Paradoxical phosphorylation of skeletal muscle glycogen synthase by in vivo insulin in very lean young adult rhesus monkeys

Calorie restriction (CR) has previously been shown to unexpectedly induce a reversal of in vivo insulin action (phosphorylation instead of dephosphorylation) on skeletal muscle glycogen synthase (GS) in four out of six long-term calorie-restricted (CR) monkeys. The purpose of the present study was to determine whether this increase in Ka (concentration of glucose 6-phosphate [G6P] at which GS activity is half-maximal) during insulin is also present in very lean (VL) young adult monkeys maintained on a controlled feeding regimen. Muscle samples from 10 VL monkeys (10 +/- 2% body fat; 7 years old) were obtained before and during a euglycemic hyperinsulinemic clamp and the Ka was determined and compared to the Ka of two other groups of monkeys, one matched in age but fully ad libitum (AL)-fed (n = 9.8 +/- 1 years old, 20 +/- 3% body fat, p = 0.01 vs. VL monkeys), and the other our previously described weight-clamped long-term CR monkeys (n = 6.20 +/- 1 years old, 21 +/- 2% body fat, p = 0.01 vs. VL monkeys). All of the AL monkeys had the expected decrease in Ka with insulin; however, similar to the 4 out of 6 CR monkeys, 7 out of 10 VL monkeys had an increase in Ka with insulin. The 11 monkeys with an increase in Ka (+Ka) (7 VL + 4 CR) were compared to the 14 monkeys with a decrease in Ka with insulin (-Ka) (3 VL + 2 CR + 9 AL). The +Ka monkeys had lower basal Ka (p = 0.0001), higher basal GS fractional activity (p = 0.0003), lower basal G6P content (p = 0.002), lower glycogen phosphorylase fractional activity (p = 0.01), and lower whole-body insulin-mediated glucose disposal rate (p < 0.05) than the -Ka monkeys. We conclude that the condition of steady-state restrained calorie intake (as in the CR monkeys and in the controlled feeding VL monkeys) produces the paradoxical action of in vivo insulin to phosphorylate muscle GS, and raises the possibility that the presence of the unusual response to insulin may serve as a marker in calorie-restrained individuals for the genotype of obesity, insulin resistance and/or Type 2 diabetes.

Neuroendocrine regulation of nutrient partitioning

Leptin is a satiety factor which acts within the hypothalamus to decrease the levels of several neuropeptides stimulating food intake (among them, neuropeptide Y [NPY]), while increasing those that inhibit food intake. These effects of leptin bring about decreased body weight. In vivo, leptin potentiates basal and insulin-stimulated glucose utilization, presumably its oxidation, and decreases fat storage. Leptin increases sympathetic-mediated energy dissipation, and the expression of uncoupling proteins-1, -2, and -3. In peripheral tissues (muscles, adipose, others), leptin decreases triglyceride content by increasing fatty acid oxidation, decreasing the activity/expression of esterification and lipogenic enzymes, and favoring lipolysis. It decreases the lipogenic activity of insulin. Ultimately, leptin depletes fat stores and promotes leanness. NPY, taken as one example of what an orexigenic agent may produce, increases food intake and body weight. It favors fat storage in adipose tissue by stimulating lipogenic activity. It decreases glucose utilization by muscles, making more glucose carbon available for lipogenesis. Effects of NPY result from vagus nerve-mediated hyperinsulinemia and overactivity of the hypothalamo-pituitary-adrenal axis. Thus, NPY favors fat stores, and ultimately obesity. Glucocorticoids are necessary for NPY effects to occur, because central administration of the neuropeptide in adrenalectomized animals is ineffective. Glucocorticoids also have genuine effects when administered centrally to normal rats. They increase the hypothalamic content of NPY and decrease that of CRH. This double neuro-peptidic change stimulates food intake, insulin output, adipose tissue storage ability, decreases the expression of uncoupling proteins-1 and -3, and increases body weight. Body weight homeostasis appears to require a finely tuned regulation of both leptin and glucocorticoids, with their respective opposite effects.

Regulation of gene expression by activation of the peroxisome proliferator-activated receptor gamma with rosiglitazone (BRL 49653) in human adipocytes

To better define the mechanism of action of the thiazolidinediones, we incubated freshly isolated human adipocytes with rosiglitazone and investigated the changes in mRNA expression of genes encoding key proteins of adipose tissue functions. Rosiglitazone (10(-6) M, 4 h) increased p85alphaphosphatidylinositol 3-kinase (p85alphaPI-3K) and uncoupling protein-2 mRNA levels and decreased leptin expression. The mRNA levels of insulin receptor, IRS-1, Glut 4, lipoprotein lipase, hormone-sensitive lipase, acylation-stimulating protein, fatty acid transport protein-1, angiotensinogen, plasminogen activator inhibitor-1, and PPARgamma1 and gamma2 were not modified by rosiglitazone treatment. Activation of RXR, the partner of PPARgamma, in the presence of rosiglitazone, increased further p85alphaPI-3K and UCP2 mRNA levels and produced a significant augmentation of Glut 4 expression. Because p85alphaPI-3K is a major component of insulin action, the induction of its expression might explain, at least in part, the insulin-sensitizing effect of the thiazolidinediones.

