Secreted amyloid beta-protein similar to that in the senile plaques of Alzheimer's disease is increased in vivo by the presenilin 1 and 2 and APP mutations linked to familial Alzheimer's disease

To determine whether the presenilin 1 (PS1), presenilin 2 (PS2) and amyloid beta-protein precursor (APP) mutations linked to familial Alzheimer's disease (FAD) increase the extracellular concentration of amyloid beta-protein (A beta) ending at A beta 42(43) in vivo, we performed a blinded comparison of plasma A beta levels in carriers of these mutations and controls. A beta 1-42(43) was elevated in plasma from subjects with FAD-linked PS1 (P < 0.0001), PS2N1411 (P = 0.009), APPK670N,M671L (P < 0.0001), and APPV7171 (one subject) mutations. A beta ending at A beta 42(43) was also significantly elevated in fibroblast media from subjects with PS1 (P < 0.0001) or PS2 (P = 0.03) mutations. These findings indicate that the FAD-linked mutations may all cause Alzhelmer's disease by increasing the extracellular concentration of A beta 42(43), thereby fostering cerebral deposition of this highly amyloidogenic peptide.

Role of nonexercise activity thermogenesis in resistance to fat gain in humans

Humans show considerable interindividual variation in susceptibility to weight gain in response to overeating. The physiological basis of this variation was investigated by measuring changes in energy storage and expenditure in 16 nonobese volunteers who were fed 1000 kilocalories per day in excess of weight-maintenance requirements for 8 weeks. Two-thirds of the increases in total daily energy expenditure was due to increased nonexercise activity thermogenesis (NEAT), which is associated with fidgeting, maintenance of posture, and other physical activities of daily life. Changes in NEAT accounted for the 10-fold differences in fat storage that occurred and directly predicted resistance to fat gain with overfeeding (correlation coefficient = 0.77, probability < 0.001). These results suggest that as humans overeat, activation of NEAT dissipates excess energy to preserve leanness and that failure to activate NEAT may result in ready fat gain.

Influence of body fat distribution on free fatty acid metabolism in obesity

In order to determine whether differences in body fat distribution result in specific abnormalities of free fatty acid (FFA) metabolism, palmitate turnover, a measure of systemic adipose tissue lipolysis, was measured in 10 women with upper body obesity, 9 women with lower body obesity, and 8 nonobese women under overnight postabsorptive (basal), epinephrine stimulated and insulin suppressed conditions.

RESULTS

Upper body obese women had greater (P less than 0.005) basal palmitate turnover than lower body obese or nonobese women (2.8 +/- 0.2 vs. 2.1 +/- 0.2 vs. 1.8 +/- 0.2 mumol.kg lean body mass (LBM)-1.min-1, respectively), but a reduced (P less than 0.05) net lipolytic response to epinephrine (59 +/- 7 vs. 79 +/- 5 vs. 81 +/- 7 mumol palmitate/kg LBM, respectively). Both types of obesity were associated with impaired suppression of FFA turnover in response to euglycemic hyperinsulinemia compared to nonobese women (P less than 0.005). These specific differences in FFA metabolism may reflect adipocyte heterogeneity, which may in turn affect the metabolic aberrations associated with different types of obesity. These findings emphasize the need to characterize obese subjects before studies.

Leptin acts on human marrow stromal cells to enhance differentiation to osteoblasts and to inhibit differentiation to adipocytes

Both bone mass and serum leptin levels are increased in obesity. Because osteoblasts and adipocytes arise from a common precursor in bone marrow, we assessed the effects of human recombinant leptin on a conditionally immortalized human marrow stromal cell line, hMS2-12, with the potential to differentiate to either the osteoblast or adipocyte phenotypes. By RT-PCR and Western immunoblot analysis, the hMS2-12 cells expressed messenger RNA (mRNA) and protein for the leptin receptor. Leptin did not affect hMS2-12 cell proliferation, but resulted in dose- and time-dependent increases in mRNA and protein levels of alkaline phosphatase, type I collagen, and osteocalcin, and in a 59% increase in mineralized matrix. Leptin increased mRNA levels of lipoprotein lipase at 3 days, but decreased mRNA levels of adipsin and leptin at 9 days and decreased lipid droplet formation by 50%. Leptin did not affect the expression of Cbfa1 or peroxisome proliferator-activated receptor-gamma2, transcription factors involved in commitment to the osteoblast and adipocyte pathways, respectively. Thus, leptin acts on human marrow stromal cells to enhance osteoblast differentiation and to inhibit adipocyte differentiation. Our data support the hypothesis that leptin is a previously unrecognized, physiological regulator of these two differentiation pathways, acting primarily on maturation of stromal cells into both lineages.

