Cortisol increases gluconeogenesis in humans: its role in the metabolic syndrome.

Android obesity is associated with increased cortisol secretion. Direct effects of cortisol on gluconeogenesis and other parameters of insulin resistance were determined in normal subjects. Gluconeogenesis was determined using the reciprocal pool model of Haymond and Sunehag (HS method), and by the Cori cycle/lactate dilution method of Tayek and Katz (TK method). Glucose production (GP) and gluconeogenesis were measured after a 3 h baseline infusion and after a 4-8 h pituitary-pancreatic infusion of somatostatin, replacement insulin, growth hormone (GH), glucagon and a high dose of cortisol (hydrocortisone). The pituitary-pancreatic infusion maintains insulin, GH and glucagon concentrations within the fasting range, while increasing the concentration of only one hormone, cortisol. Two groups of five subjects were each given high-dose cortisol administration, and results were compared with those from a group of six 'fasting alone' subjects (no infusion) at 16 and 20 h of fasting. Fasting GP (12 h fasting) was similar in all groups, averaging 12.5+/-0.2 micromol x min(-1) x kg(-1). Gluconeogenesis, as a percentage of GP, was 35+/-2% using the HS method and 40+/-2% using the TK method. After 16 h of fasting, GP had fallen (11.5+/-0.6 micromol x min(-1) x kg(-1)) and gluconeogenesis had increased (55+/-5% and 57+/-5% of GP by the HS and TK methods respectively; P<0.05). High-dose cortisol infusion for 4 h increased serum cortisol (660+/-30 nmol/l; P<0.05), blood glucose (7.9+/-0.5 mmol/l; P<0.05) and GP (14.8+/-0.8 micromol x min(-1) x kg(-1); P<0.05). The increase in GP was due entirely to an increase in gluconeogenesis, determined by either the HS or the TK method (66+/-6% and 65+/-5% of GP respectively; P<0.05). Thus cortisol administration in humans increases GP by stimulating gluconeogenesis. Smaller increases in serum cortisol may contribute to the abnormal glucose metabolism known to occur in the metabolic syndrome.     

Insulin regulation of renal glucose metabolism in conscious dogs.

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

Hepatic sugar phosphate levels reflect gluconeogenesis in lung cancer: simultaneous turnover measurements and 31P magnetic resonance spectroscopy in vivo

Stable-isotope tracers were used to assess whether levels of phosphomonoesters (PME) and phosphodiesters (PDE) in the livers of lung cancer patients, as observed by (31)P magnetic resonance (MR) spectroscopy, reflect elevated whole-body glucose turnover and gluconeogenesis from alanine. Patients with advanced non-small-cell lung cancer without liver metastases (n=24; weight loss 0-24%) and healthy control subjects (n=13) were studied after an overnight fast. (31)P MR spectra of the liver in vivo were obtained, and glucose turnover and gluconeogenesis from alanine were determined simultaneously using primed-constant infusions of [6, 6-(2)H(2)]glucose and [3-(13)C]alanine. Liver PME concentrations were 6% higher in lung cancer patients compared with controls (not significant); PME levels in patients with >/=5% weight loss were significantly higher than in patients with <5% weight loss (P<0.01). PDE levels did not differ between the groups. In lung cancer patients, whole-body glucose production was 19% higher (not significant) and gluconeogenesis from alanine was 42% higher (P<0. 05) compared with healthy subjects; turnover rates in lung cancer patients with >/=5% weight loss were significantly elevated compared with both patients with <5% weight loss and healthy subjects (P<0. 05). PME levels were significantly correlated with glucose turnover and gluconeogenesis from alanine in lung cancer patients (r=0.48 and r=0.48 respectively; P<0.05). In conclusion, elevated PME levels in lung cancer patients appear to reflect increased glucose flux and gluconeogenesis from alanine. These results are consistent with the hypothesis that elevated PME levels are due to contributions from gluconeogenic intermediates.     

Type 2 diabetic patients have increased gluconeogenic efficiency to substrate availability, but intact autoregulation of endogenous glucose production

