Reversal of steroid-induced insulin resistance by a nicotinic-acid derivative in man.

A recent report suggested that the glucose-free fatty acid (FFA) cycle may contribute to steroid-induced insulin resistance in rats, and that glucose tolerance could be restored to normal when FFA levels were lowered with nicotinic acid. To test this hypothesis in man, we measured insulin sensitivity (by euglycemic insulin clamp in combination with indirect calorimetry and infusion of tritiated glucose) before and after short-term administration of a nicotinic-acid derivative (Acipimox) in 10 steroid-treated, kidney transplant patients with insulin resistance. Thirty-five healthy subjects served as controls. Six of them received Acipimox. Total body glucose metabolism was reduced in steroid-treated patients compared with control subjects (41.7 +/- 3.3 v 50.0 +/- 2.2 mumol/kg lean body mass [LBM].min, P less than .05). The reduction in insulin-stimulated glucose uptake was mainly due to an impairment in nonoxidative glucose metabolism (primarily glucose storage as glycogen) (18.3 +/- 2.8 v 27.2 +/- 2.2 mumol/kg LBM.min, P less than .01). Acipimox lowered basal FFA concentrations (from 672 +/- 63 to 114 +/- 11 mumol/L, P less than .05) and the rate of lipid oxidation measured in the basal state (1.5 +/- 0.2 to 0.6 +/- 0.1 mumol/kg LBM.min, P less than .01) and during the clamp (0.7 +/- 0.2 to 0.03 +/- 0.2 mumol/kg LBM.min, P less than .05). In addition, Acipimox administration normalized total glucose disposal (to 54.4 +/- 4.4 mumol/kg LBM.min), mainly due to enhanced nonoxidative glucose metabolism (to 28.9 +/- 3.9 mumol/kg LBM.min) in steroid-treated patients (both P less than .05 v before Acipimox).(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of lipolysis during acute GH exposure increases insulin sensitivity in previously untreated GH-deficient adults

OBJECTIVE: Previous studies evaluating the lipolytic effect of GH have in general been performed in subjects on chronic GH therapy. In this study we assessed the lipolytic effect of GH in previously untreated patients and examined whether the negative effect of enhanced lipolysis on glucose metabolism could be counteracted by acute antilipolysis achieved with acipimox. METHODS: Ten GH-deficient (GHD) adults participated in four experiments each, during which they received in a double-blind manner: placebo (A); GH (0.88+/-0.13 mg) (B); GH+acipimox 250 mg b.i.d. (C); and acipimox b.i.d. (no GH) (D), where GH was given the night before a 2 h euglycemic, hyperinsulinemic clamp combined with infusion of [3-(3)H]glucose and indirect calorimetry. RESULTS: GH increased basal free fatty acid (FFA) levels by 74% (P=0.0051) and insulin levels by 93% (P=0.0051). This resulted in a non-significant decrease in insulin-stimulated glucose uptakes (16.61+/-8.03 vs 12.74+/-5.50 micromol/kg per min (s.d.), P=0.07 for A vs B). The rates of insulin-stimulated glucose uptake correlated negatively with the FFA concentrations (r=-0.638, P<0.0001). However, acipimox caused a significant improvement in insulin-stimulated glucose uptake in the GH-treated patients (17.35+/-5.65 vs 12.74+/-5.50 micromol/kg per min, P=0.012 for C vs B). The acipimox-induced enhancement of insulin-stimulated glucose uptake was mainly due to an enhanced rate of glucose oxidation (8.32+/-3.00 vs 5.88+/-2.39 micromol/kg per min, P=0.07 for C vs B). The enhanced rates of glucose oxidation induced by acipimox correlated negatively with the rate of lipid oxidation in GH-treated subjects both in basal (r=-0.867, P=0.0093) and during insulin-stimulated (r=-0.927, P=0.0054) conditions. GH did not significantly impair non-oxidative glucose metabolism (6.86+/-5.22 vs 8.67+/-6.65 micromol/kg per min, P=NS for B vs A). The fasting rate of endogenous glucose production was unaffected by GH and acipimox administration (10.99+/-1.98 vs 11.73+/-2.38 micromol/kg per min, P=NS for B vs A and 11.55+/-2.7 vs 10.99+/-1.98 micromol/kg per min, P=NS for C vs B). On the other hand, acipimox alone improved glucose uptake in the untreated GHD patients (24.14+/-8.74 vs 16.61+/-8.03 micromol/kg per min, P=0.0077 for D vs A) and this was again due to enhanced fasting (7.90+/-2.68 vs 5.16+/-2.28 micromol/kg per min, P=0.01 for D vs A) and insulin-stimulated (9.78+/-3.68 vs 7.95+/-2.64 micromol/kg per min, P=0.07 for D vs A) glucose oxidation. CONCLUSION: The study of acute administration of GH to previously untreated GHD patients provides compelling evidence that (i) GH-induced insulin resistance is mainly due to induction of lipolysis by GH; and (ii) inhibition of lipolysis can prevent the deterioration of insulin sensitivity. The question remains whether GH replacement therapy should, at least at the beginning of therapy, be combined with means to prevent an excessive stimulation of lipolysis by GH.     

