Plasma glucose and insulin responses to oral glucose in nonobese subjects and patients with endogenous hypertriglyceridemia

Triglycerides-diabetes association in healthy middle-aged men: modified by physical fitness? A long term follow-up of 1962 Norwegian men in the Oslo Ischemia Study

AIMS

To examine the impact of physical fitness (PF) on the association between fasting serum triglycerides (FTG) and diabetes risk and whether temporal changes in FTG predict diabetes risk in healthy middle-aged men.

METHODS

FTG and PF (bicycle exercise test) were measured in 1962 men aged 40-59 years in 1972-1975 (Survey 1) and repeated in 1387 still healthy men on average 7.3 years later (Survey 2). Diabetes was diagnosed according to WHO 1985-criteria.

RESULTS

During 35 years follow-up 202/1962 (10.3%) men developed diabetes. Compared with the lowest, the upper FTG tertile had a 2.58-fold (95% CI: 1.81-3.74) diabetes risk adjusted for age, fasting blood glucose and maternal diabetes, and a 2.29-fold (95%CI: 1.60-3.33) when also adjusting for PF. Compared with unchanged (±25%) FTG levels (n=664), FTG reduction of more than 25% (n=261) was associated with 56% lower (0.44; 95% CI: 0.24-0.75) diabetes risk, while FTG increase of more than 25% (n=462) was associated with similar risk. These associations were unchanged when adjusted for PF and PF change.

CONCLUSIONS

High FTG-levels predicted long-term diabetes risk in healthy middle-aged men, and the association was only modestly weakened when adjusted for PF. A reduction in FTG was associated with decreased diabetes risk.

Effects of a meal rich in 1,3-diacylglycerol on postprandial cardiovascular risk factors and the glucose-dependent insulinotropic polypeptide in subjects with high fasting triacylglycerol concentrations

It was previously reported that compared to triacylglycerol (TAG) oil, diacylglycerol (DAG) oil improves postprandial lipid response. However, the effects of DAG oil on postprandial hyperglycemia and incretin response have not yet been determined. In this study, the effects of DAG oil on both postprandial hyperlipidemia and hyperglycemia and the response to the glucose-dependent insulinotropic polypeptide (GIP) were studied. This randomized, double-blind, crossover study analyzed data for 41 individuals with high fasting triacylglycerol concentrations. The subjects ingested test meals (30.3 g of protein, 18.6 g of fat, and 50.1 g of carbohydrate) containing 10 g of DAG oil (DAG meal) or TAG oil (TAG meal) after fasting for at least 12 h. Blood samples were collected prior to and 0.5, 2, 3, 4, and 6 h after ingestion of the test meal. Postprandial TAG concentrations were significantly lower after the DAG meal compared with the TAG meal. Postprandial TAG, insulin, and GIP concentrations were significantly lower after the DAG meal compared with the TAG meal in 26 subjects with fasting serum TAG levels between 1.36 and 2.83 mmol/L. DAG-oil-based meals, as a replacement for TAG oil, may provide cardiovascular benefits in high-risk individuals by limiting lipid and insulin excursions.

Low glycemic diet for weight loss in hypertriglyceridemic patients attending a lipid clinic

PURPOSE

To assess the effectiveness of low glycemic dietary counseling for weight loss among moderately hypertriglyceridemic patients in an academic referral lipid clinic.

METHODS

During 1998 to 2000, weight loss advice followed traditional guidelines. Beginning in 2001, hypertriglyceridemic patients were advised to greatly reduce intake of high glycemic carbohydrates. The clinic database was queried for all patients initiating consultative treatment from 1998 through 2004. Subjects were included if initial fasting triglyceride was 200 to 800 mg/dL and if at least two follow-up visits were made during a period of 365 days or more. Mean percent changes from baseline in weight and lipid/lipoproteins beyond 1 year were calculated. Macronutrient composition was determined 3- to 5-day food diaries submitted by subjects from the highest quartile of weight loss.

