Characterization of an early decline in baseline plasma glucose concentration after acute insulin elevation during euglycemic hyperinsulinemic clamp in patients with type 2 diabetes mellitus

To investigate the contribution of the liver to whole-body insulin resistance in patients with type 2 diabetes mellitus, we analyzed the early decline (slope "a") in the baseline plasma glucose level following acute hyperinsulinemia in the initial phase of a euglycemic hyperinsulinemic clamp study, rather than using an isotope-dilution method. Slope "a" was comparable among groups of diabetic and non-diabetic subjects, and did not correlate well with glucose infusion rate (GIR), an index of peripheral (primarily skeletal muscle) insulin resistance. In contrast, slope "a" was significantly lower in obese (BMI > 25) type 2 diabetic patients compared with their non-obese counterparts, consistent with the general belief that obesity is a condition of insulin resistance in liver as well as in peripheral tissues. A subset of six insulin-resistant (nearly zero GIR) type 2 diabetic patients (pubertal adolescents) demonstrated a markedly blunted slope "a". Their insulin resistance (GIR) substantially recovered concomitant with an increase in slope "a" after pretreatment with somatostatin analogue in two cases studied, suggesting possible suppression of hepatic glucose production through lowering of plasma glucagon concentrations. Furthermore, slope "a" correlated significantly (r = -0.480, p<0.0001) with HOMA index (FPG x FIRI), the latter being recently regarded as an index of hepatic insulin resistance. These data showed that slope "a" obtained from euglycemic hyperinsulinemic clamp may be a clinically useful index of hepatic insulin resistance rather than an index of peripheral insulin resistance.

Plasma concentration of immunoreactive vascular endothelial growth factor and its relation to smoking

We determined the plasma concentration of immunoreactive vascular endothelial growth factor (IR-VEGF) and searched for a relationship between it and the degree of microangiopathy. The plasma VEGF level was measured using an enzyme immunoassay in 110 non-insulin-dependent diabetes mellitus (NIDDM) patients with varying degrees of nephropathy or retinopathy (RP) and in 39 healthy controls and 30 nondiabetic patients for comparison. One fourth of the control subjects, 60% of whom were currently smokers, had plasma levels of IR-VEGF higher than the lower limit (15.6 pg/mL) of detection for this assay, whereas this was the case in half of the NIDDM patients. Plasma IR-VEGF was detectable in all patients with cerebral infarction, chronic renal failure, and severe infection, suggesting that tissue hypoxia might be a common cause for the elevation of plasma VEGF in these disorders. The prevalence of measurable plasma IR-VEGF levels increased in parallel with increases in the urinary albumin excretion rate ([UAER] 35.1% for UAER <30 mg/24 h, 54.8% for UAER 30 to 300 mg/24 h, and 61.3% for UAER >300 mg/24 h; P < .05 v UAER <30 mg/24 h). The mean measurable plasma concentration tended to increase with increasing UAER. However, there was no such correlation with the severity of RP. Smoking caused an acute increase of plasma IR-VEGF in only 22.6% (12 of 53) of the patients with a smoking habit. In conclusion, these findings suggest that circulating IR-VEGF may be linked to the progression of nephropathy, and smoking may facilitate this process by causing tissue hypoxia in susceptible patients.

Assessment of insulin resistance in acromegaly associated with diabetes mellitus before and after transsphenoidal adenomectomy

With a euglycemic hyperinsulinemic clamp method, whole-body insulin resistance was assessed in 6 cases with acromegaly associated with diabetes mellitus before and after transsphenoidal adenomectomy. The glucose infusion rate (GIR) correlated well with the plasma IGF-I level but poorly with that of GH. Further improvement in insulin sensitivity occurred 3-4 months after operation without substantial changes in plasma levels of both GH and IGF-I or glycemic control. These results indicate that GH excess can induce insulin resistance in association with plasma IGF-I and also through undefined secondary effect.

Urinary albumin excretion rate is related to insulin resistance in normotensive subjects with impaired glucose tolerance

Microalbuminuria has been reported to precede the development of NIDDM and to be a risk marker for cardiovascular disease. Therefore, the present study investigated the relationship between urinary albumin excretion rate (UAER) and the degree of insulin resistance in Japanese subjects with impaired glucose tolerance (IGT). Thirty-three normotensive IGT subjects were divided into three groups and twenty hypertensive IGT subjects were divided into two groups according to the degree of insulin resistance (GIR value) estimated by the euglycemic hyperinsulinemic clamp method. UAER was significantly higher in the lower GIR group in normotensive subjects (highest GIR group, 6.6 +/- 0.9 mg/24 h; intermediate group, 10.5 +/- 3.0 mg/24 h; lowest group, 21.3 +/- 3.8 mg/24 h; P<0.01 between highest and both of the other groups), but not in hypertensive subjects. The lowest GIR was associated with higher fasting plasma insulin, increased insulin response to glucose, higher plasma triglyceride and uric acid, and lower high-density-lipoprotein cholesterol, but not with increased creatinine clearance rate in normotensive subjects. A similar tendency was also found in hypertensive subjects. It is concluded that UAER is related to insulin resistance in normotensive subjects with IGT through a mechanism other than glomerular hyperfiltration.