The effect of long-term pharmacological antilipolysis on substrate metabolism in growth hormone (GH)-substituted GH-deficient adults

The lipolytic properties of GH are essential for the acute effects on glucose metabolism and insulin sensitivity, whereas its more long-term impact on substrate metabolism is uncertain. The aim of the study was to evaluate the influence of pharmacological antilipolysis on substrate metabolism during constant and continued GH exposure. Seven adult GH-deficient (GHD) patients were studied twice in a double-blind randomized order: 1) after 4 wk of acipimox treatment (250 mg, orally, three times daily) and 2) after 4 wk of placebo treatment. Daily GH replacement was continued throughout both study periods. At the end of each period glucose and lipid oxidation rates were assessed by indirect calorimetry, and the protein oxidation rate was estimated by urinary excretion of urea. Endogenous glucose production and whole body protein metabolism were assessed by isotope dilution techniques using tritiated glucose and stable phenylalanine and tyrosine isotopes, respectively. GH and IGF-I levels were not different between periods, whereas FFA and glycerol levels were distinctly suppressed after 4 wk of pharmacological antilipolysis [FFA, 256 +/- 63 (acipimox) vs. 596 +/- 69 (placebo) micromol/liter; P = 0.001]. Likewise, plasma levels of total and low density lipoprotein cholesterol as well as triglycerides were significantly reduced after acipimox. Despite this, lipid oxidation rates were identical at the end of the two treatment periods [589 +/- 106 (acipimox) vs. 626 +/- 111 (placebo) kcal/24 h; P = 0.698]. The total and oxidative rates of glucose as well as protein oxidation and urea excretion were identical at the end of the two treatment periods (P > 0.05). Phenylalanine flux, a measure of protein turnover, was increased [34.62 +/- 1.83 (acipimox) vs. 33.15 +/- 1.61 (placebo) micromol/kg.h; P = 0.049] as was phenylalanine incorporation into protein, a measure of protein synthesis [30.79 +/- 1.67 (acipimox) vs. 28.97 +/- 1.51 (placebo) micromol/kg.h; P = 0.035]. The following conclusions were reached: 1) prolonged antilipolysis by means of acipimox stimulates protein turnover without affecting net protein balance; and 2) acipimox in combination with constant GH exposure results in sustained suppression of circulating levels of FFA, glycerol, and triglycerides without a reduction in the rate of lipid oxidation. The site and origin of lipid fuels for oxidation during suppression of lipolysis remain to be determined.     

The control on growth hormone release by free fatty acids is maintained in acromegaly

Free fatty acids (FFA) physiologically regulate GH release via a negative feedback. The aim of this study was to examine whether such feedback is preserved in acromegaly, a condition in which alterations in other regulatory mechanisms of GH release occur. Eight acromegalic patients (group 1: five women and three men, 43.0 +/- 4.2 yr old, mean +/- SE) received per os on two different days, at a 3 day-interval, in a random order, placebo or 250 mg of acipimox, an inhibitor of lipolysis analogous to nicotinic acid, at 0700 and 1100 h. In both tests GHRH (1-29 NH2), 50 microg, was administered i.v. at 1300 h. Blood samples for GH, FFA, immunoreactive insulin (IRI), and glucose were taken from 0900 to 1500 h, and the time period considered for statistical analysis was 1200-1500 h, representative of steady-state condition for FFA, IRI, and glucose. Mean plasma FFA levels (1200-1500 h) were significantly lower after acipimox than after placebo (0.05 +/- 0.01 vs. 0.17 +/- 0.01 g/L, P < 0.01). In contrast, both mean basal GH levels (1200-1300 h) and the mean GH response to GHRH (GH delta area, 1300-1500 h) were significantly higher after acipimox than after placebo (12.0 +/- 1.9 vs. 7.8 +/- 1.2 microg/L, P < 0.01; 2937 +/- 959 vs. 1154 +/- 432 microg/L x 120 min, P < 0.01). The increase in both basal GH levels and GH delta area occurred in all eight patients. Acipimox also reduced mean serum IRI (83 +/- 12 vs. 112 +/- 14 pmol/L) and blood glucose (5.1 +/- 0.1 vs. 5.7 +/- 0.1 mmol/L) levels, as compared with placebo (P < 0.03 or less). Eight acromegalic patients (group 2: six women and two men, 46.6 +/- 5.7 yr old) underwent a constant i.v. 10% lipid infusion (150 mL/h), started at 0900 h and continued until 1500 h. Mean plasma FFA levels (1200-1500 h) were significantly higher during lipid infusion than after placebo (0.27 +/- 0.01 vs. 0.16 +/- 0.01 g/L, P < 0.02); in contrast, mean basal GH levels (1200-1300 h) were reduced by lipid infusion, as compared with placebo (9.9 +/- 3.1 vs. 16.6 +/- 4.4 microg/L, P < 0.01), and the same occurred for the GH delta area after GHRH (2498 +/- 1643 vs. 4512 +/- 1988 microg/L x 120 min, P < 0.01). Serum IRI and blood glucose levels were similar after placebo and during lipid infusion. These data indicate that, in acromegaly, the acute reduction of circulating FFA levels results in increased GH release, whereas the increase in circulating FFA levels is accompanied by a reduced GH release. Taken together, these findings suggest that, in acromegaly, the control of FFA on GH release is preserved.     

Effects of prolonged Acipimox treatment on glucose and lipid metabolism and on in vivo insulin sensitivity in patients with non-insulin dependent diabetes mellitus.

