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A new aluminosilicate zeolite, denoted EMM-37, with a 3D small pore channel system, has been synthesized using a diquaternary ammonium molecule as the structure directing agent (SDA) and metakaolin as the aluminum source. The structures of both as-made and calcined forms of EMM-37 were solved and refined using continuous rotation electron diffraction (cRED) data. cRED is a powerful method for the collection of 3D electron diffraction data from submicron- and nanosized crystals, which allows for successful solution and refinement of complex structures in symmetry as low as P1.

A new catalytically active zeolite, designated EMM-17 (ExxonMobil Material-17), with a three-dimensional (3D) 11 × 10 × 10-ring topology has been discovered from high throughput experiments while evaluating a family of new organic structure directing agents (OSDAs), 1-alkyl-4-(pyrrolidin-1-yl)pyridin-1-ium hydroxide. The framework structure was determined by model building techniques and confirmed by diffraction calculations. The EMM-17 structure is a random intergrowth of two polymorphs which have a 3D arrangement of intersecting 11 × 10 × 10-ring pores. EMM-17 is stable to calcination to remove the OSDA and can be reproducibly synthesized in the presence of fluoride using common, inexpensive reagents over a wide Si/Al range from 15 to infinity, enabling the catalyst acidity to be tailored to almost any petrochemical application. Unlike OSDAs for many new zeolite structures, the OSDAs for EMM-17 are prepared in one simple alkylation step, making EMM-17 an easy to prepare, highly accessible, catalytically active zeolite. Zeolites containing odd numbered channel sizes are rare, and this is the first confirmed example of a 3D 11-ring aluminosilicate zeolite with a pore size in between those of the commercially important 10- and 12-ring zeolites such as ZSM-5 and Zeolite-Y, respectively. Catalysts prepared from EMM-17 exhibit significantly higher activity for catalytic isomerization with no loss in selectivity than current state of the art catalysts. Catalytic isomerization of linear to branched alkanes is a critical component of commercial dewaxing, allowing for the improvement of cold flow properties of hydrocarbon fuels and lubricants through selective hydroisomerization of normal paraffins.

A new borosilicate zeolite |N2H36C16|[Si22B2O48]·H2O, denoted as EMM-26, has been synthesized by employing a linear dicationic organic structure directing agent 1,6-bis(N-methylpyrrolidinium)hexane (OSDA). EMM-26 has a novel zeolite framework and contains two-dimensional (2D) intersecting 10 × 10-ring channels. Its structure was solved from sub-micrometer sized crystals using rotation electron diffraction (RED) and refined against both the RED and synchrotron powder diffraction data. We have shown for the first time that RED data alone can be used to accurately determine zeolite structures. The OSDAs can be removed from the framework generating permanent pores. EMM-26 shows good CO2 uptake and CO2/CH4 selectivity.

The aluminosilicate zeolite ZSM-43 (where ZSM = Zeolite Socony Mobil) was first synthesized more than 3 decades ago, but its chemical structure remained unsolved because of its poor crystallinity and small crystal size. Here we present optimization of the ZSM-43 synthesis using a high-throughput approach and subsequent structure determination by the combination of electron crystallographic methods and powder X-ray diffraction. The synthesis required the use of a combination of both inorganic (Cs+ and K+) and organic (choline) structure-directing agents. High-throughput synthesis enabled a screening of the synthesis conditions, which made it possible to optimize the synthesis, despite its complexity, in order to obtain a material with significantly improved crystallinity. When both rotation electron diffraction and high-resolution transmission electron microscopy imaging techniques are applied, the structure of ZSM-43 could be determined. The structure of ZSM-43 is a new zeolite framework type and possesse...

Stable, multidimensional, and extra-large pore zeolites are desirable by industry for catalysis and separation of bulky molecules. Here we report EMM-23, the first stable, three-dimensional extra-large pore aluminosilicate zeolite. The structure of EMM-23 was determined from submicron-sized crystals by combining electron crystallography, solid-state nuclear magnetic resonance (NMR), and powder X-ray diffraction. The framework contains highly unusual trilobe-shaped pores that are bound by 21-24 tetrahedral atoms. These extra-large pores are intersected perpendicularly by a two-dimensional 10-ring channel system. Unlike most ideal zeolite frameworks that have tetrahedral sites with four next-nearest tetrahedral neighbors (Q(4) species), this unusual zeolite possesses a high density of Q(2) and Q(3) silicon species. It is the first zeolite prepared directly with Q(2) species that are intrinsic to the framework. EMM-23 is stable after calcination at 540 °C. The formation of this highly interrupted structure is facilitated by the high density of extra framework positive charge introduced by the dicationic structure directing agent.