[Hyperuricemia and insulin resistance]

Hyperuricemia is often associated with obesity, hypertension and dyslipidemia, and is thought to be a risk factor for cardiovascular disease, thereby making resemblance to the insulin resistance syndrome. Our data showed a low, but significant correlation between serum uric acid concentration and the degree of insulin resistance (GIR) estimated by euglycemic hyperinsulinemic clamp method in 67 subjects with combined normal glucose tolerance and IGT(r = -0.278, p < 0.05). Plasma HDL-C and TG levels were also correlated with uric acid levels. One hundred sixty NIDDM patients who had undergone the clamp study were stratified into 5 groups according to the serum uric acid level. In the top quintile (UA : 7.8 +/- 0.8 mg/dl), BMI, male prevalence, plasma TG, HDL-C, fasting IRI, and total IRI response(0 + 60 + 120 min) during meal tolerance test were significantly higher, while age and GIR value tended to be lower without significance compared with those in the bottom quintile (UA : 3.4 +/- 0.5 mg/dl). These results, which are in agreement with the previous studies, support the notion that elevated serum uric acid is a feature of insulin resistance syndrome.

Lack of C-peptide suppression by exogenous hyperinsulinemia in subjects with symptoms suggesting reactive hypoglycemia

The C-peptide suppression test employing the euglycemic hyperinsulinemic clamp technique has been proposed as a useful diagnostic measure for insulinoma. To examine the specificity of the C-peptide suppression, we applied this test to subjects with symptoms suggesting reactive hypoglycemia. Five subjects studied had never experienced fasting hypoglycemia, and were negative in ultrasound, CT and MRI of the pancreas. Plasma C-peptide was not suppressed by physiological (50-100 microU/ml) and supraphysiological (200-500 microU/ml) hyperinsulinemia (% of baseline: 97.3 +/- 8.6% and 90.6 +/- 10.4%, +/- SEM, respectively, both NS). Three subjects were re-examined one year later, when their hypoglycemic episodes were noticeably attenuated. No significant suppression was found. Significant suppression was observed when plasma glucose was clamped at 50-60 mg/dl in four of five subjects (61.7 +/- 11.5%, P < 0.05), but one subject responded to neither higher plasma insulin nor low-normal glucose. In contrast, normal glucose tolerance (n = 13), IGT (n = 12) and obese NIDDM (n = 31) subjects showed highly significant suppression during euglycemic and physiological hyperinsulinemia (37.1 +/- 3.8%, 46.3 +/- 5.6%, 39.9 +/- 2.6%, respectively, all P < 0.001). In conclusion, the results of the present study indicate that a failure of hyperinsulinemic suppression of C-peptide in euglycemia is not specific for insulinoma, and that suppression of C-peptide by insulin at lower plasma glucose levels (50-60 mg/dl) would be a better diagnostic test.

Lack of acute insulin effect on plasma endothelin-1 levels in humans

Acute hyperinsulinemia does not increase circulating ET-1 levels in subjects with normal and deranged glucose metabolism.

Association of sick sinus syndrome with hyperinsulinemia and insulin resistance in patients with non-insulin-dependent diabetes mellitus: report of four cases

We report four non-insulin-dependent diabetic (NIDDM) patients accompanied by a unique combination of sick sinus syndrome (SSS) and hyperinsulinemia of unknown etiology. SSS of all four cases was due to sinus arrest in association with paroxysmal atrial fibrillation (Rubenstein-III). Of special interest is that one patient showed a high prevalence of SSS and NIDDM among her close relatives. Hyperinsulinemia of moderate degree was seen at fasting state or after carbohydrate ingestion in the absence of obesity. The resistance to the action of insulin on glucose metabolism which was evaluated in three patients by the euglycemic hyperinsulinemic clamp study was found to be comparable to the lowest quartile level for common NIDDM patients. Because insulin is a physiological regulator of cell-membrane Na+/K+-ATPase, we speculate that malfunction of the sinus node automaticity may be caused by chronic exposure to hyperinsulinemia secondary to insulin resistance in these NIDDM patients.