Quantitation of blood-brain barrier defect by magnetic resonance imaging and gadolinium-DTPA in patients with multiple sclerosis and brain tumors

In this study quantitation of the degree of deficiency of the blood-brain barrier (BBB) in patients with multiple sclerosis or brain tumors, by using MRI, is shown to be possible. As a measure of permeability of the BBB to Gadolinium-DTPA (Gd-DTPA) the flux per unit of distribution volume per unit of brain mass was used. This quantity was found by introducing the longitudinal relaxation rate (R1) as a measure of concentration of Gd-DTPA in the brain tissue in the mathematical model for the transcapillary transport over the BBB. High accordance between the observed data points and the model was found, and the results were comparable to results obtained from similar studies using positron emission tomography. The improved possibility of quantitating the defect of the BBB by MRI may give new information about pathogenesis or etiology, and leads to improved methods in monitoring the efficacy of treatments in intracranial diseases.

Quantification of liver fat using magnetic resonance spectroscopy

Localized proton MR spectroscopy using stimulated echoes was used to quantify the liver fat concentration in patients with various degrees of fatty liver due to alcohol abuse. Ten patients underwent a liver biopsy followed by chemical triglyceride estimation of the fatty content. A statistically significant correlation was found between the fat concentration measured in the liver biopsies, and the concentration calculated from the spectroscopic experiments (r = 0.9, p < .001). Quantitative assessment of liver fat concentrations using localized spectroscopy is superior to methods based on differences in relaxation times, and can be used to estimate the fat concentration over the full range of fat content in contrast to the spectroscopic imaging methods. Localized spectroscopy may replace liver biopsy in the diagnosis of diffuse fatty infiltrations, and can be used for follow-up, due to its noninvasive nature.

Measurement of abdominal and visceral fat with computed tomography and dual-energy x-ray absorptiometry

These studies were undertaken to compare dual-energy x-ray absorptiometry (DXA) and computed tomography (CT) measurements of abdominal fat and to determine whether anthropometry could be combined with DXA to predict intraabdominal (visceral) fat mass in humans. Twenty-one volunteers underwent abdominal CT scans, DXA, and anthropometry. DXA- and CT-measured total abdominal fat were similar (8448 +/- 5005 and 8066 +/- 5354 mL, respectively; NS) and were highly correlated (r = 0.985, P < 0.001). The combination of anthropometry and DXA was a suboptimal predictor of CT-measured intraabdominal fat (r = 0.61, P < 0.05); however, the combination of a single CT slice (to assess the ratio of intraabdominal to total abdominal adipose tissue) and DXA-measured abdominal fat was an excellent predictor of CT-measured intraabdominal fat (r = 0.98, P < 0.001). We conclude that a single-slice CT scan (or other imaging technique) with or without DXA is required for accurate predictions of intraabdominal fat.

Energy expenditure of nonexercise activity

BACKGROUND

We found recently that changes in nonexercise activity thermogenesis (NEAT) mediate resistance to weight gain with overfeeding in sedentary adults. A potentially important, yet seldom investigated, component of NEAT is the energy expenditure of fidgeting-like activities.

OBJECTIVE

Our goal was to measure changes in energy expenditure with fidgeting-like activities.

DESIGN

Energy expenditure was measured in 24 subjects (17 women and 7 men x+/- SD body weight: 76 +/- 21 kg) while recumbent at rest, sitting motionless, standing motionless, partaking of self-selected fidgeting-like movements while seated and while standing, and walking on a treadmill at 1.6, 3.2, and 4.8 km/h (1, 2, and 3 mph). Measurements were performed by using a high-precision, indirect calorimeter connected to the subject via a transparent, lightweight facemask that enabled almost unrestricted movement.