OBJECTIVE: An autoregulatory mechanism involving a reciprocal relationship between gluconeogenesis and glycogenolysis regulates endogenous glucose production (EGP) in healthy individuals. In type 2 diabetes, fasting hyperglycemia may be due to increased EGP. MATERIAL AND METHODS: To examine gluconeogenesis and autoregulation of EGP in type 2 diabetes, 9 type 2 diabetics and 8 healthy controls were studied during a 3-h infusion of 30 micromol/kg/min Na-lactate. The diabetics were also studied during a control infusion of Na-bicarbonate. To standardize levels of glucoregulatory hormones, plasma insulin, growth hormone, and glucagon were clamped at identical levels during the three experiments. Glucagon levels were elevated from basal levels to approximately 330 ng/l when the lactate or bicarbonate infusions were started, in order to mimic the hyperglucagonemia often seen in diabetes. Lactate gluconeogenesis and total EGP were measured by infusions of [6-(3)H] glucose and [U-14C] lactate. RESULTS: In the bicarbonate experiments, hyperglugagonemia increased lactate gluconeogenesis in the diabetic patients from 4.3+/-1.8 to 6.1+/-2.4 micromol/kg/min (p=0.04). EGP did not change significantly (basal EGP: 15.3+/-3.9, EGP at the end of the study: 14.2+/-3.9 micromol/kg/min, p=0.14). During both lactate experiments, plasma lactate increased more than 4-fold. The increase in lactate gluconeogenesis was significantly higher in diabetics than in controls (values obtained at the end of experiments minus basal values: 10.8+/-3.6 versus 6.4+/-3.6 micromol/kg/min, p=0.03). Compared with normal subjects, the diabetic patients had higher EGP values both at basal conditions (p=0.001) and during lactate infusion (p=0.005). Despite augmented gluconeogenesis, EGP did not change during lactate and glucagon infusion in any of the groups (diabetics, basal EGP: 15.4+/-2.7 versus EGP at the end of experiments: 15.6+/-3.6 micromol/kg/min, p>0.30. Controls, basal EGP: 11.8+/-0.8 versus EGP at the end of experiments: 11.6+/-1.9 micromol/kg/min, p>0.30). CONCLUSIONS: Although type 2 diabetics have increased EGP and increased lactate gluconeogenesis, the hepatic autoregulation of EGP during increased substrate-induced gluconeogenesis seems to be intact.     

The influence of alanine infusion on glucose production in 'malnourished' African children with falciparum malaria

By US standards, about half of African children are malnourished, although most appear clinically normal. It is possible that precursor supply for gluconeogenesis is limited to a greater extent in these seemingly malnourished African children than in healthy children, consequently limiting glucose production. Since in malaria peripheral glucose utilization is increased, precursor supply could play an even more critical role in maintaining glucose production in African children suffering from falciparum malaria. We studied the effect of alanine infusion (1.5 mg/kg/min) on glucose production (measured by infusion of [6,6-2H2]glucose) and plasma glucose concentration in 10 consecutive children with acute, uncomplicated falciparum malaria. By US standards, six children were below the 10th percentile of weight for height and seven were below the 10th percentile of height for age. Plasma concentrations of alanine increased during alanine infusion from 153 +/- 21 to 468 +/- 39 mumol/l, whereas plasma lactate concentrations did not change (1.4 +/- 0.2 vs. 1.3 +/- 0.2 mmol/l). Plasma glucose concentration and glucose production did not change during alanine infusion: 4.6 +/- 0.3 vs. 4.5 +/- 0.3 mmol/l and 5.8 +/- 0.4 vs. 5.7 +/- 0.3 mg/kg/min, respectively. Gluconeogenic precursor supply is sufficient for maintainance of glucose production in African children with uncomplicated malaria who are malnourished by US standards.      

Low-dose ethanol predisposes elderly fasted patients with type 2 diabetes to sulfonylurea-induced low blood glucose

OBJECTIVE: It has previously been demonstrated that the risk of hypoglycemia is low among otherwise healthy elderly fasted patients with type 2 diabetes taking oral sulfonylurea medications. Nevertheless, these agents do cause hypoglycemia in clinical practice, suggesting that accompanying factors must typically be present for hypoglycemia to occur. Ethanol is one putative risk factor that has not been evaluated as a mechanism for low blood glucose among sulfonylurea users. We hypothesized that low concentrations of ethanol would reduce blood glucose concentrations in elderly type 2 diabetic patients receiving sulfonylureas during a short-term fast. RESEARCH DESIGN AND METHODS: A total of 10 type 2 diabetic patients, aged 68 +/- 3 years and receiving 20 mg glyburide daily, participated in a prospective double-blind placebo-controlled in-patient study consisting of two 24-h fasts at least 1 week apart. During hours 14 and 15 of the fasting studies, subjects received intravenous infusions of either 4.35 mmol.kg-1.h-1 ethanol (equivalent to one or two alcoholic beverages) or saline placebo in random order. Ethanol, plasma glucose, insulin, and counterregulatory hormones were assessed very 30-60 min during the final 10 h of the fast. RESULTS: Blood ethanol levels peaked at 17 +/- 2 mmol/l (the lower legal limit of intoxication in New Mexico) during the ethanol study. Plasma glucose concentrations did not differ at baseline (placebo 8.5 +/- 1.8 vs. ethanol 8.7 +/- 1.7 mmol/l; P = 0.50), but nadir plasma glucose was lower after the ethanol infusion compared with placebo (4.4 +/- 1.2 vs. 5.0 +/- 1.4 mmol/l; P = 0.01), and the absolute decline in plasma glucose was also greater during the ethanol study than the placebo study (4.7 +/- 0.9 vs. 3.6 +/- 1.2 mmol/l; P = 0.01). Counterregulatory hormone levels were increased during the ethanol study and nonesterified fatty acid concentrations were suppressed compared with the placebo study. CONCLUSIONS: Low doses of ethanol predispose fasted elderly type 2 diabetic patients to low blood glucose during a short-term fast. This may be one of several mechanisms by which sulfonylurea-induced hypoglycemia occurs in elderly patients.     

