Dust emission source characterization for visibility hazard assessment on Lordsburg Playa in Southwestern New Mexico, USA.

In drylands around the world, ephemeral lakes (playas) are common. Dry, wind-erodible playa sediments are potent local and regional sources of dust and PM10 (airborne particles with diameters less than 10 µm). Dust clouds often cause sudden and/or prolonged loss of visibility to travelers on downwind roadways. Lordsburg Playa, in southwestern New Mexico, USA is bisected by Interstate Highway 10. Dust storms emanating from the playa have been responsible for numerous visibility-related road closures (including 39 road closures between 2012 and 2019) causing major economic losses, in addition to well over a hundred dust-related vehicle crashes causing at least 41 lost lives in the last 53 years. In order to improve understanding of the surfaces responsible for the dust emissions, we investigated the critical wind friction velocity thresholds and the dust emissivities of surfaces representing areas typical of Lordsburg Playa's stream deltas, shorelines, and ephemerally flooded lakebed using a Portable In-Situ Wind ERosion Laboratory (PI-SWERL). Mean threshold friction velocities for PM10 entrainment ranged from less than 0.30 m s- 1 for areas in the delta and shoreline to greater than 0.55 m s- 1 for ephemerally flooded areas of the lakebed. Similarly, we quantified mean PM10 vertical flux rates ranging from less than 500 µg m- 2 s- 1 for ephemerally flooded areas of lakebed to nearly 25,000 µg m- 2 s- 1 for disturbed delta surfaces. The unlimited PM10 supply of the relatively coarse sediments along the western shoreline is problematic and indicates that this may be the source area for longer-term visibility reducing dust events and should be a focus area for dust mitigation efforts.

Evidence for regional aeolian transport of freshwater micrometazoans in arid regions.

While separated by large expanses of dry terrain unsuitable for aquatic biota, aridland waters possess high biodiversity. How aquatic micrometazoans disperse to, and colonize, these isolated ephemeral habitats are not well understood. We used a multi-faceted approach including wind tunnel and rehydration experiments, and next-generation sequencing to assess potential movement of diapausing propagules of aquatic invertebrates by anemochory across regional scales (102-105 km). Wind tunnel experiments using dry playa sediments with added micrometazoan propagules demonstrated that after entrainment by saltation and downwind transport were subsequently recoverable as viable animals when rehydrated. Further, rehydration of fallen natural dust yielded micrometazoans, including rotifers, gastrotrichs, microcrustaceans, and nematodes. Using conserved DNA primers, we identified >3,300 eukaryotic Operational Taxonomic Units (excluding fungi) in the dust including some taxa found in rehydration experiments. Thus, we provide strong evidence that anemochory can disperse micrometazoans among isolated, ephemeral ecosystems in North American deserts and likely elsewhere.

Striking differences in estimates of infant adiposity by new and old DXA software, PEAPOD and skin-folds at 2 weeks and 1 year of life.

BACKGROUND: Infant adiposity better predicts childhood obesity/metabolic risk than weight, but technical challenges fuel controversy over the accuracy of adiposity estimates. OBJECTIVE: We prospectively measured adiposity (%fat) in term newborns (NB) at 2 weeks (n = 41) and 1 year (n = 30). METHODS: %fat was measured by dual X-ray absorptiometry (DXA), PEAPOD and skin-folds (SF). DXAs were analyzed using Hologic Apex software 3.2(DXAv1) and a new version 5.5.2(DXAv2). RESULTS: NB %fat by DXAv2 was 55% higher than DXAv1 (14.2% vs. 9.1%), 45% higher than SF (9.8%), and 36% higher than PEAPOD (10.4%). Among NB, Pearson correlations were 0.73-0.89, but agreement (intra-class correlations) poor between DXAv2 and DXAv1 (0.527), SF (0.354) and PEAPOD (0.618). At 1 year, %fat by DXAv2 was 51% higher than DXAv1 (33.6% vs. 22.4%), and twice as high compared with SF (14.6%). Agreement was poor between DXAv2 and DXAv1 (0.204), and SF (0.038). The absolute increase in %fat from 2 weeks to 1 year was 19.7% (DXAv2), 13.6% (DXAv1) and only 4.8% by SF. CONCLUSION: Analysis of the same DXA scans using new software yielded considerably higher adiposity estimates at birth and 1 year compared with the previous version. Using different modalities to assess body composition longitudinally is problematic. Standardization is gravely needed to determine how early life exposures affect childhood obesity/metabolic risk.