RESULTS

Compared with metabolic rate in the supine position (5.4 +/- 1.5 kJ/min), energy expenditure increased while sitting motionless by 4 +/- 6%, while fidgeting while seated by 54 +/- 29% (P: < 0.0001), while standing motionless by 13 +/- 8% (P: < 0.0001), while fidgeting while standing by 94 +/- 38% (P: < 0.0001), while walking at 1.6 km/h by 154 +/- 38% (P: < 0.0001), while walking at 3.2 km/h by 202 +/- 45% (P: < 0.0001), and while walking at 4.8 km/h by 292 +/- 81% (P: < 0.0001). There was a significant, positive correlation between changes in energy expenditure and body weight for fidgeting-like activities while standing (r = 0.43, P: = 0.02) but not while seated.

CONCLUSIONS

There is marked variance between subjects in the energy expenditure associated with self-selected fidgeting-like activities. The thermogenic potential of fidgeting-like and low-grade activities is sufficiently great to substantively contribute to energy balance.

Effects of body fat distribution on regional lipolysis in obesity

To determine the contribution of the major body fat depots to systemic free fatty acid (FFA) availability, palmitate ([1-14C]-palmitate) release was measured from leg (lower body) and non-leg (upper body) fat in eight upper body obese (UB Ob), six lower body obese (LB Ob), and six nonobese (Non Ob) age-matched premenopausal women in the overnight postabsorptive state. Splanchnic palmitate release was determined in 16 of these subjects.

RESULTS

total palmitate release was greater in UB Ob (P less than 0.005) than LB Ob or Non Ob women (161 +/- 16 vs. 111 +/- 9 vs. 92 +/- 9 mumol/min, respectively). Despite increased leg fat mass in obese women, leg palmitate release was similar in each group. Therefore, leg fat palmitate release was greater in Non Ob women than LB Ob (P less than 0.01) or UB Ob (P = 0.06) women (3.7 +/- 0.3 vs. 2.4 +/- 0.2 vs. 2.7 +/- 0.2 mumol.kg fat-1.min-1, respectively). Upper body fat palmitate release was less (P less than 0.01) in LB Ob than Non Ob or UB Ob women (3.0 +/- 0.4 vs. 5.0 +/- 0.3 vs. 4.9 +/- 0.4 mumol.kg fat-1.min-1, respectively). Splanchnic palmitate release accounted for 20-32% of upper body fat palmitate release in each group (P = NS between groups). Leg fat palmitate release was significantly less than upper body fat palmitate release. We conclude that the major difference in resting FFA metabolism between UB Ob and LB Ob women is the ability of the later to down-regulate upper body fat lipolysis to maintain normal FFA availability.

Body-composition changes in patients who gain weight while receiving megestrol acetate

PURPOSE

Randomized placebo-controlled clinical trials have now established that megestrol acetate causes appetite stimulation and weight gain in patients with anorexia and/or cachexia. There is a paucity of available data to delineate the substance of this increased weight.

PATIENTS AND METHODS

Using dual-energy x-ray absorptiometry and tritiated body water methodologies, we performed body-composition measurements in 12 patients with advanced cancer before the institution of oral megestrol acetate (800 mg/d) and at subsequent 2-month intervals.

RESULTS

Seven of the 12 patients gained weight (2.1 to 16.5 kg) and had repeat body-composition measurements performed at the time of maximum weight gain. The vast majority of the gained weight was clearly from an increase in adipose tissue, while there was a suggestion that an increase in body fluid was responsible for a minority of the weight gain.

CONCLUSION

Megestrol acetate-induced weight gain is primarily the result of an increase in body mass.

Regional postprandial fatty acid metabolism in different obesity phenotypes

To examine if postprandial splanchnic/hepatic free fatty acid (FFA) delivery is increased in upper-body (UB) obesity, and to determine the adipose tissue depots responsible for the greater postprandial FFA availability, we measured systemic and regional uptake and release of FFAs ([1-(14)C]palmitate) before and during a 5-h frequent-feeding mixed meal in eight UB and eight lower-body (LB) obese women. Postabsorptive FFA flux and splanchnic FFA delivery were not different in UB and LB obese women; however, postprandial FFA concentrations (257 +/- 45 vs. 81 +/- 12 micromol/l, P < 0.0001), FFA flux (8.5 +/- 1.2 vs. 3.9 +/- 0.8 micromol x kg(-1) fat-free mass x min(-1), P < 0.0001), splanchnic FFA delivery (275 +/- 45 vs. 88 +/- 24 micromol/min, respectively, P < 0.005), and estimated hepatic FFA delivery were greater in UB than LB obese women. Nonsplanchnic UB adipose tissue FFA release was greater in UB than in LB obese women (276 +/- 71 vs. 97 +/- 37 micromol/min, respectively, P < 0.05) and accounted for the greater postprandial FFA availability in UB obesity. Postprandial leg glucose uptake was less in UB than in LB obese women (8.4 +/- 5.1 vs. 22.9 +/- 2.6 micromol x kg(-1) leg fat-free mass x min(-1), P < 0.05). We conclude that the elevated postprandial FFA release observed in UB obese women originates from the nonsplanchnic UB fat, not visceral fat. These results suggest that visceral fat may be a marker for, but not the source of, excess postprandial FFAs in obesity.