Controlling preparation variables in supported cobalt Fischer–Tropsch catalysts has a dramatic effect on the dispersion and distribution of cobalt, and determines how active and selective the resulting catalyst will be. We detail specific examples of catalyst synthesis strategies for modifying interactions between the support and the cobalt precursor, promoting reduction, stabilizing catalysts to high-temperature treatments, minimizing deleterious support metal interactions, and controlling the distribution of cobalt on large support particles. It is important to optimize the support and precursor interaction strength, so that it is strong enough to obtain good dispersion but not too strong to prevent low temperature reduction. We show examples in which formation of surface complexes and epitaxial matching of precursor and support structures improves dispersion dramatically. Reduction promoters can help in those cases where support–precursor interactions are too strong. We show how substitutions of silicon into a titania lattice stabilizes surface area and retards formation at high oxidation temperatures of cobalt ternary oxides that reduce only at very high temperatures—an important consideration if oxidative coke removal is necessary. In addition, surface treatment of TiO2 with an irreducible oxide like ZrO2 can inhibit deleterious support interactions that can block surface cobalt sites. Selectivity can also be dramatically altered by catalyst synthesis. We illustrate a case of large (2 mm) SiO2 particles onto which cobalt can be added either uniformly or in discrete eggshells, with the eggshell catalysts having substantially higher C5+ selectivity. These approaches can lead to optimal Fischer–Tropsch catalysts with high activity and C5+ selectivity, good physical integrity, and a long life.

Physiological responses were compared in nine stable male cardiac patients (mean +/- standard error (SE): age, 68.3 +/- 8.1 years; height, 172.7 +/- 3.9cm; weight, 72.8 +/- 14.5kg) during stationary cycling in the supine, recumbent, and upright positions. A discontinuous exercise protocol was performed in which each stage included 3 minutes of exercise and 1 minute of recovery. Each subject's workload started at 150kgm.min-1 and increased by 150kgm.min-1 per stage until volitional fatigue. Testing sessions were randomized and performed 1 week apart. Subjects continued their normal medication regimen. All subjects were participants in a community-based cardiac rehabilitation program. Dependent variables were assessed at two different intensities; submaximal (300kgm.min +/- 1) and maximal. A two-way repeated measures ANOVA found no significant differences in systolic blood pressure (SBP), diastolic blood pressure (DBP), minute ventilation (VE), respiratory exchange ratio (R), rate pressure product (RPP), and rating of perceived exertion (RPE) at submaximal (300kgm.min +/- 1) and maximal exercise efforts. Heart rate (HR) was significantly lower (p < or = .05) in the supine position compared with either the upright or recumbent positions during the submaximal workload. In addition, oxygen uptake (VO2) was significantly lower in the supine position at the submaximal workload (p < or = .05) compared with both upright and recumbent. No difference in HR or VO2 was observed at maximal exercise. Regressions of HR on VO2 showed similar slopes and intercepts for supine, recumbent, and upright ergometry.(ABSTRACT TRUNCATED AT 250 WORDS)

Hand-held dynamometry has proven reliable in assessing adult strength. The primary purpose of this study was to determine its reliability in children. Secondary purposes included investigating strength differences between males and females and between dominant (D) and nondominant (ND) sides. Subjects were 8-, 9-, and 10-year-old boys (n=63) and girls (n=54). The Nicholas Manual Muscle Tester (NMMT) was used to measure maximum isometric force of D and ND elbow flexors, elbow extensors, and shoulder abductors. Retest measurements were taken 4 to 7 days later. Results indicated that (a) correlation coefficients ranging from .72 to .90 were statistically significant; (b) except for males’ ND elbow extensor strength, a series of paired t tests revealed no significant differences between test and retest strength values; (c) a series of paired t tests revealed no significant strength differences between D and ND sides other than for males’ elbow extensor strength for the test phase; and (d) a series of unpaired t tests revealed statistically significant differences between males and females on a majority of the muscle groups. The NMMT appears to be a quick and reliable testing instrument for determining maximal isometric force in children.

