Influence of a 60-hour fast on insulin-mediated splanchnic and peripheral glucose metabolism in humans.

A brief period of starvation (2-3) depletes the hepatic glycogen stores but results in only a limited reduction of the muscle glycogen depots. In this situation insulin resistance contributes to the glucose intolerance, but it is not known which tissue or tissues are responsible for the decreased insulin sensitivity. The present study was therefore undertaken to examine the influence of a 60-h fast on insulin sensitivity in splanchnic and peripheral tissues in normal humans. Euglycemic (95 mg/dl) 1-mU insulin and hyperglycemic (215-225 mg/dl) glucose clamp studies were conducted for 2 h in overnight (12 h) and prolonged (60 h) fasted nonobese subjects. Splanchnic exchange of glucose and gluconeogenic precursors was measured using the hepatic vein catheter technique. During the euglycemic clamp, insulin infusion resulted in similar steady state insulin levels in 60-h and 12-h fasted subjects (73 +/- 7 vs. 74 +/- 5 microU/ml). Total glucose disposal was reduced by 45% after 60 h of fasting (4.0 +/- 0.3 vs. 7.6 +/- 1.1 mg/kg per min, P less than 0.05) and the splanchnic glucose balance reverted from a net release in the basal state (12 h fast, -1.7 +/- 0.2, and 60-h fast, -0.9 +/- 0.1 mg/kg per min, P less than 0.01) to a net uptake during the clamps that was similar after 60 h and 12 h of fasting (0.6 +/- 0.1 vs. 0.6 +/- 0.2 mg/kg per min). During the hyperglycemic clamp, insulin levels rose rapidly in all subjects. In the 12-h fasted group this rise was followed by a further gradual one, reaching significantly higher values than in 60-h fasted subjects during the second hour (67 +/- 15 vs. 25 +/- 2 microU/ml, P less than 0.05). Total glucose disposal was lower, though not significantly so, after the 60-h fast (2.6 +/- 0.4 vs. 5.4 +/- 1.3 mg/kg per min, 0.05 less than P less than 0.10), and as with the euglycemic clamp, the splanchnic glucose balance was altered from a basal net release to a net uptake during the clamp (1.3 +/- 0.2 vs. 1.1 +/- 0.2 mg/kg per min). After an overnight fast, splanchnic lactate uptake fell and the arterial lactate concentration rose in response to both hyperglycemia and hyperinsulinemia, whereas these variables were unchanged in the 60-h fasted subjects during both types of clamp studies.     

An in vivo and in vitro study of the mechanism of prednisone-induced insulin resistance in healthy subjects.

Prednisone-induced insulin resistance may depend on either reduced sensitivity (receptor defect) or reduced response to insulin (postreceptor defect). To clarify the mechanism of prednisone-induced insulin resistance, a [3H]glucose infusion (1 microCi/min) was performed for 120 min before and during a euglycemic clamp repeated at approximately 100, approximately 1,000, and approximately 10,000 microU/ml steady state plasma insulin concentration in 10 healthy, normal weight subjects, aged 35 +/- 7 yr. Each test was repeated after 7-d administration of placebo or prednisone (15 plus 15 mg/d per subject), in a randomized sequence with an interval of 1 mo between the two tests. Mean fasting blood glucose (89.5 +/- 2.1 vs. 83.7 +/- 1.9 mg/dl) and mean fasting plasma insulin values (17.8 +/- 1.2 vs. 14.3 +/- 0.8 microU/ml) were significantly higher (P less than 0.01) after prednisone. The insulin sensitivity index (glucose metabolic clearance rate in ml/kg per min) was significantly lower (P less than 0.001) after prednisone at all three steady state plasma insulin levels: 2.8 +/- 0.3 vs. 7.4 +/- 1.1 at approximately 100 microU/ml; 6.0 +/- 0.5 vs. 12.2 +/- 1.1 at approximately 1,000 microU/ml; 7.4 +/- 0.6 vs. 14.4 +/- 0.5 at approximately 10,000 microU/ml. Fasting glucose production (in mg/kg per min) was significantly higher after prednisone: 3.7 +/- 0.2 vs. 2.9 +/- 0.2, P less than 0.001. Suppression of glucose production at steady state plasma insulin level of approximately 100 microU/ml was less after prednisone (1.01 +/- 0.35 vs. 0.14 +/- 0.13, NS), and total at approximately 1,000 and approximately 10,000 microU/ml after both prednisone and placebo. The metabolic kinetic parameters of insulin after prednisone were not significantly different from those after placebo. In addition, insulin binding and 3-ortho-methyl-glucose transport were studied in vitro on fat cells from 16 normal-weight surgical candidates aged 40 +/- 8 yr (10 treated with placebo and 6 with prednisone as above). No significant difference was observed with regard to specific insulin binding (tested with 1 ng/ml hormone only), whereas significant transport differences were noted at the basal level (0.40 +/- 0.10 vs. 0.54 +/- 0.12 pmol/10(5) cells, P less than 0.05), and at increasing concentrations up to the maximum stimulation values (5 ng/ml): 0.59 +/- 0.04 vs. 0.92 +/- 0.12 pmol/10(5) cells, P less than 0.005. These results suggest that (a) administration of an anti-inflammatory dose of prednisone for 7 d induces insulin resistance in man; (b) this is more dependent on depressed peripheral glucose utilization than on increased endogenous production; (c) total insulin binding on isolated adipocytes is not significantly affected; (d) insulin resistance is primarily the outcome of postreceptor defect (impaired glucose transport).     

