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.

Insulin receptor substrate (IRS) 1 is reduced and IRS-2 is the main docking protein for phosphatidylinositol 3-kinase in adipocytes from subjects with non-insulin-dependent diabetes mellitus

The large docking protein IRS-1 is a major substrate for the insulin receptor and other tyrosine kinases. It plays a key role in eliciting many of insulin's actions, including binding and activation of phosphatidylinositol (PI) 3-kinase and the subsequent increase in glucose transport. Gene disruption of IRS-1 in mice is associated with an impaired insulin-stimulated glucose disposal in vivo and glucose transport in vitro, but the survival of the animals and residual insulin sensitivity is dependent on the presence of the alternative docking protein IRS-2. We examined the expression and function of IRS-1 and IRS-2 in adipocytes from healthy and diabetic individuals. Cells from subjects with non-insulin-dependent diabetes mellitus (NIDDM), but not with insulin-dependent diabetes mellitus, had an impaired insulin effect and a marked reduction (70 +/- 6%) in the expression of IRS-1 protein, whereas IRS-2 was unchanged. In normal cells, IRS-1 was the main docking protein for the binding and activation of insulin-stimulated PI 3-kinase; IRS-2 was also functional but required a higher insulin concentration for a similar binding and activation of PI 3-kinase. In contrast in NIDDM cells with a low IRS-1 content, IRS-2 became the main docking protein. These findings may provide important reasons for the insulin resistance in NIDDM.

The insulin resistance syndrome and postprandial lipid intolerance in smokers

BACKGROUND

The effects of cigarette smoking on insulin resistance, postprandial lipemia following a mixed meal, lipoproteins and other aspects of the insulin resistance syndrome (IRS) were investigated in healthy middle-aged men.

METHODS

36 smoking and 25 age- and body mass index (BMI)-matched non-smoking men participated. They were non-obese (BMI < 27), healthy and without any medication. The smokers had been smoking more than 10 cigarettes per day for more than 20 years; the non-smokers had never been habitual smokers. Body composition and several metabolic and cardiovascular risk factors were studied, including the prevalence of small dense LDL-particles, lipoprotein and hepatic lipase activity and triglyceride levels after a mixed test meal. For determination of degree of insulin sensitivity the euglycemic hyperinsulinemic clamp technique was used.

RESULTS

The smokers had lower HDL-cholesterol and lipoprotein A-I levels but higher fasting triglycerides, as well as an increased proportion of small dense LDL-particles and higher postheparin hepatic lipase activity. They also had higher levels of fibrinogen, plasminogen activator inhibitor 1 (PAI-1) activity and fasting and steady-state C-peptide levels during the clamp. The smokers were insulin resistant and lipid intolerant with an impaired triglyceride clearance after a mixed test meal. This lipid intolerance was not mirrored by fasting hypertriglyceridemia.

CONCLUSIONS

This study, using the euglycemic hyperinsulinemic clamp technique, shows that smokers are both insulin resistant and lipid intolerant. The postprandial lipid intolerance is also seen in individuals with normal fasting triglyceride levels and is related to an increased prevalence of atherogenic small dense LDL. IRS is likely to be an important reason for the increased cardiovascular morbidity in smokers.

Insulin promotes and cyclic adenosine 3',5'-monophosphate impairs functional insertion of insulin receptors in the plasma membrane of rat adipocytes: evidence for opposing effects of tyrosine and serine/threonine phosphorylation