Neglect-like symptoms in complex regional pain syndrome: results of a self-administered survey

Reflex sympathetic dystrophy (RSD), recently reclassified as a complex regional pain syndrome, type I (CRPS-I), is best known for its disabling sensory symptoms, including pain, allodynia, and abnormal skin temperature. Yet, motor dysfunction is common in CRPS and can result in major disability. In addition to weakness of the involved limb, CRPS patients may develop symptoms akin to a neurological neglect-like syndrome, whereby the limb may feel foreign ("cognitive neglect") and directed mental and visual attention is needed to move the limb ("motor neglect"). Members of the patient support group, the Reflex Sympathetic Dystrophy Syndrome Association (RSDSA), were mailed a questionnaire inserted in their newsletter which inquired about the presence of these neglect-like symptoms; in addition, a separate medical history questionnaire was included to assess adequate documentation for the diagnosis of CRPS. A total of 242 patients returned the questionnaire but only 224 of the questionnaires were analyzed; 15 were excluded due to inadequate documentation of CRPS and 3 were excluded due to non-limb involvement. Eighty-four percent (84%) of these respondents endorsed the presence of at least one neglect symptom and 47% indicated they had both "cognitive" and "motor" neglect symptoms. Of interest, approximately 33% of respondents spontaneously wrote comments regarding the significant disability due to these neglect symptoms and the difficulty explaining these unusual symptoms to their health care providers and family. This patient survey confirms the presence of neglect-like symptoms in a subset of CRPS patients. Neglect-like symptoms need to be addressed and validated by health care providers.

Insulin regulation of lipolysis in nondiabetic and IDDM subjects

To determine whether insulin regulation of lipolysis is abnormal in subjects with poorly controlled insulin-dependent diabetes mellitus (IDDM), free-fatty acid flux ([1-14C]palmitate) was measured under conditions ranging from complete insulin withdrawal to hyperinsulinemia. Seven nondiabetic and seven IDDM subjects were studied with the pancreatic clamp technique to control plasma insulin, growth hormone, and glucagon concentrations at the desired levels. Preliminary studies were performed to validate the experimental design. The palmitate flux response to insulin withdrawal (2.5 +/- 0.2 vs. 2.5 +/- 0.2 mumol.kg-1.min-1) and maximally antilipolytic insulin concentrations (0.17 +/- 0.02 vs. 0.23 +/- 0.03 mumol.kg-1.min-1) were not different in nondiabetic and IDDM subjects, respectively. In contrast, IDDM subjects required significantly greater plasma free-insulin concentrations to result in equivalent suppression of palmitate flux compared with nondiabetic subjects. Lipolysis was found to be very sensitive to insulin in nondiabetic humans, with half-maximal suppression occurring at plasma free-insulin concentrations of approximately 12 pM (less than 2 microU/ml). We conclude that adipose tissue lipolysis is normally exquisitely sensitive to insulin and that sensitivity, but not responsiveness to insulin, is impaired in poorly controlled IDDM.

