.005). In lean subjects epinephrine produced significant increases in plasma glucose levels, but no appreciable changes in plasma insulin, C-peptide, or glucagon. Infusion of beta-endorphin in the same subjects caused plasma glucose and glucagon to rise, but insulin and C-peptide levels did not change. The simultaneous infusion of epinephrine and beta-endorphin produced a glycemic response which, although greater, was not significantly different than the sum of the responses to the individual hormone infusions. However, the two hormones had a synergistic interaction on plasma glucagon levels [total glucagon response, 2275 +/- 370 pg/min.mL (ng/min.L); sum of single effects, 750 +/- 152 (+/- SE) pg/min.mL (ng/min.L); P less than 0.01]. The plasma epinephrine [207 +/- 21, 607 +/- 70, and 1205 +/- 134 pg/mL (1130 +/- 115, 3640 +/- 382, and 6577 +/- 691 pmol/L] and beta-endorphin [875 +/- 88, 1250 +/- 137, and 1562 +/- 165 pg/mL (250 +/- 25, 358 +/- 39, and 447 +/- 47 pmol/L] concentrations attained during the infusions of each single hormone were not different from those recorded during the combined hormonal infusion. In obese subjects epinephrine raised plasma glucose levels and caused dose-related increments of plasma glucagon concentrations. Plasma insulin and C-peptide concentrations remained low and rebounded at the end of the infusions. In the same subjects, beta-endorphin produced elevations of plasma glucose, insulin, C-peptide, and glucagon. When the combined hormonal infusion was given to obese subjects, the plasma epinephrine and beta-endorphin concentrations rose to values not significantly different from those in normal weight subjects. However, there was a dramatic increase in plasma glucose exceeding 200 mg/dL (11.1 mmol/L), which remained elevated 30 min after the infusion. The glucagon response was not greater than the sum of the single effects.(ABSTRACT TRUNCATED AT 400 WORDS)     

Feedback inhibition of insulin secretion is altered in cirrhosis

Hyperinsulinemia in human cirrhosis is generally considered an expression of reduced hepatic insulin degradation. To determine whether hyperinsulinemia may also depend on an altered feedback inhibition of insulin secretion, we performed euglycemic hyperinsulinemic clamp studies, infusing 40, 372, or 1280 mU/m2 X min biosynthetic human insulin in 30 compensated cirrhotic patients with portal hypertension and impaired glucose tolerance and 25 normal subjects, matched for age, sex, and weight. Mean fasting plasma insulin was significantly higher in cirrhotic patients [26.1 +/- 2.3 vs. 12.4 +/- 0.6 (+/- SE) microU/ml; P less than 0.001], while fasting plasma glucose levels were similar in the 2 groups. The mean plasma C-peptide level was significantly higher in cirrhotic patients, both basally (2.7 +/- 0.1 vs. 1.7 +/- 0.1 ng/ml; P less than 0.001) and during the clamp studies. Suppression of C-peptide at 120 min of the clamp was significantly less in cirrhotic patients (37 +/- 7% vs. 79 +/- 4%, 52 +/- 9% vs. approximately 100%, and 54 +/- 4% vs. approximately 100% during the 40, 372, and 1280 mU/m2 X min insulin infusions, respectively). The fasting C-peptide to insulin molar ratio was significantly lower in cirrhotic patients (5.4 +/- 0.3 vs. 6.4 +/- 0.3; P less than 0.005). The MCR of insulin at the three steady states was not significantly different between the 2 groups, whereas the basal systemic delivery rate of insulin was significantly higher in cirrhotic patients (14.7 +/- 1.7 vs. 6.5 +/- 0.4 mU/m2 X min; P less than 0.001). These results suggest that reduced feedback inhibition of insulin secretion may contribute to the hyperinsulinemia associated with cirrhosis.     