The aim of the present study was to elucidate events in the plasma membrane (PM) associated with the previously described effect of insulin to rapidly enhance the number of cell surface insulin binding sites in rat adipocytes. [125I]insulin was cross-linked to cell surface insulin receptors of intact cells that had been preincubated with or without insulin. Subsequently prepared PM displayed a approximately 3-fold increase in bound [125I]insulin when cells had been pretreated with 6 nM insulin for 20 min compared to membranes from control cells, and SDS-PAGE with autoradiography showed that this occurred at the insulin receptor alpha-subunit. The magnitude of the effect was similar to that found for insulin binding to intact cells that had been preincubated with insulin. In contrast, the insulin binding capacity in the PM was not affected by prior treatment of cells with insulin when assessed with the addition of [125I]insulin directly to solubilized PM; this suggests an unchanged total number of PM receptors. Thus, the enhancement of cell surface insulin binding capacity produced by insulin is not due to the translocation of receptors, but instead appears to be confined to receptors already present in the PM. The addition of phospholipase C (from Clostridium perfringens), which cleaves PM phospholipids, mimicked the effect of insulin to enhance cell surface binding in adipocytes, and this suggests a pool of cryptic PM receptors. Both the nonmetabolizable cAMP analog N6-monobutyryl cAMP (N6-mbcAMP) and the serine/threonine phosphatase inhibitor okadaic acid abolished the effect of concomitant insulin treatment to increase binding capacity. In contrast, the tyrosine phosphatase inhibitor vanadate increased insulin binding even in the presence of okadaic acid or N6-mbcAMP. The effect of N6-mbcAMP to impair cell surface insulin binding was also evident in the presence of a peptide derived from the major histocompatibility complex type I that effectively impairs receptor internalization, but the amount of PM receptors assessed by immunoblot was unaltered. Taken together, the data suggest that insulin exposure leads to the uncovering of cryptic receptors associated with the PM. It is also suggested that tyrosine phosphorylation promotes this process, whereas enhanced serine phosphorylation, e.g. produced by cAMP, impairs the functional insertion of the receptors, rendering them unable to bind insulin.

Suppression of the nocturnal free fatty acid levels by bedtime cornstarch in NIDDM subjects

The aim of the present study was to examine the effects of a large dose of slow-release carbohydrates (CHOs) at bedtime on the nocturnal glucose, insulin and free fatty acid (FFA) levels, and to assess the putative effects on morning fasting and post-prandial glucose levels in patients with moderately controlled non-insulin-dependent diabetes mellitus (NIDDM). Unheated cornstarch (106 g of CHO) or a mixed equicaloric meal (58 g of CHO) was given at 22.00 hours to 10 NIDDM patients. For comparison, the patients were also given a smaller mixed meal at 22.00 hours on a third occasion (17 g of CHO). Compared with the mixed meals, cornstarch led to a slightly elevated early-morning plasma insulin level and a suppression of the nocturnal FFA level (P < 0.05), as well as to a reduced incremental glucose level (IAUC) after breakfast the next morning by approximately 30% (P < 0.05). There was a significant and linear relationship between the nocturnal FFA level and the glucose IAUC after breakfast (r = 0.44, P < 0.02), indicating that the effect may have been mediated by the suppressive effect of cornstarch on nocturnal lipolysis. In summary, bedtime intake of unheated cornstarch in NIDDM subjects is associated with a suppression of the nocturnal FFA levels and a reduced glucose IAUC after breakfast. As the treatment did not improve overall glucose control, studies of the effects of an individually titrated amount of cornstarch are proposed to further explore the putative favourable effects of bedtime cornstarch in the treatment of NIDDM.

Long-term use of nicotine gum is associated with hyperinsulinemia and insulin resistance

BACKGROUND

Insulin sensitivity and cardiovascular risk profile were examined in 20 healthy, nonobese, middle-aged men who were long-term users of nicotine-containing chewing gum and in 20 matched control subjects who did not use nicotine.

METHODS AND RESULTS

Long-term use of nicotine-containing chewing gum was associated with insulin resistance and hyperinsulinemia. The degree of insulin sensitivity correlated negatively to the extent of nicotine use measured as plasma cotinine levels.

CONCLUSIONS

These findings suggest that nicotine is the major constituent in cigarette smoke that leads to insulin resistance, metabolic abnormalities associated with the insulin resistance syndrome, and increased cardiovascular morbidity. Thus, the use of nicotine replacement therapy during smoking cessation should be transient and limited.

Gastric emptying in type 2 diabetes: quick or slow?

Although it is now widely accepted that around one-half of patients with Type 1 diabetes have delayed gastric emptying of both solid and liquid meals, the situation with respect to patients with Type 2 diabetes is less clear cut. Recent reports in the literature suggest that gastric emptying, at least of liquids, is more rapid than normal for patients with "early' Type 2 diabetes, whereas patients with later stages of the disease may have delayed or normal emptying of solids. Given the large number of possible confounding factors, such as age, gender, and previous dietary history in this population, as well as the influences of hyperglycaemia and hyperinsulinaemia on gastric emptying, this area clearly requires further investigation under more stringent conditions.