Although recent data from our laboratory have established the occurrence of receptor-mediated endocytosis in intrahepatic bile duct epithelial cells (IBDEC) isolated from normal rat liver, no studies have assessed the role of isolated IBDEC in fluid-phase endocytosis. Therefore, to determine if IBDEC participate in fluid-phase endocytosis, we incubated morphologically polar doublets of IBDEC isolated from normal rat liver with horseradish peroxidase (HRP, 5 mg/ml), a protein internalized by fluid-phase endocytosis, and determined its intracellular distribution by electron microscopic cytochemistry. Pulse-chase studies using quantitative morphometry were also performed to assess the fate of HRP after internalization. After incubation at 37 degrees C, IBDEC internalized HRP exclusively at the apical (i.e., luminal) domain of their plasma membrane; internalization was completely blocked at 4 degrees C. After internalization, HRP was seen in acid phosphatase-negative vesicles and in acid phosphatase-positive multivesicular bodies (i.e., secondary lysosomes). Small acid phosphatase-negative vesicles containing HRP moved progressively from the apical to the basal domain of IBDEC. Pulse-chase studies showed that HRP was then discharged by exocytosis at the basolateral cell surface. These results demonstrate that IBDEC prepared from normal rat liver participate in fluid-phase endocytosis. After internalization, HRP either is routed to secondary lysosomes or undergoes exocytosis after transcytosis from the luminal to the basolateral cell surface. Our results suggest that IBDEC modify the composition of bile by internalizing both biliary proteins and fluid via endocytic mechanisms.

We have reported that retroviral particles adhered to the surface of antigen-specific T cells can be carried to metastases following adoptive transfer in vivo, a process we have called viral hitch hiking. Following antigen-driven T-cell accumulation at tumors, viral particles productively infect tumor cells via envelope/receptor dependent interactions ('hand on' of virus from the T cell to the tumor cell). We describe here a second envelope/receptor independent pathway of viral hand on from T cells, dependent on T-cell activation. We show that the endosomolytic property of perforin promotes release of viral particles from endosomes into which they are co-delivered along with cytotoxic granules from the activated T cell. Therefore, hand on of MLV particles lacking any envelope can be used for in vivo delivery of vectors, where targeting is at the extremely specific level of recognition of antigen by the T-cell receptor, thereby dispensing with the need to engineer viral envelopes. These data reveal a novel pathway by which MLV viral particles exploit a functional immunological synapse and present new opportunities both to improve the efficacy of adoptive T-cell transfer and to target vectors for systemic gene delivery.

Because blood lactic acid (LA) levels may be important in prescribing exercise for cardiac patients, this study documented the LA response to four different circuit weight training (CWT) protocols and compared these responses to both maximal treadmill and LA threshold values.Intervention study following a crossover trial design.A phase III community-based setting.All subjects had documented cardiac disease and were volunteers.We used 40% and 60% of the one-repetition maximum (1-RM) for six exercises and 30 or 60sec of rest between each station, resulting in four protocols, performed in random order. A discontinuous treadmill test was conducted, and the LA threshold was determined.The main dependent variable was LA after each CWT protocol.No signs or symptoms suggestive of cardiovascular distress during any of the four CWT protocols were reported. A repeated-measures analysis of variance showed that the LA threshold value was significantly less than all four CWT protocols (p.05). The CWT responses were also compared with the traditional LA threshold value of 4.0mmol/L, and both 60% protocols were significantly elevated (p.05).Because no positive signs or symptoms were reported, we recommend starting stable cardiac patients on a CWT program with an initial load between 40% and 60% 1-RM and allowing at least 60sec of rest between exercises.

