Stig Attvall

Smoking induces insulin resistance—a potential link with the insulin resistance syndrome

Abstract. Objectives. The acute effect of smoking and snuffing on insulin sensitivity was studied in a group of healthy habitual smokers.

Effects of treatment with recombinant human growth hormone on insulin sensitivity and glucose metabolism in adults with growth hormone deficiency.

In a double-blind, cross-over, placebo-controlled trial, the effect of 26 weeks of replacement therapy with recombinant human growth hormone (rhGH) on insulin sensitivity and glucose metabolism in nine patients with adult-onset growth hormone deficiency was studied with a euglycemic clamp. Glucose production and utilization were studied with D-(3-3H)-glucose infusions. Comparisons were made with placebo treatment for 6 and 26 weeks, respectively. GH therapy for 6 weeks increased fasting plasma concentrations of glucose and insulin. However, after 26 weeks of GH treatment, no significant changes in glucose or insulin concentrations were recorded. GH treatment induced a marked change in insulin action evident after 6 weeks of therapy as shown by lower glucose infusion rates (GIRs) during the clamp compared with placebo treatment (2.6 +/- 0.4 v 4.1 +/- 0.7 mg.kg-1.min-1). This change in insulin action was due to a decreased insulin effect on glucose utilization. After 26 weeks of GH therapy, there was no significant difference in GIRs. During placebo treatment, insulin sensitivity and insulin, glucose, and nonesterified fatty acid (NEFA) concentrations were unchanged compared with concentrations measured before the study. Thus GH replacement therapy induces a change in insulin action in GH-deficient individuals. Whether this change represents a decrease in insulin action (ie, insulin resistance) or a restoration of action to normal is presently unclear, since a healthy control group was not included in the study. During long-term treatment, the present study suggests that the change in insulin action can be reversed, probably secondarily to changes in body composition.

The insulin resistance syndrome in smokers is related to smoking habits.

The relationship between smoking habits, insulin resistance, and related risk factors for cardiovascular disease was examined in 57 middle-aged male smokers whose degree of insulin resistance was quantified by using the euglycemic clamp technique. Smoking habits correlated with degree of insulin resistance and consequently with various manifestations of the insulin resistance syndrome including levels of insulin, high-density lipoprotein cholesterol, triglycerides, and plasminogen activator inhibitor-1 (PAI-1) activity. Smoking habits, independent of degree of insulin resistance, were also related to levels of total cholesterol and low-density lipoprotein cholesterol as well as triglycerides. Stepwise regression analyses considering the effects of age, lean body mass, body fat, body mass index, waist/hip ratio, and alcohol consumption showed that only smoking habits and percent body fat were independently related to degree of insulin resistance. This study shows that insulin resistance and the insulin resistance syndrome are important but not unique contributors to the strong risk profile for cardiovascular disease in middle-aged men who smoke.

Smoking cessation improves insulin sensitivity in healthy middle‐aged men

Cigarette smokers have recently been shown to exhibit insulin resistance, dyslipidaemia and markers of the insulin resistance syndrome (IRS). The aim of this study was to examine the effects of smoking cessation on insulin sensitivity and IRS. Forty male, non‐obese healthy smokers participated in this open parallel study with 8 weeks of follow‐up. Seventeen subjects were able to stop smoking, while 23 subjects continued to smoke and served as a controls group. Anthropometric and metabolic data were measured. Degree of insulin sensitivity was determined with the euglycaemic hyperinsulinaemic clamp technique. Smoking cessation increased insulin sensitivity and improved the lipoprotein profile in spite of a modest increase in body weight. Initial smoking habits correlated positively with the increase in BMI as well as the improvements in the metabolic variables after smoking cessation. These data support the view that smoking causes insulin resistance and IRS, and also demonstrate that the beneficial metabolic effects of smoking cessation override the effects of an accompanying modest increase in body weight.