Mechanisms of glucagon secretion during insulin-induced hypoglycemia in man. Role of the beta cell and arterial hyperinsulinemia

To elucidate the mechanisms controlling the response of glucagon to hypoglycemia, a vital component of the counterregulatory hormonal response, the role of intraislet insulin was studied in seven normal subjects and five subjects with insulin-dependent diabetes mellitus (IDDM) (of less than 15-mo duration). In the normal subjects, hypoglycemia (arterial plasma glucose [PG] 53 +/- 3 mg/dl) induced by an intravenous insulin infusion (30 mU/m2 X min for 1 h, free immunoreactive insulin [FIRI] 58 +/- 2 microU/ml) elicited a 100% fall in insulin secretion and an integrated rise in glucagon of 7.5 ng/ml per 120 min. When endogenous insulin secretion was suppressed by congruent to 50 or congruent to 85% by a hyperinsulinemic-euglycemic clamp (FIRI 63 +/- 1.5 or 147 +/- 0.3 microU/ml, respectively) before hypoglycemia, the alpha cell responses to hypoglycemia were identical to those of the control study. When the endogenous insulin secretion was stimulated by congruent to 100% (hyperinsulinemic-hyperglycemic clamp, FIRI 145 +/- 1.5 microU/ml, PG 132 +/- 2 mg/dl) before hypoglycemia, the alpha cell responses to the hypoglycemia were also superimposable on those of the control study. Finally, in C-peptide negative diabetic subjects made euglycemic by a continuous overnight intravenous insulin infusion, the alpha cell responses to hypoglycemia were comparable to those of normal subjects despite absent beta cell secretion, and were not affected by antecedent hyperinsulinemia (hyperinsulinemic-euglycemic clamp for 2 h, FIRI 61 +/- 2 microU/ml). These results indicate that the glucagon response to insulin-induced hypoglycemia is independent of the level of both endogenous intraislet and exogenous arterial insulin concentration in normal man, and that this response may be normal in the absence of endogenous insulin secretion, in contrast to earlier reports. Thus, loss of beta cell function is not responsible for alpha cell failure during insulin-induced hypoglycemia in IDDM.     

Comparison of glargine insulin versus rosiglitazone addition in poorly controlled type 2 diabetic patients on metformin plus sulfonylurea

OBJECTIVE: We sought to examine the mechanisms by which the addition of glargine insulin or rosiglitazone improves glycemic control in type 2 diabetic subjects poorly controlled on maximally effective doses of metformin plus sulfonylurea. RESEARCH DESIGN AND METHODS: Subjects (aged 47 +/- 11 years, BMI 31 +/- 5 kg/m(2), HbA(1c) [A1C] 9.4 +/- 1.3%) received bedtime glargine insulin (titrated based on the fasting plasma glucose [FPG], n = 10) or rosiglitazone (4 mg twice daily, n = 10). At baseline and after 4 months, A1C was measured and an oral glucose tolerance test and a 3-h euglycemic insulin (80 mU/m(2) per min) clamp with [3-(3)H]glucose were performed. RESULTS: A1C and FPG decreased similarly in the glargine insulin (9.1 +/- 0.4 to 7.6 +/- 0.3% and 212 +/- 14 to 139 +/- 5 mg/dl, respectively, both P < 0.0001) and rosiglitazone (9.4 +/- 0.3 to 7.6 +/- 0.4% and 223 +/- 14 to 160 +/- 19 mg/dl, respectively, both P < 0.005) groups. After 4 months, endogenous glucose production (EGP) declined similarly with glargine insulin (2.27 +/- 0.10 to 1.73 +/- 0.12 mg . kg(-1) . min(-1), P < 0.0001) and rosiglitazone (2.21 +/- 0.12 to 1.88 +/- 0.12 mg . kg(-1) . min(-1), P = 0.01). The hepatic insulin resistance index declined in the rosiglitazone group (32 +/- 3 to 21 +/- 1 mg . kg(-1) . min(-1) x microU/ml, P = 0.03 vs. baseline and P < 0.05 vs. glargine insulin) and did not change in the glargine group (22 +/- 5 to 20 +/- 3 mg . kg(-1) . min(-1) x microU/ml, P = NS). At 4 months, glargine insulin (3.6 +/- 0.5 to 4.2 +/- 0.4 mg . kg(-1) . min(-1), P < 0.01) and rosiglitazone (2.7 +/- 0.3 to 3.8 +/- 0.3 mg . kg(-1) . min(-1), P < 0.0005) increased R(d), but the increment was greater in the rosiglitazone group (P < 0.05). Diastolic blood pressure was reduced only by rosiglitazone (P < 0.01). CONCLUSIONS: Triple therapy with glargine insulin or rosiglitazone similarly reduced A1C, primarily by suppressing basal EGP (hepatic). Glargine insulin reduced basal EGP by increasing plasma insulin levels, while rosiglitazone decreased basal hepatic glucose production by improving hepatic insulin sensitivity.     

Evidence that the brain of the conscious dog is insulin sensitive.