BACKGROUND While most studies suggest circuit weight training (CWT) to be safe in cardiac rehabilitation populations, few investigators have controlled variables known to impact CWT intensity. Therefore, the purposes of this study were to determine the energy cost and evaluate safety of cardiac patients while varying rest interval duration and lifting load in a CWT format. METHODS Nine male subjects with documented coronary artery disease had maximal oxygen uptake (VO2max), one-repetition maximum (1-RM), and body composition tested. In random order and on separate days, 4 CWT sessions using either 40% or 60% of the 1-RM, and either 30 or 60 seconds of rest between stations were completed. Energy cost, heart rate (HR), blood pressure (BP), and rate-pressure product (RPP) were measured. Data were analyzed with a repeated measures analysis of variance, and Tukey's post-hoc test was performed when significant results were found. The alpha level was set at < .05. RESULTS Subjects exercised at 25% to 32% of VO2max (58%-67% of HRmax) during CWT. The HR and RPP responses were lower during all CWT protocols than at 85% of the treadmill VO2max. No subject displayed any ST-segment depression or angina during CWT. The 40%-60-second protocol had an energy cost (2.98 kcal/min) that was lower (P < .05) than the other protocols (3.48-3.81 kcal/min). Increasing the lifting load resulted in increases (P < .05) in energy cost, and decreasing the rest interval increased energy cost only during the 40% 1-RM protocols. CONCLUSIONS Results indicate that CWT protocols of varied intensity are safe for cardiac patients when compared to treadmill exercise, and changes in rest interval duration and load can impact the energy cost.

The study of intrahepatic bile duct epithelial cells (i.e., cholangiocytes) has been limited by the lack of a polarized in vitro model that allows easy access to both apical and basolateral cell surfaces. Therefore, we developed a cell line of polarized normal rat cholangiocytes (NRCs) and established conditions that produced a confluent monolayer of cells grown on collagen-coated filters of tissue culture inserts. We passaged NRCs at high density to collagen-coated, tissue-culture inserts and measured transepithelial electrical resistance. We evaluated ultrastructural features by transmission and scanning electron microscopy. gamma-glutamyl-transpeptidase (gamma GT) was visualized in cultured cells by enzyme histochemistry, and cytokeratin (CK)-7, CK-19, vimentin, and desmin staining was done by immunohistochemistry. We studied the biologic responsiveness and functional polarity of NRCs by measuring their levels of cyclic AMP after addition of forskolin with or without somatostatin to either the apical or basolateral chambers. When seeded with approximately 1 x 10(5) cells/cm2, the NRCs formed a confluent monolayer in 72 hr. Transepithelial electrical resistance increased over time, achieving a maximum of 625 (+- 25) ohms.cm2 by 1 week after confluence. Transmission and electron microscopy scanning showed the apical cell surface to be tightly packed with microvilli with a heterogeneous display of cilia ranging from none to 20 to 30 cilia/cell. On transmission, apically positioned tight junctions and vesicles were apparent; nuclei were oriented basally and the basolateral surface was characterized by membrane interdigitations. NRCs stained positively for the cholangiocyte marker proteins, gamma-glutamyl-transpeptidase, CK-7, and CK-19, and negative for the mesenchymal markers, vimentin, and desmin. Exposure of the basolateral (but not the apical) cell surface to somatostatin caused a 60% inhibition of forskolin-induced increases in intracellular levels of cyclic AMP, suggesting the presence of somatostatin receptors exclusively on the basolateral plasma membrane domain. We have developed a unique model of primary cultures of normal rat cholangiocytes in which the apical and basolateral surfaces are easily accessible; the cells develop intermediate-strength tight junctions, retain their cholangiocyte phenotype, display morphologic and functional polarity, and are responsive to hormones. This model should be useful for the assessment of vectorial transport of solutes and other constituents of blood and bile, as well as for studying growth regulation of cholangiocytes.

The development of new and refined separation techniques--including FACS, FFE, CFE and isopyknic gradients--has had a profound impact on the ability of investigators to isolate specific cell types from the liver. Although some of these techniques, such as FFE, may be of limited preparative value, they are nonetheless important analytical tools that detect subtle differences among cell subpopulations. The isolation of highly purified preparations of liver cells in large yields requires the use of more conventional purification methods such as CFE and isopyknic centrifugation. Immunological approaches represent a key development for the isolation of specific liver cell types, especially when they are used in combination with other techniques. Excellent, reliable and relatively simple techniques now exist to isolate highly purified preparations of hepatocytes, cholangiocytes, KCs, SCs, FSC, myofibroblasts and pit cells. Additional work is necessary to refine techniques for the isolation of dendritic cells and lymphocytes.