The effect of prolonged treatment with Acipimox on in vivo peripheral insulin sensitivity, and on glucose and lipid metabolism, was investigated in patients with NIDDM in a double-blind study. Twelve NIDDM patients were randomized to treatment with either placebo or Acipimox in pharmacological doses (250 mg x 3) for three months. Fasting plasma glucose, insulin, C-peptide and HbA1c concentrations were unaffected after three months of acipimox treatment. However, fasting plasma non-esterified fatty acid (NEFA) concentrations were twofold elevated after Acipimox treatment (1.34 +/- 0.09 vs 0.66 +/- 0.09 mmol/l; p < 0.05). Despite this, repeated acute Acipimox administration after the three months' treatment period enhanced total insulin-stimulated glucose disposal to the same extent as acute Acipimox administration before the treatment period (367 +/- 59 vs 392 +/- 66 mg.m-2.min-1, NS; both p < 0.05 vs placebo glucose disposal) (267 +/- 44 mg.m-2.min-1). In conclusion, insulin resistance or tachyphylaxis towards the effects of Acipimox on insulin stimulated glucose disposal was not induced during prolonged Acipimox treatment. The lack of improvement of blood glucose control in the patients with NIDDM may be due to the demonstrated rebound effect of lipolysis.     

Mediation of the hepatic effects of growth hormone by its lipolytic activity.

The aim of the study was to investigate the acute effect of GH per se, independent from its lipolytic activity, on glucose and lipid oxidation and glucose turnover in seven healthy subjects. Five tests lasting 360 min were performed. Each test consisted of a 4-h equilibration period followed by a euglycemic hyperinsulinemic (25 mU/kg x h) clamp lasting 2 h. In test 1 (control experiment) saline was infused, leaving GH and FFA at basal levels. In tests 2, 3, and 4, GH was infused (80 ng/kg x min) to increase GH levels. Whereas in test 2 FFA levels were free to increase due to GH lipolytic activity, in test 3 FFA elevation was prevented by using an antilipolytic compound (Acipimox) that allowed evaluation of the effect of GH at low FFA levels. In test 4 (GH+Acipimox+heparin) GH infusion was associated with the administration of Acipimox and heparin to maintain FFA at the basal level to evaluate the effect of GH per se independent from GH lipolytic activity. In test 5 Acipimox and a variable heparin infusion were given to evaluate possible effects of Acipimox other than the inhibition of lipolysis. During the euglycemic hyperinsulinemic clamp in the presence of high GH and FFA levels (test 2), glucose oxidation was significantly lower and lipid oxidation was significantly higher than in tests 1, 3, 4, and 5. During the same period, hepatic glucose production was completely suppressed in the control study (test 1; 94%) and in test 5 (99.6%), whereas it was significantly less inhibited (65%, 74%, and 73%) when GH was administered in tests 2, 3, and 4. In conclusion, these results suggest that GH directly mediates the reduction of insulin's effect on the liver. In addition, the effect of GH on glucose and lipid oxidation is not direct, but is mediated by its lipolytic activity.     

Insulin mediated inhibition of hormone sensitive lipase activity in vivo in relation to endogenous catecholamines in healthy subjects

The regulation of hormone-sensitive lipase activity in vivo has not been studied in detail before. We have performed noninvasive in vivo tests to measure hormone-sensitive lipase activity under high plasma levels of endogenous insulin and catecholamines. For this purpose, two mental stress tests were carried out at random in 13 healthy volunteers. The subjects ingested 200 ml of a placebo solution or 20% glucose, followed by 1 h of rest, 20 min of mental stress, and 40 min of rest. Twenty minutes after the ingestion of glucose, insulin levels increased from 6.8 +/- 1.6 to a maximum of 30.5 +/- 4.8 mU/liter (P < 0.01), whereas the increase in insulin was significantly less after placebo (from 5.7 +/- 0.9 to 9.5 +/- 1.5 mU/liter; P < 0.01). The increase in heart rate, as an estimate of the amount of stress, was similar in both tests (12% increase). During stress, plasma norepinephrine and epinephrine concentrations increased by 24% and 44%, respectively, after glucose and by 4% and 21%, respectively, after placebo (n = 6). Fasting plasma FFA were similar in both tests (placebo, 0.35 +/- 0.07 mM; glucose, 0.46 +/- 0.08 mM). Forty minutes after ingestion of placebo, plasma FFA concentrations decreased to 0.27 +/- 0.07 mM, compared with a stronger suppression to 0.11 +/- 0.02 mM after ingestion of glucose (P < 0.01). By 10 min after mental stress, plasma FFA concentrations increased by 53% after placebo (P < 0.01), in contrast to unchanged FFA concentrations after ingestion of glucose. Taken together, these results suggest that the suppression of hormone-sensitive lipase by endogenous insulin in healthy, insulin-sensitive subjects is stronger than the stimulation by endogenous catecholamines.     