The aim of this study was to determine whether a selective increase in the level of insulin in the blood perfusing the brain is a determinant of the counterregulatory response to hypoglycemia. Experiments were carried out on 15 conscious 18-h-fasted dogs. Insulin was infused (2 mU/kg per min) in separate, randomized studies into a peripheral vein (n = 7) or both carotid and vertebral arteries (n = 8). This resulted in equivalent systemic insulinemia (84 +/- 6 vs. 86 +/- 6 microU/ml) but differing insulin levels in the head (84 +/- 6 vs. 195 +/- 5 microU/ml, respectively). Glucose was infused during peripheral insulin infusion to maintain the glucose level (56 +/- 2 mg/dl) at a value similar to that seen during head insulin infusion (58 +/- 2 mg/dl). Despite equivalent peripheral insulin levels and similar hypoglycemia; steady state plasma epinephrine (792 +/- 198 vs. 2394 +/- 312 pg/ml), norepinephrine (404 +/- 33 vs. 778 +/- 93 pg/ml), cortisol (6.8 +/- 1.8 vs. 9.8 +/- 1.6 micrograms/dl) and pancreatic polypeptide (722 +/- 273 vs. 1061 +/- 255 pg/ml) levels were all increased to a greater extent during head insulin infusion (P < 0.05). Hepatic glucose production, measured with [3-3H]glucose, rose from 2.6 +/- 0.2 to 4.3 +/- 0.4 mg/kg per min (P < 0.01) in response to head insulin infusion but remained unchanged (2.6 +/- 0.5 mg/kg per min) during peripheral insulin infusion. Similarly, gluconeogenesis, lipolysis, and ketogenesis were increased twofold (P < 0.001) during head compared with peripheral insulin infusion. Cardiovascular parameters were also significantly higher (P < 0.05) during head compared with peripheral insulin infusion. We conclude that during hypoglycemia in the conscious dog (a) the brain is directly responsive to physiologic elevations of insulin and (b) the response includes a profound stimulation of the autonomic nervous system with accompanying metabolic and cardiovascular changes.     

Defective suppression by insulin of leucine-carbon appearance and oxidation in type 1, insulin-dependent diabetes mellitus. Evidence for insulin resistance involving glucose and amino acid metabolism.

To determine whether a resistance to insulin in type 1, insulin-dependent diabetes mellitus (IDDM) is extended to both glucose and amino acid metabolism, six normal subjects and five patients with IDDM, maintained in euglycemia with intravenous insulin administration, were infused with L-[4,5-3H]leucine (Leu) and [1-14C]alpha ketoisocaproate (KIC). Steady-state rates of leucine-carbon appearance derived from protein breakdown (Leu + KIC Ra) and KIC (approximately leucine) oxidation were determined at basal and during sequential euglycemic, hyperinsulinemic (approximately 40, approximately 90 and approximately 1,300 microU/ml) clamps. In the euglycemic postabsorptive diabetic patients, despite basal hyperinsulinemia (24 +/- 6 microU/ml vs. 9 +/- 1 microU/ml in normals, P less than 0.05), Leu + KIC Ra (2.90 +/- 0.18 mumol/kg X min), and KIC oxidation (0.22 +/- 0.03 mumol/kg X min) were similar to normal values (Leu + KIC Ra = 2.74 +/- 0.25 mumol/kg X min) (oxidation = 0.20 +/- 0.02 mumol/kg X min). During stepwise hyperinsulinemia, Leu + KIC Ra in normals decreased to 2.08 +/- 0.19, to 2.00 +/- 0.17, and to 1.81 +/- 0.16 mumol/kg X min, but only to 2.77 +/- 0.16, to 2.63 +/- 0.16, and to 2.39 +/- 0.08 mumol/kg X min in the diabetic patients (P less than 0.05 or less vs. normals at each clamp step). KIC oxidation decreased in normal subjects to a larger extent than in the diabetic subjects. Glucose disposal was reduced at all insulin levels in the patients. In summary, in IDDM: (a) Peripheral hyperinsulinemia is required to normalize both fasting leucine metabolism and blood glucose concentrations. (b) At euglycemic hyperinsulinemic clamps, lower glucose disposal rates and a defective suppression of leucine-carbon appearance and oxidation were observed. We conclude that in type 1 diabetes a resistance to the metabolic effects of insulin on both glucose and amino acid metabolism is present.     

Role of parathyroid hormone in the glucose intolerance of chronic renal failure.