The purpose of this study was to assess the relations among physical activity, adherence, and frequency and duration of exercise sessions for 33 male and female sedentary university students. Analysis indicated that frequency and duration of the exercise program did not significantly affect adherence. However, frequency and duration of the exercise sessions did significantly affect leisure activity once the structured exercise program terminated.

The effect of endurance training on reflex venomotor control during an orthostatic challenge was investigated in 11 sedentary male volunteers. An exercise (E) group (n = 6) underwent 12 weeks of endurance exercise training, whereas a control (C) group (n = 5) remained sedentary. Training significantly increased VO2max values in E (pre-training: 37.0 +/- 2.5 ml.kg-1.min-1; post training: 44.6 +/- 2.5 ml.kg-1.min-1), while C showed no significant change. During exposures to two levels of lower body negative pressure (-10 and -40 mm Hg), both C and E groups showed similar graded decreases in forearm venous volume (FVV). The magnitude of the FVV decreases did not differ between groups or when comparing pre-training and post-training values. We conclude that the reflex venoconstrictor response to LBNP was not affected by endurance training.

This study determined the effects of a 10-week strength training program on running economy in 12 female distance runners who were randomly assigned to either an endurance and strength training program (ES) or endurance training only (E). Training for both groups consisted of steady-state en

Many research studies report the long-lasting elevation of metabolism following exercise. However, little is known regarding the impact of duration and intensity on this phenomenon, particularly in trained women in whom the time of the menstrual cycle has been controlled. This study examined the effects of a constant walking intensity (70% of maximal oxygen uptake (VO2max)) on the treadmill at various levels of duration (20, 40, and 60 min) on 3-h recovery of oxygen uptake (VO2). Eight trained (mean +/- SD) (VO2max = 47.6 +/- 3.2 ml.kg-1.min-1) females (mean age = 30.2 +/- 5.0 yr, mean weight = 58.7 +/- 7.6 kg, mean height = 165.6 +/- 7.0 cm) participated in the study. Subjects reported to the lab for a maximal oxygen consumption test and returned on four additional occasions (control, 20, 40, 60 min) in random fashion. Treadmill speed and grade were established to yield the appropriate intensity for each subject. Following each exercise bout subjects sat quietly for a 3-h time period. Variables measured included VO2, minute ventilation (VE), respiratory exchange ratio (RER), heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and core (rectal) temperature (Tc). Variables were measured each 15 min of recovery. An ANOVA was used to assess differences due to duration. Excess postexercise oxygen consumption (EPOC) was calculated by subtracting the resting VO2 from the absolute VO2 and summing the individual EPOCs during each 3-h postexercise session and comparing these individual values to the preexercise VO2 values. The EPOC was significantly elevated (P < 0.05) in each of the three durations as compared with the control (sitting) and preexercise periods. The total EPOC was significantly higher for the 60-min duration (15.2 l) as compared with either 20-min (8.b l) or 40-min (9.8 l) duration (P < 0.05). This was observed without significant changes in VE, RER, HR, SBP, DBP, or Tc. Additionally, there were no differences during exercise across the three durations in VO2, VE, RER, HR, SBP, DBP, or Tc. These data suggest that exercise duration increases EPOC significantly and that a 60-min duration yields approximately twice the EPOC than either 20 or 40 min.

Use of personal protective devices in the workplace, while intended to diminish risk of injury, may in some cases increase personal risk from environmental hazards. A case of a juvenile diabetic with complaints of near syncope while working in a plastics laminating process is analyzed. Although his symptoms might be attributed to a variety of causes, they were traced to the effects of heat stress related to wearing vapor-barrier disposable coveralls in a warm environment (85 degrees F). A field study of asbestos workers involved in abatement of asbestos steam pipe insulation illustrates how clothing impermeable to sweat may result in elevation of core body temperature. When workers use vapor-barrier coveralls, work practices or wet bulb globe temperature limits may need to be revised to prevent heat-related injury.