Effects of morning cortisol replacement on glucose and lipid metabolism in GH-treated subjects

OBJECTIVE: Insulin resistance is a frequent consequence of GH replacement therapy but patients on GH replacement therapy often also have replacement of other hormone deficiencies which theoretically could modify the metabolic effects of GH. In particular, cortisol replacement if given in supra physiologic doses immediately before the evaluation of insulin sensitivity could influence insulin sensitivity. The aim of this study was thus to evaluate the effect of morning cortisol replacement given prior to a euglycaemic clamp combined with infusion of [3-(3)H]glucose and indirect calorimetry on glucose and lipid metabolism. METHODS: Ten GH/ACTH-deficient adults received, in a double-blind manner, either cortisol (A) or placebo (B) before the clamp whereas five GH-deficient-ACTH-sufficient adults participated in a control (C) clamp experiment. All subjects received GH replacement therapy. RESULTS: Serum cortisol levels were significantly higher after cortisol than after placebo (324+/-156 vs 132+/-136 mmol/l; P=0.006) and similar to controls (177+/-104 mmol/l). As a measure of the biological effect of cortisol, eosinophil leukocyte counts in peripheral blood decreased (164+/-91 x 10(9)/l vs 216+/-94 x 10(9)/l; P=0.04). Cortisol replacement had no significant effect on insulin-stimulated glucose uptake (11.8+/-1.8 vs 13.2+/-3.9 micromol/kg min), either on glucose oxidation or on glucose storage. There was also no significant effect of cortisol on fasting endogenous glucose production and no effect was seen on serum free fatty acid concentrations. CONCLUSION: Administration of cortisol in the morning before a clamp cannot explain the insulin resistance seen with GH replacement therapy.     

The impact of pegvisomant treatment on substrate metabolism and insulin sensitivity in patients with acromegaly

CONTEXT: Pegvisomant is a specific GH receptor antagonist that is able to normalize serum IGF-I concentrations in most patients with acromegaly. The impact of pegvisomant on insulin sensitivity and substrate metabolism is less well described. PATIENTS AND METHODS: We assessed basal and insulin-stimulated (euglycemic clamp) substrate metabolism in seven patients with active acromegaly before and after 4-wk pegvisomant treatment (15 mg/d) in an open design. RESULTS: After pegvisomant, IGF-I decreased, whereas GH increased (IGF-I, 621 +/- 82 vs. 247 +/- 33 microg/liter, P = 0.02; GH, 5.3 +/- 1.5 vs. 10.8 +/- 3.3 microg/liter, P = 0.02). Basal serum insulin and plasma glucose levels decreased after treatment (insulin, 54 +/- 5.9 vs. 42 +/- 5.3 pmol/liter, P = 0.001; glucose, 5.7 +/- 0.1 vs. 5.3 +/- 0.0 mmol/liter, not significant), whereas palmitate kinetics were unaltered. During the clamp, the glucose infusion rate increased after pegvisomant (3.1 +/- 0.5 vs. 4.4 +/- 0.6 mg/kg.min, P = 0.02), whereas the suppression of endogenous glucose production tended to increase (0.7 +/- 0.0 vs. 0.5 +/- 0.1 mg/kg.min, not significant). Total resting energy expenditure decreased after pegvisomant treatment (1703 +/- 109 vs. 1563 +/- 101 kcal/24 h, P = 0.03), but the rate of lipid oxidation did not change significantly. CONCLUSIONS: 1) Pegvisomant treatment for 4 wk improves peripheral and hepatic insulin sensitivity in acromegaly. 2) This is associated with a decrease in resting energy expenditure, whereas free fatty acid metabolism is unaltered. 3) The data support the important direct effects of GH on glucose metabolism and add additional benefits to pegvisomant treatment for acromegaly.     

Effects of growth hormone administration on protein dynamics and substrate metabolism during 4 weeks of dietary restriction in obese women

OBJECTIVE: Treatment of obesity with very low calorie diet (VLCD) is complicated by protein loss. We evaluated the effects of coadministration of GH on protein turnover, substrate metabolism, and body composition in VLCD treated obesity. DESIGN AND PATIENTS: Fifteen obese women underwent 4 weeks of very low calorie diet (VLCD) in parallel with GH treatment (n = 7) or placebo (n = 8). MEASUREMENTS: Protein metabolism and total glucose turnover were isotopically assayed. Plasma concentrations of amino acids were determined by an HPLC system. Estimated rates of lipid and glucose oxidation were obtained by indirect calorimetry. Fat free mass was determined by DEXA-scan. RESULTS: Protein breakdown decreased in both groups (tyrosine flux micromol/h): -12% +/- 3 (GH) vs. - 9% +/- 3 (placebo)). Phenylalanine degradation in relation to phenylalanine concentration decreased by 9% in the GH group, whereas an increase of 8% was observed in the placebo group (P = 0.1). Plasma concentrations of several amino acids were significantly decreased in the placebo group, while urea excretion decreased in the GH group. A decrease in FFM was found in placebo treated patients (2.14% +/- 1.9 (GH) vs. - 3.54% +/- 1.6 (placebo), P < 0.05). Rates of lipid oxidation tended to be increased by GH treatment (lipid oxidation (mg/minutes): 79.7 +/- 5.9 (GH) vs. 64.6 +/- 5.9 (placebo), P = 0.1). CONCLUSION: During dietary restriction GH primarily seems to conserve protein by a reduced hepatic degradation of amino acids.     

