Body fat mass and the proportion of very large adipocytes in pregnant women are associated with gestational insulin resistance.

BACKGROUND/OBJECTIVES: Pregnancy is accompanied by fat gain and insulin resistance. Changes in adipose tissue morphology and function during pregnancy and factors contributing to gestational insulin resistance are incompletely known. We sought to characterize adipose tissue in trimesters 1 and 3 (T1/T3) in normal weight (NW) and obese pregnant women, and identify adipose tissue-related factors associated with gestational insulin resistance. SUBJECTS/METHODS: Twenty-two NW and 11 obese women were recruited early in pregnancy for the Pregnancy Obesity Nutrition and Child Health study. Examinations and sampling of blood and abdominal adipose tissue were performed longitudinally in T1/T3 to determine fat mass (air-displacement plethysmography); insulin resistance (homeostasis model assessment of insulin resistance, HOMA-IR); size, number and lipolytic activity of adipocytes; and adipokine release and density of immune cells and blood vessels in adipose tissue. RESULTS: Fat mass and HOMA-IR increased similarly between T1 and T3 in the groups; all remained normoglycemic. Adipocyte size increased in NW women. Adipocyte number was not influenced, but proportions of small and large adipocytes changed oppositely in the groups. Lipolytic activity and circulating adipocyte fatty acid-binding protein increased in both groups. Adiponectin release was reduced in NW women. Fat mass and the proportion of very large adipocytes were most strongly associated with T3 HOMA-IR by multivariable linear regression (R(2)=0.751, P<0.001). CONCLUSIONS: During pregnancy, adipose tissue morphology and function change comprehensively. NW women accumulated fat in existing adipocytes, accompanied by reduced adiponectin release. In comparison with the NW group, obese women had signs of adipocyte recruitment and maintained adiponectin levels. Body fat and large adipocytes may contribute significantly to gestational insulin resistance.

A maternal diet of fatty fish reduces body fat of offspring compared with a maternal diet of beef and a post-weaning diet of fish improves insulin sensitivity and lipid profile in adult C57BL/6 male mice.

AIM: The maternal diet during pregnancy and lactation may affect the long-term health of the offspring. Our aim was to study how a fish or meat diet perinatal and after weaning affects body composition, insulin sensitivity and the profile of n-3 and n-6 polyunsaturated fatty acids (PUFAs) in breast milk, fat depots, skeletal muscle and liver in male adult mice offspring. METHODS: During gestation and lactation, C57BL/6 dams were fed a herring- or beef-based diet. Half of the pups in each group changed diets after weaning. In offspring, body composition measured by DEXA, plasma lipid profile and insulin sensitivity measured by euglycemic clamp or QUICKI were monitored to adulthood. Analysis of total FAs by GC-MS were performed in the diet, breast milk and in different tissues. RESULTS: At 9 week of age, offspring of herring-fed dams had less body fat than offspring of beef-fed dams. Mice fed herring after weaning had increased insulin sensitivity at 15 week of age, reduced total plasma cholesterol and triglyceride levels, and compared with beef-fed mice, larger interscapular brown adipose tissue depots. The FA composition of the maternal diet was mirrored in breast milk, and the herring diet significantly affected the FA profile of different tissues, leading to an increased content of n-3 PUFAs. CONCLUSION: A herring-based maternal diet reduces body fat in the offspring, but the insulin sensitivity, plasma lipids and amount of brown adipose tissue are affected by the offspring's own diet; the herring diet is more beneficial than the beef diet.

Influence of having a male twin on body mass index and risk for dyslipidemia in middle-aged and old women.