Effects of massive obesity on insulin sensitivity and insulin clearance and the metabolic response to insulin as assessed by the euglycemic clamp technique

Insulin sensitivity was studied in nine nondiabetic massively obese patients (one male and eight females ages 39.0 +/- 2.7 years, body mass index 47.1 +/- 1) by the euglycemic clamp technique (40 microU/m2/min) and compared to seven lean control subjects (three males and three females, ages 34.8 +/- 2.5 years, body mass index 23 +/- 1.1). Fasting plasma glucose, immunoreactive insulin, and C-peptide concentrations were higher in the massively obese patients than in the controls (P less than 0.025). Following exogenous insulin infusion, immunoreactive glucagon and C-peptide concentrations decreased similarly in the massively obese patients and controls, indicating normal sensitivity of the alpha and beta cell to insulin. Glucose uptake (M) expressed either as mg X min-1 of fat free mass was significantly reduced in the massively obese patients compared to the controls (P less than 0.001). Similarly, the M/I ratio (glucose uptake per unit of insulin) was significantly reduced in the massively obese patients (P less than 0.001). Free fatty acids and glycerol concentrations measured in the fasting state were significantly elevated in the massively obese patients (free fatty acids 678 +/- 51 v 467 +/- 55 mumol/L, P less than 0.05; glycerol 97 +/- 9 v 59 +/- 11 mumol/L, P less than 0.02). The effects of insulin on antilipolysis was assessed by measuring the reductions in free fatty acids and glycerol concentration during the glucose clamp study. Although the absolute levels remained higher in the massively obese patients, inhibition of lipolysis was similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Suppression of basal, but not of glucose-stimulated insulin secretion by human insulin in healthy and obese hyperinsulinemic subjects

To evaluate the suppressive effect of biosynthetic human insulin (BHI; 2.5 U/m2 . h) on basal and glucose-stimulated insulin secretion in healthy and obese hyperinsulinemic subjects, the plasma C-peptide response was measured during maintenance of euglycemia and hyperglycemia by means of the glucose clamp technique. In five healthy subjects in whom arterial insulin concentration was increased to 94 +/- 8 microU/mL, but euglycemia was maintained at the fasting level. C-peptide concentration fell from 1.3 +/- 1.0 ng/mL by 21 +/- 8% (P less than 0.05). When hyperglycemia of 7 mmol/L above basal was induced by a variable glucose infusion, the C-peptide response was similar in the control (5.0 +/- 0.6 ng/mL) and BHI experiments (4.7 +/- 0.6 ng/mL) and was paralleled by an identical increase in plasma insulin above the prevailing insulin concentration. In seven obese patients plasma C-peptide fell from 3.5 +/- 0.4 to 2.8 +/- 0.5 ng/mL (P less than 0.05) when BHI was infused at the same rate of euglycemia maintained as in the lean subjects. As in healthy subjects, however, the plasma C-peptide response to the hyperglycemic stimulus (8.7 +/- 0.9 ng/mL) was not altered by BHI (7.9 +/- 0.8 ng/mL). Glucose utilization as determined by the glucose infusion rate necessary to maintain the desired glucose level was reduced by half in the obese patients compared with that of normal subjects. From these data we conclude that in healthy as well as obese hyperinsulinemic subjects, insulin at concentrations capable of suppressing its basal secretion fails to suppress its glucose-stimulated secretion.     

Peripheral insulin parallels changes in insulin secretion more closely than C-peptide after bolus intravenous glucose administration

The changes in peripheral serum insulin and plasma C-peptide levels and in the insulin secretory rate in response to iv glucose (0.5 g/kg BW) administration were studied in seven normal subjects. Insulin secretory rates were calculated according to a two-compartment model of distribution for C-peptide, using individual C-peptide kinetics calculated from iv bolus injections of biosynthetic human C-peptide. The mean plasma glucose level increased from a fasting level of 5.1 +/- 0.1 (+/- SE) to a peak of 24.0 +/- 1.0 mmol/L at 3 min and reached basal levels 101 +/- 6 min after glucose administration. The mean serum insulin value increased from 50 +/- 12 to a peak of 405 +/- 58 pmol/L at 3 min and then declined to fasting levels 139 +/- 14 min after the stimulus. In contrast, the mean plasma C-peptide level increased from 390 +/- 50 to a peak of 1460 +/- 210 pmol/L at 3 min and only began declining 45 min after glucose administration, reaching fasting levels 191 +/- 15 min after the stimulus. The mean insulin secretory rate increased from 69.8 +/- 19.9 to a peak of 1412.7 +/- 159.1 pmol/min at 3 min (15.3 +/- 2.5-fold elevation over baseline) and reached basal levels 135 +/- 12 min after the stimulus. The clearance of endogenous insulin during the basal period (2.505 +/- 0.365 L/min) and that during the 4 h after the stimulus (2.319 +/- 0.230 L/min) were similar. In conclusion, after bolus iv glucose administration: 1) the insulin secretory rate is more closely represented by changes in peripheral serum insulin than in plasma C-peptide levels; and 2) no change in endogenous insulin clearance occurs.     