An evaluation of resting energy expenditure in hospitalized, severely underweight patients

A prospective trial was conducted with 14 hospitalized patients who were severely underweight with a mean weight of 40.9+/-5.1 kg and 70.7+/-7.8% of ideal body weight, to compare estimates of resting energy expenditure (REE) with measured values. The 9 women and 3 men, whose mean age was 66.5+/-13.9 y, underwent nutritional assessment and measurement of their REE by indirect calorimetry using the Sensormedics Deltatrac MBM100 indirect calorimeter. Their REE was also estimated by the Harris-Benedict formula (mean 1032+/-66 kcal/d) as well as a previously established empirical formula where REE = 25 x body weight in kg (mean 1023+/-129 kcal/d). Results by both estimates were significantly lower than the measured resting energy expenditure (MREE) in this group of patients (P<0.0001). The percentage difference between MREE and estimated REE by the Harris-Benedict formula was 18.4+/-9.4% and 20.9+/-7.5% by the empirical formula. The MREE exceeded the estimated REE in each individual. The correlation between MREE and body weight (r2 = 0.558, r = 0.005) was better than that between MREE and estimated REE by Harris-Benedict formula (r2 = 0.275, P = 0.08) suggesting that weight was the principal determinant rather than the other components (height, age, sex) of the Harris-Benedict formula. Our data shows that commonly employed formulae routinely underestimate the energy needs of severely underweight patients below 50 kg in body weight. The Harris-Benedict equation had limited predictive value for the individual, explaining approximately 25% of the variance in energy expenditure. Given the particular importance of matching energy intake to needs in this group of patients with limited reserves, many of whom are critically ill, we suggest an empirical equation using 30-32 kcal/kg be used to estimate the energy requirements of severely underweight patients when direct measurements are unavailable or clinically less imperative.

Plasma electrolytes, total cholesterol, liver enzymes, and selected antioxidant status in protein energy malnutrition

Golden and Ramdath proposed the free radical theory of kwashiorkor, suggesting that the changes seen in kwashiorkor may be the result of an imbalance between the production and safe disposal of free radicals. In malnourished children, mineral metabolism and antioxidant status need renewed attention especially in relation to cause and functional significance of the changes in concentration of these substances. In the present study, the modified Wellcome classification was used to classify the protein energy malnourished children into kwashiorkor marasmic-kwashiorkor, marasmus and underweight. Twenty-six healthy and normal children were used as controls. Standard procedures were used for the analyses of the biochemical parameters. Our results showed that plasma total cholesterol, sodium, potassium and bicarbonate, beta-carotene, retinol and uric acid were significantly lower in the malnourished group than the control group (P < 0.05), while transaminases were significantly increased in the malnourished group (P < 0.05). These findings suggest an altered electrolyte and antioxidant status in protein energy malnutrition.

Modulation of epinephrine-stimulated gluconeogenesis by insulin in hepatocytes isolated from genetically obese (fa/fa) Zucker rats

Genetically obese (fa/fa) Zucker rats present an impaired response of hepatic glucose production to the inhibition by insulin. In this work, we have investigated the modulation by this hormone of epinephrine-stimulated gluconeogenesis, in hepatocytes isolated from obese (fa/fa) rats and their lean (Fa/-) littermates. Epinephrine (1 microM) caused a maximal stimulation of [14C]lactate conversion to [14C]glucose in hepatocytes isolated from either obese or lean animals. The stimulation of gluconeogenesis by epinephrine was accompanied by a significant reduction of fructose 2,6-bisphosphate levels, an inactivation of both pyruvate kinase and 6-phosphofructo 2-kinase, and by a 2-fold increase in the cellular concentrations of cAMP. The presence of insulin in the incubation medium antagonized, in a concentration-dependent manner, the effects of epinephrine. In hepatocytes isolated from lean rats, the reversion caused by insulin was complete, the concentration required for half-maximal insulin action ranging from 0.22 to 0.56 nM. In contrast, in obese rat hepatocytes, insulin only partially blocked epinephrine-mediated effects, and the sensitivity to insulin was 2- to 4-fold lower, as indicated by the corresponding half-maximal insulin action values. Furthermore, insulin (10 nM) almost completely blocked the increase in cAMP levels induced by epinephrine in lean rat hepatocytes, whereas it only provoked a small and nonsignificant reduction of epinephrine-stimulated levels of the cyclic nucleotide in hepatocytes obtained from obese rats.