BACKGROUND: Animal experiments suggest that exposure to elevated levels of androgens during development by means of so-called hormonal programming causes metabolic aberrations at adulthood. An indirect strategy to address the possible importance of such an influence also in humans would be to study female dizygotic twins, presuming that those with a twin brother--due to diffusion of testosterone--have been exposed to higher androgen levels prenatally. DESIGN: We have compared 8409 women with a male twin with 9166 women with a dizygotic female twin with respect to self-reported indices of anthropometry and metabolic aberrations at age 42 or older. RESULTS: Body mass index (BMI), body weight and rate of dyslipidemia were moderately, but significantly, higher in women from opposite-sexed (OS) twin pairs; splitting for age revealed this difference to be present in those ≥ 60 years of age only. CONCLUSION: The results (i) support the notion that comparisons of women with a twin brother with women from same-sexed twin pairs may be used to shed light on possible long-term effects of interindividual variations in early androgen exposure, and (ii) suggest that the effects of early androgen exposure on metabolism previously observed in animal experiments are of relevance also for humans.

Influence of herring (Clupea harengus) and herring fractions on metabolic status in rats fed a high energy diet.

AIM: Few dietary studies have looked beyond fish oil to explain the beneficial metabolic effects of a fish-containing diet. Our aim was to study whether addition of herring, or sub-fractions of herring, could counteract negative metabolic effects known to be induced by a high-fat, high-sugar diet. METHODS: Rats were given six different diets: standard pellets; high energy diet with chicken mince (HiE control); high energy diet with herring mince (HiE herring); and high energy diet with chicken mince and either herring oil (HiE herring oil), herring press juice, PJ (HiE PJ) or herring low molecular weight PJ (HiE LMW-PJ). Factors associated with the metabolic syndrome were measured. RESULTS: There were no differences in energy intake or body weight between the groups, but animals fed high energy diets had a higher body fat content compared with the pellet group, although not statistically significant in all groups. Mesenteric adipocyte size was smaller in the HiE herring oil group compared with the HiE control. Glucose clamp studies showed that, compared with the pellet group, the HiE control and HiE herring diets, but not the HiE herring oil diet, induced insulin resistance. Addition of herring or herring oil to the high energy diet decreased total cholesterol levels, triacylglycerols and the atherogenic index compared with the HiE control group. CONCLUSIONS: The results suggest that addition of herring or herring oil counteracts negative effects on blood lipids induced by a high energy diet. The lipid component of herring thus seems to be responsible for these beneficial effects.

Cardiac concentric remodelling induced by non-aromatizable (dihydro-)testosterone is antagonized by oestradiol in ovariectomized rats.

Previous studies on the cardiovascular effects of androgens in females, most of them using testosterone treatment, have yielded conflicting results. Testosterone is metabolized into oestradiol (E2) and dihydrotestosterone (DHT) within cardiovascular tissues. The aim of the present study was to explore the cardiovascular effects exerted by E2 and the non-aromatizable androgen DHT and to study possible interactions between these in female rats. Ovariectomized rats were treated with DHT, E2, or DHT+E2 for 6 weeks. DHT increased left-ventricular posterior wall thickness, assessed by echocardiography, whereas left-ventricular dimension, as well as total heart weight and calculated left-ventricular mass, were unchanged. DHT also increased the levels of insulin-like growth factor-I mRNA in the left ventricle. E2 abolished the effect of DHT on left-ventricular remodelling and insulin-like growth factor-I mRNA when the two treatments were given in combination. E2 also reduced androgen receptor mRNA levels in the heart. Neither E2 nor DHT changed blood pressure measured by telemetry. In conclusion, treatment with the endogenous non-aromatizable androgen DHT causes cardiac concentric remodelling in ovariectomized rats, possibly mediated by increased local levels of insulin-like growth factor-I. The effect of DHT on cardiac wall thickness was antagonized by E2, possibly through downregulation of cardiac androgen receptors. These mechanisms may be of importance for the concentric left-ventricular geometric pattern developing in women after menopause.

Effect of exercise on ovarian morphology and expression of nerve growth factor and alpha(1)- and beta(2)-adrenergic receptors in rats with steroid-induced polycystic ovaries.