Okadaic acid exerts a full insulin-like effect on glucose transport and glucose transporter 4 translocation in human adipocytes. Evidence for a phosphatidylinositol 3-kinase-independent pathway

The effects of the serine/threonine phosphatase inhibitor, okadaic acid, and insulin on glucose transport activity, glucose transporter 4 translocation to the plasma membrane, and the signaling pathway of insulin were examined in human adipocytes. Okadaic acid consistently produced a greater increase than insulin in the rate of glucose transport, and both agents together had a partial additive effect. Both insulin alone and okadaic acid alone stimulated the translocation of glucose transporter 4 to the plasma membrane. Insulin, but not okadaic acid, stimulated phosphatidylinositol 3-kinase (PI 3-kinase) activity, and wortmannin completely inhibited the effect of insulin on glucose transport. When the cells were incubated with both agents, okadaic acid inhibited insulin-stimulated PI 3-kinase activity but did not block the association of the p85 or p110 subunits of PI 3-kinase with insulin receptor substrate 1. Insulin-stimulated tyrosine phosphorylation of insulin receptor substrate 1 was only slightly reduced (15-30%) by okadaic acid. These data demonstrate that okadaic acid exerts a full insulin-like effect independent of the activation of PI 3-kinase. Thus, PI 3-kinase lipid kinase is not essential for glucose transporter 4 translocation in human adipocytes, and different pathways exist that lead to glucose transporter 4 translocation and increased glucose transport.

Insulin action and age. European Group for the Study of Insulin Resistance (EGIR)

Evidence that age is associated with insulin resistance is discordant. We analyzed euglycemic insulin clamp (1 mU x min(-1) x kg(-1)) data collected at 20 centers throughout Europe from 1,146 men and women with normal glucose tolerance, ranging in age from 18 to 85 years. In the whole group, insulin action (as the M value) declined slightly with age (at a rate of 0.9 micromol x min(-1)-kg(-1) per decade of life, 95% CI = 0.4-1.3, P = 0.0002). When adjusted for BMI, this relationship was no longer statistically significant. The same result was obtained whether insulin action was expressed per kilogram of body weight or per kilogram of fat-free mass, expressed as the M:I ratio, or estimated from fasting plasma insulin concentrations. Subgroup analysis showed that a significant BMI-adjusted decrease in insulin action with age was present only in lean (BMI <25 kg/m2) women (a rate of 1.6 micromol x min(-1) x kg(-1) per decade, 95% CI = 0.6-2.5, P = 0.001), in whom percentage fat mass also increased with age (by 0.38% body weight per decade, P = 0.0007). Insulin action was positively associated with insulin suppression of circulating free fatty acids (FFAs) (+1.5 micromol x min(-1) x kg(-1) for each 10% increase in FFA suppression, P < 0.0001) in a multivariate model accounting for sex, BMI, age, and fasting FFA levels. Furthermore, insulin suppression of FFAs improved with age in men (2% per decade, P < 0.0001) but not in women. In the subgroup of lean women in whom insulin action declined with age, adding FFA suppression to a multiple regression equation canceled the association between age and insulin action. Thus, the small effect of age on insulin action could be adequately explained on the basis of age-related changes in body composition and substrate competition. We conclude that in healthy Europeans, age per se is not a significant cause of insulin resistance of glucose metabolism or lipolysis.

Effects of peroxovanadate and vanadate on insulin binding, degradation and sensitivity in rat adipocytes

The effects of vanadate and the stable peroxovanadate compound bpV(pic) on insulin binding and degradation were investigated in rat adipocytes under conditions of ongoing receptor cycling. Both bpV(pic) and vanadate increased 125I-insulin binding to intact cells through an increase in apparent receptor affinity. The maximal effect of bpV(pic) was to increase binding approximately 4-fold (EC50 0.06 +/- 0.01 mM), whereas vanadate increased binding approximately 2-fold (EC50 1.4 +/- 0.2 mM). Removal of cell surface insulin-receptor complexes with trypsin showed that the effects on binding exerted by bpV(pic) and vanadate were due to a similar increase in both cell surface binding and intracellular accumulation of radioactivity. Both bpV(pic) and vanadate inhibited the degradation of 125I-insulin in medium containing 1% bovine serum albumin. The ratio of degraded/intact intracellular 125I-insulin was also markedly reduced by these agents, suggesting that they inhibit intracellular insulin-degrading proteases. Similar to previous findings with vanadate, bpV(pic) stimulated glucose transport and, at low concentrations, enhanced insulin sensitivity. Taken together, these data demonstrate that both bpV(pic) and vanadate inhibit insulin degradation. In addition, they significantly enhance cell surface insulin binding in rat fat cells and this is associated with an improved insulin sensitivity.