Continuation of growth hormone (GH) therapy in GH-deficient patients during transition from childhood to adulthood: impact on insulin sensitivity and substrate metabolism

The appropriate management of GH-deficient patients during transition from childhood to adulthood has not been reported in controlled trials, even though there is evidence to suggest that this phase is associated with specific problems in relation to GH sensitivity. An issue of particular interest is the impact of GH substitution on insulin sensitivity, which normally declines during puberty. We, therefore, evaluated insulin sensitivity (euglycemic glucose clamp) and substrate metabolism in 18 GH-deficient patients (6 females and 12 males; age, 20 +/- 1 yr; body mass index, 25 +/- 1 kg/m2) in a placebo-controlled, parallel study. Measurements were made at baseline, where all patients were on their regular GH replacement, after 12 months of either continued GH (0.018 +/- 0.001 mg/kg day) or placebo, and finally after 12 months of open phase GH therapy (0.016 mg/kg x day). Before study entry GH deficiency was reconfirmed by a stimulation test. During the double-blind phase, insulin sensitivity and fat mass tended to increase in the placebo group [deltaM-value (mg/kg x min), -0.7 +/- 1.1 (GH) vs. 1.3 +/- 0.8 (placebo), P = 0.18; deltaTBF (kg), 0.9 +/- 1.2 (GH) vs. 4.4 +/- 1.6 (placebo), P = 0.1]. Rates of lipid oxidation decreased [delta lipid oxidation (mg/kg x min), 0.02 +/- 0.14 (GH) vs. -0.32 +/- 0.13 (placebo), P < 0.05], whereas glucose oxidation increased in the placebo-treated group (P < 0.05). In the open phase, a decrease in insulin sensitivity was found in the former placebo group, although they lost body fat and increased fat-free mass [M-value (mg/kg x min), 5.1 +/- 0.7 (placebo) vs. 3.4 +/- 1.0 (open), P = 0.09]. In the group randomized to continued GH treatment almost all hormonal and metabolic parameters remained unchanged during the study. In conclusion, 1) discontinuation of GH therapy for 1 yr in adolescent patients induces fat accumulation without compromising insulin sensitivity; and 2) the beneficial effects of continued GH treatment on body composition in terms of decrease in fat mass and increase in fat-free mass does not fully balance the direct insulin antagonistic effects.     

Sustained reduction in plasma free fatty acid concentration improves insulin action without altering plasma adipocytokine levels in subjects with strong family history of type 2 diabetes

To investigate the effect of a sustained (7-d) decrease in plasma free fatty acid (FFA) concentration in individuals genetically predisposed to develop type 2 diabetes mellitus (T2DM), we studied the effect of acipimox, a potent inhibitor of lipolysis, on insulin action and adipocytokine concentrations in eight normal glucose-tolerant subjects (aged 40 +/- 4 yr, body mass index 26.5 +/- 0.8 kg/m(2)) with at least two first-degree relatives with T2DM. Subjects received an oral glucose tolerance test (OGTT) and 120 min euglycemic insulin clamp (80 mU/m(2).min) with 3-[(3)H] glucose to quantitate rates of insulin-mediated whole-body glucose disposal (Rd) and endogenous (primarily hepatic) glucose production (EGP) before and after acipimox, 250 mg every 6 h for 7 d. Acipimox significantly reduced fasting plasma FFA (515 +/- 64 to 285 +/- 58 microm, P < 0.05) and mean plasma FFA during the OGTT (263 +/- 32 to 151 +/- 25 microm, P < 0.05); insulin-mediated suppression of plasma FFA concentration during the insulin clamp also was enhanced (162 +/- 18 to 120 +/- 15 microm, P < 0.10). Following acipimox, fasting plasma glucose (5.1 +/- 0.1 vs. 5.2 +/- 0.1 mm) did not change, whereas mean plasma glucose during the OGTT decreased (7.6 +/- 0.5 to 6.9 +/- 0.5 mm, P < 0.01) without change in mean plasma insulin concentration (402 +/- 90 to 444 +/- 102 pmol/liter). After acipimox Rd increased from 5.6 +/- 0.5 to 6.8 +/- 0.5 mg/kg.min (P < 0.01) due to an increase in insulin-stimulated nonoxidative glucose disposal (2.5 +/- 0.4 to 3.5 +/- 0.4 mg/kg.min, P < 0.05). The increment in Rd correlated closely with the decrement in fasting plasma FFA concentration (r = -0.80, P < 0.02). Basal EGP did not change after acipimox (1.9 +/- 0.1 vs. 2.0 +/- 0.1 mg/kg.min), but insulin-mediated suppression of EGP improved (0.22 +/- 0.09 to 0.01 +/- 0.01 mg/kg.min, P < 0.05). EGP during the insulin clamp correlated positively with the fasting plasma FFA concentration (r = 0.49, P = 0.06) and the mean plasma FFA concentration during the insulin clamp (r = 0.52, P < 0.05). Plasma adiponectin (7.1 +/- 1.0 to 7.2 +/- 1.1 microg/ml), resistin (4.0 +/- 0.3 to 3.8 +/- 0.3 ng/ml), IL-6 (1.4 +/- 0.3 to 1.6 +/- 0.4 pg/ml), and TNFalpha (2.3 +/- 0.3 to 2.4 +/- 0.3 pg/ml) did not change after acipimox treatment.We concluded that sustained reduction in plasma FFA concentration in subjects with a strong family history of T2DM increases peripheral (muscle) and hepatic insulin sensitivity without increasing adiponectin levels or altering the secretion of other adipocytokines by the adipocyte. These results suggest that lipotoxicity already is well established in individuals who are genetically predisposed to develop T2DM and that drugs that cause a sustained reduction in the elevated plasma FFA concentration may represent an effective modality for the prevention of T2DM in high-risk, genetically predisposed, normal glucose-tolerant individuals despite the lack of an effect on adipocytokine concentrations.     