Cerebrospinal fluid A beta42 is increased early in sporadic Alzheimer's disease and declines with disease progression

All mutations known to cause familial Alzheimer's disease (AD) act by increasing the levels of soluble beta-amyloid peptide (A beta), especially the longer form, A beta42. However, in vivo elevation of soluble A beta in sporadic AD has so far not been shown. In the present study, we used enzyme-linked immunosorbent assays specific for A beta42 and A beta40 to investigate cerebrospinal fluid from sporadic AD at different stages of disease severity, to clarify the roles of A beta42 and A beta40 during disease progression. We also evaluated three other groups--one group of patients with mild cognitive impairment who were at risk of developing dementia, a cognitively intact, nondemented reference group diagnosed with depression, and a perfectly healthy control group. We found that A beta42 is strongly elevated in early and mid stages of AD, and thereafter it declines with disease progression. On the contrary, A beta40 levels were decreased in early and mid stages of AD. The group of cognitively impaired patients and the depression reference group had significantly higher levels of A beta42 than the healthy control group, implying that A beta42 is increased not only in AD, but in other central nervous system conditions as well. Our data also point out the importance of having thoroughly examined control material. The initial increase and subsequent decrease of A beta42 adds a new biochemical tool to follow the progression of AD and might be important in the monitoring of therapeutics.

Assessment of body composition with use of dual-energy x-ray absorptiometry: evaluation and comparison with other methods

Dual-energy x-ray absorptiometry (DEXA) is a relatively new method of assessing body composition in humans. In the current study, DEXA was analyzed for accuracy and precision by using both anthropomorphic phantoms and a combination of body composition techniques in humans. Satisfactory precision for measurement of total body fat, fat-free mass, and total body bone mineral could be demonstrated in vivo and in vitro. Predictions of lean body mass in humans on the basis of DEXA, total body water, and total body potassium were significantly different. The results of multiple regression analysis suggested that a component of total body water was related to body potassium, and another component was predicted by body fat. In addition, extracellular fluid volume, as measured by the bromide space technique, was significantly associated with both fat-free mass and fat mass as measured by DEXA. These findings have implications for the interpretation of body composition data in humans.

Obesity is associated with a decreased leptin transport across the blood-brain barrier in rats

Leptin exerts important effects on the regulation of food intake and energy expenditure by acting in the brain. Leptin is secreted by adipocytes into the bloodstream and must gain access to specific regions in the brain involved in regulating energy balance. Its action is mediated by interaction with a receptor that is mainly expressed in the hypothalamus but is also present in other cerebral areas. To reach these target areas, leptin most likely needs to cross the blood-brain barrier (BBB). In this study, we compared the permeability of leptin at the BBB in homozygous lean (FA/FA), high-fat diet-induced (HFD) obese rats (FA/FA rats on a highfat diet), and genetically obese fa/fa Zucker rats by quantifying the permeability coefficient surface area (PS) product after correction for the residual plasma volume (Vp) occupied by leptin in the vessel bed of different brain regions. The intravenous bolus injection technique was used in the cannulated brachial vein and artery using leptin radioiodinated with 2 isotopes of iodine (125I and 131I) to separately determine the PS and Vp values. The PS for leptin at the BBB in lean FA/FA rats ranged from 11.0 +/- 1.6 at the cortex to 14.8 +/- 1.4 x 10(-6) ml x g(-1) x ml(-1) at the posterior hypothalamus. The PS for leptin in HFD obese FA/FA and obese fa/fa rats ranged from 3.0- to 4.0-fold lower than in lean FA/FA rats. The Vp values were not significantly different among the 3 groups studied. SDS-PAGE analysis of the radioiodinated leptin after 60 min of uptake revealed intact protein in the 8 different brain regions. Plasma leptin levels were significantly higher in both obese rat groups compared with those in lean FA/FA rats. Leptin levels in cerebrospinal fluid were not significantly different among the 3 groups of rats. These findings strongly suggest that the leptin receptor (OB-R) in the BBB can be easily saturated. Saturation of the BBB OB-R in obese individuals would explain the defect in leptin transport into the brain described in this study.

Lipolysis during fasting. Decreased suppression by insulin and increased stimulation by epinephrine

These studies were designed to determine whether the insulin resistance of fasting extends to its antilipolytic effects and whether fasting enhances the lipolytic effects of adrenergic stimulation independent of changes in plasma hormone and substrate concentrations. Palmitate flux was determined isotopically ([1-14C]palmitate) before and during epinephrine infusion in normal volunteers after a 14-h (day 1) and an 84-h (day 4) fast. Using a pancreatic clamp, constant plasma hormone and glucose concentrations were achieved on both study days in seven subjects. Six subjects were infused with saline and served as controls. During the pancreatic clamp, palmitate flux was greater (P less than 0.01) on day 4 than day 1, despite similar plasma insulin, glucagon, growth hormone, cortisol, epinephrine, norepinephrine, and glucose concentrations. The lipolytic response to epinephrine was greater (P less than 0.05) on day 4 than day 1 in both groups of subjects. In conclusion, lipolysis during fasting is less completely suppressed by insulin and more readily stimulated by epinephrine.