RESULTS

Patients (n = 56) first seen in 1998-2000 had 0.2 ± 0.7% mean weight gain beyond one year compared with 3.0 ± 0.5% weight loss for patients (n = 141) initially seen in 2001 to 2004 (P < .001 comparing groups). Weight loss correlated with triglyceride reduction (-2.6 mg/dL per kilogram body weight, r = 0.29, P < .001) and with HDL-C increase (0.22 mg/dL per kilogram body weight, r = 0.16; P = .038). Highest quartile weight losers in the low glycemic group (n = 15) reported consuming 44% carbohydrate calories, 32% fat, 22% protein, and 2% alcohol.

CONCLUSION

Hypertriglyceridemic patients who received low glycemic dietary counseling and maintained clinic attendance more than 1 year achieved mean 3.0% weight loss. This was improved compared with historical controls with traditional dietary counseling. Food diaries from successful weight losers suggested compliance with a low glycemic, moderately reduced carbohydrate diet plan.

The hypolipidemic action of bezafibrate therapy in hypertriglyceridemia is mediated by upregulation of lipoprotein lipase: no effects on VLDL substrate affinity to lipolysis or LDL receptor binding

Fibrates are regarded as drugs of choice in hypertriglyceridemia (HTG). Downregulation of apolipoprotein (apo) C-III gene expression and upregulation of lipoprotein lipase (LPL) gene expression have been suggested to explain the hypolipidemic action of fibrates. This study was designed to study the effects of bezafibrate therapy on very low density lipoprotein (VLDL) susceptibility to lipolysis, VLDL binding to the low density lipoprotein (LDL) receptor and postheparin LPL activities in patients with HTG. VLDL lipolysis was studied with heparan sulfate proteoglycan-bound LPL. Binding affinity of VLDL to the LDL receptor was determined in J774 cells with 125I-labeled control LDL. Eighteen HTG patients were randomized to receive, in a double-blind placebo-controlled cross-over fashion, 400 mg bezafibrate once daily for 6 weeks. In response to bezafibrate therapy, plasma triglyceride and apoC-III levels decreased by 69 and 42%, respectively. HTG VLDL was lipolyzed less efficiently compared to control VLDL, and lipolysis did not improve by bezafibrate therapy. VLDL binding affinity to the LDL receptor was comparable between the control group and HTG group, and did not change upon bezafibrate therapy. However, the post-heparin LPL activity in the HTG patients increased from 153 to 192 U/l (P = 0.025). A strong inverse relation was observed between the change in LPL activities and the change in triglyceride levels (r = -0.62, P = 0.006). In conclusion, the hypolipidemic action of bezafibrate therapy in HTG may be attributed to increased LPL activity, whereas VLDL susceptibility to lipolysis and LDL receptor binding are not affected.

Impaired myocardial vasodilation during hyperemic stress with dipyridamole in hypertriglyceridemia

OBJECTIVES

This study sought to investigate the specific role of hypertriglyceridemia in the myocardial hyperemic stress with dipyridamole/rest flow ratio (MDR).

BACKGROUND

Reduced MDR has been reported in hypercholesterolemic patients without evidence of ischemia. However, the specific role of hypertriglyceridemia in MDR has not been studied.

METHODS

Fifteen nondiabetic normocholesterolemic hypertriglyceridemic patients and 13 age-matched control subjects were studied. Myocardial blood flow (MBF) during dipyridamole administration and baseline MBF in hypertriglyceridemic patients and control subjects were measured using positron emission tomography and nitrogen-13 ammonia, after which the MDR was calculated.