Evidence has accumulated suggesting that the state of secondary hyperparathyroidism and the elevated blood levels of parathyroid hormone (PTH) in uremia participate in the genesis of many uremic manifestations. The present study examined the role of PTH in glucose intolerance of chronic renal failure (CRF). Intravenous glucose tolerance tests (IVGTT) and euglycemic and hyperglycemic clamp studies were performed in dogs with CRF with (NPX) and without parathyroid glands (NPX-PTX). There were no significant differences among the plasma concentrations of electrolytes, degree of CRF, and its duration. The serum levels of PTH were elevated in NPX and undetectable in NPX-PTX. The NPX dogs displayed glucose intolerance after CRF and blood glucose concentrations during IVGTT were significantly (P less than 0.01) higher than corresponding values before CRF. In contrast, blood glucose levels after IVGTT in NPX-PTX before and after CRF were not different. K-g rate fell after CRF from 2.86 +/- 0.48 to 1.23 +/- 0.18%/min (P less than 0.01) in NPX but remained unchanged in NPX-PTX (from 2.41 +/- 0.43 to 2.86 +/- 0.86%/min) dogs. Blood insulin levels after IVGTT in NPX-PTX were more than twice higher than in NPX animals (P less than 0.01) and for any given level of blood glucose concentration, the insulin levels were higher in NPX-PTX than NPX dogs. Clamp studies showed that the total amount of glucose utilized was significantly lower (P less than 0.025) in NPX (6.64 +/- 1.13 mg/kg X min) than in NPX-PTX (10.74 +/- 1.1 mg/kg X min) dogs. The early, late, and total insulin responses were significantly (P less than 0.025) greater in the NPX-PTX than NPX animals. The values for the total response were 143 +/- 28 vs. 71 +/- 10 microU/ml, P less than 0.01. There was no significant difference in the ratio of glucose metabolized to the total insulin response, a measure of tissue sensitivity to insulin, between the two groups. The glucose metabolized to total insulin response ratio in NPX (5.12 +/- 0.76 mg/kg X min per microU/ml) and NPX-PTX (5.18 +/- 0.57 mg/kg X min per microU/ml) dogs was not different but significantly (P less than 0.01) lower than in normal animals (9.98 +/- 1.26 mg/kg X min per microU/ml). The metabolic clearance rate of insulin was significantly (P less than 0.02) reduced in both NPX (12.1 +/- 0.7 ml/kg X min) and NPX-PTX (12.1 +/- 0.9 ml/kg X min) dogs, as compared with normal animals (17.4 +/- 1.8 ml/kg X min). The basal hepatic glucose production was similar in both groups of animals and nor different from normal dogs; both the time course and the magnitude of suppression of hepatic glucose production by insulin were similar in both in groups. There were no differences in the binding affinity, binding sites concentration, and binding capacity of monocytes to insulin among NPX, NPX-PTX, and normal dogs. The data show that (a) glucose intolerance does not develop with CRF in the absence of PTH, (b) PTH does not affect metabolic clearance of insulin or tissue resistance to insulin in CRF, and (c) the normalization of metabolism in CRF in the absence of PTH is due to increased insulin secretion. The results indicate that excess PTH in CRF interferes with the ability of the beta-cells to augment insulin secretion appropriately in response to the insulin-resistant state.     

Thermic effect of glucose in man. Obligatory and facultative thermogenesis.

The contribution of the sympathetic nervous system to the thermic effect of intravenously infused glucose and insulin was studied in 10 healthy young men before and after beta-adrenergic receptor blockade with propranolol during conditions of normoglycemia (90 mg/dl) at two levels of hyperinsulinemia (approximately 90 microU/ml and approximately 620 microU/ml). During steady state conditions of glucose uptake (0.515 +/- 0.046 and 0.754 +/- 0.056 g/min), significant increases were observed in energy expenditure (0.10 +/- 0.02 kcal/min, P less than 0.001, and 0.21 +/- 0.02 kcal/min, P less than 0.01, respectively). Similarly, glucose oxidation increased from 0.100 +/- 0.015 to 0.266 +/- 0.022 g/min (P less than 0.001) at approximately microU/ml insulin and from 0.082 +/- 0.013 to 0.295 +/- 0.018 g/min (P less than 0.001) at approximately 620 microU/ml insulin. Concomitantly, the rate of nonoxidative glucose disposal or "glucose storage" was 0.249 +/- 0.033 and 0.459 +/- 0.048 g/min, respectively. At this time the thermic effect of infused glucose/insulin was 5.3 +/- 0.9 and 7.5 +/- 0.7%, and the energy cost of "glucose storage" was 0.50 +/- 0.16 kcal/g and 0.47 +/- 0.04 kcal/g at the two different levels of glucose uptake. After beta-adrenergic receptor blockade with propranolol, glucose uptake, oxidation, and "storage" were unchanged in both studies, but significant decreases in energy expenditure were observed (1.41 +/- 0.06-1.36 +/- 0.05 kcal/min, P less than 0.01 at approximately 90 microU/ml insulin, and 1.52 +/- 0.07-1.43 +/- 0.05 kcal/min, P less than 0.005 at approximately 620 microU/ml insulin) causing significant falls in both the estimated thermic effect of infused glucose/insulin and the energy cost of "glucose storage". Regression analysis of the results from both studies indicated a mean energy cost for "glucose storage" of 0.36 kcal/g (r = 0.74, P less than 0.001), which fell significantly (P less than 0.005) to 0.21 kcal/g (r = 0.49, P less than 0.05) during beta-adrenergic receptor blockade with propranolol. The latter is in close agreement with that calculated on theoretical grounds for the metabolic cost of glucose storage as glycogen, i.e., obligatory thermogenesis. It is concluded that beta-adrenergically mediated sympathetic nervous activity is responsible for almost the entire rise in energy expenditure in excess of the obligatory requirements for processing and storing glucose during conditions of normoglycemia and hyperinsulinemia in healthy man, and that the energy cost of "glucose storage" is not different at normal (approximately 90 microU/ml) and supraphysiological (approximately 620 microU/ml) plasma insulin concentrations.     

Characterization of the insulin resistance of aging.