Endogenous glucose production, gluconeogenesis and liver glycogen concentration in obese non-diabetic patients

Resting, post-absorptive endogenous glucose production (EGP), fractional gluconeogenesis and liver glycogen concentration were assessed in 6 lean and 5 obese non-diabetic subjects undergoing elective abdominal surgery. During the 2 days preceding these measurements, 0.3 g/day U-13C glucose had been added to their usual diet to label their endogenous glycogen stores. On the morning of day 3, EGP was measured with 6,6-2H glucose. Their endogenous 13C glycogen enrichment was calculated from 13CO2 and respiratory gas exchanges. Fractional gluconeogenesis was assessed as 1-(13C glucose/13C glycogen)100. EGP was similar in lean subjects (113 +/- 5 mg/min) and in obese subjects (111 +/- 6). Fractional gluconeogenesis was higher in obese (59 +/- 10%) than in lean subjects (29 +/- 8%). However, overall EGP remained constant due to a decrease in glycogenolysis. Since an increased gluconeogenesis and a decreased glycogenolysis may both contribute to increase liver glycogen concentration in obesity, hepatic glycogen concentrations were assessed in hepatic needle biopsies obtained during surgery. Hepatic glycogen concentrations were increased in obese patients (515 +/- 38 mg/g protein) compared to lean subjects (308 +/- 58, p < 0.05). It is concluded that in obese patients: a) fractional gluconeogenesis is increased; b) overall EGP is unchanged due to a proportional inhibition of glycogenolysis; c) liver glycogen concentration is increased.

Abnormal glucose transport and GLUT1 cell-surface content in fibroblasts and skeletal muscle from NIDDM and obese subjects

Glucose transport and GLUT1 expression were studied in fibroblasts from 7 lean and 5 obese non-insulin-dependent diabetic (NIDDM) subjects with at least 2 NIDDM first-degree relatives and from 12 lean and 5 obese non-diabetic subjects with no family history of diabetes. The obese individuals also had a strong family history of obesity. Fibroblasts from all of the subjects exhibited no difference in insulin receptor binding, autophosphorylation, and kinase and hexokinase activity. At variance, basal 2-deoxyglucose (2-DG) uptake and 3H-cytochalasin B binding were 50% increased in cells from individuals with NIDDM (p < 0.001) and/or obesity (p < 0.01) as compared to the lean non-diabetic subjects. Insulin-dependent (maximally stimulated-basal) 2-DG uptake and cytochalasin B binding were decreased three-fold in cells from the diabetic and/or obese subjects (p < 0.01). GLUT1 mRNA and total protein levels were comparable in fibroblasts from all the groups. However, basal GLUT1 cell-surface content was 50% greater in fibroblasts from the NIDDM and/or obese subjects as compared to the lean non-diabetic individuals while insulin-dependent GLUT1 recruitment at the cell surface was diminished three-fold. Increased basal GLUT1 content in the plasma membrane was also observed in skeletal muscle of 4 NIDDM and 3 non-diabetic obese individuals (p < 0.05 vs the lean non diabetic subjects). Basal 2-DG uptake in fibroblasts from diabetic/obese individuals and lean control subjects strongly correlated with the in vivo fasting plasma insulin concentration of the donor. A negative correlation was demonstrated between the magnitude of insulin-dependent glucose uptake by the fibroblasts and plasma insulin levels in vivo. We conclude that a primary abnormality in glucose transport and GLUT1 cell-surface content is present in fibroblasts from NIDDM and obese individuals. The abnormal GLUT1 content is also present in skeletal muscle plasma membranes from NIDDM and obese individuals.

Insulin secretion, glucose production, and insulin sensitivity in underweight and normal-weight volunteers, and in underweight and normal-weight cancer patients: a Clinical Research Center study