Effect of guar on second-meal glucose tolerance in normal man

Whole body glucose turnover and absorption of a 50 g glucose drink was studied in six healthy volunteers on two occasions, 4 h after a 'breakfast' of 50 g of glucose, mixed on one occasion with 20 g of guar gum. Plasma glucose concentrations were significantly reduced with guar gum compared with those obtained without guar gum (P less than 0.0001). Whole body glucose turnover studied by an intravenous primed dose constant infusion technique using D-[3-3H]glucose showed no significant difference between the two groups: 353 +/- 15 mmol with guar and 350 +/- 9 mmol without guar. Total oral glucose absorption, followed with a D-[1-14C]glucose tracer, was significantly decreased by guar treatment, being 219 +/- 3 mmol with guar and 239 +/- 5 mmol without guar (P less than 0.05). Serum insulin levels were lowered by guar treatment (P less than 0.05) while those of C-peptide, gastric inhibitory polypeptide, glucagon, cortisol and pancreatic polypeptide did not differ significantly. Blood lactate concentrations were raised in the guar treated group (P less than 0.05) whereas pyruvate, alanine, glycerol and 3-hydroxybutyrate concentrations did not differ significantly. These results support the suggestion that guar improves second-meal tolerance to glucose by decreasing absorption.     

Effect of pioglitazone on the metabolic and hormonal response to a mixed meal in type II diabetes

We explored the mechanisms by which a 4-month, placebo-controlled pioglitazone treatment (45 mg/day) improves glycemic control in type II diabetic patients (T2D, n=27) using physiological testing (6-h mixed meal) and a triple tracer technique ([6,6-(2)H(2)]glucose infusion, (2)H(2)O and [6-(3)H]glucose ingestion) to measure endogenous glucose production (EGP), gluconeogenesis (GNG), insulin-mediated glucose clearance and beta-cell glucose sensitivity (by c-peptide modeling). Compared to sex/age/weight-matched non-diabetic controls, T2D patients showed inappropriately (for prevailing insulinemia) raised glucose production (1.05[0.53] vs 0.71[0.36]mmol min(-1) kg(ffm)(-1) pM, P=0.03) because of enhanced GNG (73.1+/-2.4 vs 59.5+/-3.6%, P<0.01) persisting throughout the meal, reduced insulin-mediated glucose clearance (6[5] vs 12[13]ml min(-1) kg(ffm)(-1) nM(-1), P<0.005), and impaired beta-cell glucose-sensitivity (27[38] vs 71[37]pmol min(-1) m(-2) mM(-1), P=0.002). Compared to placebo, pioglitazone improved glucose overproduction (P=0.0001), GNG and glucose underutilization (P=0.05) despite lower insulinemia. GNG improvement was quantitatively related to raised adiponectin. beta-cell glucose sensitivity was unchanged. In mild-to-moderate T2D, pioglitazone monotherapy decreased fasting and post-prandial glycemia, principally via inhibition of gluconeogenesis, improved hepatic and peripheral insulin resistance.     