The relationship between insulin resistance and insulin secretion in Japanese subjects with borderline glucose intolerance

Insulin resistance and impaired insulin secretion can be involved in the development of non-insulin-dependent diabetes mellitus (NIDDM), but their relative importance or temporal relationship are poorly understood. To elucidate this issue, we studied 51 subjects with borderline glucose intolerance (BGI) and 18 normal glucose tolerant subjects (NGT) according to the Japan Diabetes Society criteria. The glucose infusion rate (GIR, mg/kg/min), an index of whole body insulin resistance (IR), was measured by the euglycemic (80 mg/dl) hyperinsulinemic clamp technique (insulin infusion rate 1.12 mU/kg/min). Insulinogenic index (delta IRI/delta BS at 30 min) and the insulin area under the curve during a 75-g oral glucose tolerance test (OGTT) were estimated. In the BGI subjects, the GIR values showed marked variation ranging from 2.24 to 10.44 mg/kg/min (5.54 +/- 0.31, mean +/- S.E.M.). The GIR values were lower in obese BGI subjects compared with non-obese BGI and NGT subjects, and the insulin area was markedly higher in BGI subjects with increased insulin resistance. There was a significant negative correlation between the GIR values and the insulin area or delta IRI/delta BS (30') ratio in the subjects with BGI either in the whole group or solely in the non-obese group. We conclude that the increased insulin secretion compensates for the peripheral insulin resistance of subjects with slightly deteriorated glucose tolerance, implying that insulin resistance plays an important role in the pathogenesis of NIDDM in some fraction of Japanese population.

Hyperglycemia facilitates urinary excretion of C-peptide by increasing glomerular filtration rate in non-insulin-dependent diabetes mellitus

We have evaluated the feasibility of monitoring the 24-hour urinary excretion rate of C-peptide (U-CPR) as a measure of integrated beta-cell function in patients with non-insulin-dependent diabetes mellitus (NIDDM). In 37 normoalbuminuric patients, U-CPR of 117.9 +/- 9.1 micrograms/d (mean +/- SEM) during the poorly controlled glycemic phase (fasting plasma glucose [FPG], 171 +/- 7 mg/dL; hemoglobin A1C [HbA1c], 8.8% +/- 0.4%) was significantly higher than the value of 83.3 +/- 13.7 micrograms/d (P < .001) during the well-controlled phase (FPG, 135 +/- 6 mg/dL; HbA1c, 7.0% +/- 0.2%), although the plasma insulin response to meals was lower during the former phase (53.3 +/- 6.3 microU/mL) versus the latter phase (65.7 +/- 6.6, P < .005). Endogenous creatinine clearance (Ccr) was significantly elevated during the poorly controlled phase (105.4 +/- 7.3 v 88.7 +/- 4.7 mL/min, P < .005). In 26 microalbuminuric patients, the plasma insulin response was greater during good glycemic control, but U-CPR did not differ between the two phases. Ccr was comparable at two phases in this group (92.7 +/- 7.4 v 91.1 +/- 5.9 mL/min, NS). U-CPR correlated positively with Ccr in both groups (r = .593, P < .001 in normoalbuminuria; r = .585, P < .001 in microalbuminuria). In addition, when biosynthetic human C-peptide was infused intravenously at an identical rate in two healthy subjects, resulting steady-state plasma levels of CPR were lower, and fractional U-CPR was higher during the moderately hyperglycemic phase versus the euglycemic phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of macro- and microvascular diseases in non-insulin-dependent diabetic and borderline glucose-intolerant subjects with insulin resistance syndrome