Severe malnutrition (< 65% ideal body weight [IBW]) is associated with reduced insulin secretion, decreased receptor affinity, and glucose intolerance. To characterize the abnormality of mild malnutrition in terms of insulin action, both the insulin sensitivity index and insulin secretion were measured in 15 underweight and 15 normal-weight volunteers. Ten patients had localized squamous cell carcinomas of the head and neck, and 20 were normal controls. After a 10-hour overnight fast, all volunteers were studied using Bergman's modified intravenous (IV) glucose tolerance test (IVGTT). Body weight and diagnosis were compared using a 2 x 2 ANOVA. The acute insulin response to IV glucose was reduced in normal-weight and underweight cancer patients by approximately 40% to 50% (P < .05). Both groups of cancer patients had a significantly reduced rate of glucose disposal (1.25 +/- 0.29 and 1.27 +/- 0.23 %/min) compared with the healthy volunteers (1.82 +/- 0.21 and 1.81 +/- 0.24 %/min, respectively, P < .05). Glucose production (GP) was significantly increased in the underweight cancer patients versus the weight-matched volunteers (13.9 +/- 1.3 v 10.8 +/- 0.5 micromol/kg/min, P < .05). Normal-weight and underweight cancer patients had a 32% to 44% reduction in insulin sensitivity (P < .05). In contrast to the effects of cancer, underweight controls had twice the insulin sensitivity compared with normal-weight controls (P < .01). Since insulin secretion decreased in underweight controls, the increased insulin sensitivity may have been due to an increased insulin action and to factors associated with leanness.

Expression of corticotropin-releasing factor and its receptors in the brain of lean and obese Zucker rats

Expression of CRF messenger RNA (mRNA) and heteronuclear RNA (hnRNA) as well as the mRNAs encoding the CRF receptors of type 1 (CRF1R) and type 2 alpha (CFR2R) in the brain has been investigated in lean (Fa/?) and obese (fa/fa) Zucker rats. Exonic and intronic in situ hybridization histochemistry was employed to measure the mRNA and hnRNA levels in rats killed before (resting state), during, and 120 min after a treadmill running session. The resting expression of CRF hnRNA in the hypothalamic paraventricular nucleus (PVN) of obese rats was minimal and comparable to that of lean rats. However, during treadmill running, this expression was higher in obese than in lean rats. In obese rats, the transcription of the CRF1R mRNA in the PVN was high under resting conditions, dropped considerably during running, and rose again to elevated levels 120 min after the treadmill session. In lean rats, CRF1R mRNA in the PVN was minimal before and during running, but rose to a value similar to that in obese rats 120 min after running. In the PVN of obese rats, expression of the CRF1R gene measured during resting conditions was comparable to the level seen after running and proved to be dependent upon the feeding state of the rats. Expression of the CRF2R transcript was reduced in the ventromedial nucleus of the hypothalamus (VMH) of the obese rat. Plasma ACTH concentrations during treadmill running were lower in obese than in lean animals. Basal and postrunning levels of circulating corticosterone were higher in fa/fa than in Fa/? rats. However, there was no difference in corticosterone levels between lean and obese animals during running. The present results provide evidence for differences between lean and obese rats in the expression of CRF and its receptor within selective hypothalamic nuclei. Given the anorectic and thermogenic properties of CRF and the roles of PVN and VMH in the regulation of energy balance, it can be argued that the observed alterations in the biosynthesis of CRF and its receptors within the PVN and VMH might be related to the development of obesity.

VLDL triglyceride kinetics in Wistar fatty rats, an animal model of NIDDM: effects of dietary fructose alone or in combination with pioglitazone

The effects of dietary fructose alone or in combination with a new oral agent, pioglitazone, on VLDL-triglyceride (TG) turnover were studied in genetically obese Wistar fatty rats characterized by hyperinsulinemia (7,488 +/- 954 pmol/l), hyperglycemia, (22.5 +/- 1.4 mmol/l), and hypertriglyceridemia (4.39 +/- 0.54 mmol/l). They had an increased hepatic TG production (16.2 +/- 0.1 micromol/min; lean rats, 5.4 +/- 0.3 micromol/min) as well as a longer half-life of VLDL-TG from lean donors (8.8 +/- 1.4 min, lean recipients; 2.3 +/- 0.9 min). In addition, in lean recipients, the half-life of VLDL-TG from fatty donors was longer than that from lean donors (4.80 +/- 0.56 vs. 3.14 +/- 0.23 min). Although feeding fructose into fatty rats did not change plasma glucose and insulin levels, it produced a twofold increase in TG levels (8.74 +/- 1.15 mmol/l). This was associated with a 1.7-fold increase in TG production to 27.5 +/- 1.2 micromol/min, while no significant change was found in the half-life of lean VLDL-TG in fructose-fed fatty recipients (10.9 +/- 2.4 min) or in that of VLDL-TG from fructose-fed fatty donors in lean recipients (4.46 +/- 0.76 min). Daily administration of pioglitazone (3 mg/kg body weight) in fructose-fed fatty rats ameliorated glycemia and triglyceridemia to the level of lean rats (8.1 +/- 0.7 and 1.18 +/- 0.05 mmol/l, respectively) and insulinemia to a lesser extent (2,712 +/- 78 pmol/l). A fall in TG levels was associated with improvement of an impairment in the ability of fructose-fed fatty rats to remove lean VLDL-TG (half-fife: 2.6 +/- 0.6 min). Pioglitazone, however, produced no change in TG production (25.9 +/- 2.7 micromol/min), the half-life of VLDL-TG from fructose-fed fatty donors in lean recipients (4.17 +/- 0.38 min), or the activity of lipoprotein lipase and hepatic lipase in postheparin plasma. We conclude that in Wistar fatty rats 1) hypertriglyceridemia is attributed to TG overproduction and impaired TG catabolism, and the latter is due to changes in both VLDL, such that they are less able to be removed, and changes in the nature of Wistar fatty rats, such that they are less able to remove VLDL-TG; 2) fructose further increases hepatic TG production with a resultant deterioration in hypertriglyceridemia; 3) pioglitazone normalizes TG levels by altering the physiology of the Wistar fatty rats in a manner that increases their ability to remove VLDL-TG from the circulation.