In vivo modulation of plasma free fatty acids in patients with familial combined hyperlipidemia using lipid-lowering medication

One of the best studied aspects of the insulin resistance syndrome in familial combined hyperlipidemia (FCHL) is impaired insulin-mediated suppression of FFA by diminished inhibition of hormone-sensitive lipase (HSL). In vitro experiments have shown that stimulation of HSL activity by catecholamines is decreased in FCHL. The aim of this study was to investigate HSL inhibition by insulin and stimulation by endogenous catecholamines in vivo in FCHL patients. Twelve FCHL subjects using lipid-lowering medication and 12 controls underwent a mental stress test after random ingestion of either 50 g glucose or placebo. After ingestion of glucose, insulin concentrations increased from 76.8 +/- 21.5 pM to a maximum of 520.2 +/- 118.4 pM (P < 0.01) in FCHL and from 38.0 +/- 5.0 to 221.7 +/- 25.1 pM (P < 0.01) in controls. The percent decreases in plasma FFA during the first hour after glucose ingestion were similar in FCHL and controls (67 +/- 5% vs. 72 +/- 3%, respectively), suggesting a comparable inhibition of HSL in both. During the placebo test, FFA increased similarly in FCHL (56 +/- 9%) and controls (57 +/- 19%). In contrast, FFA concentrations did not change during mental stress after ingestion of glucose (from 0.17 +/- 0.02 to 0.15 +/- 0.02 mmol/liter in FCHL and from 0.11 +/- 0.02 to 0.12 +/- 0.02 mmol/liter in controls). In conclusion, the present study provides in vivo evidence for intact insulin-mediated suppression of FFA in FCHL, although this inhibition of HSL was achieved by higher insulin levels, suggesting insulin resistance at the level of HSL. Secondly, the induction of HSL activity by endogenous catecholamines in vivo is not decreased in FCHL, in contrast to earlier in vitro findings. Finally, catecholamine-induced HSL activation can be inhibited by insulin in a similar manner in both FCHL and controls.     

Effects of a physiological growth hormone pulse on substrate metabolism in insulin-dependent (type 1) diabetic subjects.

When present in inappropriate amounts GH induces substantial insulin resistance and it has furthermore been suggested that modest nocturnal surges of GH may precipitate the emergence of the dawn phenomenon. To characterize the metabolic effects of physiologically relevant, small-scale GH exposure, six type 1 diabetic subjects were studied for 5 h in the postabsorptive state after an iv pulse of either 210 micrograms GH or saline. Identical amounts of insulin were infused on both occasions to maintain a prevailing blood glucose concentration of 125 +/- 12 mg/100 ml. The GH bolus caused an increase in serum GH levels to a peak value of 22 +/- 2 micrograms/L after 10 min, a 70% increase in serum FFA (from 570 +/- 80 to 980 +/- 60 mumol/L) and a 400% increase in blood 3-hydroxybutyrate (3-OHB) (from 100 +/- 15 to 420 +/- 35 mumol/l) concentrations after 180 and 240 min respectively (P less than 0.05). Blood glycerol and forearm uptake of 3-OHB rose in parallel (P less than 0.01). Plasma glucose, isotopically measured glucose turnover and forearm glucose uptake was not affected by GH. Blood lactate concentrations increased (P less than 0.05) and nonoxidative glucose use and lipid oxidation tended to increase with GH. Energy expenditure remained unaffected. These results suggest that under everyday conditions GH acts as an important regulator of fuel fluxes in type 1 diabetic subjects, the main effect being a transient stimulation of lipolysis. Since no significant effect on glucose metabolism was recorded, we do not presently find evidence to support a primary role for small surges of GH in the pathogenesis of the dawn phenomenon.     

Insulin resistance early in adulthood in subjects born with intrauterine growth retardation

In a case-control study that investigated the effect of intrauterine growth retardation (IUGR) on glucose homeostasis, 20-yr-old adults born with IUGR were shown to be hyperinsulinemic in an oral glucose tolerance test, suggestive of insulin resistance. The aim of this study was to ascertain the decreased insulin sensitivity in young IUGR-born adults compared to that in controls. We studied 26 IUGR-born subjects and 25 controls, aged 25 yr. Insulin sensitivity was assessed by peripheral glucose uptake and monitoring free fatty acid (FFA) concentrations under euglycemic hyperinsulinemic clamp. The percent body fat was significantly higher in the IUGR group (27.2 +/- 7.6% vs. 22.0 +/- 7.3%; P = 0.02), contrasting with comparable body mass index in both groups. Insulin-stimulated glucose uptake was significantly lower in IUGR-born subjects than in controls (6.7 +/- 2.9 vs. 8.0 +/- 1.9 mg/kg fat-free mass x min; P = 0.05), and the difference remained significant after adjustment for body mass index, total body fat, or waist to hip ratio. In IUGR-born subjects, insulin-stimulated FFA suppression correlated significantly with peripheral glucose uptake (r2 = 0.23; P = 0.02). First phase insulin release in the iv glucose tolerance test, adjusted for insulin sensitivity, did not significantly differ between IUGR and control groups (442 +/- 284 vs. 391 +/- 209 pmol/L; P = 0.86). In conclusion, IUGR subjects have decreased insulin-stimulated glucose uptake as early as 25 yr of age without major impairment of insulin secretion. Low glucose uptake is associated with a lesser degree of FFA suppression in adipose tissue, which suggests a role of adipose tissue at an early stage of insulin resistance in these subjects.     