Control of postprandial hyperglycemia: optimal use of short-acting insulin secretagogues

OBJECTIVE: This study was designed to compare the efficacy of acute premeal administration of glipizide versus nateglinide in controlling postprandial hyperglycemia in subjects with non-insulin-requiring type 2 diabetes. RESEARCH DESIGN AND METHODS: A total of 20 subjects (10 female, 10 male) with non-insulin-requiring type 2 diabetes were admitted overnight to the General Clinical Research Center on four occasions. In random order, 10 mg glipizide (30 min premeal), 120 mg nateglinide (15 min premeal), 10 mg glipizide plus nateglinide (30 and 15 min premeal, respectively), or placebo pills (30 and 15 min premeal) were administered in a double-blind fashion before a standardized breakfast. Blood was drawn for analysis of glucose, insulin, and C-peptide at -0.05, 0, 0.5, 1, 2, 3, and 4 h relative to the meal. RESULTS: The subjects were aged 56 +/- 2 years and were moderately obese (BMI 31 +/- 1 kg/m(2)), with a mean HbA(1c) of 7.4 +/- 0.4%. The peak postprandial glucose excursion above baseline was higher with placebo (6.1 +/- 0.5 mmol/l) than glipizide (4.3 +/- 0.6 mmol/l, P = 0.002), nateglinide (4.2 +/- 0.4 mmol/l, P = 0.001), or glipizide plus nateglinide (4.1 +/- 0.5 mmol/l, P = 0.001). The area under the curve for the glucose excursion above baseline was also higher with placebo (14.1 +/- 1.8 mmol/h. l) compared with glipizide (6.9 +/- 2.4 mmol/h. l, P = 0.002), nateglinide (9.7 +/- 2 mmol/h. l, P = 0.004), or glipizide plus nateglinide (5.6 +/- 2.2 mmol/h. l, P < 0.001). Peak and integrated glucose excursions did not differ significantly between glipizide and nateglinide. However, by 4 h postmeal, plasma glucose levels were significantly higher with nateglinide (9 +/- 0.9 mmol/l) compared with the premeal baseline (7.8 +/- 0.6 mmol/l, P = 0.04) and compared with the 4-h postprandial glucose level after administration of glipizide (7.6 +/- 0.6 mmol/l, P = 0.02). Integrated postprandial insulin levels were higher with glipizide (1,556 +/- 349 pmol/h. l) than nateglinide (1,364 +/- 231 pmol/h. l; P = 0.03). Early insulin secretion, as measured by insulin levels at 30 min postmeal, did not differ between glipizide and nateglinide. CONCLUSIONS: Acute premeal administration of nateglinide or glipizide has equal efficacy in controlling postbreakfast hyperglycemia in type 2 diabetes when each drug is administered at the optimum time before the meal. Glipizide causes a more pronounced and sustained postmeal insulin secretory response compared with nateglinide. Glipizide facilitates the return to near-fasting glucose levels at 4 h postmeal, but with the possible risk of increased frequency of postmeal hypoglycemia in drug-naive patients. The clinical decision to use glipizide versus nateglinide should be based on factors other than the control of postprandial hyperglycemia in type 2 diabetes.     

Increased myocardial performance following acute hyperglycaemia in insulin-dependent diabetic patients. A consequence of increased peripheral blood flow?

Cardiac function during acute hyperglycaemia was investigated by means of echocardiography in eight insulin-dependent (type 1) diabetic patients without microvascular or cardiac disease. Blood glucose was raised from 5.1 +/- 0.8 to 13.0 +/- 0.9 mmol/l for 1 h and then to 20.1 +/- 1.2 mmol/l for 1 h. A saline control study was performed to obtain an equal amount of plasma volume expansion. The left ventricular end-diastolic diameter increased significantly in both studies, however, significantly more following glucose infusion (3.3% at blood glucose of 13.0 mmol/l, 5.4% at blood glucose of 20.1 mmol/l versus 2.7% after both saline infusions). At the blood glucose level of 20.1 mmol/l, fractional shortening of the left ventricle and cardiac output were increased as compared with the baseline level and the level during moderate hyperglycaemia, and also increased compared with values of non-diabetics. In conclusion acute hyperglycaemia is followed by increased myocardial performance, probably as a consequence of increased peripheral blood flow.     

Metabolic effects of the nocturnal rise in cortisol on carbohydrate metabolism in normal humans.

Glucocorticoid concentrations vary throughout the day. To determine whether an increase in cortisol similar to that present during sleep is of physiologic significance in humans, we studied the disposition of a mixed meal when the nocturnal rise in cortisol was mimicked or prevented using metyrapone plus either a variable or constant hydrocortisone infusion. When glucose concentrations were matched with a glucose infusion, hepatic glucose release (2.6 +/- 0.2 vs. 1.5 +/- 0.4 nmol/kg per 6 h) was higher (P < 0.05) while glucose disappearance (5.9 +/- 0.3 vs. 7.3 +/- 0.9 mmol/kg per 6 h) and forearm arteriovenous glucose difference (64 +/- 24 vs. 231 +/- 62 mmol/dl per 6 h) were lower (P < 0.05) during the variable than basal infusion. The greater hepatic response during the variable cortisol infusion was mediated (at least in part) by inhibition of insulin and stimulation of glucagon secretion as reflected by lower (P < 0.05) C-peptide (0.29 +/- 0.01 vs. 0.38 +/- 0.04 mmol/liter per 6 h) and higher (P < 0.05) glucagon (42.7 +/- 2.0 vs. 39.3 +/- 1.8 ng/ml per 6 h) concentrations. In contrast, the decreased rates of glucose uptake appeared to result from a state of "physiologic" insulin resistance. The variable cortisol infusion also increased (P < 0.05) postprandial palmitate appearance as well as palmitate, beta-hydroxybutyrate, and alanine concentrations, suggesting stimulation of lipolysis, ketogenesis, and proteolysis. We conclude that the circadian variation in cortisol concentration is of physiologic significance in normal humans.     