Increased insulin sensitivity in the high sodium one-kidney, one figure-8 hypertensive rat.

This study examines the relation between sympathetic activity and in vivo insulin-mediated glucose metabolism in a rat model of acquired hypertension. Two groups of conscious, unrestrained rats were studied in the postabsorptive state: sham-operated normotensive rats (n = 10) and renal-wrapped hypertensive rats (n = 10). Mean arterial pressure was increased in the hypertensive compared with the normotensive group in the fed (184 +/- 9 versus 144 +/- 6 mm Hg; p less than 0.01) and in the fasting (147 +/- 8 versus 112 +/- 7 mm Hg; p less than 0.01) state. After a 24-hour fast, hepatic glucose production, plasma glucose, insulin, and norepinephrine concentrations were similar in the two groups. Blood pressure did not change in either group during the 3-milliunits/kg.min euglycemic insulin clamp study; however, plasma norepinephrine concentration rose significantly in hypertensive (207 +/- 24 versus 329 +/- 11 pg/ml; p less than 0.05) but not in normotensive rats (229 +/- 23 versus 267 +/- 27 pg/ml; p = NS). During the insulin clamp study, the hepatic glucose production was similar in the hypertensive (3.8 +/- 0.8 mg/kg.min) compared with the normotensive (4.0 +/- 0.3 mg/kg.min) rats. Insulin-mediated glucose uptake was significantly higher in hypertensive than in normotensive rats (33.0 +/- 0.7 versus 25.8 +/- 0.8; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of increased plasma non-esterified fatty acids (NEFAs) on arginine-stimulated insulin secretion in obese humans

Aims/hypothesis: We have shown previously that the increase of plasma non-esterified fatty acids for 48 h results in decreased glucose-stimulated insulin secretion in lean and non-diabetic obese subjects. It is currently not known if a prolonged increase in non-esterified fatty acids also impairs the insulin secretory response to non-glucose secretagogues. Methods: Heparin and intralipid (to increase plasma non-esterified fatty acid concentrations by about two- to fourfold) or normal saline was infused intravenously for 48 h in 14 non-diabetic obese subjects. On the third day in both studies, insulin, C-peptide, proinsulin, and insulin secretion rate were assessed in response to an intravenous arginine infusion at fasting glucose concentration and a second arginine infusion after a 60-min 11 mmol/l hyperglycaemic clamp. Results: There were no significant differences detected in acute (5 min) or total (90 min) arginine-stimulated C-peptide or insulin secretion response in the heparin-intralipid study compared with the control group at fasting glucose or during hyperglycaemia. Conclusion/interpretation: We have shown that a prolonged increase in plasma NEFA does not blunt arginine-stimulated insulin secretion or plasma insulin concentrations in non-diabetic obese subjects. These findings suggest that the previously demonstrated NEFA-induced impairment in insulin secretory response to glucose cannot be generalized for non-glucose secretagogues. [Diabetologia (2001) 44: 1989–1997] Received: 27 November 2001 and in revised form: 2 August 2001     

Effects of hyperglycaemia and hyperinsulinaemia on plasma amino acid levels in obese subjects with normal glucose tolerance