Timing of Estradiol Treatment After Menopause May Determine Benefit or Harm to Insulin Action.

CONTEXT: Type 2 diabetes (T2D) is reduced in postmenopausal women randomized to estrogen-based hormone therapy (HT) compared with placebo. Insulin sensitivity is a key determinant of T2D risk and overall cardiometabolic health, and studies indicate that estradiol (E2) directly impacts insulin action. OBJECTIVE: We hypothesized that the timing of E2 administration after menopause is an important determinant of its effect on insulin action. DESIGN: We performed a randomized, crossover, placebo-controlled study. PARTICIPANTS: Study participants were early postmenopausal (EPM; ≤ 6 years of final menses; n = 22) and late postmenopausal (LPM; ≥ 10 years since last menses; n = 24) women naive to HT. INTERVENTION: Study interventions included short-term (1 week) transdermal E2 and placebo. MAIN OUTCOMES AND MEASURES: The study's main outcome was insulin-mediated glucose disposal (glucose disposal rate [GDR]) via hyperinsulinemic-euglycemic clamp. RESULTS: Compared to EPM women, LPM women were older (mean ± SD; 63 ± 3 vs 56 ± 4 years, P < .05) and more years past menopause (12 ± 2 vs 3 ± 2 years, P < .05). Body mass index (24 ± 3 vs 25 ± 7 kg/m(2)) and fat mass (25 ± 7 vs 23 ± 6 kg) did not differ between groups, but fat-free mass (FFM) was lower in LPM women compared to EPM women (40 ± 4 vs 43 ± 5 kg, P < .05). Baseline GDR did not differ between groups (11.7 ± 2.8 vs 11.5 ± 2.9 mg/kg FFM/min). In support of our hypothesis, 1 week of E2 decreased GDR in LPM women compared to an increase in EPM women (+0.44 ± 1.7 vs - 0.76 ± 2.1 mg/kg FFM/min, P < .05). CONCLUSIONS: There was not an apparent decline in GDR with age or time since menopause per se. However, E2 action on GDR was dependent on time since menopause, such that there was an apparent benefit early (≤ 6 years) compared to harm later (≥ 10 years) in menopause. E2-mediated effects on insulin action may be one mechanism by which HT reduces the incidence of T2D in early postmenopausal women.

Adipose tissue insulin resistance in adolescents with and without type 2 diabetes.

BACKGROUND: The incidence of type 2 diabetes mellitus (T2D) is increasing in youth, yet little is known about the underlying pathophysiology. Decreased insulin suppression of lipolysis and elevated non-esterified free fatty acid (NEFA) concentrations are known to be associated with insulin resistance and T2D in adults, but less is known about the relationship in adolescents. OBJECTIVES: This study aimed to assess adipose tissue insulin resistance (IR; insulin suppression of lipolysis) and its metabolic correlates in lean, obese and T2D adolescents. METHODS: Forty-seven lean, obese and T2D youth underwent hyperinsulinaemic (80 mU*m(-2) *min(-1)) euglycaemic clamps. NEFAs were measured at baseline and during steady state. Insulin-mediated suppression of lipolysis (%NEFA suppression from baseline) was calculated, and metabolic risk factors were assessed by %NEFA suppression tertile. RESULTS: There was expected variability in %NEFA suppression within obese and T2D youth, but a subset had significantly reduced suppression of lipolysis. NEFA suppression tertile was significantly inversely associated with fasting triglycerides (P = 0.0001), log alanine aminotransferase (ALT; P = 0.02) and low-density lipoprotein cholesterol (P = 0.0002). CONCLUSIONS: Marked adipose tissue IR occurs in some obese and T2D adolescents, which may result in release of triglycerides into the circulation and liver deposition of fatty acids, as evidenced by higher ALT in poor NEFA suppressors.

Estrogen or raloxifene during postmenopausal weight loss: adiposity and cardiometabolic outcomes.