Metabolic rate, organ mass, and mitochondrial proton leak variations in lean and obese rats

The purpose of this study was to determine if differences in metabolic rate between lean and obese strains of rats were associated with differences in proton leak across the inner mitochondrial membrane. Metabolic rates were determined for each of five obese Zucker, Sprague-Dawley, and Fisher 344 rats and three lean Zucker rats by 24-hour indirect respiration calorimetry measurements. Feed intakes were different (P < 0.05) among all strains, with the obese Zucker rats having the greatest intakes. Adjusted to a common dietary intake, the obese Zucker rats had at least 21% lower heat productions than the lean strains of rats. Following the calorimetry measurements, the rats were sacrificed, internal organs were removed and weighed and mitochondria were isolated from the liver. Internal organs composed a larger proportion of lean body mass in obese compared to lean rats. Respiration rates and membrane potentials of the mitochondria were then determined. Proton leak kinetics were visualized by plotting proton leak (calculated from respiration rate) against membrane potential. The lean rats had a 2-3-fold higher proton leak rate than the obese Zucker rats at the same membrane potential. A low mitochondrial proton leak rate may explain part of the abnormal heat productions and bioenergetic efficiencies in the obese Zucker rat.

Effects of fasting on hepatic and peripheral glucose metabolism in conscious rats with near-total fat depletion

Experimental diabetes and fasting are both associated with hypoinsulinaemia and share several other metabolic features. We investigated hepatic and peripheral glucose metabolism in young rats after near-total depletion of their fat mass. Conscious rats were fasted for 72 h (n = 13), while 6 h-fasted animals (n = 14) served as controls. Rats were studied either during saline infusion or insulin (18 m-units/kg per min)-clamp studies. In fasting, despite a 2-fold increase in hepatic glucose-6-phosphatase (Glc-6-Pase) Vmax. (from 16 +/- 2 mumol/g of liver per min in control; P < 0.001), the basal hepatic glucose production (HGP) decreased by 47% [from 88 +/- 3 mumol/kg lean body mass (LBM) per min in control; P < 0.01]. The decreased HGP in fasting was associated with a 70% decrease in the hepatic levels of glucose 6-phosphate (Glc-6-P) (from 366 +/- 53 nmol/g wet wt. in control; P < 0.01). Thus Glc-6-Pase activity assayed in the presence of the Glc-6-P levels found in vivo was decreased by 44%. During hyperinsulinaemia, peripheral glucose uptake was decreased by 15% with 3 days of fasting (from 272 +/- 17 mumol/kg LBM per min in control; P < 0.01). This was completely accounted for by a 42% decrease in whole-body glycolysis (P < 0.01), while the rate of glycogen synthesis was unchanged. Thus fasting (after near-total fat depletion) differs from experimental diabetes because: (1) despite markedly increased Glc-6-Pase, HGP is decreased in fasting, due to a marked decrease in the substrate level (Glc-6-P) in vivo; and (2) the impairment in peripheral insulin sensitivity in fasting is due to a decrease in the glycolytic, and not the glycogen-synthetic, pathway.