Failure of substrate-induced gluconeogenesis to increase overall glucose appearance in normal humans. Demonstration of hepatic autoregulation without a change in plasma glucose concentration.

It has been proposed that increased supply of gluconeogenic precursors may be largely responsible for the increased gluconeogenesis which contributes to fasting hyperglycemia in non-insulin-dependent diabetes mellitus (NIDDM). Therefore, to test the hypothesis that an increase in gluconeogenic substrate supply per se could increase hepatic glucose output sufficiently to cause fasting hyperglycemia, we infused normal volunteers with sodium lactate at a rate approximately double the rate of appearance observed in NIDDM while clamping plasma insulin, glucagon, and growth hormone at basal levels. In control experiments, sodium bicarbonate was infused instead of sodium lactate at equimolar rates. In both experiments, [6-3H]-glucose was infused to measure glucose appearance and either [U-14C]lactate or [U-14C]alanine was infused to measure the rates of appearance and conversion of these substrates into plasma glucose. Plasma insulin, glucagon, growth hormone, C-peptide, and glycerol concentrations, and blood bicarbonate and pH in control and lactate infusion experiments were not significantly different. Infusion of lactate increased plasma lactate and alanine to 4.48 +/- 3 mM and 610 +/- 33 microM, respectively, from baseline values of 1.6 +/- 0.2 mM and 431 +/- 28 microM, both P less than 0.01; lactate and alanine rates of appearance increased to 38 +/- 1.0 and 8.0 +/- 0.3 mumol/kg per min (P less than 0.01 versus basal rates of 14.4 +/- 0.4 and 5.0 +/- 0.5 mumol/kg per min, respectively). With correction for Krebs cycle carbon exchange, lactate incorporation into plasma glucose increased nearly threefold to 10.4 mumol/kg per min and accounted for about 50% of overall glucose appearance. Alanine incorporation into plasma glucose increased more than twofold. Despite this marked increase in gluconeogenesis, neither overall hepatic glucose output nor plasma glucose increased and each was not significantly different from values observed in control experiments (10.8 +/- 0.5 vs. 10.8 +/- 0.5 mumol/kg per min and 5.4 +/- 0.4 vs. 5.3 +/- 0.3 mM, respectively). We, therefore, conclude that in normal humans there is an autoregulatory process independent of changes in plasma glucose and glucoregulatory hormone concentrations which prevents a substrate-induced increase in gluconeogenesis from increasing overall hepatic glucose output; since this process cannot be explained on the basis of inhibition of gluconeogenesis from other substrates, it probably involves diminution of glycogenolysis. A defect in this process could explain at least in part the increased hepatic glucose output found in NIDDM.     

Increased lipolysis and its consequences on gluconeogenesis in non-insulin-dependent diabetes mellitus.

The present studies were undertaken to determine whether lipolysis was increased in non-insulin-dependent diabetes mellitus (NIDDM) and, if so, to assess the influence of increased glycerol availability on its conversion to glucose and its contribution to the increased gluconeogenesis found in this condition. For this purpose, we infused nine subjects with NIDDM and 16 age-, weight-matched nondiabetic volunteers with [2-3H] glucose and [U-14C] glycerol and measured their rates of glucose and glycerol appearance in plasma and their rates of glycerol incorporation into plasma glucose. The rate of glycerol appearance, an index of lipolysis, was increased 1.5-fold in NIDDM subjects (2.85 +/- 0.16 vs. 1.62 +/- 0.08 mumol/kg per min, P less than 0.001). Glycerol incorporation into plasma glucose was increased threefold in NIDDM subjects (1.13 +/- 1.10 vs. 0.36 +/- 0.02 mumol/kg per min, P less than 0.01) and accounted for twice as much of hepatic glucose output (6.0 +/- 0.5 vs. 3.0 +/- 0.2%, P less than 0.001). Moreover, the percent of glycerol turnover used for gluconeogenesis (77 +/- 6 vs. 44 +/- 2, P less than 0.001) was increased in NIDDM subjects and, for a given plasma glycerol concentration, glycerol gluconeogenesis was increased more than two-fold. The only experimental variable significantly correlated with the increased glycerol gluconeogenesis after taking glycerol availability into consideration was the plasma free fatty acid concentration (r = 0.80, P less than 0.01). We, therefore, conclude that lipolysis is increased in NIDDM and, although more glycerol is thus available, increased activity of the intrahepatic pathway for conversion of glycerol into glucose, due at least in part to increased plasma free fatty acids, is the predominant mechanism responsible for enhanced glycerol gluconeogenesis. Finally, although gluconeogenesis from glycerol in NIDDM is comparable to that of alanine and about one-fourth that of lactate is terms of overall flux into glucose, glycerol is probably the most important gluconeogenic precursor in NIDDM in terms of adding new carbons to the glucose pool.     