RESULTS

Baseline MBF (ml/min per 100 g heart weight) in hypertriglyceridemic patients (mean +/- SD 73.6 +/- 24.1) did not differ significantly from that in control subjects (81.6 +/- 37.2). MBF during dipyridamole loading in hypertriglyceridemic patients (198 +/- 106) was significantly reduced compared with that in control subjects (313 +/- 176, p < 0.05), as was the MDR (2.71 +/- 1.07 vs. 3.73 +/- 1.14, respectively, p < 0.05). Spearman rank-order correlation analysis showed a significant relation between plasma triglyceride concentration and MDR (r = -0.466, asymptotic SE 0.157, p = 0.0125); however, no such significant relation was seen between total plasma cholesterol concentration and MDR (r = -0.369, asymptotic SE 0.130, p = 0.059).

CONCLUSIONS

Impaired myocardial vasodilation was suggested in hypertriglyceridemic patients without symptoms and signs of ischemia.

Glucose intolerance in familial combined hyperlipidaemia. EUFAM study group

BACKGROUND

Familial combined hyperlipidaemia (FCHL) is a common hereditary disorder. Hypertriglyceridaemia is associated with glucose intolerance and insulin resistance.

METHODS

To study glucose tolerance in FCHL patients with different lipid phenotypes [hypercholesterolaemia (IIA), mixed hyperlipidaemia (IIB), hypertriglyceridaemia (IV)], we investigated 253 family members and 92 spouses arising from 33 well-defined Finnish FCHL pedigrees.

RESULTS

In oral glucose tolerance tests the affected family members had higher values for glucose area under the curve than did non-affected family members [673+/-127 min mmolL(-1), 754+/-145 min mmol L(-1), 846+/-180 min mmol L(-1) and 838+/-183 min mmol L(-1) for phenotypes normal, IIA, IIB and IV respectively; P < 0.001 after adjustment for body mass index, waist circumference and age]. Impaired glucose tolerance and diabetes were more common among affected than non-affected family members (prevalences of normal glucose tolerance 94.0%, 80.0%, 54.3% and 58.5% for phenotypes normal, IIA, IIB and IV).

CONCLUSION

Affected FCHL family members were more glucose intolerant than non-affected family members. In men, this disturbance was not related to lipid phenotype nor was it explained by obesity.

Hyperinsulinaemia of hypertriglyceridaemia: a reappraisal

The peripheral hyperinsulinaemia of hypertriglyceridaemic subjects has only been defined using insulin immunoassays in which proinsulin and proinsulin fragments cross-react. Relative contributions of pancreatic secretion and hepatic extraction of insulin to this hyperinsulinaemia have not been studied. We, therefore, reassessed the hyperinsulinaemia of hypertriglyceridaemia by measuring fasting plasma concentrations of intact proinsulin, glucose, insulin, and C-peptide in 24 hypertriglyceridaemic subjects with normal glucose tolerance (n = 14) and with impaired glucose intolerance (n = 10) and in normal subjects (n = 14). Hypertriglyceridaemic subjects had higher (p < 0.01) fasting concentrations of insulin and C-peptide and greater (p < 0.01) fasting insulin: C-peptide molar ratios than in control subjects. Fasting intact proinsulin concentrations were similar in hypertriglyceridaemic subjects with normal glucose tolerance and control subjects but these were lower (p < 0.01) than in hypertriglyceridaemic subjects with impaired glucose tolerance. These results suggest that the fasting peripheral hyperinsulinaemia of hypertriglyceridaemic subjects is due to increased pancreatic secretion and reduced hepatic fractional extraction of insulin. The peripheral hyperinsulinaemia of hypertriglyceridaemia appears to reflect peripheral insulin resistance and is not attributable to elevated proinsulin concentrations which are characteristic of impaired glucose tolerance and Type 2 (non-insulin-dependent) diabetes mellitus.