OBJECTIVE: To investigate the effects of hyperglycaemia and hyperinsulinaemia on amino acid disposal in human obesity. DESIGN: Four sequential experimental conditions: (1) overnight fasting; (2) hyperglycaemia with hyperinsulinaemia (2 h hyperglycaemic clamp at 11 mmol/l); (3) hyperglycaemia with basal insulin (1 h hyperglycaemic clamp during somatostatin infusion), (4) hyperglycaemia with resuming hyperinsulinaemia (1 h hyperglycaemic clamp after somatostatin discontinuation). SUBJECTS: Seven non-obese and seven obese non-diabetic, normo-insulinaemic subjects. MEASUREMENTS: Glucose infused to maintain steady-state hyperglycaemia. Plasma insulin, glucagon, free fatty acid and amino acid concentrations in the last 20 min of the four experimental conditions. Net rates of plasma amino acid disappearance and appearance (micromol/l per hour), calculated as the slopes of the regression of amino acid concentration on time. RESULTS: The amount of glucose infused to maintain hyperglycaemia was reduced by nearly 50% in obese subjects. During hyperinsulinaemia, FFA suppression was lower in obese subjects. In all experimental conditions plasma amino acid levels were slightly, non-significantly higher in obese than in non-obese subjects. In both groups plasma amino acids decreased slightly with ongoing fasting, decreased remarkably during hyperglycaemia-hyperinsulinaemia, rose promptly when insulin concentration was suppressed by somatostatin infusion, and declined again after somatostatin discontinuation. Also the time-course of plasma branched-chain amino acids, which paralleled that of total amino acids, was similar in the two groups. The net rates of amino acid disappearance from plasma did not differ in obese and non-obese subjects both at fasting and during hyperglycaemia-hyperinsulinaemia. Also plasma amino acid appearance during hyperglycaemia with basal insulin was not different in the two groups. CONCLUSION: The net traffic of amino acids to and from plasma in relation to insulin drive and prevailing glucose is not impaired in obese subjects with normal glucose tolerance, in spite of a decreased insulin sensitivity of glucose and lipid metabolism.     

Glucose and insulin suppression of plasma free fatty acids in obese subjects with normal glucose tolerance or mild, newly diagnosed type 2 (non-insulin-dependent) diabetes

The in vivo suppressive effect of glucose and insulin on plasma free fatty acid concentrations was investigated in obese subjects with (n = 6) and without (n = 6) Type 2 (non-insulin-dependent) diabetes mellitus during a 4h-hyperglycemic glucose clamp (about 11.2 mmol/l). Somatostatin was infused (250 micrograms/h) during the third h of glucose clamp to inhibit glucose-stimulated insulin secretion. Plasma insulin values were similar in the two groups at fasting and all throughout the study (F = 0.04; p = NS, two way analysis of variance), while the amount of glucose metabolized during the clamp was lower in diabetic subjects. Plasma free fatty acid concentrations, which were similar in the two groups at fasting, decreased during hyperglycemia and glucose-induced hyperinsulinemia (0-120 min; 180-240 min), and rose during hyperglycemia and somatostatin-inhibited insulin secretion (120-180 min). However, plasma free fatty acid concentrations were significantly higher in diabetic subjects all along the study period both in absolute terms (F = 11.4; p less than 0.0001) and when individual data were recalculated as percent of fasting value (F = 13.3; p less than 0.0001). Our data suggest that suppressibility of fasting plasma free fatty acids is lower in obese Type 2 diabetes in comparison with obese non-diabetic subjects.     

Peripheral and hepatic insulin antagonism in hyperthyroidism

Eight hyperthyroid and eight normal subjects underwent 2-h oral glucose tolerance tests (OGTT) and euglycemic clamp studies to assess the presence of peripheral and hepatic insulin antagonism in hyperthyroidism. Although the mean total glucose area during the OGTT was similar in the hyperthyroid patients and normal subjects [16.4 +/- 0.8 (+/- SE) vs. 15.8 +/- 0.7 mmol/L.h], the mean insulin area was significantly elevated in the hyperthyroid group (1413 +/- 136 vs. 1004 +/- 122 pmol/L.h; P less than 0.05). Basal hepatic glucose production was measured during the second hour of a primed [3-3H]glucose infusion. A two-insulin dose euglycemic clamp study with [3-3H]glucose and somatostatin (500 micrograms/h) was carried out during the next 6 h. The insulin infusion rate was 0.05 mU/kg.min during the third, fourth, and fifth hours and 0.60 mU/kg.min during the sixth, seventh, and eighth hours. Hepatic glucose production and glucose utilization were measured during the final 0.5 h of each clamp period. Serum C-peptide concentrations were measured in the initial sample and in the last sample of each clamp period. The mean equilibrium serum insulin concentrations were similar in both groups during the final 0.5 h of the low (90 +/- 8 vs. 79 +/- 6 pmol/L) and high (367 +/- 11 vs. 367 +/- 15 pmol/L) insulin infusion rates. Basal serum C-peptide levels were significantly increased in the hyperthyroid patients (596 +/- 17 vs. 487 +/- 43 pmol/L; P less than 0.05) but were suppressed equally in both groups at the end of both clamp periods. The MCRs of insulin were similar in the hyperthyroid and normal subjects during the low (6.7 +/- 1.1 vs. 5.6 +/- 0.5 mL/kg.min) and high (11.9 +/- 0.4 vs. 12.1 +/- 0.5 mL/kg.mm) insulin infusion rates. Glucose production was significantly increased in the hyperthyroid patients during the basal state (17.6 +/- 0.9 vs. 11.5 +/- 0.5 mumol/kg.min; P less than 0.001) and remained elevated during the final 0.5 h of the low (12.1 +/- 1.1 vs. 5.9 +/- 1.7; P less than 0.01) and high (3.2 +/- 1.2 vs. 0.5 +/- 0.3; P less than 0.05) insulin infusion rates. Peripheral insulin action, assessed by Bergman's sensitivity index, was significantly decreased in the hyperthyroid patients (7.4 +/- 2.2 vs. 15.6 +/- 2.1 L/kg min-1/pmol/L; P less than 0.02). In conclusion, hyperthyroidism is characterized by 1) hyperinsulinemia after oral glucose loading, 2) increased basal hepatic glucose production, 3) impairment of insulin-mediated suppression of hepatic glucose production, and 4) antagonism to insulin-stimulated peripheral glucose utilization.     

