Influence of age and normal plasma fibrinogen levels on flow-mediated dilation in healthy adults.

This study examined the effects of age-associated increases in fibrinogen on brachial artery flow-mediated dilation in 30 healthy nonsmokers. The findings demonstrate an inverse association between normal plasma fibrinogen levels and vascular function (r = -0.56, p = 0.001), suggesting elevated plasma fibrinogen may decrease the artery's responsiveness to certain vasodilatory signals, such as shear stress.

Differential response to low-fat diet between low and normal HDL-cholesterol subjects.

Heart attacks frequently occur in normolipidemic subjects with low concentration of high density lipoproteins (35 mg/dL). We hypothesized that as subjects with low HDL-C already have low HDL concentrations, the major decrease of HDL-C will occur in subjects with normal HDL-C when a low-fat diet is consumed. Normolipidemic male subjects consumed three diets differing in total fat and saturated fat composition (AAD: 37%, Step-1: 28%, Step-2: 24% total fat) for 6 weeks in a three-period double-blind randomized crossover design. Plasma lipids and apolipoproteins were determined and changes in distribution of HDL subpopulations were evaluated. As a result of a low-fat diet, low HDL-C individuals slightly decreased their HDL-C, but substantially decreased their LDL-C resulting in a significant improvement in the LDL-C/HDL-C ratio. However, subjects with normal HDL-C levels decreased both their LDL-C and HDL-C resulting in an unchanged LDL-C/HDL-C ratio. We also observed significant differences in response to low-fat diets in HDL-C and alpha(1) concentrations between low and normal HDL-C subjects. In the normal HDL-C group, consumption of a low-fat diet also resulted in redistribution of apoA-I-containing HDL subpopulations, indicated by a decrease in the large apoA-I-only alpha(1) subpopulation. These data demonstrate that male subjects with low HDL-C respond to a low-fat diet differently than individuals with normal HDL-C.

Influence of a carbohydrate drink on nutritional status, body composition and mood during desert training.

BACKGROUND: Nutritional intake by military personnel is typically inadequate during field exercises, potentially compromising health and performance. HYPOTHESIS: Drinking a supplemental carbohydrate (CHO) beverage will increase total caloric intake and maintain nutritional status during military training in the desert. METHODS: A total of 63 volunteers were randomly assigned to one of two groups to receive either a CHO or placebo beverage with military rations during an 11-d desert field exercise. Fluid intake was ad libitum and adequate rations were provided. Blood samples were collected twice to assess nutritional status, and nutrient intake was determined with consumption data. Mood state was examined by questionnaire. RESULTS: Energy intake was significantly higher in the CHO group (3050 kcal x d(-1) vs. 2631 kcal x d(-1)), with additional CHO from the beverage providing energy with some compensation by reduced fat and protein intake. Intakes of energy, folacin, calcium, magnesium, iron, and zinc in both groups were inadequate, with intakes significantly lower (p<0.05) for calcium, magnesium, and zinc in the CHO beverage group. Blood parameters of nutritional status remained within normal ranges with no differences between groups, but significant decreases were seen in pre-albumin. No changes in mood were seen during the training, nor after exposure to desert conditions. CONCLUSIONS: The operational ration supplemented with a CHO beverage significantly increases CHO and energy intakes compared with standard rations and maintains nutritional status for short exercises. Fortification with micronutrients most at risk for deficient intake from foods may be needed for longer deployments.

Prevention of hydrolytic rancidity in rice bran during storage.

The effect of microwave heating, packaging, and storage temperature on the production of free fatty acids (FFA) in rice bran was examined. Freshly milled raw rice bran was adjusted to 21% moisture content and heated in a microwave oven at 850 W for 3 min. Raw and microwave-heated rice bran were packed in zipper-top bags or vacuum-sealed bags and stored at 4-5 or 25 degrees C for 16 weeks. FFA content of bran was measured at 4-week intervals. Total FFA increased rapidly over the 16-week period from the initial value of 2.5% in raw bran stored at 25 degrees C to 54.9% in vacuum bags and 48.1% in zipper-top bags. However, total FFA of raw bran stored at 4-5 degrees C increased at a slower rate from an initial value of 2. 5 to 25.4% in vacuum bags and 19.5% in zipper-top bags. After 16 weeks of storage, total FFA of microwave-heated bran stored at 25 degrees C increased from 2.8 to 6.9 and 5.2%, respectively, for samples stored in vacuum bags and zipper-top bags. Total FFA of microwave-heated samples stored at 4-5 degrees C did not change significantly with storage time. Results showed that hydrolytic rancidity of rice bran can be prevented by microwave heating and that the recommended storage condition for microwaved rice bran is 4-5 degrees C in zipper-top bags.

Low-dose T(3) improves the bed rest model of simulated weightlessness in men and women.