This study was undertaken to ascertain whether patients with insulin resistance syndrome, a cluster of risk factors for coronary artery disease (CAD), are really a high risk population for macro- and microvascular diseases in Japanese NIDDM and borderline glucose-intolerant subjects. A diagnosis of insulin resistance syndrome was made if four of the six following criteria are satisfied: glucose disposal rate < 2.2 mg/kg/min, fasting plasma IRI > 15 microU/ml or peak plasma IRI > 100 microU/ml during meal tolerance test, plasma triglyceride > 150 mg/dl at fasting or > 200 mg/dl after meal, serum HDL-cholesterol < 40 mg/dl, blood pressure > 140 mm Hg systolic and > 90 mm Hg diastolic or treatment with antihypertensive agents, and body mass index (BMI) > 27 for men or > 25 for women. We compared the prevalence of CAD, cerebral vascular disease (CVD), peripheral vascular disease (PVD), retinopathy and nephropathy between the insulin resistance syndrome group (group A, n = 57) and the remaining group (group B, n = 164). Both groups did not differ with respect to age, duration of diabetes, BMI, fasting plasma glucose, HbA1c, composition of NIDDM and borderline glucose-intolerance (BGI) or treatment modality. The prevalence of CAD was significantly higher in group A compared with that in group B (31.6% vs. 14.0%, P < 0.002), but not for CVD (8.8% vs. 3.7%, respectively, P = 0.12) or PVD (1.8% vs. 2.4%, respectively, P = 0.76). The prevalence of late-stage retinopathy in group A was significantly higher than that in group B (12.3% vs. 2.4%, respectively, P < 0.005). Macroalbuminuria, but not microalbuminuria, was significantly higher in group A than that in group B (12.3% vs. 3.6%, P < 0.02). We conclude that the insulin resistance syndrome preferentially increases the development of CAD, and is also involved in the progression of microvascular diseases.

Insulin resistance is associated with high plasma ouabain-like immunoreactivity concentration in NIDDM

The aim of the present study was to elucidate the pathophysiologic significance of circulating ouabain as a link between insulin resistance (IR) and hypertension (HT) in NIDDM. Euglycaemic (4.5 mmol/l) hyperinsulinaemic (360-580 pmol/l) clamping was performed using an artificial endocrine pancreas. Plasma ouabain-like immunoreactivity (OLI) was determined by radioimmunoassay using a highly specific antibody to ouabain. HT was defined as systolic blood pressure > 140 mm Hg and/or diastolic > 90 mm Hg or being treated with antihypertensive agents. The values (mean +/- SEM) of glucose infusion rate (GIR) and plasma OLI were compared among the four groups classified using IR and HT as factors. Group I (IR-/HT-, n = 15): GIR 7.20 +/- 0.36 mg.kg-1.min-1, OLI 130.8 +/- 20.9 pmol/l, which was not different from that in eight normal control subjects (7.69 +/- 0.40 mg.kg-1.min-1 and 142.6 +/- 32.3 pmol/l, respectively); Group II (IR-/HT+, n = 13): 5.89 +/- 0.36 mg.kg-1.min-1, 172.5 +/- 35.0 pmol/l; Group III (IR+/HT-, n = 14) 1.91 +/- 0.28 mg.kg-1.min-1, 576.6 +/- 161.5 pmol/l (p < 0.01 vs Group I and II); Group IV (IR+/HT+, n = 15) 1.79 +/- 0.22 mg.kg-1.min-1, 703.1 +/- 170.1 pmol/l (p < 0.01 vs Group I and II), respectively. Six of 57 NIDDM patients studied exhibited very high (> 1500 pmol/l) plasma OLI concentrations, showed marked insulin resistance and were all hypertensive. When analysed as a whole, plasma OLI was negatively correlated with GIR (p < 0.001), but was not correlated with arterial blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between insulin resistance and risk factors for cardiovascular disease in Japanese non-insulin-dependent diabetic patients

To investigate whether a resistance to insulin-stimulated glucose uptake (IR) is associated with the risk factors (RF) for cardiovascular disease (CVD) in non-insulin-dependent diabetic (NIDDM) patients, we determined the degree of IR in 135 adult NIDDM patients who had no advanced diabetic complications. The euglycemic (80 mg/dl) hyperinsulinemic clamp (insulin infusion rate 1.12 mU/kg per min) was performed and the average glucose infusion rate (GIR) during a steady-state euglycemia was determined as a measure of IR. Hypertension was more common among NIDDM patients with an increased IR and was highest in the group of patients with CVD. CVD-RF such as hypertension, hypertriglyceridemia, low HDL-cholesterol and obesity tended to cluster in the NIDDM patients who had lower GIR values and higher fasting IRI levels. GIR values were compared between a set of groups extracted from the 135 NIDDM patients that were matched for age, sex, body mass index and HbA1c levels. The CVD-positive group had the significantly lower GIR value than the CVD-negative group (2.06 +/- 0.66 vs. 3.45 +/- 1.75, P < 0.005). The GIR value was also significantly lower in the hypertriglyceridemic group compared with the normotriglyceridemic group (2.50 +/- 1.36 vs. 4.03 +/- 1.82, P < 0.0005). However, there was no significant difference between the hypertensive and normotensive groups and between the high cholesterol or low HDL-cholesterol groups and their respective control groups. In conclusion, these results suggest that IR contributes to the clustering of CVD-RFs which may accelerate the development of CVD in the subgroup of Japanese NIDDM patients.