Differences in pharmacokinetics and pharmacodynamics of insulin lispro and aspart in healthy volunteers.

Pharmacokinetic and pharmacodynamic profiles of the rapid-acting insulin analogues lispro and aspart were compared in a randomized, double-blind crossover study of 20 fasting healthy men following a single subcutaneous injection. Either insulin lispro or aspart, 0.05 U/kg-body-weight, was injected subcutaneously and followed by determination of 5-h profiles of plasma glucose, serum C-peptide and insulin concentrations. Lowest glucose concentrations were observed after 50 min in the aspart group (3.2 +/- 0.1 mmol/l versus lispro 3.5 +/- 0.1 mmol/l; p = 0.026) and after 60 min in the lispro group (3.4 +/- 0.1 mmol/l). For blood glucose t min was 59.3 +/- 3.4 min in the aspart and 63.5 +/- 5.3 min in the lispro group (ns). After 40 min a lower C-peptide was determined for aspart (225 +/- 21 pmol/l versus lispro 309 +/- 33 pmol/l; p = 0.031), whereas minimal C-peptide concentrations were reached in both groups after 105 min (lispro 117 +/- 21 pmol/l versus aspart 105 +/- 18 pmol/l). The maximal concentration of insulin was detected in both groups after 40 min (lispro 20.8 +/- 1.1 mU/l versus aspart 24.6 +/- 1.3 mU/l; p = 0.032). For insulin t max was 33.0 +/- 2.6 min in the aspart versus 33.3 +/- 2.6 min in the lispro group (ns). The present results indicate a more rapid absorption of insulin aspart in comparison to insulin lispro. Higher insulin concentrations after subcutaneus injection may be advantageous in meal-related treatment of diabetes.     

Glucagon release and glucose counter-regulation during hypoglycaemia. Modifying effect of the previous glucose level

The importance of a short-term elevation of the ambient glucose level for the release of counter-regulatory hormones and the glucose recovery rate during a subsequent hypoglycaemia was studied in healthy subjects. Hypoglycaemia was induced with insulin infusion after a previous 80 min of euglycaemic (E: 5 mmol/l) or hyperglycaemic (H: 15 mmol/l) glucose clamp. By infusing insulin during the euglycaemic clamp similar levels were reached during both glucose clamps. The same level of hypoglycaemia was reached in both studies (E: 1.5 +/- 0.1, H: 1.5 +/- 0.2 mmol/l) and the insulin levels were also similar both at glucose nadir and during the recovery period. In spite of this, both the mean glucagon levels at nadir at the mean individual maximal increase were significantly lower after the hyperglycaemic clamp (E: 101 +/- 25, H: 54 +/- 7 pg/ml, P less than 0.05). The glucose recovery rate was also significantly impaired following the hyperglycaemic clamp. The results show that a short-term elevation of the ambient glucose level impairs the glucagon release during a subsequent hypoglycaemia. This finding may be of importance for the development of the blunted glucagon release in response to low glucose levels in diabetics.