Oestadiol valerate (EV)-induced polycystic ovaries (PCO) in rats cause anovulation and cystic ovarian morphology. Denervation of ovarian sympathetic nerves restores ovulatory disruption. In the present study, we determined whether 5 weeks of voluntary exercise influence ovarian morphology and the expression of sympathetic markers in the EV-induced PCO rat model. The effect of exercise on (i) ovarian morphology; (ii) mRNA and protein expression of nerve growth factor (NGF); and (iii) mRNA and number of ovarian-expressing cells for the NGF receptor (p75 neurotrophin receptor) and the alpha(1a)-, alpha(1b)-, alpha(1d)- and beta(2)-adrenergic receptors (ARs) in rats with EV-induced PCO was evaluated. PCO was induced by a single i.m. injection of EV, and controls were injected with oil alone in adult cycling rats. The rats were divided into four groups: (i) control (oil); (ii) exercise group (oil + exercise); (iii) a PCO group (EV); and (iv) a PCO exercise group (EV + exercise). The exercise and PCO exercise groups ran voluntarily for 5 weeks in computer-monitored wheels placed in the cages where they were housed. The results obtained indicated that ovarian morphology was almost normalised in the PCO exercise group; NGF mRNA and protein concentrations were normalised in the PCO exercise group; high numbers of NGF receptor expressing cells in PCO ovaries were lowered by exercise; and the number of immunopositive cells of the different AR subtypes were all reduced after exercise in the PCO group, except for the alpha(1b)- and beta(2)-AR whereas the mRNA levels were unaffected, indicating transcriptional regulation. In conclusion, our data indicate a beneficial effect of regular exercise, as a modulator of ovarian sympathetic innervation, in the prevention and treatment of human PCOS.

Short-term infusion of interleukin-6 does not induce insulin resistance in vivo or impair insulin signalling in rats.

AIMS/HYPOTHESIS: Interleukin-6 has been implicated in the insulin resistance associated with obesity and impaired glucose tolerance. Previous studies in vitro have shown that IL-6 rapidly (1-2 h) impairs cellular insulin signalling and action through an increased expression of suppressor of cytokine signalling (SOCS)-3. In the present study, IL-6 or saline was infused in rats that were simultaneously in a state of hyperinsulinaemia. Muscle, liver and adipose tissue were excised after 2 h to examine potential effects on insulin signalling or gene expression. METHODS: The rats were infused with IL-6 or saline during a euglycaemic-hyperinsulinaemic clamp and the glucose infusion rate was measured after 90 to 120 min. Signal transducer and activator of transcription (STAT)3 phosphorylation and insulin-stimulated tyrosine phosphorylation of the insulin receptors and IRS were measured with immunoblotting and gene expression through real-time PCR. RESULTS: No inhibitory effect of IL-6 on insulin-stimulated whole-body glucose uptake was seen in spite of high circulating levels of IL-6 (0.85+/-0.08 nmol/l). Tyrosine phosphorylation of the insulin receptors and IRS was also unchanged in the liver, skeletal muscles and adipose tissue. However, tyrosine phosphorylation of STAT3 was increased in all tissues, showing that IL-6 signalling was activated. IL-6 mRNA tended to increase, while GLUT4, peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1) and adiponectin gene expression were unchanged. CONCLUSIONS/INTERPRETATION: Infusion of IL-6 for 120 min in rats during euglycaemic-hyperinsulinaemic conditions did not alter the effect of insulin on whole-body glucose homeostasis, plasma adiponectin levels or insulin signalling in target tissues. Thus, the acute effects of IL-6, associated with SOCS-3 induction, do not lead to whole-body insulin resistance. These data further underscore the importance of the chronic, and potentially tissue-specific effects of IL-6 on insulin signalling and action.

Reductions in adipose tissue and skeletal growth in rat adult offspring after prenatal leptin exposure.