OBJECTIVE: Estrogen-based hormone therapy (HT) attenuates abdominal fat gain after menopause, but whether HT improves abdominal fat loss during weight loss is unknown. It was hypothesized that HT or a selective estrogen receptor modulator (raloxifene) would augment reductions in abdominal visceral fat during weight loss when compared to placebo, potentially increasing improvements in glucose tolerance and lipid profile. METHODS: Healthy postmenopausal women (n = 119; age 50-70 yr) underwent a 6-month weight-loss (primarily exercise) intervention with randomization to raloxifene (60 mg/d), HT (conjugated estrogens, 0.625 mg/d), or placebo. Outcomes were change in total and abdominal (visceral and subcutaneous) fat mass, lipid profile, and fasting and post-challenge glucose and insulin. RESULTS: Neither HT nor raloxifene augmented loss of total or abdominal fat mass during exercise-induced weight loss when compared with placebo. Weight loss-induced improvements in risk factors were similar among the three groups, except for a greater reduction in fasted glucose in the HT group (difference in change [95%CI] from placebo; -0.40 [-0.76, -0.05]) and greater reductions in LDL (-0.36 [-0.63, -0.09]) and increases in HDL (0.15 [0.07, 0.24]) in both treatment groups. CONCLUSIONS: Postmenopausal HT and raloxifene did not increase abdominal fat loss during weight loss, but did improve some cardiometabolic outcomes.

Pyrosequencing reveals bacteria carried in different wind-eroded sediments.

Little is known about the microbial communities carried in wind-eroded sediments from various soil types and land management systems. The novel technique of pyrosequencing promises to expand our understanding of the microbial diversity of soils and eroded sediments because it can sequence 10 to 100 times more DNA fragments than previous techniques, providing enhanced exploration into what microbes are being lost from soil due to wind erosion. Our study evaluated the bacterial diversity of two types of wind-eroded sediments collected from three different organic-rich soils in Michigan using a portable field wind tunnel. The wind-eroded sediments evaluated were a coarse sized fraction with 66% of particles >106 µm (coarse eroded sediment) and a finer eroded sediment with 72% of particles <106 µm. Our findings suggested that (i) bacteria carried in the coarser sediment and fine dust were effective fingerprints of the source soil, although their distribution may vary depending on the soil characteristics because certain bacteria may be more protected in soil surfaces than others; (ii) coarser wind-eroded sediment showed higher bacterial diversity than fine dust in two of the three soils evaluated; and (iii) certain bacteria were more predominant in fine dust (, , and ) than coarse sediment ( and ), revealing different locations and niches of bacteria in soil, which, depending on wind erosion processes, can have important implications on the soil sustainability and functioning. Infrared spectroscopy showed that wind erosion preferentially removes particular kinds of C from the soil that are lost via fine dust. Our study shows that eroded sediments remove the active labile organic soil particulates containing key microorganisms involved in soil biogeochemical processes, which can have a negative impact on the quality and functioning of the source soil.

Automatic Detection and Visualization of Qualitative Hemodynamic Characteristics in Cerebral Aneurysms.

Cerebral aneurysms are a pathological vessel dilatation that bear a high risk of rupture. For the understanding and evaluation of the risk of rupture, the analysis of hemodynamic information plays an important role. Besides quantitative hemodynamic information, also qualitative flow characteristics, e.g., the inflow jet and impingement zone are correlated with the risk of rupture. However, the assessment of these two characteristics is currently based on an interactive visual investigation of the flow field, obtained by computational fluid dynamics (CFD) or blood flow measurements. We present an automatic and robust detection as well as an expressive visualization of these characteristics. The detection can be used to support a comparison, e.g., of simulation results reflecting different treatment options. Our approach utilizes local streamline properties to formalize the inflow jet and impingement zone. We extract a characteristic seeding curve on the ostium, on which an inflow jet boundary contour is constructed. Based on this boundary contour we identify the impingement zone. Furthermore, we present several visualization techniques to depict both characteristics expressively. Thereby, we consider accuracy and robustness of the extracted characteristics, minimal visual clutter and occlusions. An evaluation with six domain experts confirms that our approach detects both hemodynamic characteristics reasonably.

Chemical constituents of fugitive dust.