Carotid Artery Wall Intima-Media Thickness Is Associated With Insulin-Mediated Glucose Disposal in Men at High and Low Coronary Risk

BACKGROUND AND PURPOSE The aim of this investigation was to examine the relationship between insulin sensitivity and intima-media thickness in the common carotid artery. METHODS Ultrasound examinations of the common carotid artery and hyperinsulinemic euglycemic clamp examinations were performed in a group (n = 25) of men aged 57 to 77 years at high risk for atherosclerotic disease (hypertension and at least one of the following factors: hypercholesterolemia and/or smoking) and in an age-matched low-risk group (n = 23) with no cardiovascular risk factors. Subjects with cardiovascular disease or diabetes mellitus were excluded. RESULTS A significant negative relationship between insulin sensitivity index and common carotid maximum intima-media thickness was observed in both the high-risk group (r = -.45, P < .05) and in the low-risk group (r = -.59, P < .01). CONCLUSIONS Our results suggest that an increase in intimamedia thickness, as a possible expression of early atherosclerosis, is negatively related to insulin sensitivity.

EFFECTS OF HYPERGLYCEMIA ON INTERDIGESTIVE GASTROINTESTINAL MOTILITY IN HUMANS

BACKGROUND Gastrointestinal motility disorders are common in patients with diabetes mellitus. Recent studies indicate that hyperglycemia can affect gastric emptying and gastric motility in healthy subjects and diabetics. METHODS The effect of acute hyperglycemia on gastrointestinal motility was studied with a manometric technique in healthy subjects. Seven individuals, four men and three women, 23-34 years old, were studied on 2 different days. On 1 of the days a 5-h registration was performed after an overnight fast. On another day and after an initial basal period, acute steady-state hyperglycemia was induced by intravenous glucose infusion for 90 min. Motility variables were evaluated in four segments: in the gastric antrum, the proximal duodenum, the distal duodenum, and the proximal jejunum. RESULTS Fasting migrating motor complex rhythm including migration of phase III prevailed during hyperglycemia. Compared with euglycemia, the motility index in phase II was lower during hyperglycemia in all segments studied. In the antrum the difference was 62% (p < 0.01); in the proximal duodenum, 37% (p < 0.01); in the distal duodenum, 44% (p < 0.05); and in the jejunum, 58% (p < 0.01). During hyperglycemia the prevalence of propagated contractions in phase II was significantly lower than during euglycemia both in the antrum and the proximal duodenum. In the last part of phase III in proximal duodenum most individual contractions were propagated in orad direction compared with early phase III, and this difference persisted during hyperglycemia. The number of long clusters was significantly increased during hyperglycemia as compared with euglycemia: 2.0 +/- 0.6 per hour versus 0.4 +/- 0.14 (p < 0.01). In late phase II plasma levels of motilin and pancreatic polypeptide were significantly decreased during hyperglycemia. CONCLUSION Hyperglycemia not only reduces the motility in the stomach but also inhibits motility in both the duodenum and the jejunum. The results show that acute hyperglycemia has an important impact on small-intestinal motility.

Characterization of the insulin-antagonistic effect of growth hormone in man.

SummaryThe insulin-antagonistic effect of growth hormone was characterized by infusing the hormone at three different infusion rates (6, 12 or 24 mU·kg−1·min−1) for one h in 11 healthy subjects. The insulin effect was measured with the euglycaemic clamp technique combined with D-(3-3H)-glucose infusion to evaluate glucose production and utilization. A control study with NaCl (154 mmol·l−1) infusion was also performed. The insulin levels during the clamps were similar in all studies (36±0.2 mU·l−1). Peak growth hormone levels were reached at 60 min (growth hormone 6mU·kg−1·h−1: 31±5; growth hormone 12 mU·kg−1·h−1: 52±4 and growth hormone 24 mU·kg−1·h−1: 102±8mU·l−1). The insulin-antagonistic effect of growth hormone started after ∼2 h, was maximal after 4–5 h (∼39% inhibition of glucose infusion rate between control and growth hormone 24 mU·kg−1·h−1) and lasted for 6–7 h after peak levels. The resistance was due to a less pronounced insulin effect both to inhibit glucose production and to stimulate glucose utilization. Growth hormone infusion of 12 mU·kg−1·h−1 induced a similar insulin-antagonistic effect as the higher infusion rate whereas 6 mU·kg−1·h−1 induced a smaller response with a duration of 1 h between 3–4 h after peak levels of growth hormone. The present study demonstrates that growth hormone levels similar to those frequently seen in Type 1 (insulin-dependent) diabetic patients during poor metabolic control or hypoglycaemia, have pronounced insulin-antagonistic effects. The effects starts after about 2–3 h, is maximal after 4–5 h and lasts for about 6–7 h. Both duration and inhibitory effect of growth hormone are related to the plasma levels, where a maximal effect is seen at about 50 mU·l−1 or higher.