Leptin is involved in regulating food intake, energy balance and bone formation. Increasing evidence suggests that leptin is also involved in fetal growth and development. The aim of this study was to determine if increased maternal leptin is followed by changes in body composition, skeletal growth or hormonal regulation in the adult rat offspring. Pregnant rats were given injections of either human recombinant leptin (3.5 mg/kg, i.p.) or vehicle on days 8, 10 and 12 of gestation. Both genders of leptin-exposed offspring showed significantly reduced adipose tIssue weight at adult age. Skeletal growth and cortical bone dimensions were significantly reduced. Circulating testosterone levels were significantly increased in female leptin-exposed offspring, and male leptin-exposed offspring had significant testicular enlargement. No significant effects were seen on circulating leptin levels or hypothalamic protein levels of the leptin receptor. The results demonstrate that maternally administered leptin is involved in fetal growth and development, leading to lean offspring with reduced skeletal growth.

Affected skeletal growth but normal bone mineralization in rat offspring after prenatal dexamethasone exposure.

Events occurring early in life or prenatally are able to play important roles in the pathogenesis of diseases in adult life. Different sorts of stress or hormonal influences, during particular periods of pregnancy, may result in persisting or transient changes in physiology. Glucocorticoids are used for the treatment of a variety of diseases, to promote organ maturation and to prevent preterm delivery. Glucocorticoids are also known to affect skeletal growth and adult bone metabolism. The aim of the present study was to investigate whether exposure to dexamethasone (Dex) during fetal life has any effect on skeletal growth and/or bone mineral density in adult rat offspring. Pregnant rats were given injections of either Dex (100 micro g/kg) or vehicle on days 9, 11 and 13 of gestation. Dex-exposed male but not female rat offspring showed transient increases in crown-rump length and tibia and femur lengths at 3-6 weeks of age. In contrast, the cortical bone dimensions were altered in 12-week-old female but not male Dex-exposed offspring. The areal bone mineral densities of the long bones and the spine, as determined by dual X-ray absorptiometry, and trabecular as well as cortical volumetric bone mineral density, as measured using peripheral quantitative computerized tomography, were unchanged in both male and female Dex-exposed offspring. In conclusion, prenatal Dex exposure affects skeletal growth in a gender-specific manner, while the mineralization of bones is unaffected in both male and female offspring.

Prenatal cytokine exposure results in obesity and gender-specific programming.

Prenatal events appear to program hormonal homeostasis, contributing to the development of somatic disorders at an adult age. The aim of this study was to examine whether maternal exposure to cytokines or to dexamethasone (Dxm) would be followed by hormonal consequences in the offspring at adult age. Pregnant rats were injected on days 8, 10, and 12 of gestation with either human interleukin-6 (IL-6) or tumor necrosis factor-alpha (TNF-alpha) or with Dxm. Control dams were injected with vehicle. All exposed offspring developed increased body weight (P < 0.05--0.001), apparently due to an increase of 30--40% in adipose tissue weight (P < 0.05--0.01). Corticosterone response to stress was increased in the IL-6 group (P < 0.05-0.01). Dxm-treated male rats exhibited blunted Dexamethasone suppression test results. In male rats, insulin sensitivity was decreased after IL-6 exposure (P < 0.01), whereas basal insulin was elevated in the TNF-alpha group (P < 0.01). In female rats, plasma testosterone levels were higher in all exposed groups compared with controls (P < 0.01--0.001), with the exception of Dxm-exposed offspring. Males in the TNF-alpha group showed decreased locomotor activity (P < 0.05), and females in the IL-6 group showed increased locomotor activity (P < 0.05). These results indicate that prenatal exposure to cytokines or Dxm leads to increased fat depots in both genders. In females, cytokine exposure was followed by a state of hyperandrogenicity. The results suggest that prenatal exposure to cytokines or Dxm can induce gender-specific programming of neuroendocrine regulation with consequences in adult life.

Insulin insensitivity and delayed transcapillary delivery of insulin in oophorectomized rats treated with testosterone.