Effect of pioglitazone on circulating adipocytokine levels and insulin sensitivity in type 2 diabetic patients

We examined the effect of pioglitazone (PIO) on circulating adipocytokine levels to elucidate the mechanisms by which thiazolidinediones improve insulin resistance in type 2 diabetes mellitus (T2DM). Twenty-three subjects with T2DM (age 54 +/- 2 yr, body mass index 29 +/- 1 kg/m(2)) were randomly assigned to receive placebo (n = 11) or PIO, 45 mg/d (n = 12), for 4 months. Before and after treatment, subjects received a 75-g oral glucose tolerance test (OGTT); euglycemic insulin clamp (40 mU/m(2).min) with 3-(3)H-glucose; determination of fat mass ((3)H(2)O); and measurement of fasting glucose, free fatty acids (FFAs), leptin, adiponectin, and TNFalpha concentrations. After 4 months of PIO, fasting plasma glucose concentration (Delta = -2.7 mol/liter), mean plasma glucose during OGTT (Delta = -3.8 mol/liter), and hemoglobin A(1c) (Delta = 1.7%) decreased (P < 0.05 vs. placebo) without change in fasting or post-OGTT plasma insulin levels. Fasting FFAs (Delta = 168 micromol/liter) and TNFalpha (Delta = 0.7 pg/ml) concentrations decreased (P < 0.05 vs. placebo), whereas adiponectin (Delta = 8.7 microg/ml) increased (P < 0.01 vs. placebo). Despite the increase in body fat mass (Delta = 3.4 kg) after PIO, plasma leptin concentration did not change significantly. No changes in plasma glucose, FFAs, or adipocytokine levels were observed in placebo-treated subjects. During the insulin clamp, endogenous (hepatic) glucose production decreased (Delta = -2.67 micromol/fat-free mass.min, P < 0.05 vs. placebo), whereas metabolic clearance rate of glucose (MCR) increased (Delta = 0.58 ml/fat-free mass.min, P < 0.05 vs. placebo) after PIO. In all subjects, before and after PIO, the decrease in plasma FFA concentration was correlated with the changes in both endogenous (hepatic) glucose production (r = 0.47, P < 0.05) and MCR (r = -0.41, P < 0.05), whereas the increase in plasma adiponectin concentration was correlated with the change in endogenous (hepatic) glucose production (r = -0.70, P < 0.01) and MCR (r = 0.49, P < 0.05). These results suggest that the direct effects of PIO on adipose tissue to decrease plasma FFA levels and increase plasma adiponectin contribute to the improvements in hepatic and peripheral insulin sensitivity and glucose tolerance in patients with T2DM.     

Peroxisome proliferator-activated receptor gamma agonism modifies the effects of growth hormone on lipolysis and insulin sensitivity

Context  Peroxisome proliferator-activated receptor gamma (PPAR-γ) agonists such as thiazolidinediones (TZDs) improve insulin sensitivity in type 2 diabetes mellitus (T2DM) through effects on fat metabolism whereas GH stimulates lipolysis and induces insulin resistance.
Objective  To evaluate the impact of TZDs on fat metabolism and insulin sensitivity in subjects exposed to stable GH levels.
Design  A randomized, placebo-controlled, double-blind parallel-group study including 20 GH-deficient patients on continued GH replacement therapy. The patients were studied before and after 12 weeks.
Intervention  Patients received either pioglitazone 30 mg ( N  = 10) or placebo ( N  = 10) once daily for 12 weeks.
Results  Adiponectin levels almost doubled during pioglitazone treatment ( P =  0·0001). Pioglitazone significantly decreased basal free fatty acid (FFA) levels ( P =  0·02) and lipid oxidation ( P =  0·02). Basal glucose oxidation rate ( P =  0·004) and insulin sensitivity ( P =  0·03) improved in the patients who received pioglitazone treatment. The change in insulin-stimulated adiponectin level after pioglitazone treatment was positively correlated to the change in insulin-stimulated total glucose disposal ( R  = 0·69, P  = 0·04).
Conclusion  The impact of GH on lipolysis and insulin sensitivity can be modified by administration of TZDs.     

Growth hormone replacement therapy induces insulin resistance by activating the glucose-fatty acid cycle