To clarify the nature of the insulin resistance of aging we studied the dose response for insulin-induced glucose disposal and the binding of insulin to circulating monocytes in healthy young and old men. A total of 49 two-hour euglycemic insulin clamp studies were performed in 17 young and 10 old healthy nonobese subjects. While the old group had lower estimates of lean body mass and greater estimates of total body fat than the young group, these differences did not exceed 5% and did not reach statistical significance. Insulin was infused at 20 mU/m2 per min (young = 8, old = 5); 80 mU/m2 per min (young = 13, old = 9); 200 mU/m2 per min (young = 9, old = 5). Increasing levels of hyperinsulinemia were associated with dose-dependent increases in steady-state glucose infusion rates in young and old. The maximal glucose infusion rates (milligrams per kilogram body weight per minute) were the same for young and old. However, the dose-response curve was shifted to the right in the old subjects. In the four individuals in each age group in whom studies were performed at each dose level, the Km was 54 +/- 14 microU/ml in the young and 113 +/- 11 microU/ml in the old (P less than 0.02). Correction of glucose infusion rate for lean body mass had no effect on comparisons between age groups. These data indicate an age-associated decline in sensitivity of peripheral tissues to insulin without a change in maximal tissue responsiveness. Studies of insulin binding with 14 young and 9 old subjects indicated no effect of age on the insulin binding to receptors on circulating monocytes (young = 5.25 +/- 0.35; old = 6.22 +/- 0.53% of 125I-insulin bound/10(7) cells). These studies suggest that aging may be associated with a postreceptor defect in insulin action manifested by decreased whole-body tissue sensitivity to insulin without a change in tissue responsiveness.     

Impaired insulin sensitivity, insulin secretion, and glucose effectiveness predict future development of impaired glucose tolerance and type 2 diabetes in pre-diabetic African Americans: implications for primary diabetes prevention

OBJECTIVE: We examined the determinants of impaired glucose tolerance (IGT) and type 2 diabetes in first-degree relatives of African-American type 2 diabetic patients over 5-8 years (median 6). RESEARCH DESIGN AND METHODS: A total of 81 healthy subjects (age 41.5 +/- 4.8 years; BMI 31.3 +/- 3.6 kg/m(2)) participated in the study. Each subject underwent an oral glucose tolerance test (OGTT) and a frequently sampled intravenous glucose tolerance test at baseline. Insulin sensitivity index (S(i)) and glucose effectiveness index (S(g)) were determined by the minimal model method. Homeostasis model assessment (HOMA) was used to estimate insulin resistance (HOMA-IR) and beta-cell function (HOMA-%B). A total of 18 subjects progressed to either IGT or type 2 diabetes (progressors), whereas 19 subjects maintained normal glucose tolerance (nonprogressors). RESULTS: Comparing the progressors and nonprogressors, mean fasting serum glucose levels (95 +/- 8 vs. 80 +/- 14 mg/dl, P < 0.01) and 2-h serum glucose levels (149 +/- 27 vs. 100 +/- 60 mg/dl, P < 0.01) as well as 2-h serum insulin levels (117 +/- 81 vs. 72 +/- 87 microU/ml, P < 0.01) during OGTT were higher at baseline. Mean acute first-phase insulin secretion (205 +/- 217 vs. 305 +/- 230 microU/ml), HOMA-%B (148 +/- 60 vs. 346 +/- 372, P < 01), S(i) (1.61 +/- 1.13 vs. 2.48 +/- 1.25 x 10(-4). min(-1) [microU/ml](-1)), and S(g) (1.48 +/- 0.61 vs. 2.30 +/- 0.97 x 10(-2). min(-1)) were lower in the progressors than in the nonprogressors at baseline. Mean HOMA-IR (3.31 +/- 1.64 vs. 2.36 +/- 1.64) was significantly greater in the progressors than the nonprogressors. At the time of diagnosis of glucose intolerance (IGT + diabetes), HOMA-%B (101 +/- 48 vs. 148 +/- 60, P < 0.001) and HOMA-IR (5.44 +/- 2.55 vs. 3.31 +/- 1.64, P < 0.003) deteriorated in the progressors versus baseline. CONCLUSIONS: We conclude that nondiabetic, first-degree relatives of African-American type 2 diabetic patients who progressed to IGT and type 2 diabetes manifest triple defects (decreased insulin secretion, insulin action, and glucose effectiveness) that antecede the disease.     

Mechanism of insulin resistance in human liver cirrhosis. Evidence of a combined receptor and postreceptor defect.

Insulin resistance in liver cirrhosis may depend on either reduced sensitivity (receptor defect) and/or reduced response to insulin (postreceptor defect). To clarify the mechanism of such resistance, a [3H]glucose infusion (0.2 microCi/min) was performed for 120 min before and during a euglycemic clamp at approximately 100, 1,000, and 10,000 microU/ml steady state plasma insulin concentration in 18 compensated cirrhotics with portal hypertension and impaired glucose tolerance, and 18 healthy volunteers with no family history of diabetes, matched for sex, age, and weight. Mean fasting plasma insulin (29.2 +/- 3.4 SEM vs. 14.8 +/- 1.1 microU/ml) was significantly higher (P less than 0.001) in cirrhotics, while fasting plasma glucose was much the same in the two groups. Glucose use (milligrams per kilogram per minute) was significantly lower in cirrhotics at all three steady state plasma insulin levels: 3.04 +/- 0.34 vs. 7.72 +/- 0.61 (P less than 0.001) at approximately 100; 6.05 +/- 1.07 vs. 11.45 +/- 1.24 (P less than 0.001) at approximately 1,000; and 11.69 +/- 0.69 vs. 14.13 +/- 0.74 (P less than 0.05) at approximately 10,000 microU/ml. Mean plasma C-peptide was significantly higher in cirrhotics both basally and during the steady states (P less than 0.001); it was completely suppressed at approximately 10,000 microU/ml in controls and only 57.5% of the baseline in cirrhotics. Endogenous glucose production (milligrams per kilogram per minute) was much the same in the two groups in the fasting state and almost entirely suppressed in the controls (0.10 +/- 0.05 vs. 0.48 +/- 0.11, P less than 0.001) at approximately 100 microU/ml; at approximately 1,000 microU/ml a residual glucose production, 0.07 +/- 0.05, was observed in the cirrhotics only. In addition, insulin binding and 3-ortho-methyl-glucose transport were studied in vitro in six cirrhotics and six controls. Insulin binding to circulating monocytes and isolated adipocytes was significantly lower (P less than 0.025) in cirrhotics in all insulin concentration studies. Glucose transport values on isolated adipocytes were significantly lower in cirrhotics both basally (P less than 0.001) and at maximal insulin concentration (P less than 0.05). These results suggest that insulin resistance in human cirrhosis is more dependent on depressed peripheral glucose use than on increased endogenous glucose production, and that a combined receptor and postreceptor defect in insulin action on target cells seems to be present.     