Differential effect of maturation on insulin- vs. contraction-stimulated glucose transport in Zucker rats

Insulin-stimulated glucose transport has been shown to decline during maturation in lean rats. To determine whether this maturation-induced decrease occurred in the muscle of obese rats and whether the contraction-stimulated pathway for glucose transport was similarly affected, glucose transport rates were measured in insulin- and electrically stimulated skeletal muscle during hindlimb perfusion of 10- and 29-wk-old lean and obese male Zucker rats. Glucose transporter (GLUT-4) protein was also measured. Insulin-stimulated glucose transport rates were significantly decreased (36-56%) in 29-wk compared with 10-wk-old lean rats. There was no maturation-related decrease in GLUT-4. Insulin-mediated glucose transport was unaltered by maturation in skeletal muscle of obese rats. Differential effects of maturation on lean and obese rats caused the effect of obesity on maximally insulin-stimulated glucose transport to be much greater in 10- than 29-wk-old animals. Maturation had no effect on contraction-stimulated glucose transport rates in either lean or obese animals. The combined effect of maximal insulin plus contraction was not altered with maturity in lean animals but was significantly increased in 29- compared with 10-wk-old obese rats. Absence of a change in GLUT-4 content together with uncompromised contraction-stimulated glucose transport suggests that the maturation-induced decrease in insulin-stimulated glucose transport in lean rats is due to a defect in the insulin signaling pathway.

Increased adipose tissue expression of tumor necrosis factor-alpha in human obesity and insulin resistance

Obesity is frequently associated with insulin resistance and abnormal glucose homeostasis. Recent studies in animal models have indicated that TNF-alpha plays an important role in mediating the insulin resistance of obesity through its overexpression in fat tissue. However, the mechanisms linking obesity to insulin resistance and diabetes in humans remain largely unknown. In this study we examined the expression pattern of TNF-alpha mRNA in adipose tissues from 18 control and 19 obese premenopausal women by Northern blot analysis. TNF-alpha protein concentrations in plasma and in conditioned medium of explanted adipose tissue were measured by ELISA. Furthermore, the effects of weight reduction by dietary treatment of obesity on the adipose expression of TNF-alpha mRNA were also analyzed in nine premenopausal obese women, before and after a controlled weight-reduction program. These studies demonstrated that obese individuals express 2.5-fold more TNF-alpha mRNA in fat tissue relative to the lean controls (P < 0.001). Similar increases were also observed in adipose production of TNF-alpha protein but circulating TNF-alpha levels were extremely low or undetectable. A strong positive correlation was observed between TNF-alpha mRNA expression levels in fat tissue and the level of hyperinsulinemia (P < 0.001), an indirect measure of insulin resistance. Finally, body weight reduction in obese subjects which resulted in improved insulin sensitivity was also associated with a decrease in TNF-alpha mRNA expression (45%, P < 0.001) in fat tissue. These results suggest a role for the abnormal regulation of this cytokine in the pathogenesis of obesity-related insulin resistance.

Interstitial insulin concentrations determine glucose uptake rates but not insulin resistance in lean and obese men

Insulin action and obesity are both correlated with the density of muscle capillary supply in humans. Since the altered muscle anatomy in the obese might affect interstitial insulin concentrations and reduce insulin action, we have cannulated peripheral lymphatic vessels in lean and obese males, and compared peripheral lymph insulin concentrations with whole body glucose uptake during a euglycemic, hyperinsulinemic clamp. Lymph insulin concentrations in the lower limb averaged only 34% of arterial insulin concentrations during 150 min of insulin infusion. Obese subjects had the highest arterial (P < or = 0.0001) and lymph insulin (P < 0.005) concentrations, but the lowest glucose uptake rates (P < 0.002). In contrast to the initial steep rise then plateau of arterial insulins, both lymph insulin and whole body glucose uptake rates rose slowly and did not consistently reach a plateau. In each individual, the glucose uptake closely correlated with peripheral lymphatic insulin concentrations (mean r2 = 0.95). The coupling between glucose uptake and lymph insulin (glucose uptake/pmol insulin) was much steeper in lean subjects than in the obese (P < or = 0.0001). These results indicate that even if insulin diffusion into tissues is rate limiting for insulin action, a tissue defect rather than an insulin diffusion defect causes insulin resistance in obese subjects.

Lactate release from the subcutaneous tissue in lean and obese men

Lactate concentration in the subcutaneous interstitial fluid and adipose tissue blood flow (ATBF, ml/100 g.min) were simultaneously measured with the microdialysis technique combined with 133Xe clearance in the abdominal and femoral subcutaneous adipose tissue in nine lean and nine obese men. The studies were performed both in the postabsorptive state and 2 h after an oral glucose load and the results compared to the lactate levels in arterialized venous plasma. After an overnight's fast, arterial lactate was 738 +/- 49 and 894 +/- 69 microM (mean +/- SE) (P < 0.05) in the lean and obese subjects, respectively. The interstitial lactate levels were significantly higher than blood lactate in both subject groups without any regional differences. Abdominal and femoral ATBF was 3.2 +/- 0.6 vs. 2.8 +/- 0.4 and 1.7 +/- 0.3 vs. 2.4 +/- 0.4 ml/100 g.min (P < 0.05) in lean and obese subjects, respectively. Mean apparent lactate release from the abdominal vs. femoral adipose tissue in the fasting state was 10.5 +/- 3.1 vs. 8.6 +/- 2.3 and 6.0 +/- 2.3 vs. 8.5 +/- 2.3 mumol/kg.min (NS) in lean and obese subjects, respectively. Both plasma and interstitial lactate levels increased significantly after an oral glucose load in both subject groups. However, apparent lactate release increased significantly only in the lean group. It is concluded that subcutaneous adipose tissue is a significant source of whole-body lactate release in the postabsorptive state and that this is further enhanced in obese subjects due to their large adipose mass.