Peripheral and hepatic insulin sensitivity in healthy elderly human subjects

Insulin resistance has been reported in normal ageing but discrepancies between such studies may be related to compounding factors such as body composition and exercise patterns. We employed a two-step hyperinsulinaemic euglycaemic clamp to assess peripheral and hepatic tissue insulin sensitivity and glucose recycling in 13 elderly (E) and 14 young (Y) healthy subjects controlling for the above factors. There was no difference in basal hepatic glucose production (E: 2.36 +/- 0.06, Y: 2.47 +/- 0.1 mg kg-1 min-1; P = 0.4). At step 1 (insulin infusion 15 mU kg-1 h-1) glucose turnover was similar (E: 2.65 +/- 0.13, Y: 2.88 +/- 0.22 mg kg-1 min-1; P = 0.4) but hepatic glucose production was lower in the elderly group (0.20 +/- 0.16 vs 0.64 +/- 0.10 mg kg-1 min-1; P = 0.03). At step 2 (insulin infusion 50 mU kg-1 h-1) glucose turnover was similar (E: 7.60 +/- 0.24, Y: 8.05 +/- 0.34 mg kg-1 min-1; P = 0.3) and hepatic glucose production was equal but negative (E: -1.35 +/- 0.18, Y: -1.34 +/- 0.22 mg kg-1 min-1; P = 0.9). Glucose recycling did not differ between the groups at any stage. Similar serum insulin levels were achieved in both groups at each step. Decreased glucose tolerance was confirmed in E with a higher 2 h blood glucose after an OGTT (5.3 +/- 0.4 vs 4.1 +/- 0.3 mmol l-1; P = 0.03) but incremental insulin response was similar (E: 3236 +/- 289, Y: 3586 +/- 463 mU l-1 min-1; P = 0.5). We conclude that changes in hepatic tissue insulin sensitivity do not cause the deterioration in glucose tolerance observed with age. A small reduction in both peripheral tissue insulin sensitivity and late insulin secretion may be responsible.     

Comparison of the effects of recombinant human insulin-like growth factor-I and insulin on glucose and leucine kinetics in humans.

To compare the metabolic effects of elevated plasma concentrations of IGF-I and insulin, overnight-fasted normal subjects were studied twice, once receiving IGF-I and once insulin at doses that resulted in identical increases in glucose uptake during 8-h euglycemic clamping. Recombinant human IGF-I or insulin were infused in one group at high doses (30 micrograms/kg per h IGF-I or 0.23 nmol/kg per h insulin) and in another group at low doses (5 micrograms/kg per h IGF-I or 0.04 nmol/kg per h insulin). Glucose rate of disappearance (measured by [6,6-D2]-glucose infusions) increased from baseline by 239 +/- 16% during high dose IGF-I vs 197 +/- 18% during insulin (P = 0.021 vs IGF-I). Hepatic glucose production decreased by 37 +/- 6% during high dose IGF-I vs 89 +/- 13% during insulin (P = 0.0028 vs IGF-I). IGF-I suppressed whole body leucine flux ([1-13C]-leucine infusion technique) more than insulin (42 +/- 4 vs 32 +/- 3% during high doses, P = 0.0082). Leucine oxidation rate decreased during high dose IGF-I more than during insulin (55 +/- 4 vs 32 +/- 6%, P = 0.0001). The decreases of plasma concentrations of free fatty acids, acetoacetate, and beta-hydroxybutyrate after 8 h of IGF-I and insulin administration were similar. Plasma C-peptide levels decreased by 57 +/- 4% during high doses of IGF-I vs 36 +/- 6% during insulin (P = 0.005 vs IGF-I). The present data demonstrate that, compared to insulin, an acute increase in plasma IGF-I levels results in preferential enhancement of peripheral glucose utilization, diminished suppression of hepatic glucose production, augmented decrease of whole body protein breakdown (leucine flux), and of irreversible leucine catabolism but in similar antilipolytic effects. The data suggest that insulin-like effects of IGF-I in humans are mediated in part via IGF-I receptors and in part via insulin receptors.     