Wind erosion selectively winnows the fine, most chemically concentrated portions of surface soils and results in the inter-regional transport of fugitive dust containing plant nutrients, trace elements and other soil-borne contaminants. We sampled and analyzed surface soils, sediments in transport over eroding fields, and attic dust from a small area of the Southern High Plains of Texas to characterize the physical nature and chemical constituents of these materials and to investigate techniques that would allow relatively rapid, low cost techniques for estimating the chemical constituents of fugitive dust from an eroding field. From chemical analyses of actively eroding sediments, it would appear that Ca is the only chemical species that is enriched more than others during the process of fugitive dust production. We found surface soil sieved to produce a sub-sample with particle diameters in the range of 53-74 microm to be a reasonably good surrogate for fugitive dust very near the source field, that sieved sub-samples with particle diameters <10 microm have a crustal enrichment factor of approximately 6, and that this factor, multiplied by the chemical contents of source soils, may be a reasonable estimator of fugitive PM(10) chemistry from the soils of interest. We also found that dust from tractor air cleaners provided a good surrogate for dust entrained by tillage and harvesting operations if the chemical species resulting from engine wear and exhaust were removed from the data set or scaled back to the average of enrichment factors noted for chemical species with no known anthropogenic sources. Chemical analyses of dust samples collected from attics approximately 4 km from the nearest source fields indicated that anthropogenic sources of several environmentally important nutrient and trace element species are much larger contributors, by up to nearly two orders of magnitude, to atmospheric loading and subsequent deposition than fugitive dust from eroding soils.

Wind-induced dust generation and transport mechanics on a bare agricultural field.

Strong atmospheric winds may cause wind erosion and dust emissions on bare, dry, erodible fields. Since these dust emissions may exceed particulate matter limits established by the United States Environmental Protection Agency, information on dust generation and transport mechanics is needed to determine the particulate hazard of dust sources. Measurements of climatic variables and airborne sediment mass and concentration were made during three strong wind events on a bare, fine sandy loam field in west Texas. This study clearly shows that dust flux estimates were very sensitive to dust concentration measurement height. PM10 flux values estimated between heights of 2 and 5m were 2-5 times those estimated between heights of 5 and 10 m. Tower placement in relation to the upwind unerodible boundary produced significant differences in dust flux that varied with storm intensity. During the most intense storm event, the PM10 flux between heights of 2 and 5m measured at the tower 200 m from the unerodible boundary was almost 2.5 times as that measured at the tower 100 m from the unerodible boundary. Vertical PM10 dust flux was closely related with horizontal sediment flux only when the winds came from the same direction during the entire duration of horizontal sediment flux measurements.

Lower-body adiposity and metabolic protection in postmenopausal women.

CONTEXT: It has been suggested that the propensity to store fat in the gluteal-femoral region may be cardioprotective. OBJECTIVE: The primary aim of this study was to test whether the favorable associations of leg fat with risk factors for cardiovascular disease persist after controlling for the highly unfavorable effects of abdominal (visceral or sc) adiposity in postmenopausal women. STUDY PARTICIPANTS: The study included 95 postmenopausal women [age, 60 +/- 8 yr (mean +/- SD)]. MAIN OUTCOMES: Whole-body and regional fat distribution was measured using dual-energy x-ray absorptiometry and abdominal computed tomography. Markers of insulin resistance and dyslipidemia were determined from oral glucose tolerance tests and fasted lipid and lipoprotein measurements, respectively. Primary outcomes were: fasting insulin (INS0), area under the insulin curve (INS(AUC)), product of the oral glucose tolerance test insulin and glucose AUC (INS(AUC) - GLU(AUC)), serum triglycerides (TG), and high-density lipoprotein (HDL) cholesterol. RESULTS: Controlling for trunk fat revealed a favorable effect of leg fat on INS0, INS(AUC), INS(AUC) x GLU(AUC), TG, and HDL. However, after controlling for either visceral or sc abdominal adiposity, TG was the only risk factor for which the favorable effect of leg fat persisted. CONCLUSIONS: The lack of an association between leg fat and most of the risk factors, after adjusting for abdominal visceral or sc fat, suggests an overriding deleterious influence of abdominal adiposity on cardiovascular risk. Nevertheless, our finding that regional adipose tissue depots have apparent independent and opposing effects on serum TG supports the need for further research into the physiological mechanisms governing these effects.

Protection of bone mass by estrogens and raloxifene during exercise-induced weight Loss.