A liver-specific nuclear protein represses transcription of the S14 gene in vitro and in vivo

P1 is a nuclear protein found exclusively in rat liver and binds to a motif that spans nucleotides -310 to -288 of the thyroid hormone responsive gene, S14. We expect P1 to play an important role in regulating gene expression because the binding motif for this factor is contained within a DNase I-hypersensitive site of S14 chromatin. In this report, we have attempted to define the function of P1 by correlating its DNA binding activity with levels of mRNA-S14 in response to aging and obesity. Results of all studies revealed inverse relationships between the activity of P1 and levels of mRNA-S14, thus suggesting that P1 may function as a repressor of S14 gene expression. Accordingly, we tested the repressor hypothesis using cell-free transcription and transient transfection assays to measure the activity of reporter constructs with and without the P1 binding motif. In the presence of the P1 motif, S14 promoter activity was repressed and the negative effect on gene transcription was further enhanced by thyroid hormone. These observations are consistent with P1 being a repressor of S14 gene transcription.

Postprandial thermogenesis in leanness and anorexia nervosa

Resting energy expenditure (REE) and postprandial thermogenesis (PPT) after the ingestion of a mixed test meal (3.56 MJ, 850 kcal) were determined in 7 anorectic patients, 7 very lean women and 8 control women. REE is absolute value was sharply decreased in the anorectics, but did not significantly differ between the very lean and the control subjects. On the other hand, when adjusted for body weight, REE only tended (p = 0.18) to be lower in the anorectics in comparison to the control women. PPT was similar in the anorectics (187.2 +/- 24.6 kJ/4 h) and the controls (200.7 +/- 16.8 kJ/4 h), but lower in the lean subjects (137.5 +/- 20.0 kJ/4h: p less than 0.05) than in the other two groups. The present study shows that the thermic response to the ingestion of a mixed test meal was not decreased in undernourished anorectic patients whereas it was significantly reduced in very lean healthy women.

The thermic effect of food in underweight patients with emphysematous chronic obstructive pulmonary disease

Malnutrition and weight loss commonly occur in patients with the emphysematous type of chronic obstructive pulmonary disease (COPD), despite normal energy intakes. The present study was designed to assess energy expenditure, basal metabolic rate (BMR) and diet-induced thermogenesis (DIT) in ten patients with COPD, together with the oxidation rates of carbohydrate, protein and fat. The BMR was elevated when tested against the Harris-Benedict equation (p less than 0.001) or when compared with six age- and sex-matched controls (11.11 +/- 2.52 vs 8.12 +/- 1.31 kJ.h-1.kg muscle-1, p less than 0.05). The main difference in fuel oxidation rate was an elevated fasting fat oxidation rate in the patients compared with controls (8.31 +/- 3.09 vs 4.76 +/- 2.53 kJ.h-1.kg muscle-1, p less than 0.05). The overall thermic response to food (41.2 kJ.kg-1 liquid meal) as a percentage of energy intake was greater in the patients (49.5 +/- 6.3 vs 39.8 +/- 2.9%, p less than 0.01). The patients also displayed a greater post-prandial rate of protein oxidation as a percentage of protein intake than controls (56.9 +/- 18.5 vs 34.1 +/- 6.5%, p less than 0.05). These data suggest an increased energy cost of feeding and fasting in patients with the emphysematous type of COPD.

Does infant feeding method influence maternal postpartum weight loss?

We conducted a retrospective study of 411 women to determine whether a significant relationship existed between method of infant feeding (breast vs bottle) and postpartum weight loss at 6 weeks and 12 months. In addition to method of infant feeding, the variables parity, gravidity, mode of delivery, maternal age, maternal prepregnancy weight, infant sex, and payment status (whether receiving assistance from the Aid to Dependent Children [ADC] program) were studied in terms of their association with weight loss. In general, no consistent relationship was found between method of infant feeding and postpartum weight loss. However, in the ADC group at 6 weeks and in the non-ADC group at 12 months, nonlactating women had lost more weight than had their lactating counterparts, in spite of the theoretical energy deficiency of breast-feeding women. Women who gained more weight during pregnancy consistently lost more weight following delivery, regardless of their prepregnancy weight. These results indicate that infant feeding method was not related to differences in postpartum weight loss between lactating and nonlactating counterparts.