Metabolic effects of Troglitazone in patients with diet-controlled type 2 diabetes

BACKGROUND: In order to study the mechanisms of action of Troglitazone (TGZ) in vivo in Type 2 diabetes, its effects were studied on glucose metabolism, lipolysis and very low-density lipoprotein (VLDL) apolipoprotein B100 (apoB) kinetics. MATERIALS AND METHODS: A placebo-controlled, double-blind study was performed in 24 diet-treated patients randomized to receive TGZ 600 mg day(-1), TGZ 200 mg day(-1) or placebo for 8 weeks. Glucose and glycerol turnover were assessed after an overnight fast, and during sequential low-dose insulin infusions (0.01 U kg(-1) h(-1) followed by 0.015 U kg(-1) h(-1)) using 6,6-2H Glucose and 1,2,3-2H Glycerol. Very low-density lipoprotein apoB secretion was measured using l-13C-leucine, monitoring isotopic enrichment by gas chromatography-mass spectrometry. Treatment effects were analyzed by analysis of covariance, adjusting for baseline. RESULTS: Therapy resulted in a significant group differences in fasting plasma glucose adjusting for baseline (P=0.039). This was most evident at TGZ 600 mg daily [glucose decrease from (mean +/- SD) 9.2 +/- 2.7 to 6.6 +/- 0.9 mmol L(-1)]. HbA1c and insulin levels did not change significantly. Plasma nonesterified fatty acid (NEFA) levels decreased (P=0.045), most evidently at TGZ 200 mg daily, but glycerol was not significantly affected. Although no significant effects were observed on VLDL apoB or triglyceride concentrations, there were treatment differences in the absolute secretion rate of VLDL apoB of borderline (P=0.056) statistical significance, with a decrease observed at TGZ 600 mg daily [geometric mean, SD range, 0.94 (0.41-2.15) to 0.40 (0.14-1.13 mg kg(-1) h(-1))]. Very low-density lipoprotein apoB fractional secretion rate and pool size were unaffected. The VLDL triglyceride: apoB molar ratio differed between treatment groups (P=0.013), being higher in the TGZ 600 mg group [5714 (4128-7741) to 8092 (5669-11552)]. Neither glucose nor glycerol rates of appearance were significantly altered by TGZ and nor did TGZ affect their suppression by insulin. DISCUSSION: The PPARgamma agonist, troglitazone, decreases fasting glucose and NEFA levels in diet-treated Type 2 diabetes. It may also decrease VLDL particle secretion. These effects would be considered beneficial. The biological importance of the increase in VLDL-triglyceride enrichment warrants further study.     

Osmoregulation of thirst and vasopressin secretion in insulin-dependent diabetes mellitus

1. Osmotically stimulated thirst and vasopressin release were studied during infusions of hypertonic sodium chloride and hypertonic D-glucose in euglycaemic clamped diabetic patients and healthy controls. 2. Infusion of hypertonic sodium chloride caused similar elevations of plasma osmolality in diabetic patients (288.0 +/- 1.0 to 304.1 +/- 1.6 mosmol/kg, mean +/- SEM, P less than 0.001) and controls (288.6 +/- 0.9 to 305.7 +/- 0.6 mosmol/kg, P less than 0.001), accompanied by progressive increases in plasma vasopressin (diabetic patients, 0.9 +/- 0.3 to 7.7 +/- 1.5 pmol/l, P less than 0.001; controls 0.5 +/- 0.1 to 6.5 +/- 1.0 pmol/l, P less than 0.001) and thirst ratings (diabetic patients 1.0 +/- 0.2 to 7.1 +/- 0.5 cm, P less than 0.001; controls 1.8 +/- 0.4 to 8.0 +/- 0.5 cm, P less than 0.001) in both groups. 3. Drinking rapidly abolished thirst and vasopressin secretion before major changes in plasma osmolality occurred in both diabetic patients and healthy controls. 4. There were close and significant correlations between plasma vasopressin and plasma osmolality (diabetic patients, r = +0.89, controls r = +0.93) and between thirst and plasma osmolality (diabetic patients r = +0.95, controls r = +0.97) in both diabetic patients and healthy controls during hypertonic saline infusion. 5. Hypertonic D-glucose infusion caused similar elevations in blood glucose in diabetic patients (4.0 +/- 0.2 to 20.1 +/- 1.2 mmol/l, P less than 0.001) and healthy controls (4.3 +/- 0.1 to 19.3 +/- 1.2 mmol/l, P less than 0.001) but did not change plasma vasopressin or thirst ratings.(ABSTRACT TRUNCATED AT 250 WORDS)     

Insulin-mediated reduction of whole body protein breakdown. Dose-response effects on leucine metabolism in postabsorptive men.