The importance of transcapillary insulin delivery as a regulated step was explored in an insulin resistant rat model. Oophorectomized female rats were exposed to testosterone (OVX + T) for 8 weeks and examined with insulin clamps, muscle microdialysis, and analyses of insulin distribution kinetics. The results were compared with those obtained in sham-operated control rats. After OVX + T, onset of glucose uptake in skeletal muscle was significantly (P < 0.001-0.05) delayed compared with controls as measured by the glucose infusion rate (GIR) during a euglycaemic, hyperinsulinaemic clamp (5 mU kg-1 min-1). The increase in interstitial insulin concentrations was also significantly (P < 0.05) delayed (15-20% lower) in OVX + T treated rats compared with control rats, but to such a small magnitude that this alone could not explain the late onset of the insulin effect. Skeletal muscle capillary density, examined histochemically, was diminished (P < 0.01-0.001) by 20-25% after treatment with OVX + T compared with control animals, as was the peripheral blood flow (P < 0.05) by 40-45%, measured with the microsphere technique. Insulin binding was reduced in proportion to the reduced (P < 0.01) vascular surface area by OVX + T treatment. Transcapillary transport rate of insulin, measured by comparisons of the kinetics of inulin and insulin spaces in muscle with time, tended (ns) to be lower after OVX + T compared with control rats (30-40%) as a reflection of the lower capillary surface area. The data suggest that the delayed onset of insulin action after OVX + T results from combined defects in the muscle cell at a postreceptor level and, to a lesser extent, from retarded transcapillary delivery of insulin.

Maternal endotoxemia results in obesity and insulin resistance in adult male offspring.

Events in utero appear to be important factors contributing to the development of somatic disorders at adult age. The aim of this study was to examine whether maternal immune challenge would be followed at adult age by metabolic and endocrine abnormalities in the offspring. Pregnant rats were given injections of either endotoxin (Escherichia coli lipopolysaccharide; 0.79 mg/kg, ip) or vehicle on days 8, 10, and 12 of gestation. Adult male offspring to lipopolysaccharide-exposed dams were heavier than controls (P < 0.05) and showed increased adipose tissue weights (P < 0.05), elevated food intake (P < 0.05), and increased circulating leptin (P < 0.01). The effect of insulin on glucose uptake was reduced, as measured by an euglycemic hyperinsulinemic clamp technique (P < 0.05). Serum levels of 17beta-estradiol and progesterone were elevated (P < 0.01 and P < 0.05, respectively). Baseline levels of corticosterone were normal, but the corticosterone response to stress was attenuated (P < 0.05), and hippocampal glucocorticoid receptor protein was up-regulated (P < 0.05). Female offspring were uninfluenced, except for increased testosterone levels (P < 0.05), increased baseline corticosterone levels (P < 0.05), and enlargement of heart and adrenals (P < 0.05). The results indicate that maternal endotoxemia leads to obesity, insulin resistance, and high serum levels of leptin in the adult male offspring. This study reports a novel animal model of obesity with features of the metabolic syndrome.

Myocardial insulin-mediated glucose uptake and left ventricular geometry.

Whole-body insulin sensitivity has been shown to be impaired in subjects with increased left ventricular relative wall thickness (RWT) and in hypertensive subjects with left ventricular hypertrophy, but the relation between myocardial insulin sensitivity and RWT or left ventricular mass index (LVMI) in normotension is not known. We measured myocardial and skeletal muscle glucose uptake with [18F]fluorodeoxyglucose and positron emission tomography during hyperinsulinemic euglycemic clamp in nine men with wide ranges of echocardiographic RWT and LVMI. The subjects were male, 72-74 years old, normotensive and free from medication or history of heart disease. RWT correlated inversely with skeletal muscle glucose uptake (r = -0.69, p = 0.04), borderline significantly directly with myocardial glucose uptake (r = 0.62, p = 0.07), and directly with the ratio between myocardial and skeletal muscle glucose uptake (r = 0.77, p = 0.02) during hyperinsulinemic euglycemic clamp. LVMI was not related to insulin-mediated myocardial or skeletal muscle glucose uptake or the ratio between myocardial and skeletal muscle glucose uptake. In conclusion, RWT was inversely related to insulin sensitivity in skeletal muscle and borderline significantly directly related to insulin sensitivity in the myocardium in healthy normotensive elderly men, whereas LVMI was not related to myocardial or skeletal muscle insulin sensitivity.