Skeletal and body-composition effects of anorexia nervosa

Eleven female patients (aged 18-46 y) with anorexia nervosa were measured by use of dual-photon absorptiometry for 1) bone mineral content (BMC, in g) and bone mineral density (BMD, in g/cm2) of the total skeleton and its regions, 2) BMD of the lumbar spine and the proximal femur, and 3) total body soft-tissue composition. The patients weighed 44.4 kg, approximately 15 kg less than normal peers (n = 22). The fat mass (3.35 kg) and content of soft tissue (7.8%) were four and three times lower (p less than 0.001) respectively, than those in normal women (15.1 kg and 26%, respectively). The total skeleton mineral (1921 g) was approximately 25% less than that of young normal women. The BMC as a fraction of the lean tissue mass was approximately 4.9% in the patients and 5.9% in normal women. Total body and femoral BMD averaged only 10% and 13% lower than those of normal women, respectively; however, spinal BMD was particularly reduced (approximately 25%, p less than 0.001).

Diet composition, energy intake, and exercise in relation to body fat in men and women

This study examined the relationships among body fat, diet composition, energy intake, and exercise in adults. Male (n = 107) and female (n = 109) adults aged 18-71 y (36.6 +/- 1.0 y, means +/- SEM) were hydrostatically weighed to determine body fat (5.7-49.0% of total weight). Diet and exercise behaviors were determined by use of a questionnaire. As body fat increased, percent of energy intake derived from fat increased (p less than 0.001) whereas the percent from carbohydrate decreased (p less than 0.001). There was no relationship between energy intake and adiposity although leanness and exercise were related (p less than 0.001). When subgroups of lean and obese subjects were compared, the lean subjects derived approximately 29% of their energy from fat and 53% from carbohydrate vs 35% and 46%, respectively, for the obese subjects. No differences were found between groups for energy intake but the lean individuals exercised more often than did the obese individuals. These data suggest that diet composition may play as important a role in fat deposition as do energy intake and lack of exercise.

Alterations in the binding characteristics of glucocorticoid receptors from obese Zucker rats

Obese Zucker rats appear to lack a circadian rhythm of serum corticosterone and maintain relatively high concentrations throughout the 24-h day. The binding characteristics of glucocorticoid receptors in lean and obese Zucker rats were examined in three tissues suggested to be involved in the feedback inhibition of corticosterone: the anterior pituitary, hypothalamus and hippocampus. Hepatic glucocorticoid receptors were also examined to determine if receptor alterations exist in a peripheral tissue. The dissociation constant (Kd) of glucocorticoid receptors in the anterior pituitary of obese rats was 50% greater than the Kd of receptors derived from lean rats. This suggests a decrease in the affinity of these receptors and could indicate a reduced feedback inhibition of corticosterone at the anterior pituitary. Hepatic glucocorticoid receptors of obese rats also showed an increase (150%) in the Kd of binding and a reduction (40%) in the number of receptors. No difference was observed in the Kd or maximal binding of receptors from the hypothalamus or hippocampus of lean and obese rats. It appears that glucocorticoid receptor alterations exist in obese Zucker rats and that these alterations may affect the drive of the pituitary-adrenal axis and possibly the expression of obesity.

Ketone body metabolism in lean male adults during short-term starvation, with particular reference to forearm muscle metabolism

1. Thirty-three arteriovenous forearm catheterization studies were carried out in 19 lean subjects starving for 12-14 h (n = 13), 30-36 h (n = 7) and 60-66 h (n = 13). Forearm blood flow was measured in order to calculate the flux of various substrates. At the same time, whole-body oxidation of fat, carbohydrate and protein was calculated using indirect calorimetry and urinary nitrogen excretion. 2. After an overnight fast (12-14 h), whole-body resting energy expenditure was accounted for by the oxidation of protein (15%), carbohydrate (17%) and fat (68%). At 30-36 h and 60-66 h of starvation, essentially all the non-protein energy was derived from the oxidation of fat (directly plus indirectly via ketone bodies). 3. After an overnight fast, acetoacetate and 3-hydroxybutyrate were taken up by forearm muscle at a rate which could account for 5% of the resting O2 consumption of this tissue. As starvation progressed, forearm muscle took up more acetoacetate and released 3-hydroxybutyrate so that the net uptake of ketone bodies was sufficient to account for about 10% of the resting O2 consumption at 30-36 h of starvation and about 20% at 60-66 h of starvation.(ABSTRACT TRUNCATED AT 250 WORDS)