In vivo effects of insulin on plasma leucine and alanine kinetics were determined in healthy postabsorptive young men (n = 5) employing 360-min primed, constant infusions of L-[1-13C]leucine and L-[15N]alanine during separate single rate euglycemic insulin infusions. Serum insulin concentrations of 16.4 +/- 0.8, 29.1 +/- 2.7, 75.3 +/- 5.0, and 2,407 +/- 56 microU/ml were achieved. Changes in plasma 3-methyl-histidine (3-MeHis) were obtained as an independent qualitative indicator of insulin-mediated reduction in proteolysis. Hepatic glucose output was evaluated at the lowest insulin level using D-[6,6-2H2]glucose. The data demonstrate a dose-response effect of insulin to reduce leucine flux, from basal values of 77 +/- 1 to 70 +/- 2, 64 +/- 3, 57 +/- 3, and 52 +/- 4 mumol(kg X h)-1 at the 16, 29, 75, and 2,407 microU/ml insulin levels, respectively (P less than 0.01). A parallel, progressive reduction in 3-MeHis from 5.8 +/- 0.3 to 4.3 +/- 0.3 microM was revealed. Leucine oxidation estimated from the 13C-enrichment of expired CO2 and plasma leucine (12 +/- 1 mumol[kg X h]-1) and from the 13C-enrichment of CO2 and plasma alpha-ketoisocaproate (19 +/- 2 mumol[kg X h]-1) increased at the 16 microU/ml insulin level to 16 +/- 1 and 24 +/- 2 mumol(kg X h)-1, respectively (P less than 0.05 for each), but did not increase at higher insulin levels. Alanine flux (206 +/- 13 mumol(kg X h)-1) did not increase during the clamp, but alanine de novo synthesis increased in all studies from basal rates of 150 +/- 13 to 168 +/- 23, 185 +/- 21, 213 +/- 29, and 187 +/- 15 mumol(kg X h)-1 at 16, 29, 75, and 2,407 microU/ml insulin levels, respectively (P less than 0.05). These data indicate the presence of insulin-dependent suppression of leucine entry into the plasma compartment in man secondary to a reduction in proteolysis and the stimulation of alanine synthesis during euglycemic hyperinsulinemia.     

Effect of insulin on intracellular pH and phosphate metabolism in human skeletal muscle in vivo.

1. 31P nuclear magnetic resonance spectroscopy and the hyperinsulinaemic-euglycaemic clamp were used simultaneously to assess the effect of insulin on intracellular pH and the major phosphorus-containing metabolites of normal human skeletal muscle in vivo in four normal subjects. 2. Insulin and glucose were infused for 120 min. Plasma insulin increased approximately 10-fold over preclamp levels (5.6 +/- 0.9 m-units/l pre-clamp and 54 +/- 5 m-units/l over the last hour of infusion; mean +/- SEM, n = 4). Plasma glucose concentration did not change significantly (5.4 +/- 0.2 mmol/l pre-clamp and 5.5 +/- 0.1 mmol/l over the last hour of infusion). 3. Insulin and glucose infusion resulted in a decline in the intracellular pH of forearm muscle of 0.027 +/- 0.007 unit/h (P less than 0.01), whereas in control studies of the same subjects, pH rose by 0.046 +/- 0.005 unit/h (P less than 0.001). 4. In the clamp studies, intracellular inorganic phosphate concentration rose by 18%/h, whereas ATP, phosphocreatine and phosphomonoester concentrations did not change. In plasma, inorganic phosphate concentration was 1.16 +/- 0.05 mmol/l before infusion, and this decreased by a mean rate of 0.14 mmol h-1 l-1. No change was observed in any of these intracellular metabolites in the control studies. 5. The results show that, under physiological conditions, insulin does not raise intracellular pH in human muscle, and thus cannot influence muscle metabolism by this mechanism. The results also suggest that insulin causes a primary increase in the next flux of inorganic phosphate across the muscle cell membrane.     

Loss of hepatic autoregulation after carbohydrate overfeeding in normal man.

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