Effects of long-term fasting on insulin responses to fatty acids in man

OBJECTIVE: To investigate whether the prolonged physiological elevation of nonesterified fatty acids (NEFA) seen in man during fasting associates with an altered acute insulin response to NEFA. SUBJECTS AND METHODS: Fourteen non-diabetic subjects, age 18-25 years, BMI 23.2 +/- 0.8 kg/m2 underwent hyperglycemic clamps (blood glucose 11 mM) for 120 min, during which either saline or Intralipid was administered in the last 60 min. Subjects were tested after an overnight as well as after a 58 h fast. RESULTS: After the overnight fast, insulin levels increased during Intralipid infusion, at min 120 reaching an increment of 33.0 +/- 8.5 microU/ml vs. 9.5 +/- 4.4 microU/ml during saline; p<0.05 for difference. Conversely, after the 58 h fast. Intralipid failed to promote a successive increase of insulin levels (increment during Intralipid at min 120: 0.5 +/- 5.8 microU/ml vs. -4.3 +/- 2.5 microU/ml during saline, NS). Insulin sensitivity as assessed by the amount of infused glucose and its ratio to insulin was enhanced by Intralipid after an overnight fast, but was decreased after a 58 h fast. CONCLUSION: Long-term elevated NEFA during fasting associates with diminished beta cell responsiveness to an acute elevation of fatty acids in conjunction with negative effects on insulin sensitivity.     

Regulation by insulin of myocardial glucose and fatty acid metabolism in the conscious dog.

In vivo small doses of insulin inhibit lipolysis, lower plasma FFA, and stimulate glucose disposal. Lowering of plasma FFA, either in the absence of a change in insulin or during combined hyperglycemia and hyperinsulinemia, promotes glucose uptake by heart muscle in vivo. In the isolated perfused heart, large doses of insulin directly stimulate heart glucose uptake. To assess the effect of physiological elevations of plasma insulin upon myocardial glucose and FFA uptake in vivo independent of changes in plasma substrate concentration, we measured arterial and coronary sinus concentrations of glucose, lactate, and FFA, and coronary blood flow in conscious dogs during a 30 min basal and a 2 h experimental period employing three protocols: (a) euglycemic hyperinsulinemia (insulin clamp, n = 5), (b) euglycemic hyperinsulinemia with FFA replacement (n = 5), (c) hyperglycemic euinsulinemia (hyperglycemic clamp with somatostatin, n = 5). In group 1, hyperinsulinemia (insulin = 73 +/- 13 microU/ml) stimulated heart glucose uptake (7.3 +/- 4.4 vs. 28.2 +/- 2.8 mumol/min, P less than 0.002), lowered plasma FFA levels by 80% (P less than 0.05), and decreased heart FFA uptake (28.4 +/- 4 vs. 1.5 +/- 0.9, P less than 0.01). When the fall in plasma FFA was prevented by FFA infusion (group 2), hyperinsulinemia (86 +/- 10 microU/ml) provoked a lesser (P less than 0.05) stimulation of glucose uptake (delta = 8.2 +/- 4.2 mumol/min) than in group 1, and there was no significant change in FFA uptake (25.3 +/- 16 vs. 16.5 +/- 4). Hyperglycemia (plasma glucose = 186 +/- 8 mg/100 ml) during somatostatin infusion resulted in only a small rise in plasma insulin (delta = 12 +/- 7 microU/ml), and although plasma FFA tended to decline, heart glucose uptake did not rise significantly (delta = 5.5 +/- 3.2 mumol/min, P = NS). There was no significant change in coronary blood flow during any of the three study protocols. We conclude that, in the dog, insulin at physiologic concentrations: (a) stimulates heart glucose uptake, both directly and by suppressing the plasma FFA concentration, and (b) does not alter coronary blood flow. Hyperglycemia per se has little effect on heart glucose uptake.     

Indices of insulin action,disposal, and secretion derived from fasting samples and clamps in normal glucose-tolerant black and white children