Five healthy male volunteers performed 20 min of both seated and supine cycle-ergometer exercise (intensity, 50% maximal O2 uptake) in a warm environment (Tdb = 30 degrees C, relative humidity = 40–50%) with and without breathing 10 cmH2O of continuous positive airway pressure (CPAP). The final esophageal temperature (Tes) at the end of 20 min of seated exercise was significantly higher during CPAP (mean difference = 0.18 +/- 0.04 degree C, P less than 0.05) compared with control breathing (C). The Tes threshold for forearm vasodilation was significantly higher (P less than 0.05) during seated CPAP exercise than C (C = 37.16 +/- 0.13 degrees C, CPAP = 37.38 + 0.12 degree C). The highest forearm blood flow (FBF) at the end of exercise was significantly lower (P less than 0.05) during seated exercise with CPAP (mean +/- SE % difference from C = -30.8 +/- 5.8%). During supine exercise, there were no significant differences in the Tes threshold, highest FBF, or final Tes with CPAP compared with C. The added strain on the cardiovascular system produced by CPAP during seated exercise in the heat interacts with body thermoregulation as evidenced by elevated vasodilation thresholds, reduced peak FBF, and slightly higher final esophageal temperatures.

Five obese (% body fat greater than or equal to 27%) and five relatively lean (% body fat less than 20%) men performed upright exercise on a cycle ergometer at intensities of 30, 50, and 70% of their maximal aerobic power [VO2max (ml X kg fat-free wt-1 X min-1)] in both a thermoneutral [dry bulb temperature (Tdb) = 22 degrees C, wet bulb temperature (Twb) = 14 degrees C] and a hot (Tdb = 38 degrees C, Twb = 20 degrees C) ambient environment. Cardiac output (Q) was measured by CO2 rebreathing and forearm blood flow (FBF) was measured by venous occlusion plethysmography. Esophageal temperature (Tes) was measured by a thermocouple placed in the esophagus at approximately heart level, and mean skin temperature (Tsk) was calculated from the average of thermocouple readings from six skin sites. When the exercise intensity was normalized for metabolic body mass by dividing by fat-free weight, Q was similar between lean and obese at all exercise intensities and in both ambient environments. No differences between the two groups were found in Tes and Tsk under all conditions. The obese had significantly lower FBF compared with the lean during the higher exercise intensities in the hot ambient environment. In both ambient environments, the slope of the FBF-Tes relationship was significantly less in the obese group. It was concluded that body composition may alter the balance between the two opposing sets of cutaneous vascular reflexes (baroreceptor-induced vasoconstriction and thermoregulatory vasodilation) that regulate the competition for blood flow between the skin and working muscle during exercise in the heat.

Pulmonary function was assessed in supine subjects before, during, and after three separate bed-rest studies of 11 and 12 days duration. Forced vital capacity (FVC) increased during bed rest in each subject. Total lung capacity (TLC) was measured by helium dilution in one bed-rest study and increased in each subject, while residual volume and functional residual capacity of the respiratory system did not change. No change in FVC was found in an ambulatory control group using identical measurement techniques. Maintaining base-line plasma volume during one bed rest by the use of exogenous estrogen did not prevent an increase in FVC, and decreasing plasma volume with diuretics in ambulatory subjects to the same degree as seen in the bed rests did not cause an increase in FVC. We conclude that prolonged bed rest results in a small significant increase in TLC and that this change is not dependent on alterations in plasma volume.

We investigated the effects of a decrease in plasma volume (PV) and an increase in plasma osmolality during exercise on circulatory and thermoregulatory responses. Six subjects cycled at approximately 65% of their maximum O2 uptake in a warm environment (30 degrees C, 40% relative humidity). After 30 min of control (C) exercise (no infusion), PV decreased 13.0%, or 419 +/- 106 (SD) ml, heart rate (HR) increased to 167 +/- 3 beats/min, and esophageal temperature (Tes) rose to 38.19 +/- 0.09 degrees C (SE). During infusion studies (INF), infusates were started after 10 min of exercise. The infusates contained 5% albumin suspended in 0.45, 0.9, or 3.0% saline. The volume of each infusate was adjusted so that during the last 10 min of exercise PV was maintained at the preexercise level and osmolality was allowed to differ. HR was significantly lower (10-16 beats/min) during INF than during C. Tes was reduced significantly during INF, with trends for increased skin blood flow and decreased sweating rates. No significant differences in HR, Tes, or sweating rate occurred between the three infusion conditions. We conclude that the decrease in PV, which normally accompanies moderate cycle exercise, compromises circulatory and thermal regulations. Increases in osmolality appear to have small if any effects during such short-term exercise.