The effect of an antilipolytic agent (acipimox) on the insulin resistance of lipid and glucose metabolism in hypertriglyceridaemic patients

Hypertriglyceridaemia is associated with insulin resistance of both lipid and glucose metabolism. It is not known whether the insulin resistance affects both glucose oxidation and glycogen formation. To study the oxidative and non-oxidative pathways of non-esterified fatty acids (NEFA) and glucose metabolism, eight male hypertriglyceridaemic subjects were studied during insulin infusion (75 and 340 pmol/m2.min) in combination with indirect calorimetry and infusions of [3-3H]glucose and [1-14C]palmitate before and after 4 weeks of treatment with the antilipolytic agent acipimox (250 mg three times daily). Compared with eight healthy subjects the hypertriglyceridaemic subjects were resistant to the antilipolytic effect of insulin, both in the basal state (P < 0.05) and during insulin infusion (P < 0.05). This was associated with impaired insulin-stimulated glucose uptake (P < 0.05), predominantly in the non-oxidative pathway (P < 0.05). Acipimox decreased basal NEFA concentrations (P < 0.01) and reduced lipid oxidation during low-dose insulin infusion (P < 0.05). Glucose uptake, predominantly glycogen formation, was stimulated by acipimox (P < 0.05). In conclusion, the insulin resistance of glucose metabolism associated with hypertriglyceridaemia is largely due to a defect in non-oxidative glucose metabolism. Acipimox improves glucose metabolism both by affecting glucose oxidation (low-dose insulin) and non-oxidative glucose metabolism (high-dose insulin).

Insulin resistance in type 2 (non-insulin-dependent) diabetic patients with hypertriglyceridaemia

Hypertriglyceridaemia, which is frequently seen in Type 2 (non-insulin-dependent) diabetes mellitus, is associated with insulin resistance. The connection between hypertriglyceridaemia and insulin resistance is not clear, but could be due to substrate competition between glucose and lipids. To address this question we measured glucose and lipid metabolism in 39 Type 2 diabetic patients with hypertriglyceridaemia, i.e. mean fasting serum triglyceride level equal to or above 2 mmol/l (age 59 +/- 1 years, BMI 27.4 +/- 0.5 kg/m2, HbA1c 8.0 +/- 0.2%, serum triglycerides 3.2 +/- 0.2 mmol/l) and 41 Type 2 diabetic patients with normotriglyceridaemia, i.e. mean fasting serum triglyceride level below 2 mmol/l (age 58 +/- 1 years, BMI 27.0 +/- 0.7 kg/m2, HbA1c 7.8 +/- 0.2%, serum triglycerides 1.4 +/- 0.1 mmol/l). Insulin sensitivity was assessed using a 340 pmol.(m2)-1 x min-1 euglycaemic insulin clamp. Substrate oxidation rates were measured with indirect calorimetry and hepatic glucose production was estimated using a primed (25 microCi)-constant (0.25 microCi/min) infusion of [3-3H]-glucose. Suppression of lipid oxidation by insulin was impaired in patients with hypertriglyceridaemia vs patients with normal triglyceride levels (3.5 +/- 0.2 vs 3.0 +/- 0.2 mumol.kg-1 x min-1; p < 0.05). Stimulation of glucose disposal by insulin was reduced in hypertriglyceridaemic vs normotriglyceridaemic patients (27.0 +/- 1.3 vs 31.9 +/- 1.6 mumol.kg-1 x min-1; p < 0.05) primarily due to impaired glucose storage (9.8 +/- 1.0 vs 14.6 +/- 1.4 mumol.kg-1 x min-1; p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin resistance and action in hypertriglyceridemia