Characterization of the insulin-antagonistic effect of growth hormone in insulin-dependent diabetes mellitus

To characterize its insulin-antagonistic effect, growth hormone (GH) was infused at variable rates (24, 12 or 6 mU kg-1 min-1) for 1 h in 7 IDDM patients. Saline infusion was used as control (C) and all patients participated in all studies. The effect of insulin was measured with the euglycaemic clamp technique for 6 h combined with d-(3-3H)-glucose to evaluate glucose turnover. The insulin levels during the clamps were similar in all studies (23 +/- 3 mU l-1). The infusions produced peak GH levels of (24 rate = 24) 157 +/- 11, (12 rate = 12) 76 +/- 7, and (6 rate = 6) 45 +/- 8 mU l-1 (mean +/- SEM). The insulin-antagonistic effect of GH on glucose uptake was seen after 2 h and was at a maximum 4 to 5 h after the start of the GH infusion (difference in glucose infusion rate between C and 24 was 1.7 +/- 0.4 mg kg-1 min-1, p < 0.01). The resistance was due to a less pronounced effect of insulin to both inhibit rate of appearance and to stimulate rate of disappearance. Infusion of GH at 12 mU kg-1 min-1 induced a less pronounced insulin resistance both with regards to maximal effect (glucose infusion rate C - GH 1.4 +/- 0.5 mg kg-1 min-1, p < 0.05) and duration (3 h). At 6 mU kg-1 min-1, a clear GH-induced insulin-antagonistic effect was only seen during the third hour of the clamp (glucose infusion rate C-GH 1.3 +/- 0.5 mg kg-1 min-1, p < 0.05). GH infusion impaired the effect of insulin to lower both the levels of free fatty acids (NEFA) and glycerol between 2 and 5 h after the start of the infusion (NEFA, C:110 +/- 29, 24:303 +/- 95, p < 0.05: glycerol, C:32 +/- 4, 24:50 +/- 7 mumol l-1, p < 0.05). The present study therefore demonstrates that the insulin-antagonistic effect of GH in IDDM is related to the plasma levels both with regard to duration and response. The results also indicate that GH impairs the effect of insulin on lipolysis in IDDM after physiological peaks.

Microdialysis assessment of adipose tissue metabolism in post-absorptive obese NIDDM subjects

Lactate and glycerol turnover is enhanced in obesity and NIDDM. To evaluate the influence of NIDDM on subcutaneous adipose tissue metabolism microdialysis combined with 133Xe clearance and measurements in arterialized plasma were carried out using samples of subcutaneous abdominal fat from nine obese NIDDM subjects (glucose, 7.9 +/- 0.7 mmol L-1) (mean +/- SEM) and nine obese non-diabetic subjects (glucose, 4.9 +/- 0.1) matched for age, BMI and body fat. After an overnight fast arterialized plasma levels were 1145 +/- 110 vs. 876 +/- 59 mumol L-1 (P < 0.05) for lactate and 75 +/- 10 vs. 66 +/- 8 mumol L-1 for glycerol in the diabetic and control group, respectively. The corresponding abdominal subcutaneous interstitial lactate and glycerol concentrations were 1278 +/- 63 vs 1107 +/- 64 mumol L-1 and 314 +/- 28 vs. 311 +/- 17 mumol L-1, respectively. However, adipose tissue blood flow in the same region was lower in NIDDM subjects (1.5 +/- 0.2 vs 2.4 +/- 0.3 mL 100 g-1 min-1) (P < 0.05). Consequently, apparent subcutaneous lactate and glycerol release, estimated according to Fick, were not statistically different in the two groups (1.8 +/- 0.4 vs 2.4 +/- 0.8 and 2.1 +/- 0.4 vs 3.1 +/- 0.5 mumol kg-1 min-1 in NIDDM and control subjects, respectively). Thus, in the post-absorptive state apparent lactate and glycerol release by the abdominal subcutaneous tissue in obese NIDDM subjects was similar to that in a matched group of obese non-diabetic controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid intolerance in smokers

OBJECTIVES

Smokers have recently been shown to be insulin resistant and to exhibit several characteristics of the insulin resistance syndrome (IRS). In this study, we assessed fasting and postprandial lipid levels in healthy, normolipidaemic, chronic smokers and a matched group of non-smoking individuals.