The effects of GH replacement therapy on energy metabolism are still uncertain, and long-term benefits of increased muscle mass are thought to outweigh short-term negative metabolic effects. This study was designed to address this issue by examining both short-term (1 wk) and long-term (6 months) effects of a low-dose (9.6 micro g/kg body weight.d) GH replacement therapy or placebo on whole-body glucose and lipid metabolism (oral glucose tolerance test and euglycemic hyperinsulinemic clamp combined with indirect calorimetry and infusion of 3-[(3)H]glucose) and on muscle composition and muscle enzymes/metabolites, as determined from biopsies obtained at the end of the clamp in 19 GH-deficient adult subjects. GH therapy resulted in impaired insulin-stimulated glucose uptake at 1 wk (-52%; P = 0.008) and 6 months (-39%; P = 0.008), which correlated with deterioration of glucose tolerance (r = -0.481; P = 0.003). The decrease in glucose uptake was associated with an increase in lipid oxidation at 1 wk (60%; P = 0.008) and 6 months (60%; P = 0.008) and a concomitant decrease in glucose oxidation. The deterioration of glucose metabolism during GH therapy also correlated with the enhanced rate of lipid oxidation (r = -0.508; P = 0.0002). In addition, there was a shift toward more glycolytic type II fibers during GH therapy. In conclusion, replacement therapy with a low-dose GH in GH-deficient adult subjects is associated with a sustained deterioration of glucose metabolism as a consequence of the lipolytic effect of GH, resulting in enhanced oxidation of lipid substrates. Also, a shift toward more insulin-resistant type II X fibers is seen in muscle. Glucose metabolism should be carefully monitored during long-term GH replacement therapy.     

Site of insulin resistance in type 1 diabetes: insulin-mediated glucose disposal in vivo in relation to insulin binding and action in adipocytes in vitro

To evaluate the mechanism of insulin resistance in type 1 diabetes mellitus, we measured insulin sensitivity in vivo and insulin action in adipocytes in vitro. The study groups consisted of 18 insulin-treated type 1 diabetic patients and 14 matched normal subjects. In each subject, insulin-mediated glucose disposal in vivo was measured by the euglycemic clamp technique. An open surgical biopsy was performed in 9 diabetic and 7 healthy subjects to obtain abdominal sc adipose tissue for the measurement of [125I]insulin binding, D-[14C]-glucose transport, oxidation, and lipogenesis. During the euglycemic clamp studies, similar steady state plasma glucose (4.8 mmol/liter) and insulin (80 mU/liter = 700 pM) levels were maintained in both groups. The rate of glucose metabolism (M) was 43% lower in the diabetic patients (4.75 +/- 0.34 mg/kg X min) than in the normal subjects (8.27 +/- 0.43 mg/kg X min; P less than 0.001). [125I]Insulin binding to adipocytes was reduced in the diabetic patients (26% reduction in tracer binding; P less than 0.05) due to a reduction in receptor number. Insulin binding was not related to the M value at any insulin concentration. Basal and insulin-stimulated rates of glucose transport were not significantly different in diabetic and normal subjects. The basal glucose oxidation rate was reduced by 50% (P less than 0.02), and maximal glucose oxidation was reduced by 49% (P less than 0.03) in the diabetic patients (237 +/- 30 vs. 359 +/- 49 pmol/30,000 cells X 90 min, basal vs. maximal glucose oxidation, respectively) compared to those in normal subjects (513 +/- 101 vs. 700 +/- 133 pmol/30,000 cells X 90 min). The percentage responses of glucose oxidation and glucose transport to insulin were similar in both groups. Glucose oxidation rates at basal (r = 0.68; P less than 0.01), half-maximally (ED50; r = 0.70; P less than 0.01), and maximally (r = 0.64; P less than 0.05) effective insulin concentrations were positively related to the M value. Basal and insulin-stimulated rates of lipogenesis were comparable between the diabetic and normal subjects. In conclusion, insulin-mediated glucose disposal in vivo is reduced in conventionally treated type 1 diabetic patients. In vitro, adipocytes from diabetes bound slightly less insulin at tracer insulin concentrations, but the magnitude of this reduction was not related to impairment of glucose metabolism in vivo. Of the pathways of glucose metabolism studied, the rate of glucose oxidation was most affected. A significant relationship was found between the M value and the rate of in vitro glucose oxidation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Dose-response effects of free fatty acids on glucose and lipid metabolism during somatostatin blockade of growth hormone and insulin in humans

CONTEXT: GH and other stress hormones stimulate lipolysis, which may result in free fatty acid (FFA)-mediated insulin resistance. However, there are also indications that FFAs in the very low physiological range have the same effect. OBJECTIVE: The objective of the study was to address systematically the dose-response relations between FFAs and insulin sensitivity. DESIGN: We therefore examined eight healthy men for 8 h (6 h basal and 2 h glucose clamp) on four occasions. Intervention: Intralipid was infused at varying rates (0, 3, 6, 12 microl.kg(-1).min(-1)); lipolysis was blocked by acipimox; and endogenous GH, insulin, and glucagon secretion was blocked by somatostatin and subsequently replaced at fixed rates. RESULTS: This resulted in four different FFA levels between 50 and 2000 micromol/liter, with comparable levels of insulin and counterregulatory hormones. Both in the basal state and during insulin stimulation, we saw progressively decreased glucose disposal, nonoxidative glucose disposal, and forearm muscle glucose uptake at FFA levels above 500 micromol/liter. Apart from forearm glucose uptake, the very same parameters were decreased at low FFA levels (approximately 50 micromol/liter). FFA rate of disposal was linearly related to the level of FFAs, whereas lipid oxidation reached a maximum at FFA levels approximately 1000 micromol/liter. CONCLUSION: In the presence of comparable levels of all major metabolic hormones, insulin sensitivity peaks at physiological levels of FFAs with a gradual decrease at elevated as well as suppressed FFA concentrations. These data constitute comprehensive dose-response curves for FFAs in the full physiological range from close to zero to above 2000 micromol/liter.