To define further the characteristics of insulin insensitivity associated with hypertriglyceridemia, the metabolic responses to the euglycemic insulin clamp were evaluated in 6 hypertriglyceridemic male patients and compared to 5 normal male controls. At baseline, the hypertriglyceridemic patients had elevated triglycerides (687 +/- 172 vs 78 +/- 7 mg/dl, P less than 0.005) and free fatty acids (702 +/- 36 vs 444 +/- 42 microM/l, P less than 0.005) concentrations. During the euglycemic insulin clamp, steady-state plasma glucose concentrations were similar in both groups (90.2 +/- 1.5 vs 88.8 +/- 2.3 mg/dl, ns) as were steady state insulin levels (142 +/- 10.1 vs 132.2 +/- 6.8 microU/ml**). The amount of glucose metabolized during the last hour of the clamp (M) was significantly reduced in the hypertriglyceridemic patient (2.9 +/- 0.4 vs 6.2 +/- 0.7 mg.min-1.kg-1, P less than 0.001). Changes in free fatty acid, glycerol, B-hydroxybutyrate, lactate and pyruvate during the euglycemic insulin clamp were similar indicating a preserved antilipolytic, antiketogenic and glycolytic intermediate (lactate + pyruvate) response to insulin and glucose infusion in the hypertriglyceridemic patients. In summary, hypertriglyceridemia is associated with insulin resistance as it relates to muscle glucose utilization. However, this is not universal, as a number of other insulin responsive pathways appear to be unaffected.

The assessment of hepatic and peripheral insulin sensitivity in hypertriglyceridemia

Peripheral insulin resistance is a common finding in hypertriglyceridemia. However, hepatic insulin sensitivity has rarely been investigated. We measured hepatic and peripheral insulin sensitivity in eight nondiabetic, nonobese hypertriglyceridemic subjects (HT) with raised triglyceride concentrations (4.3 +/- 0.6 mmol.L-1, mean +/- SEM) and eight age-, sex-, and weight-matched control subjects (C) with normal triglyceride concentrations (1.2 +/- 0.2 mmol.L-1). Insulin secretion was assessed during a 75-g oral glucose tolerance test (OGTT). Glucose turnover was determined using 3(3H) glucose in the postabsorptive state and during euglycemic glucose clamps at insulin infusion rates of 0.25 and 1.0 mU.kg-1.min-1. At identical fasting glucose concentrations (HT, 5.2 +/- 0.2; C, 5.2 +/- 0.2 mmol.L-1), the glucose responses to OGTT were similar in both groups. Fasting plasma insulin (HT, 8.3 +/- 1.2; C, 4.6 +/- 0.4 mU.L-1; P = .02), and C-peptide (HT, 1.7 +/- 0.2; C, 1.1 +/- 0.1 microgram.L-1; P = .006) concentrations were higher in hypertriglyceridemic subjects. The insulin and C-peptide responses to OGTT were greater in hypertriglyceridemic subjects (insulin, P = .005; C-peptide; P = .01). Hepatic glucose appearance in the postabsorptive state was similar (HT, 11.4 +/- 0.3; C, 10.9 +/- 0.7 mumol.kg-1.min-1; NS). At low insulin concentrations (HT, 20.7 +/- 1.4; C, 20.5 +/- 1.4 mU.L-1), hepatic glucose appearance was equally suppressed (HT, 9.6 +/- 0.9; C, 10.5 +/- 1.3 mumol.kg-1.min-1; NS).(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of physical training on glucose tolerance, insulin sensitivity, and lipid and lipoprotein concentrations in middle-aged hypertriglyceridaemic, carbohydrate intolerant men

The effects of 9 weeks of moderate intensity exercise training while on a weight-maintaining diet were studied in 19 untrained middle-aged, hypertriglyceridaemic, carbohydrate intolerant men. Initial mean maximum oxygen consumption was low (29.7 +/- 1.0 ml.min-1.kg-1; mean +/- SEM) and improved (34.2 +/- 1.4 ml.min-1.kg-1, p less than 0.01) with exercise training. Fasting glucose, insulin, lipid and lipoprotein concentrations did not change. While the abnormal glucose response to oral glucose did not change with training, insulin concentrations were significantly (p less than 0.05) lower at 90 and 120 min during the final oral glucose tolerance test. Insulin mediated glucose uptake did not change, indicating that the degree of exercise training failed to improve in vivo insulin sensitivity. Significant associations were found between the following parameters measured: fasting concentrations of triglycerides and insulin, very low density lipoprotein-triglycerides and glucose, and measures of in vivo insulin resistance and fasting insulin levels, suggesting that insulin resistance in these glucose intolerant subjects may play a role in their hypertriglyceridaemia. These data indicate that moderate increases in physical training alone are not sufficient to improve the carbohydrate, insulin and lipid metabolism of hypertriglyceridaemic, glucose intolerant men.