The aim of this study was to determine whether estrogen and/or raloxifene help to conserve bone mineral density (BMD) during moderate weight loss. Postmenopausal women (n = 68) participated in a 6-month weight loss program that consisted primarily of supervised exercise training. Another 26 women were studied over 6 months of weight stability. All participants were randomized to three treatment arms: placebo, raloxifene (60 mg/d), or hormone therapy (HT; conjugated estrogens, 0.625 mg/d; trimonthly medroxyprogesterone acetate, 5 mg/d for 13 d, for women with a uterus). Changes in body weight (mean +/- se) averaged 0.8 +/- 0.5 kg in the weight-stable group and -4.1 +/- 0.4 kg in the weight loss group. Across all measured skeletal sites, average changes in BMD in weight stable women were -0.6 +/- 1.1% (n = 7), 0.9 +/- 0.6% (n = 9), and 3.0 +/- 0.7% (n = 10) in the placebo, raloxifene, and HT groups, respectively; comparable BMD changes in the weight loss groups were -1.5 +/- 0.5% (n = 22), -0.5 +/- 0.5% (n = 23), and 1.1 +/- 0.4% (n = 23). There were no significant interactions between weight loss and drug treatment on changes in BMD, but there were significant main effects of weight loss on lumbar spine (P = 0.022), total hip (P = 0.010), and trochanter BMD (P < 0.001). These findings suggest that weight loss, even when modest in magnitude and induced by exercise training, causes a reduction in BMD, particularly in women not taking raloxifene or HT. It is not known whether reductions in BMD of this magnitude increase the risk for osteoporotic fracture.

Intravenous estrogens increase insulin clearance and action in postmenopausal women.

To test the hypothesis that estrogens alter insulin action, we evaluated the effects of intravenous conjugated estrogens (CE) on insulin-stimulated steady-state glucose infusion rate (SSGIR) and suppression of plasma glycerol in postmenopausal women (mean +/- SD; 56 +/- 4 yr; n = 12) not using hormone replacement. SSGIR and glycerol were measured during a two-stage (8 and 40 mU. m-2. min-1) hyperinsulinemic euglycemic clamp on 2 days, with or without a 2.5-mg intravenous CE bolus. Serum estradiol concentrations were increased approximately 200% on the estrogen (EST) compared with the control (CON) days. Serum insulin was reduced (P < 0.01) during stage 2 of the clamp for EST (63.3 +/- 12.8 micro U/ml) vs. CON (78.2 +/- 15.8 micro U/ml). Mean SSGIR and plasma glycerol did not differ between CON and EST days. With adjustment for differences in insulin concentration between conditions, stage 2 glucose disposals were significantly higher (8.63 vs. 7.20 mg. kg-1. min-1) and plasma glycerol concentrations were significantly lower (29.4 vs. 35.0 micro mol/l) for EST vs. CON. Our findings suggest that acute CE administration increases insulin clearance and action in postmenopausal women.

Effects of estrogen replacement on metabolic factors that influence physical performance in female hypogonadism.

There is a lack of knowledge regarding the effects of estrogens on physical performance. This is related, in part, to the challenge of isolating the effects of estrogens from those of progestins, because levels of both hormones fluctuate across the menstrual cycle, both decline during the menopausal transition, and the administration oh hormones to hypogonadal women typically involves a combination of estrogens and progestins. Some research findings suggest that fluctuations in estrogen levels acutely influence factors that may affect physical performance, such as substrate utilization or maximal aerobic power, but solid evidence is lacking. The simple observation that hypogonadism is not uncommon among elite athletes in some sports suggests that estrogen deficiency does not have a major negative impact on athletic performance. However, chronic hypogonadism may ultimately lead to impaired performance by menas that are not necessarily obvious. For example, chronic estrogen deficiency has potent, deleterious effects on the skeleton that can increase risk for stress fracture and may limit the ability to sustain a high level of physical training. Estrogen deficiency also appears to promote fat accumulation and may accelerate the loss of fat-free mass, and both of these changes in body composition could impair physical performance. There is evidence that hormone replacement attenuates the negative effects of hypogonadism on body composition and bone density, and that effects are mediated primarily by estrogens rather than progestins. Further research is necessary to broaden the understanding of the role of the estrogens in physical performance.