OBJECTIVE: To validate fasting indices of insulin sensitivity and secretion in a diverse pediatric population against gold standard estimates from euglycemic and hyperglycemic clamps. RESEARCH DESIGN AND METHODS: A total of 31 children (mean BMI 25.1 +/- 4.9 kg/m(2), mean age 8.7 +/- 1.4 years, 15 girls and 16 boys, 12 black and 19 white) underwent euglycemic and hyperglycemic clamps 2-6 weeks apart to derive insulin sensitivity indices (SI (Eug clamp) and SI (Hyper clamp)). Fasting samples were used to derive the homeostasis model assessment of insulin resistance index (HOMA-IR), HOMA of percent beta-cell function (HOMA-B%), quantitative insulin sensitivity check index (QUICKI), insulinogenic index, antilipolytic insulin sensitivity index (ISI-FFA), and C-peptide-to-insulin ratio. RESULTS: The QUICKI correlated best with SI (Eug clamp) (r = 0.69, P < 0.05) and had greater correlations to SI (Eug clamp) than did either SI (Hyper clamp) (r = 0.45, P < 0.05) or the HOMA-IR (r = -0.51, P < 0.05). Both fasting insulin and the insulinogenic index correlated well with first- and steady-phase insulin secretion (r's from 0.79 to 0.86, P < 0.05). HOMA-B% was not as highly correlated (r = 0.69-0.72, P < 0.05). Fasting C-peptide-to-insulin ratio was not significantly correlated with clamp-derived metabolic clearance rate of insulin. ISI-FFA was not correlated with the degree of free fatty acid suppression obtained from the clamps. CONCLUSIONS: The QUICKI, fasting insulin, and the insulinogenic index all closely correlate with corresponding clamp-derived indices of insulin sensitivity and secretion in this diverse pediatric cohort. These results, if replicated in similarly diverse populations, suggest that estimates based on fasting samples can be used to rank order insulin secretion and sensitivity in pediatric cohorts.     

Physiological role for cholecystokinin in reducing postprandial hyperglycemia in humans.

It is known that the ingestion of glucose alone causes a greater increase in plasma glucose levels than ingestion of the same amount of glucose given with other nutrients. Since physiological plasma concentrations of cholecystokinin (CCK) prolong gastric emptying, it is proposed that after a meal, CCK may modify plasma glucose levels by delaying glucose delivery to the duodenum. To evaluate the effect of CCK on oral glucose tolerance, plasma CCK, insulin, and glucose levels and gastric emptying rates were measured in eight normal males before and after the ingestion of 60 g glucose with the simultaneous infusion of either saline or one of two doses of CCK-8 (12 or 24 pmol/kg per h). Gastric emptying rates were measured by gamma camera scintigraphy of technetium 99m sulfur colloid and plasma CCK levels were measured by a sensitive and specific bioassay. Basal CCK levels averaged 1.0 +/- 0.1 pM (mean +/- SEM, n = 8) and increased to 7.1 +/- 1.1 pM after a mixed liquid meal. After glucose ingestion, but without CCK infusion, CCK levels did not change from basal, and the gastric emptying t1/2 was 68 +/- 3 min. Plasma glucose levels increased from basal levels of 91 +/- 3.9 mg/dl to peak levels of 162 +/- 11 mg/dl and insulin levels increased from 10.7 +/- 1.8 microU/ml to peak levels of 58 +/- 11 microU/ml. After glucose ingestion, with CCK infused at 24 pmol/kg per h, plasma CCK levels increased to 8 pM and the gastric emptying t1/2 increased to 148 +/- 16 min. In concert with this delay in gastric emptying, peak glucose levels rose to only 129 +/- 17 mg% and peak insulin levels rose to only 24.2 +/- 4.2 microU/ml. With CCK at 12 pmol/kg per h, similar but less dramatic changes were seen. To demonstrate that endogenous CCK could modify the plasma glucose and insulin responses to oral glucose, oral glucose was given with 50 g of lipid containing long-chain triglycerides. This lipid increased peak CCK levels to 3.7 +/- 0.9 pM. Concomitant with this rise in CCK was a delay in gastric emptying and a lowering of plasma glucose and insulin values. To confirm that CCK reduced hyperglycemia by its effect on gastric motility, 36 g glucose was perfused directly into the duodenum through a nasal-duodenal feeding tube in four subjects. With duodenal perfusion of glucose, there was no change in plasma CCK levels, but plasma glucose levels increased from basal levels of 93+/-5 to 148+/-6 mg/dl and insulin levels rose from 10.6+/-3.5 to 29.5+/-5.2 microU/ml. When CCK was infused at 24 pmol/kg per h, neither the plasma glucose nor insulin responses to the duodenal administration of glucose were modified. Thus we conclude that CCK, in physiological concentrations, delays gastric emptying, slows the delivery of glucose to the duodenum, and reduces postprandial hyperglycemia. These data indicate, therefore, that CCK has a significant role in regulating glucose homeostasis in human.     

Hyperglucagonemia and insulin-mediated glucose metabolism.

The effect of chronic physiologic hyperglucagonemia on basal and insulin-mediated glucose metabolism was evaluated in normal subjects, using the euglycemic insulin clamp technique (+50, +100, and +500 microU/ml). After glucagon infusion fasting glucose increased from 76 +/- 4 to 93 +/- 2 mg/dl and hepatic glucose production (HGP) rose from 1.96 +/- 0.08 to 2.25 +/- 0.08 mg/kg X min (P less than 0.001). Basal glucose oxidation after glucagon increased (P less than 0.05) and correlated inversely with decreased free fatty acid concentrations (r = -0.94; P less than 0.01) and decreased lipid oxidation (r = -0.75; P less than 0.01). Suppression of HGP and stimulation of total glucose disposal were impaired at each insulin step after glucagon (P less than 0.05-0.01). The reduction in insulin-mediated glucose uptake was entirely due to diminished non-oxidative glucose utilization. Glucagon infusion also caused a decrease in basal lipid oxidation and an enhanced ability of insulin to inhibit lipid oxidation and augment lipid synthesis. These results suggest that hyperglucagonemia may contribute to the disturbances in glucose and lipid metabolism in some diabetic patients.     