Glucose tolerance and insulin response to glucose in nondiabetic young male survivors of myocardial infarction

Intravenous and oral glucose tolerance, as well as insulin response to glucose ingestion and a glucose infusion test, were investigated in 104 male nondiabetic survivors of myocardial infarction under the age of 45 years and in 100 matched control subjects randomly selected from the general population. Reduced oral glucose tolerance and hyperinsulinemic responses to both oral glucose challenge and to a glucose infusion test were present in a substantial number of the young patients. The very low density lipoprotein triglyceride concentration tended to rise progressively with increasing severity of glucose intolerance in both patients and control subjects. The magnitude of the early insulin response during the glucose infusion test, along with the high density lipoprotein cholesterol concentration, correlated inversely and independently with degree and extent of coronary atheromatosis, whereas the low density lipoprotein cholesterol level showed a positive correlation with severity of coronary atheromatosis. The present data argue against the concept of direct atherogenic action of high plasma insulin levels. In contrast, a low and delayed early insulin response might be a marker of enhanced liability to evolution of severe diffuse coronary atheromatosis.

Lack of a lipoprotein-induced insulin resistance in hepatoma cells in culture

A lipoprotein-induced resistance to the action of insulin has been postulated. To test this hypothesis, cultured rat-derived hepatoma cells, designated FAO, and human-derived hepatoma cells, designated HEP-G2, were incubated for 20 h in the presence or absence of lipoprotein; specific 125I-insulin receptor binding and labeled glucose incorporation into glycogen were then measured. Very low density lipoproteins (d less than 1.006 g/ml) in physiologic (0.5 mg/ml) or pathophysiologic (5 mg/ml) concentrations did not modify insulin receptor binding of FAO or HEP-G2 cells. This was true for very low density lipoproteins derived from normal human, diabetic human, and streptozotocin-diabetic rat plasma. Low density lipoproteins (d = 1.019 - 1.063 g/ml) isolated from normal human plasma similarly failed to modify insulin receptor binding. Concerning insulin action, the different very low density lipoprotein preparations did not modulate either basal or insulin-stimulated glucose incorporation into glycogen of the cells. Thus, very low density lipoproteins and low density lipoproteins did not induce insulin resistance in cultured hepatoma cells either at the insulin receptor level or at the post-receptor level.

Relationship of carbohydrate intolerance to serum lipoprotein profiles in childhood. The Bogalusa Heart Study

Three hundred-eighty-eight children were selected from a total community and biracial (black-white) population for a special in-depth study related to serum lipoproteins and carbohydrate metabolism. Based on two previous serum lipoprotein determinations of high and/or low beta and pre-beta-lipoprotein cholesterol, they were stratified into four groups. A glucose tolerance test was performed for fasting, 30-minute, and one-hour glucose, insulin, free fatty acids, calcium, and magnesium. Observations of height, weight, and triceps skinfold were also obtained on the children. Children in the high beta-lipoprotein cholesterol groups tended to have higher glucose levels and were more obese than the other groups, while children in the high pre-beta-lipoprotein cholesterol group tended to have high insulin levels following the glucose load. Fasting blood levels were not appreciably different in the various groups, but after the glucose load an unusually high insulin secretory response occurred in black children, especially black girls. Black girls also demonstrated somewhat lower blood sugars than the other race-sex groups. The insulin/glucose ratios were dramatically different in the black children, especially black girls. These differences were particularly noted in the groups with the high pre-beta-lipoprotein. Black children also tended to have higher insulin/free fatty acid ratios during the glucose tolerance test. These differences persisted even after adjusting for obesity. Although not significant, calcium levels consistently decreased in all groups following a glucose load. The observation of racial contrasts in glucose and insulin responses are interesting. While black girls appear to show low glucose and high insulin responses to a glucose load, low and delayed insulin response along with high glucose response occur in whites, especially white girls. Since white children have greater body fat content, these observations suggest more insulin resistance in white children. Even at low levels of obesity, subtle carbohydrate lipid metabolic aberrations are found in children having high levels of serum lipoproteins. A persistence of these conditions could contribute to accelerated atherosclerosis and subsequent coronary artery disease.

