Degree Of Insulin Sensitivity Research Articles

Leptin levels in smokers and long-term users of nicotine gum.

The aim of this study was to examine the effects of cigarette smoking and other forms of long-term nicotine consumption on circulating leptin levels as well as the relationship between leptin levels and insulin sensitivity, measured with the euglycaemic hyperinsulinaemic clamp, in healthy middle-aged men. Samples from 73 subjects were analysed: 23 non-smokers, 31 smokers and 19 long-term nicotine gum chewers (NGCs) with similar ranges of age, body mass index (BMI) and per cent body fat. Leptin levels were higher in NGCs and smokers than in the non-smoking matched control subjects. Smoking cessation for 8 weeks further increased the leptin levels, probably due to the concomitant increase in body fat (mean +/- SD, 2.2 +/- 1.8 kg). Acute administration of one dose of nicotine nasal spray or smoking one cigarette did not significantly change the circulating leptin levels during the following 60 min. Plasma leptin concentrations were positively correlated with the proportion of body fat and negatively correlated with the degree of insulin sensitivity in each of the three subject groups. In a stepwise multiple linear regression analysis, plasma leptin concentrations were significantly correlated with the proportion of body fat, degree of insulin sensitivity and smoking status. These data show that long-term use of nicotine is associated with elevated circulating leptin levels. The increased leptin levels may be an important reason for the lower body weight in smokers. The results of this study also support the view that leptin is directly or indirectly related to insulin sensitivity in men.

Insulin sensitivity, vascular reactivity, and clamp-induced vasodilatation in essential hypertension.

Insulin resistance and vascular abnormalities have both been described in patients with essential hypertension. Whether these defects are associated with one another in the same individual has not been established. Whole-body insulin sensitivity (by the insulin clamp technique), forearm minimal vascular resistances, and the dose-response curve to acetylcholine, sodium-nitroprusside, and norepinephrine were measured in a group of 29 male patients with untreated essential hypertension. When the patients were divided into tertiles according to their level of insulin sensitivity, resistant and sensitive hypertensives were matched on several potential confounders of insulin action and vascular function. These subgroups showed similar minimal vascular resistances (2.5+/-0.2 versus 3.2+/-0.6 mm Hg per mL x min(-1) x dL(-1)) and superimposable responses to graded intraarterial infusions of acetylcholine, sodium-nitroprusside, and norepinephrine. No correlation was found between the vascular parameters (slope of the curve or maximal response) and insulin-mediated glucose uptake in the whole group. During the clamp, insulin sensitive patients tended to have greater increments in forearm blood flow when compared to their insulin resistant counterparts (+53+/-21 versus +9+/-7%, P=.06); in the whole group, clamp-induced vasodilatation was weakly related to insulin-mediated glucose uptake (r=.44, P<.02) as well as to the slope of the acetylcholine dose-response curve (r=.40, P<.04). Together, these two responses explained 30% (multiple r=.55, P<.01) of the variability in insulin-induced vasodilatation. Metabolic insulin resistance in essential hypertension is not associated with abnormalities in vascular structure, acetylcholine or nitroprusside-induced vasodilatation, or vascular adrenergic reactivity. Degree of insulin sensitivity and acetylcholine sensitivity explain a small portion of the variability of the clamp-induced vasodilatation in hypertensive patients.

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.

Increased adipose tissue PC-1 protein content, but not tumour necrosis factor-alpha gene expression, is associated with a reduction of both whole body insulin sensitivity and insulin receptor tyrosine-kinase activity.