Effects of type 2 diabetes on the ability of insulin and glucose to regulate splanchnic and muscle glucose metabolism: evidence for a defect in hepatic glucokinase activity

Insulin-induced stimulation of muscle glucose uptake (MGU) is impaired in people with type 2 diabetes. To determine whether insulin-induced stimulation of splanchnic glucose uptake (SGU) is also impaired, we simultaneously measured leg glucose uptake (LGU) and SGU in 14 nondiabetic subjects and 16 subjects with type 2 diabetes using a combined organ catheterization-tracer infusion technique. Glucose was clamped at approximately 9.3 mmol/l, while insulin concentrations were maintained at approximately 72 pmol/l (low) and approximately 150 pmol/l (high) for 3 h each. Endogenous hormone secretion was inhibited with somatostatin. Total body glucose disappearance was lower (P < 0.01) and glucose production higher (P < 0.01) during both insulin infusions in the diabetic compared with the nondiabetic subjects, indicating insulin resistance. Splanchnic glucose production was higher (P < 0.05) in the diabetic subjects during the low but not the high insulin infusion. SGU was slightly lower in the diabetic than in the nondiabetic subjects during the low insulin infusion and 50-60% lower (P < 0.05) during the high insulin infusion. LGU (P < 0.001), but not SGU, was inversely correlated with the degree of visceral adiposity. The contribution of the indirect pathway to hepatic glycogen synthesis did not differ in the diabetic and nondiabetic subjects. In contrast, both flux through the UDP-glucose pool (P < 0.05) and the contribution of the direct pathway to glycogen synthesis (P < 0.01) were lower in the diabetic than in the nondiabetic subjects, indicating decreased uptake and/or phosphorylation of extracellular glucose. On the other hand, glycogenolysis was equally suppressed in both groups. In summary, type 2 diabetes impairs the ability of insulin to stimulate both MGU and SGU. The defect appears to reside at a proximal (e.g., glucokinase) metabolic step and is not related to the degree of visceral adiposity. These data suggest that impaired hepatic glucose uptake as well as MGU contribute to hyperglycemia in people with type 2 diabetes.

Localization of leptin receptor in the human brain

Leptin (OB protein), the product of the adipose-specific ob gene, exerts important effects in the regulation of food intake and energy expenditure. Based upon results from animal studies, several groups have suggested that this action may be exerted in the brain, specifically in the hypothalamic region. However, to date, the localization of the OB-R in the human brain has not been described. One aim of this study was to contribute to a better understanding of the role that the central nervous system plays in the pathogenesis of obesity in humans. A first stage was to determine the OB-R expression in the human brain by means of immunohistochemistry and Western blotting. Several brain regions from 17 lean, 14 obese, and 4 diabetic (NIDDM) subjects, obtained from archival autopsy material, were sampled. Brain samples from neocortex, hypothalamus, medualla, limbic system, pineal and cerebellum were routinely processed in paraffin and analyzed with the avidin-biotin immunoperoxidase and diaminobenzidine detection method. Western blotting (WB) analysis was done on fresh brain tissue from an obese patient. Specific OB-R immunoreactivity was localized in the choroid plexus epithelium, ependymal lining, and neurons of the hypothalamic nuclei (arcuate, suprachiasmatic, mamillary, paraventricular, dorsomedial, supraoptic and posterior), nucleus basalis of Meynert, inferior olivary nuclei and cerebellar Purkinje cells. No differences in OB-R immunoreactivity were found among the three groups examined. WB analysis yielded 97- and 125-kD bands in the hypothalamus and cerebellum. In summary, this paper presents the first evidence to indicate the specific localization of the OB-R in the brain of lean, obese and NIDDM subjects.

Gender differences in regional fatty acid metabolism before and after meal ingestion

These studies were conducted to determine whether men and women differ with regards to their overnight postabsorptive (basal) and postprandial fatty acid kinetics. Systemic oleate turnover ([9,10(3)H]oleate) was measured before and after the consumption of a mixed meal. Leg and splanchnic free fatty acid (FFA) uptake and release were measured, allowing the calculation of upper-body subcutaneous FFA release.