Effect of exercise training on glucose tolerance, in vivo insulin sensitivity, lipid and lipoprotein concentrations in middle-aged men with mild hypertriglyceridemia

The effects of 9 weeks of aerobic exercise training with maintenance of stable body weight upon insulin sensitivity and upon glucose, lipid, and lipoprotein concentrations were studied in 10 middle-aged men with mild hypertriglyceridemia. Following training, mean maximum oxygen consumption improved from 33.5 +/- 1.9 to 39.3 +/- 1.9 mL/kg/min (means +/- SEM), (P less than 0.01). Glucose concentrations, both fasting and during oral glucose tolerance testing, remained stable but both fasting insulin concentrations and insulin responses to oral glucose decreased (P less than 0.1 and less than 0.01, respectively). In vivo insulin sensitivity improved 25 +/- 6.1% (P less than 0.01) following training. Exercise training resulted in decreases in fasting serum triglyceride concentrations from 203 +/- 12.6 to 126 +/- 9.0 mg/dL (P less than 0.01), primarily as a result of the reduction in VLDL-triglycerides (P less than 0.01). The magnitude in percentage decrease of VLDL-triglycerides was found to be significantly correlated (r = 0.71, P less than 0.05) with the magnitude in percent increase in max VO2. Serum cholesterol levels declined from 211 +/- 8.9 to 193 +/- 11.9 mg/dL (P less than 0.01), and the ratio of HDL-cholesterol to total cholesterol was improved. This study demonstrates that exercise training at a level of intensity feasible for many middle-aged men has beneficial effects on several factors that have been associated with an increased risk of cardiovascular disease.

Diminished insulin receptors on monocytes and erythrocytes in hypertriglyceridemia

Carbohydrate intolerance is a common observation in endogenous hypertriglyceridemia (HL). So far the nature of this metabolic defect, which accompanies postprandial hyperinsulinemia and a reduced hypoglycemic action of insulin, has not been elucidated. We have examined cellular insulin binding in 20 subjects affected with HL (average plasma triglyceride level, 437 +/- 311 mg/dL) to test the possibility that a receptor defect is involved in peripheral insulin resistance. Monocytes from the HL subjects bound, on the average, 34% less insulin than cells from eight normotriglyceridemic controls of comparable age and body weight (average plasma TG level, 169 +/- 34 mg/dL). Likewise, erythrocytes from the HL group bound 29.6% less insulin than did those from control subjects. Scatchard analysis of the binding data revealed that the number of insulin receptors was reduced for both types of cells. To test if the abnormality in cellular insulin-binding capacity in these subjects is an inherent defect or secondary to the hypertriglyceridemia, 11 of the subjects participated in a 4-month training program (120 minutes weekly of moderate exercise at 60% VO2 max), while the remaining nine persons served as controls. Training reduced the average plasma TG level from 373 +/- 270 to 277 +/- 139 mg/dL (P less than 0.01), but cellular insulin binding was not significantly affected. In addition, no correlation was found between the individual TG plasma concentration and cellular insulin binding. Thus, training itself also proved ineffective in enhancing insulin binding, most probably due to exertion of insufficient intensity.(ABSTRACT TRUNCATED AT 250 WORDS)