Improvement in glucose tolerance after 1 wk of exercise in patients with mild NIDDM

We investigated the effects of 1 wk of intense exercise on glucose tolerance in 10 men with abnormal glucose tolerance [7 had mild non-insulin-dependent diabetes mellitus (NIDDM), and 3 had impaired glucose tolerance]. The 7 days of exercise did not result in significant changes in body weight or maximal oxygen uptake. Plasma glucose concentration at 120 min averaged 227 +/- 23 mg/dl in an oral glucose tolerance test (OGTT) before and 170 +/- 18 mg/dl after the 7 days of exercise (P less than .001). There was a 36% reduction in the area under the glucose tolerance curve. Plasma insulin concentration at 120 min of the OGTT averaged 172 +/- 27 microU/ml before and 106 +/- 13 microU/ml after 7 days of exercise (P less than .001); the area under the insulin curve was decreased by 32%. In contrast to the response to 7 days of exercise, one bout of exercise did not result in an improvement in glucose tolerance. These results provide evidence that regularly performed, vigorous exercise can be effective in decreasing insulin resistance and improving glucose tolerance within 7 days in some patients with mild NIDDM.     

Effect of insulin on motilin release in man

The effect of insulin on motilin release was investigated by use of the euglycemic glucose clamp technique. By use of this technique plasma glucose concentration was maintained constant at 80-90 mg/100 ml, and plasma insulin immunoreactivity (IRI) was increased from 15 +/- 6 microU/ml to 171 +/- 22 microU/ml in 10 min, and remained at this level for 2 hr. Plasma motilin like immunoreactivity (MLI) concentration decreased within 10 min from 199 +/- 36 pg/ml to 120 +/- 28 pg/ml and remained low during the course of study. A significant negative correlation between MLI and IRI concentrations (r = -0.72, p less than 0.01) was observed. The present results indicate that the suppressive effect of insulin on motilin release is a direct action of insulin and is not mediated by glucose.     

Gastric inhibitory polypeptide (GIP) responses after oral glucose ingestion in hyperthyroidism

Gastric inhibitory polypeptide (GIP) is a gastrointestinal hormone stimulated after oral nutrient ingestion, but not after intravenous nutrient administration. GIP stimulates insulin release in the presence of hyperglycemia and as such is considered a major enteroinsular hormone. Since elevated glucose and insulin levels are found in hyperthyroidism, we compared the GIP responses to oral glucose ingestion in 12 hyperthyroid patients and 10 age-matched controls. Seventy-five grams of oral glucose was ingested after overnight fasting and samples were obtained at 0, 30, 60, 90, 120, and 180 min for serum glucose and immunoreactive insulin (IRI) and GIP (IRGIP). The mean serum glucose levels in hyperthyroid subjects were significantly higher (P less than or equal to 0.05) at every time studied except at 180 min. At 60 min, peak mean glucose was 171 +/- 14 mg/dl versus 128 +/- 7 mg/dl in controls (P less than 0.02). Except for fasting, mean IRI levels were significantly higher (P less than 0.001) in hyperthyroid subjects than in controls at all times studied. At 60 min, IRI rose to a peak of 125 +/- 11 microU/ml in hyperthyroid subjects versus 50 +/- 9 microU/ml in controls (P less than 0.001). Mean fasting, stimulated, and incremental IRGIP levels were slightly higher but not statistically different in the hyperthyroid subjects versus controls. Glucose and IRI responses are exaggerated in hyperthyroidism after oral glucose ingestion. Even though GIP has insulinotropic action, its role in the hyperinsulinism found in hyperthyroid subjects appears to be minimal.     

Insulin transport across capillaries is rate limiting for insulin action in dogs.

This study examined the relationship between transcapillary insulin transport and insulin action in vivo. During euglycemic clamps (n = 7) in normal conscious dogs we simultaneously measured plasma and thoracic duct lymph insulin and glucose utilization (Rd). Clamps consisted of an activation phase with constant insulin infusion (0.6 mU/kg per min) and a deactivation phase. [14C]Inulin was infused as a passively transported control substance. While [14C]inulin reached an equilibrium between plasma and lymph, steady-state (ss) plasma insulin was higher than lymph (P less than 0.05) and the ratio of 3:2 was maintained during basal, activation, and deactivation phases: 18 +/- 2 vs. 12 +/- 1, 51 +/- 2 vs. 32 +/- 1, and 18 +/- 3 vs. 13 +/- 1 microU/ml. In addition, it took longer for lymph insulin to reach ss than plasma insulin during activation and deactivation: 11 +/- 2 vs. 31 +/- 5 and 8 +/- 2 vs. 32 +/- 6 min (P less than 0.02). Rd increased from 2.6 +/- 0.1 to a ss of 6.6 +/- 0.4 mg/kg per min within 50 +/- 8 min. There was a remarkable similarity in the dynamics of insulin in lymph and Rd: the time to reach ss for Rd was not different from lymph insulin (P greater than 0.1), and the relative increases of the two measurements were similar, 164 +/- 45% and 189 +/- 29% (P greater than 0.05). While there was only a modest correlation (r = 0.78, P less than 0.01) between Rd and plasma insulin, the dynamic changes of lymph insulin and Rd showed a strong correlation (r = 0.95, P less than 0.01). The intimate relationship between lymph insulin and Rd suggests that the transcapillary insulin transport is primarily responsible for the delay in Rd. Thus, transcapillary transport may be rate limiting for insulin action, and if altered, it could be an important component of insulin resistance in obesity and diabetes mellitus.