Estimations of muscle interstitial insulin, glucose, and lactate in type 2 diabetic subjects.

Previous measurement of insulin in human muscle has shown that interstitial muscle insulin and glucose concentrations are approximately 30-50% lower than in plasma during hyperinsulinemia in normal subjects. The aims of this study were to measure interstitial muscle insulin and glucose in patients with type 2 diabetes to evaluate whether transcapillary transport is part of the peripheral insulin resistance. Ten patients with type 2 diabetes and ten healthy controls matched for sex, age, and body mass index were investigated. Plasma and interstitial insulin, glucose, and lactate (measured by intramuscular in situ-calibrated microdialysis) in the medial quadriceps femoris muscle were analyzed during a hyperinsulinemic euglycemic clamp. Blood flow in the contralateral calf was measured by vein plethysmography. At steady-state clamping, at 60-120 min, the interstitial insulin concentration was significantly lower than arterial insulin in both groups (409 +/- 86 vs. 1,071 +/- 99 pmol/l, P < 0.05, in controls and 584 +/- 165 vs. 1, 253 +/- 82 pmol/l, P < 0.05, in diabetic subjects, respectively). Interstitial insulin concentrations did not differ significantly between diabetic subjects and controls. Leg blood flow was significantly higher in controls (8.1 +/- 1.2 vs. 4.4 +/- 0.7 ml. 100 g(-1).min(-1) in diabetics, P < 0.05). Calculated glucose uptake was less in diabetic patients compared with controls (7.0 +/- 1.2 vs. 10.8 +/- 1.2 micromol. 100 g(-1).min(-1), P < 0.05, respectively). Arterial and interstitial lactate concentrations were both higher in the control group (1.7 +/- 0.1 vs. 1.2 +/- 0.1, P < 0. 01, and 1.8 +/- 0.1 vs. 1.2 +/- 0.2 mmol/l, P < 0.05, in controls and diabetics, respectively). We conclude that, during hyperinsulinemia, muscle interstitial insulin and glucose concentrations did not differ between patients with type 2 diabetes and healthy controls despite a significantly lower leg blood flow in diabetic subjects. It is suggested that decreased glucose uptake in type 2 diabetes is caused by insulin resistance at the cellular level rather than by a deficient access of insulin and glucose surrounding the muscle cell.

Muscle glucose uptake is effectively activated by ischemia in type 2 diabetic subjects.