Thermoregulation is an important consideration not only for athletic performance but also for the safety of the athlete. This article presents a broad overview of the mechanisms by which body heat is dissipated in an individual exercising in a hot environment. Particularly emphasised are more recent views of body heat loss mechanisms and the influences of non-thermal inputs, such as effects due to changing blood volume or blood flow distribution. During exercise in a hot environment, metabolic heat produced by the exercising muscles is transported by the circulating blood to the surface of the body where it is released to the environment, either by radiation and convection or by evaporation of sweat. The primary drives for both the increased skin blood flow and increased body sweating are the thermal inputs which are sensed by receptors in the deep body core, with a lesser drive from skin receptors. These thermal signals are integrated in the hypothalamus and proper heat loss responses are effected. When exercise is prolonged, however, and body rehydration is not adequate, the total blood volume may be compromised. In addition, as the core temperature increases during exercise, larger proportions of the blood volume are distributed to the cutaneous vessels, thus effectively reducing cardiac return and central blood volume. During severe exercise, a reduction in cardiac filling may result in a fall in central venous pressure and stimulate baroreceptor vasoconstrictor reflexes. As discussed below, the outputs from these baroreceptors compete with and modify the thermal drives for both the control of the skin blood flow and control of the sweat glands. The effect of high ambient temperatures on exercise performance is most evident in prolonged submaximal exercise. Normally, maximal exercise performance is not altered by high temperatures unless the individual has an elevated deep body temperature before the start of the exercise task. However, submaximal exercise performance is often impaired by high ambient temperatures, but may be improved by programmes of physical training and heat acclimatisation. Both training and heat acclimatisation significantly modify the control systems which regulate skin blood flow and sweating. Only acclimatisation programmes, however, are effective in preventing heat stress during prolonged exercise in hot environments.

Bed rest (BR) is associated with a decrease in plasma volume (PV), which may contribute to the impaired orthostatic and exercise tolerances seen immediately after BR. The purpose of this study was to determine whether increases in blood estrogen concentration, either during normal menstrual cycles or during exogenous estrogen administration, would attenuate this loss of PV. Nineteen healthy women (21-39 yr of age) completed the study. Twelve women underwent duplicate 11-day BR without estrogen supplementation. PV decreased significantly (P less than or equal to 0.01) during both BR's, from 2,531 +/- 113 to 2,027 +/- 102 ml during BR1 and from 2,445 +/- 115 to 2,244 +/- 96 ml during BR2. The women who began BR in the periovulatory stage of the menstrual cycle (n = 3), a time of elevated endogenous estrogens, had a transient delay in loss of PV during the first 5 days of BR. Women who began BR during other stages of the menstrual cycle (n = 17) showed the established trend to decrease PV primarily during the first few days of BR. Seven additional women underwent a single 12-day BR while taking estrogen supplementation (1.25 mg/day premarin). PV decreased during the first 4-5 days of BR, then returned toward the pre-BR level during the remainder of the BR (pre-BR PV, 2,525 +/- 149 ml; post-BR PV, 2,519 +/- 162 ml). Thus menstrual fluctuations in endogenous estrogens appear to have only small transient effects on the loss of PV during BR, whereas exogenous estrogen supplementation significantly attenuates PV loss.

Eleven sedentary male volunteers were assigned to either an exercise (E) group (n = 6; endurance exercise for 12 weeks) or a control (C) group (n = 5; no exercise). After training, E significantly increased (p less than 0.01) their VO2max (pretraining: 37.0 +/- 2.3; posttraining: 44.6 +/- 2.5), whereas C showed no significant change. Heart rate (HR), arterial blood pressure (BP) and forearm blood flow (FBF) were measured both pre- and posttraining at rest and during 2 levels of LBNP: -10 mm Hg and -40 mm Hg. Both C and E had similar decreases in systolic BP and similar increases in HR and diastolic BP during LBNP when comparing the pre- and posttraining periods. In both groups, FBF significantly decreased during -40 mm Hg of LBNP in the pretraining period. However, after training, E had a significantly attenuated (p less than 0.05) decrease in FBF at -40 mm Hg (pretraining: -45.0 +/- 3.7%; posttraining: -29.8 +/- 3.1%). In C, there was no difference in the response of FBF to -40 mm Hg of LBNP comparing pretraining and posttraining. These findings indicate that endurance exercise training decreases the forearm vasoconstrictor response to high levels of LBNP.