Hyperinsulinaemia impairs gastrointestinal motility and slows carbohydrate absorption

SummaryExperimental euglycaemic hyperinsulinaemia (insulin levels 46±4 mU/l) impaired the postabsorptive gastrointestinal motility in healthy individuals; the effect being particularly pronounced in the upper gastrointestinal tract (stomach and proximal duodenum). The postprandial gastric emptying, measured with a standardized99mTc labelled meal, was also significantly delayed (t50 increased by 38% or 32 min). This was combined with a slower carbohydrate absorption (delay in peak blood glucose level about 40 min). Furthermore, during experimental hyperinsulinaemia higher blood glucose levels were seen at 120 min than at 60 min after food ingestion. This was not seen in any subject in the control study where only 0.9% NaCl was infused. Blood levels of the motility-stimulating hormone, motilin, were significantly lower during experimental hyperinsulinaemia. Thus, experimental hyperinsulinaemia impairs the gastrointestinal motility in both the postabsorptive and postprandial states. This effect is combined with a delayed carbohydrate absorption. Hyperinsulinaemia per se may thus lead to alterations in carbohydrate absorption and can also contribute to the gastrointestinal disturbances in diabetes. [Diabetologia (1995) 38: 79–85]

Altered Recognition of Hypoglycaemic Symptoms in Type I Diabetes during Intensified Control with Continuous Subcutaneous Insulin Infusion

The effect of intensified metabolic control obtained with continuous subcutaneous insulin infusion (CSII) on the frequency and symptoms of hypoglycaemia was studied in type I diabetic patients. The reproducibility of the questionnaire used to evaluate the hypoglycaemic symptoms was verified in a control group receiving unchanged conventional insulin therapy for 2 months. Metabolic control was significantly improved during CSII (HbA1c 6.8 ± 0.4% versus 8.7 ± 0.7%, normal range up to 5.4%) in all patients while no change was seen in the control group. The results of frequent self glucose monitoring showed that the incidence of low glucose levels (below 3.5 mmol/l) increased about threefold in the CSII group. Awareness of hypoglycaemia was clearly changed during CSII with less pronounced adrenergic symptoms while no alterations were found in the group with unchanged metabolic control. These results emphasize the importance of regular self glucose monitoring during CSII and of informing the patients that their hypoglycaemic symptoms may change during intensified control.

Influence of the sympathetic nervous system on insulin sensitivity and adipose tissue metabolism : a study in spinal cord-injured subjects

To evaluate insulin sensitivity and adipose tissue metabolism, seven spinal cord-injured (SCI) subjects (age, 43 +/- 6 years; body mass index, 22.8 +/- 1.4; mean +/- SE) and their seven siblings (age, 45 +/- 6 years; body mass index, 24.8 +/- 0.8) were studied using oral glucose (100-g) tolerance tests (OGTTs), euglycemic insulin clamps (insulin infusion, 1 mU/kg.min), and microdialysis of the subcutaneous tissue. Blood glucose and insulin after oral glucose were significantly increased in SCI subjects as compared with their siblings. During insulin clamping, plasma adrenaline increased significantly in controls, but not in SCI subjects. However, the rates of glucose production (2.02 +/- 0.36 v 1.59 +/- 0.09 mg/kg.min) and utilization (5.13 +/- 0.71 v 5.78 +/- 0.34) were similar in the two groups. Furthermore, interstitial subcutaneous glycerol and lactate concentrations before and after oral glucose were similar in the two groups, even in neurally decentralized tissue with broken connection between the central nervous system and peripheral sympathetic nerves. The data suggest that (1) well-mobilized SCI subjects show minor insulin resistance, and (2) sympathetic nervous activity has a minor influence on adipose tissue metabolism in the postabsorptive state, but may affect insulin sensitivity during euglycemic clamping.