It has previously been shown that Wortmannin, a phosphatidylinositol 3-kinase inhibitor, inhibits glucose transport activated by insulin but not by ischemia, suggesting the importance of an activating mechanism that bypasses the insulin signal. To evaluate the relevance of this insulin-independent pathway in insulin-resistant subjects, the ability of ischemia to stimulate glucose uptake was investigated in 9 patients with type 2 diabetes and in 9 healthy control subjects (fasting glucose level 9.4 +/- 0.8 vs. 5.1 +/- 0.1 mmol/l, P < 0.001, in type 2 diabetic patients and control subjects, respectively; fasting insulin level insulin 8.1 +/- 2.6 vs. 4.5 +/-0.7 mU/l, P < 0.05, respectively) matched for sex, age, and BMI. Arterial plasma and interstitial concentrations of glucose and lactate (measured by subcutaneous and muscle microdialysis) were recorded in the forearm before, during, and after ischemia induced locally for 20 min. During ischemia, the muscle interstitial glucose concentration decreased significantly from 7.7 +/- 0.6 to 5.4 +/- 0.4 mmol/l (P < 0.01) and from 4.4 +/- 0.3 to 3.6 +/- 0.3 mmol/l (P < 0.05) in type 2 diabetic patients and control subjects, respectively. The arterial-interstitial (A-I) glucose concentration difference was 1.7 +/- 0.6 and 0.7 +/- 0.3 mmol/ at basal, and it increased significantly to 3.5 +/- 0.7 (P < 0.01) and 1.4 +/-0.3 mmol/l (P < 0.05) during ischemia in each group, respectively. Interstitial lactate increased significantly during ischemia from 0.8 +/- 0.1 to 1.1 +/- 0.1 mmol/l (P < 0.05) and from 0.5 +/- 0.1 to 0.9 +/- 0.2 mmol/l (P < 0.05), respectively. The A-I glucose concentration difference was abolished immediately postischemia and regained after approximately 15 min, whereas high interstitial lactate levels remained elevated throughout the study. Subcutaneous interstitial glucose concentrations remained unchanged during ischemia and postischemia in both groups, whereas the interstitial lactate concentration in adipose tissue increased during ischemia from 1.4 +/- 0.2 to 2.0 +/- 0.2 mmol/l (P < 0.05) and from 1.1 +/- 0.1 to 1.8 +/- 0.3 mmol/l (P < 0.05) in type 2 diabetic patients and control subjects, respectively. Plasma glucose and lactate levels were unchanged in both groups during the study period. The results show that in muscle, but not in adipose tissue, glucose uptake is efficiently activated by ischemia in insulin-resistant type 2 diabetic subjects, suggesting the activation of a putative alternative pathway to the insulin signal in muscle cells.

Effects of exercise on insulin distribution and action in testosterone-treated oophorectomized female rats.

Administration of testosterone (T) to oophorectomized (Ovx) female rats is followed by severe insulin resistance, localized to postreceptor cellular events in the muscle. In this study, intervention by exercise was introduced to examine whether circulatory adaptations are involved in insulin resistance. Two groups of Ovx rats were studied: one group was given T (Ovx+T); another group had free access to running wheels (Ovx+T+Ex). In addition, one control group (sham operated) was studied. Insulin sensitivity was measured with the euglycemic hyperinsulinemic clamp technique (submaximal) for 150 min. Muscle interstitial glucose and insulin concentrations were measured by microdialysis. The measurements showed that, in Ovx+T rats, the onset of insulin action was significantly (P < 0.05) slower during the first 95 min of the clamp compared with that in Ovx+T+Ex and controls. Muscle interstitial concentrations of insulin but not glucose were lower in both Ovx+T and Ovx+T+Ex rats than in controls throughout the clamp. It was concluded that physical exercise prevented the slow onset of insulin action in Ovx+T rats without changing the distribution time of muscle interstitial insulin. The results indicate that hyperandrogenicity is characterized by delayed muscle insulin action. Physical exercise reverses these defects without any beneficial effect on muscle interstitial insulin concentrations.

Induction of insulin resistance by glucosamine reduces blood flow but not interstitial levels of either glucose or insulin.