In the present study we measured PC-1 content, tumour necrosis factor (TNF)-alpha gene expression, and insulin stimulation of insulin receptor tyrosine-kinase activity in adipose tissue from non-obese, non-diabetic subjects. These parameters were correlated with in vivo insulin action as measured by the intravenous insulin tolerance test (Kitt values). PC-1 content was negatively correlated with Kitt values (r = -0.5, p = 0.04) and positively with plasma insulin levels both fasting (r = 0.58, p = 0.009) and after 120 min during oral glucose tolerance test (OGTT) (r = 0.67, p = 0.002). Moreover, adipose tissue PC-1 content was higher in relatively insulin-resistant subjects (Kitt values lower than 6) than in relatively insulin-sensitive subjects (Kitt values higher than 6) (525 +/- 49 ng/mg protein vs 336 +/- 45, respectively, p = 0.012). Adipose tissue insulin receptor tyrosine-kinase activity in response to insulin was significantly lower at all insulin concentrations tested (p = 0.017, by two-way analysis of variance test) in insulin-resistant than in insulin-sensitive subjects (Kitt values lower or higher than 6, respectively). In contrast to PC-1, no significant correlation was observed between adipose tissue TNF-alpha mRNA content and Kitt values, and plasma insulin levels, both fasting and at after 120 min during OGTT. Also, no difference was observed in TNF-alpha mRNA content between subjects with Kitt values higher or lower than 6. These studies in adipose tissue, together with our previous studies in skeletal muscle raise the possibility that PC-1, by regulating insulin receptor function, may play a role in the degree of insulin sensitivity in non-obese, non-diabetic subjects.

Energy Balance in Human Beings: The Problems of Plenitude

This chapter discusses the energy balance in human beings. The controls of food intake and energy expenditure in human beings are not simple; they are interdependent and are subject to many influences. It is unlikely that change in any single component can explain the major disturbances of energy balance in human beings. There is a facultative component in the thermogenic responses to cold, excess caloric intake, and other stimuli of normal subjects, which originally had survival value. There is a direct relationship between degree of insulin sensitivity and facultative response to overfeeding. A likely sequence is increase in effective serum insulin → central stimulation and activation of the sympathetic nervous system → increased turnover of norepinephrine → increased activity of substrate cycles, electrolyte pumping, and protein turnover, and possibly uncoupling of mitochondrial phosphorylation in brown fat. The composition of the diet is important for energy balance and fat storage, independent of the total caloric content and palatability. Increase in the fraction of carbohydrate in the diet increases the dietary thermogenic response. Increase in the fraction of fat in isocaloric diets, at least in experimental animals, leads to a greater increase in body fat.

Relationship between insulin resistance, insulin secretion, very low density lipoprotein kinetics, and plasma triglyceride levels in normotriglyceridemic man

We have previously postulated that resistance to insulin-mediated glucose uptake was the basic metabolic abnormality in patients with endogenous hypertriglyceridemia. In this situation, glucose tolerance would tend to deteriorate, and could only be maintained by the increased secretion of insulin. Although the ensuing hyperinsulinemia might prevent the development of glucose intolerance, we suggested that it would also lead to increased hepatic very low density (VLDL) triglyceride (TG) synthesis and secretion. In the current study we have quantified these four metabolic variables in 16 nonobese human subjects with plasma TG concentrations < 175 mg/dl. The results demonstrate the following degree of correlation: insulin resistance ▪ insulin response to food ▪ VLDL-TG secretion rate ▪ plasma TG concentration. These data indicate that nonobese subjects with normal TG levels have the same relationship between degree of insulin sensitivity, insulin response to food, VLDL-TG secretion, and TG concentration previously described in patients with endogenous hypertriglyceridemia.

Effect of partial adrenal cortical atrophy on the course of alloxan diabetes.

IT IS well known that ablation of the adrenal gland (Long-Lukens animal) or of the pituitary (Houssay animal) will ameliorate pancreatic diabetes. The problem arises whether atrophy of part of the adrenal cortex produced by chemical agents might also produce this effect. The oral administration of DDD (2,2-bis (parachlorophenyl)-1,1-dichloroethane) was found by Nelson and Woodard (1949) to cause atrophy and disappearance of the inner zones of the adrenal cortex in the dog, and it has since been shown (Nichols and Gardner, 1951) that such animals show a degree of insulin sensitivity. These findings have been confirmed in the case of the rat by Brown (1952). If such atrophy of the adrenal should prevent or modify pancreatic diabetes without producing any sensitivity to potassium, the site of production of the hormone (s) responsible for maintenance of the diabetes could be presumptively localized to the inner zones of the cortex, and those responsible for electrolyte balance could be localized to the outer ...