DESIGN

A standardized mixed meal (containing 3.78 MJ and 51 g of fat) was given in the morning after an overnight fast. The smokers were either abstinent from tobacco for 48 h or were allowed to smoke freely, including being allowed to smoke six cigarettes during the study.

SUBJECTS

Twenty-two middle-aged, healthy male subjects, nine habitual smokers and 13 non-smoking control subjects, were recruited to the study. The smokers had all been smoking at least 10 cigarettes per day for at least 10 years.

RESULTS

The smokers exhibited a lipid intolerance in that their postprandial increase in triglyceride levels was more than 50% higher than in the non-smokers' group. This lipid intolerance could not be discerned in the postabsorptive state because the fasting triglyceride levels were the same in both groups, while the smokers had significantly lower high-density lipoprotein (HDL) cholesterol. The peak postprandial triglyceride level correlated closely and negatively with fasting HDL cholesterol, indicating an impaired lipolytic removal capacity in smokers.

CONCLUSIONS

Healthy, normotriglyceridaemic smokers exhibit an abnormal postprandial lipid metabolism consistent with lipid intolerance. It is suggested that postprandial hyperlipidaemia is a characteristic trait of the insulin resistance syndrome and that the defect in lipid removal is related to the low HDL cholesterol in this syndrome. The insulin resistance syndrome is likely to be an important reason for the increased propensity for cardiovascular disease in smokers.

Effects of insulin and beta-adrenergic blockade on the migrating motor complex in humans

BACKGROUND

Interdigestive small-intestinal motility is suppressed by hyperglycemia and also by hyperinsulinemia per se. Since hyperinsulinemia may increase sympathetic activity, the present study was undertaken to ascertain to what extent insulin affects phase III of the migrating motor complex (MMC) and MMC-related duodenal retroperistalsis and whether beta-adrenergic receptors may mediate the effects of insulin.

METHODS

Fasting motility was studied in eight healthy volunteers on three occasions with an eight-lumen perfused pressure catheter, with closely spaced recording points in the proximal duodenum. On the control day 5-h antroduodenojejunal manometry was performed. On another study day euglycemic hyperinsulinemic clamping was performed for 2 h after an initial basal recording. On a 3rd day motility was recorded during propranolol infusion, combined with a period of euglycemic hyperinsulinemia.

RESULTS

During hyperinsulinemia complete absence of phase III of the MMC in the gastric antrum was observed, whereas 55% of the MMC had a gastric phase-III component on the control day. The duration of phase III in the proximal duodenum was decreased during hyperinsulinemia compared with the control period (p < 0.05). This inhibitory effect of insulin on the activity front was not prevented by beta blockade. Under control conditions the proportion of retroperistaltic pressure waves in the proximal duodenum was 13 +/- 8% in early phase III, increasing in late phase III to 79 +/- 15% (p < 0.01). Duodenal phase III during hyperinsulinemia showed a similar increase in retroperistalsis, from 4 +/- 4% in early phase III to 67 +/- 21% in late phase III (p < 0.01). The corresponding proportions during beta blockade were 16 +/- 10% and 86 +/- 14%, respectively.

CONCLUSIONS

Hyperinsulinemia per se abolishes antral phase III and makes the duodenal phase III shorter but does not interrupt the distinct pattern of retroperistalsis in late phase III. Beta-adrenergic receptors seem not to be important for these effects of insulin or for the retroperistalsis in duodenal phase III.

Hyperinsulinaemia impairs gastrointestinal motility and slows carbohydrate absorption

Experimental euglycaemic hyperinsulinaemia (insulin levels 46 +/- 4 mU/l) impaired the post-absorptive 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 standardized 99mTc 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.

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.

Regulation of insulin-like growth factor binding protein-1 (IGFBP-1) in insulin-dependent diabetes mellitus. Effects of hyperglycaemia and insulin