To study the effects of a glucosamine infusion on skeletal muscle metabolism, microdialysis was performed in the medial femoral muscle in Sprague-Dawley rats during a euglycemic-hyperinsulinemic clamp (insulin infusion 18 mU x kg(-1) x min(-1)). During steady-state clamping conditions (70 min), an infusion of glucosamine (30 micromol x kg(-1) x min(-1)) or saline was given for 240 min. Blood flow was measured by the microsphere technique at the end of the clamp. An approximately 36% (P < 0.001) reduction in the glucose infusion rate was seen after 170 min in the glucosamine-treated rats compared with control rats. There were no significant differences in interstitial or plasma levels of either insulin or glucose between the two groups. Both interstitial (2.31 +/- 0.18 vs. 1.71 +/- 0.24 mmol/l, P < 0.05) and arterial plasma lactate concentrations (1.29 +/- 0.09 vs. 0.79 +/- 0.09 mmol/l, P < 0.01) were significantly higher in control rats compared with glucosamine-treated rats. Blood flow was significantly reduced in hind limb femoral muscles in the glucosamine-treated rats compared with control rats. The most pronounced reduction in blood flow was seen in the Soleus muscle (27.6 +/- 3.4 vs. 14.7 +/- 2.0 ml x 100 g(-1) x min(-1), P < 0.01). These results demonstrate that induction of insulin resistance by glucosamine results in a reduction of the blood flow rate as well as the uptake of glucose and the production of lactate in skeletal muscle. As a result of the inhibited glucose metabolism, the interstitial glucose concentration was unchanged despite the reduced blood flow after glucosamine administration. The data suggest the importance of regulation of blood flow by nonoxidative metabolism of glucose in resting muscle.

Measurement of interstitial insulin in human muscle.

Previous measurements in lymph and adipose tissue have indicated that interstitial insulin concentrations are approximately 40% lower than in plasma. Measurements of insulin in human muscle interstitial fluid have not been performed yet. We developed a new external reference technique for calibration of microdialysis catheters in situ. This technique allows correct assessments of interstitial peptide concentrations and was employed to estimate the insulin concentration in medial quadriceps femoris muscle in 11 individuals (age: 37 +/- 3 yr; body mass index: 25.2 +/- 1.2 kg/m2) during a two-step euglycemic hyperinsulinemic clamp. At steady-state insulin and glucose infusion, plasma glucose was 5.9 +/- 0.2 mmol/l, plasma insulin was 155 +/- 17 mU/l, and interstitial muscle insulin was 67 +/- 19 mU/l (n = 9; P < 0.01). At a higher insulin infusion rate, the steady-state plasma insulin concentration was 379 +/- 58 mU/l, and interstitial insulin concentration was 180 +/- 40 mU/l (P < 0.01). The data show for the first time that high physiological and supraphysiological plasma insulin levels give 30-50% lower interstitial concentrations of insulin in the muscle. The importance of capillary delivery as a rate-limiting step for the insulin effect is suggested.

Induction of rat muscle insulin resistance by epinephrine is accompanied by increased interstitial glucose and lactate concentrations.

Muscle glucose uptake and lactate release during beta-adrenergic stimulation by epinephrine (epi) and beta-adrenergic blockade by propranolol (prop) were investigated during an euglycaemic hyperinsulinaemic (30 pmol x kg(-1) x min(-1)) with or without added somatostatin (0.1 microg/min; pancreatic) clamp in female rats. To assess the interstitial insulin, glucose and lactate concentrations, microdialysis was done in the medial femoral muscle in both legs. The influence of muscle skeletal blood flow on interstitial insulin, glucose and lactate was examined with the microsphere technique, using 57Co-microspheres. Epinephrine decreased glucose infusion rate by about 75% (p < 0.0001) and increased concentrations of interstitial glucose by about 35% (p < 0.001) and lactate by about 65% (p < 0.01). Plasma insulin concentration increased during beta-adrenergic stimulation by about 25% (p < 0.05) whereas the interstitial insulin concentration was unchanged. Muscle blood flow in the hindlimb was considerably enhanced by about 130%, (p < 0.001) by epinephrine. Infusion of propranolol totally abolished all the above effects induced by epinephrine. The data show that insulin resistance and vasodilation induced by beta-adrenergic stimulation with epinephrine is accompanied by increased interstitial glucose as well as lactate concentrations in muscle. The increased interstitial glucose concentration is the result of a decreased cellular uptake of glucose together with an increased capillary delivery of glucose by vasodilation. It is concluded that the severe cellular resistance to insulin induced by epinephrine could not be overcome either by the increased insulin secretion or by vasodilation.