Contributions of total and regional fat mass to risk for cardiovascular disease in older women.

The aim of this study was to determine whether trunk fat mass, measured by dual-energy X-ray absorptiometry (DEXA), is predictive of insulin resistance and dyslipidemia, independently of arm and leg fat mass, in postmenopausal women. Total and regional body composition was measured by DEXA in 166 healthy, postmenopausal women (66 +/- 4 yr). Four primary markers of insulin resistance and dyslipidemia were assessed: 1) area under the curve for the insulin (INS(AUC)) response to an oral glucose tolerance test (OGTT), 2) product of the OGTT glucose and insulin areas (INS(AUC)xGLU(AUC)), 3) serum triglycerides (TG), and 4) high-density lipoprotein (HDL)-cholesterol. Trunk fat mass was the strongest independent predictor of each of the primary dependent variables. In multivariate regression models, trunk fat mass was associated with unfavorable levels of INS(AUC), INS(AUC)xGLU(AUC), TG, and HDL-C, whereas leg fat mass was favorably associated with each of these variables. Thus trunk fat is a strong independent predictor of insulin resistance and dyslipidemia in postmenopausal women, whereas leg fat appears to confer protective effects against metabolic dysfunction.

Age-related decline in RMR in physically active men: relation to exercise volume and energy intake.

We tested the hypothesis that resting metabolic rate (RMR) declines with age in physically active men (endurance exercise > or =3 times/wk) and that this decline is related to weekly exercise volume (h/wk) and/or daily energy intake. Accordingly, we studied 137 healthy adult men who had been weight stable for > or =6 mo: 32 young [26 +/- 1 (SE) yr] and 34 older (62 +/- 1 yr) sedentary males (internal controls); and 39 young (27 +/- 1 yr) and 32 older (63 +/- 2 yr) physically active males (regular endurance exercise). RMR was measured by indirect calorimetry (ventilated hood system) after an overnight fast and approximately 24 h after exercise. Because RMR is related to fat-free mass (FFM; r = 0.76, P < 0.001, current study), FFM was covaried to adjust RMR (RMR(adj)). RMR(adj) was lower with age in both the sedentary (72.0 +/- 2.0 vs. 64.0 +/- 1.3 kcal/h, P < 0.01) and the physically active (76.6 +/- 1.1 vs. 67.9 +/- 1.2 kcal/h, P < 0.01) males. In the physically active men, RMR(adj) was related to both exercise volume (no. of h/wk, regardless of intensity; r = 0.56, P < 0.001) and estimated energy intake (r = 0.58, P < 0.001). Consistent with these relations, RMR(adj) was not significantly different in subgroups of young and older physically active men matched either for exercise volume (h/wk; n = 11 each) or estimated energy intake (kcal/day; n = 6 each). These results indicate that 1) RMR, per unit FFM, declines with age in highly physically active men; and 2) this decline is related to age-associated reductions in exercise volume and energy intake and does not occur in men who maintain exercise volume and/or energy intake at a level similar to that of young physically active men.

Waist circumference vs body mass index for prediction of disease risk in postmenopausal women.

OBJECTIVE: To test the sensitivity of waist circumference (central adiposity) as an index of disease risk in postmenopausal women. DESIGN: Retrospective analysis of postmenopausal women tested at Washington University School of Medicine. SUBJECTS: A total of 323 healthy postmenopausal (66+/-5 y; mean+/-s.d.) women not using any hormone replacement. MEASUREMENTS: Body composition, hyperinsulinemia (insulin area), triglycerides and HDL-cholesterol. RESULTS: Excess waist size had a stronger association with hyperinsulinemia and hypertriglyceridemia than body mass index (BMI; kg/m(2)) in otherwise healthy, postmenopausal women. After adjusting for BMI, a strong relation existed between waist circumference and insulin area, HDL-cholesterol and triglycerides (P<0.01). Conversely, after adjusting for waist circumference, no relation was apparent between BMI and the dependent variables of interest. The strength of the association between waist circumference and disease risk became most apparent when analyses were restricted to normal-weight women (BMI 24--28 kg/m(2)). When BMI was held constant, hyperinsulinemia and triglyceridemia increased dose-dependently with changes in waist size. CONCLUSION: Waist circumference, an easily obtained index of central adiposity, is a more sensitive measure of relative disease risk than is BMI in middle-aged and older women, particularly in normal-weight individuals.