The aim of the present study was to characterize the effect of 44 h of hyperglycaemia on diurnal levels of insulin-like growth factor binding protein-1 (IGFBP-1), insulin-like growth factor-1 (IGF-1), growth hormone (GH) and glucagon in 7 well-controlled subjects with insulin-dependent diabetes mellitus (IDDM). Hyperglycaemia (approximately 15 mmol/l) was induced by a glucose infusion, while the degree of insulinisation was similar to that of a corresponding period with near normoglycaemia (approximately 6.9 mmol/l). Hyperglycaemia for 44 h did not alter the normal diurnal IGFBP-1 levels when the degree of insulinisation was unchanged. The diurnal secretion pattern of IGFBP-1 was preserved in both genders and without any difference between the control and hyperglycaemic periods. However, the IGFBP-1 levels were increased in these IDDM subjects despite a peripheral hyperinsulinemia. An inverse correlation was found between IGFBP-1 and peripheral insulin levels both during periods of rapid changes in IGFBP-1 and insulin concentrations (i.e. morning hours) as well as during the total 24-h sampling period. Total IGF-1 levels were low, but no further decrease was seen after 24 h of hyperglycaemia in the presence of unchanged insulin levels. In conclusion, the present study clearly shows that the increased IGFBP-1 level seen during poor metabolic control in IDDM is not caused by hyperglycaemia. Glucose levels per se do not influence either total IGF-1 or IGFBP-1 concentrations in well-insulinised diabetic patients.

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.

Effects of metformin and metoprolol CR on hormones and fibrinolytic variables during a hyperinsulinemic, euglycemic clamp in man

The aim of this study was to characterize the acute effect of euglycemic (glucose 5.2 +/- 0.6 mmol/l) hyperinsulinemia (mean 118 +/- 32 mU/l) on fibrinolytic variables, free fatty acids (FFA) and counterregulatory hormones. In addition, the effect of chronic treatment with metformin, an oral antidiabetic agent which enhances insulin action, and metoprolol CR, a relatively beta 1-selective adrenergic antagonist, was also evaluated. A randomized, double-blind, placebo-controlled, cross-over study including 18 non-obese men, aged 53 +/- 6 years, was performed. The investigations were performed after each treatment period of 6 weeks in both the postabsorptive state and during a euglycemic, hyperinsulinemic clamp. Compared to the postabsorptive state, plasminogen activator inhibitor (PAI-1) activity and antigen, tissue plasminogen activator (t-PA) antigen and FFA decreased (p < 0.001) after 120 min of euglycemic hyperinsulinemia. In addition, t-PA activity increased (p < 0.01) while blood levels of lipoprotein (a), catecholamines and cortisol remained unchanged. Growth hormone increased during the clamps and this was most pronounced after treatment with metoprolol CR. When the effect of treatment was compared, postabsorptive levels of C-peptide, FFA and t-PA antigen were lower after metformin than after the placebo period (p < 0.05). t-PA antigen also remained lower during the clamp after metformin treatment. No significant effects of metformin or metoprolol CR were seen on insulin-stimulated glucose uptake during the clamps or on postabsorptive levels of counterregulatory hormones, PAI-1 or Lp(a).(ABSTRACT TRUNCATED AT 250 WORDS)

Metformin and metoprolol CR treatment in non-obese men

OBJECTIVE

To study the effect of metformin and metoprolol CR on insulin sensitivity, blood lipids, fibrinolytic activity and blood pressure.

DESIGN

A double-blind, placebo controlled, triple cross-over study with randomization to either metformin, 850 mg b.i.d., or metoprolol CR 100 mg o.d., or placebo for a period of 18 weeks. The glucose uptake was measured with the euglycaemic clamp technique after every 6 weeks' treatment period. Blood pressure and blood samples were taken every 3rd week.

SUBJECTS

Eighteen non-obese men (53 +/- 6 years of age).

RESULTS

Metformin decreased C-peptide (P < 0.02), FFA (P < 0.003), total and low-density lipoprotein cholesterol, tissue plasminogen activator antigen and the urinary potassium excretion (P < 0.05 for all), but not blood pressure compared to placebo. Metoprolol CR reduced diastolic blood pressure and pulse rate; fasting free fatty acids and the urinary potassium increased (P < 0.05 for all). No effect of metformin or metoprolol CR was seen on the glucose disposal rate, blood glucose, plasma insulin, triglycerides, high-density lipoprotein cholesterol, lipoprotein(a), uric acid or plasminogen activator inhibitor 1 activity or antigen. The glucose uptake was not particularly decreased in these subjects.

CONCLUSION

The study shows that metformin has some favourable effects on metabolism and that metoprolol CR is fairly neutral in this regard. The lack of effect of metformin on glucose disposal rate and blood pressure can be explained by the fact that the individuals studied were neither insulin resistant nor hypertensive. The data does not preclude an antihypertensive effect by treating a concomitant insulin resistance.