RESULTS

basal oleate flux was virtually identical in men and women (3.0 +/- 3 versus 2.9 +/- 0.4 mumol.kg FFM-1.min-1), however, oleate Ra suppressed more in women than in men following meal ingestion (0.5 +/- 0.1 versus 0.8 +/- 0.1 mumol.kg FFM-1.min-1, P < 0.05). The fractional contribution of basal, regional FFA release to total FFA flux was not significantly different between men and women. In contrast, oleate release by upper-body subcutaneous adipose tissue was significantly greater (30 +/- 5 vs 8 +/- 3 mumol/min, respectively, P < 0.01) in men than in women during the meal nadir of FFA flux, whereas splanchnic oleate release was a greater percentage (39 +/- 7% vs 20 +/- 3%, respectively, P < 0.05) of nadir oleate Ra in women than in men. Thus, normal weight men and women differ significantly in the postprandial regulation of adipose tissue lipolysis in that men's upper-body subcutaneous adipose tissue is more resistant to the antilipolytic effects of meal ingestion. Differential regulation of regional adipose tissue lipolysis could contribute to the gender based differences in body fat distribution.

Measuring leg muscle and fat mass in humans: comparison of CT and dual-energy X-ray absorptiometry

Dual-energy X-ray absorptiometry (DEXA) is reported to be inferior to computed tomography (CT) to measure changes in appendicular soft tissue composition. We compared CT- and DEXA-measured thigh muscle and fat mass to evaluate the random and systematic discrepancies between these two methods. Thigh skeletal muscle area (single-slice CT) was suboptimally (r(2) = 0.74, P < 0.0001) related to DEXA-measured thigh fat-free mass (FFM). In contrast, thigh muscle and adipose tissue volumes (multislice CT) were highly related to DEXA-measured thigh FFM and fat (both r(2) = 0.96, P < 0.0001). DEXA-measured leg fat was significantly less than multislice-CT-measured leg adipose tissue volume, whereas multislice-CT-measured leg muscle mass was less (P < 0.0001) than DEXA-measured leg FFM. The systematic discrepancies between the two approaches were consistent with the 10-15% nonfat components of adipose tissue. In conclusion, CT and DEXA measures of appendicular soft tissue are highly related. Systematic differences between DEXA and CT likely relate to the underlying principles of the techniques.

Type 2 diabetes impairs splanchnic uptake of glucose but does not alter intestinal glucose absorption during enteral glucose feeding: additional evidence for a defect in hepatic glucokinase activity

We have previously reported that splanchnic glucose uptake, hepatic glycogen synthesis, and hepatic glucokinase activity are decreased in people with type 2 diabetes during intravenous glucose infusion. To determine whether these defects are also present during more physiological enteral glucose administration, we studied 11 diabetic and 14 nondiabetic volunteers using a combined organ catheterization-tracer infusion technique. Glucose was infused into the duodenum at a rate of 22 micromol. kg(-1). min(-1) while supplemental glucose was given intravenously to clamp glucose at approximately 10 mmol/l in both groups. Endogenous hormone secretion was inhibited with somatostatin, and insulin was infused to maintain plasma concentrations at approximately 300 pmol/l (i.e., twofold higher than our previous experiments). Total body glucose disappearance, splanchnic, and leg glucose extractions were markedly lower (P < 0.01) in the diabetic subjects than in the nondiabetic subjects. UDP-glucose flux, a measure of glycogen synthesis, was approximately 35% lower (P < 0.02) in the diabetic subjects than in the nondiabetic subjects. This was entirely accounted for by a decrease (P < 0.01) in the contribution of extracellular glucose because the contribution of the indirect pathway to hepatic glycogen synthesis was similar between groups. Neither endogenous and splanchnic glucose productions nor rates of appearance of the intraduodenally infused glucose in the portal vein differed between groups. In summary, both muscle and splanchnic glucose uptake are impaired in type 2 diabetes during enteral glucose administration. The defect in splanchnic glucose uptake appears to be due to decreased uptake of extracellular glucose, implying decreased glucokinase activity. Thus, abnormal hepatic and muscle (but not gut) glucose metabolism are likely to contribute to postprandial hyperglycemia in people with type 2 diabetes.