Acute exercise effect on postabsorptive serum leptin.

We postulated that high circulating cortisol levels during intense exercise would lead to increased serum leptin concentrations. Young, lean men ate a small meal and then exercised on a cycle ergometer for 41 min or rested on a control day. Serum leptin concentration was 10% greater during exercise than in the control condition (P < 0.05). Directly after exercise, serum leptin dropped to approximately 10% less than the control level (P < 0.05) but had recovered to the nonexercised level after approximately 2 h of recovery. Rapid exercise effects on circulating leptin were related to changes in hemoconcentration rather than changes in leptin mass. When serum leptin was normalized to serum protein, leptin increased by 10% in the exercise condition compared with control by the end of recovery (P < 0.05). Although exercise increased serum cortisol concentration threefold, there was no relation between differences in cortisol and exercise vs. control differences in normalized leptin. The increased leptin mass after exercise may have been related to greater plasma glucose concentration during recovery after exercise compared with the control condition.

Effects of HRT and exercise training on insulin action, glucose tolerance, and body composition in older women.

The independent and combined effects of exercise training and hormone replacement therapy (HRT) on body composition, fat distribution, glucose tolerance, and insulin action were studied in postmenopausal women, aged 68 +/- 5 yr, assigned to control (n = 19), exercise (n = 18), HRT (n = 15), and exercise + HRT (n = 16) groups. The exercise consisted of 2 mo of flexibility exercises followed by 9 mo of endurance exercise. HRT was conjugated estrogens 0.625 mg/day and trimonthly medroxyprogesterone acetate 5 mg/day for 13 days. Total and regional body composition were measured by dual-energy X-ray absorptiometry. Serum glucose and insulin responses were measured during a 2-h oral glucose tolerance test. There were significant main effects of exercise on reductions in total and regional (trunk, arms, legs) fat mass, increase in leg fat-free mass, and improvements in glucose tolerance and insulin action. There were significant main effects of HRT on the reduction of total fat mass (HRT, -3.0 +/- 4.0 kg; no HRT, -1.3 +/- 2.6 kg), with a strong trend for reductions in trunk and leg fat mass (both P = 0.07). There was also a significant improvement in insulin action in response to HRT. These results suggest that there are independent and additive effects of exercise training and HRT on the reduction in fat mass and improvement in insulin action in postmenopausal women; the effect of HRT on insulin action may be mediated, in part, through changes in central adiposity.

Relation of leptin and insulin to adiposity-associated elevations in sympathetic activity with age in humans.

OBJECTIVE: To determine whether plasma leptin and insulin concentrations are related to adiposity-associated elevations in muscle sympathetic nerve activity (MSNA) with age in healthy adult humans. DESIGN: Cross-sectional investigation of young and older adult men. SUBJECTS: Thirty healthy adult men, 16 young (25+/-1 y, mean+/-s.e.) and 14 older (61+/-1 y). MEASUREMENTS/RESULTS: The older men had higher (P<0.05) levels of body mass, BMI, total fat mass and truncal fat mass (dual energy X-ray absorptiometry) than the young men. MSNA burst frequency (microneurography) was approximately 75% higher in the older men (P<0.001). Plasma leptin concentrations were approximately 150% higher (P<0.01), whereas plasma insulin concentrations were approximately 70% higher (P<0.05) in the older subjects. MSNA was related to both total (r=0.51, P<0.01) and truncal (r=0.56, P<0.01) fat mass. Plasma leptin concentrations were related to total and truncal fat mass (both r=0.83, P<0.001), and to MSNA (r=0.49, P<0.01). Plasma insulin concentrations were related to MSNA (r=0.38, P<0.05). We used partial correlation analyses to assess whether leptin and/or insulin are potential contributors to the relation between body fat and MSNA. Adjusting for the effects of plasma leptin, but not insulin, concentrations eliminated the significant relations between MSNA and total and truncal fat mass. CONCLUSION: Our results: (1) demonstrate a positive relation between MSNA and plasma leptin concentrations in young and older healthy men; and (2) support the concept that circulating leptin concentrations may act as a humoral signal contributing to adiposity-associated elevations in MSNA with age in adult humans.