This study tested the hypothesis that low-dose 3,5, 3'-triiodothyronine (T(3)) administration during prolonged bed rest improves the ground-based model of spaceflight. Nine men (36.4 +/- 1. 3 yr) and five women (34.2 +/- 2.1 yr) were studied. After a 5-day inpatient baseline period, subjects were placed at total bed rest with 6 degrees head-down tilt for 28 days followed by 5-day recovery. Fifty micrograms per day of T(3) (n = 8) or placebo (n = 6) were given during bed rest. Serum T(3) concentrations increased twofold, whereas thyroid-stimulating hormone was suppressed in treated subjects. T(3)-treated subjects showed significantly greater negative nitrogen balance and lost more weight (P = 0.02) and lean mass (P < 0.0001) than placebo subjects. Protein breakdown (whole body [(13)C]leucine kinetics) increased 31% in the T(3) group but only 8% in the placebo group. T(3)-treated women experienced greater changes in leucine turnover than men, despite equivalent weight loss. Insulin sensitivity fell by 50% during bed rest in all subjects (P = 0.005), but growth hormone release and insulin release were largely unaffected. In conclusion, addition of low-dose T(3) to the bed rest model of muscle unloading improves the ground-based simulation of spaceflight and unmasks several important gender differences.

Comparison of a radioimmunoassay with a microparticle enzyme immunoassay of insulin for use with the minimal model method of determining whole-body insulin sensitivity.

The purpose of this study was to compare minimal model results of insulin sensitivity and glucose effectiveness using insulin levels measured by a conventional radioimmunoassay (RIA) versus an automated microparticle enzyme immunoassay (MEIA). Thirty obese subjects participated in an insulin-modified frequently sampled intravenous glucose tolerance test. The MEIA exhibited lower day-to-day variability than did the RIA. The MEIA yielded lower insulin values compared to the RIA probably because of the high cross-reactivity with proinsulin in the RIA. The MEIA yielded a good correlation with the RIA for both insulin sensitivity (r = 0.97, p = 0.0001) and for glucose effectiveness (r = 0.98, p = 0.0001). The MEIA did not significantly effect the results of the MinMod analysis and the low cross-reactivity with proinsulin makes MEIA preferable when insulin sensitivity (SI) is measured in patients with diabetes or obese individuals whose insulin:proinsulin ratio is altered.

Pilot study on the effect of hyperimmune egg protein on elevated cholesterol levels and cardiovascular risk factors.

Coronary heart disease is the leading cause of death in the United States, accounting for almost half of all deaths. Animal studies have suggested that the daily addition of "hyperimmune egg" to one's diet might reduce the risk of cardiovascular disease. Military personnel with initial total cholesterol levels higher than 180 mg/dl were randomly enrolled in a 26-week double-blind study of a drink containing a hyperimmune egg protein. Subjects were randomly assigned to three groups: control (no drink); placebo (drink without egg); and active (drink combined with hyperimmune egg). Throughout the study this physically fit group maintained a program of strenuous exercise and participated in a dietary education program intended to reduce fat and cholesterol intake. At the end of the trial, total cholesterol levels of the control and placebo groups had increased, whereas the group that consumed the drink with hyperimmune egg showed no significant change in total cholesterol. The ratio of total cholesterol to high-density lipoproteins and the apolipoprotein B level increased in both control and placebo groups but remained essentially unchanged in the group consuming hyperimmune egg. Triglyceride and apolipoprotein A-I values did not change significantly in any of the groups. These findings suggest that hyperimmune egg may beneficially modify the regulation of serum lipoprotein levels and thereby reduce the possibility of cardiovascular diseases.

ELISA detection of restriction site polymorphisms in the pig ryanodine receptor locus.

We compare two strategies for ELISA detection of restriction site polymorphisms (EDRSP) that are suitable for high-throughput genotyping of the pig ryanodine receptor point mutation (RYR1(hal)). In both procedures, target DNA is amplified by PCR with one primer that is 5' biotinylated and a second primer that is 5' fluoresceinylated. PCR products are captured in duplicate wells on a streptavidin-coated, 96-well plate. The duplicates may be treated in two ways. In a single restriction enzyme assay, one duplicate is exposed to a restriction enzyme that cuts one allele specifically, and the second duplicate is exposed to no restriction enzyme. In a dual restriction enzyme assay, the second replicate is exposed to a second restriction enzyme that cuts the alternate allele specifically. Thereafter, the two procedures are similar; anti-fluorescein antibodies conjugated to peroxidase are allowed to bind to the fluoresceinylated ends, the plate is washed, and a substrate is converted to a colored end product. The ratio of the absorbances in the two wells is used to classify subjects by genotype. When the dual restriction enzyme assay is run, three genotype groups are easily distinguishable. When the single restriction enzyme assay is run, heterozygotes generate values that may overlap with those of the homozygotes that are not cut by the restriction enzyme. Dual restriction enzyme assays are more accurate than single restriction enzyme assays; however, single restriction enzyme assays are sufficient for identifying pigs that carry RYR1(hal).

A principle-focused approach to lab management.

As in all healthcare fields, the clinical laboratory is under the stress of constant change. While planning for the financial implications is important, a more holistic approach to adaptation is for laboratorians to put the focus back where it belongs: on people, principles, and service.

Normolipidemic subjects with low HDL cholesterol levels have altered HDL subpopulations.

Epidemiological studies have established that plasma concentration of HDL is inversely correlated with the risk of coronary heart disease, even in the absence of increased LDL cholesterol levels. We postulate that specific HDL subpopulations may be responsible for antiatherogenic properties of HDL. HDL subpopulations were quantitated by two-dimensional gel electrophoresis in 79 normolipidemic healthy male subjects. To eliminate the influence of diet, volunteers consumed an average American diet for 6 weeks. After the diet period, subjects were stratified according to their HDL cholesterol (HDL-C) levels to low HDL-C < 0.91 mmol/L (< 35 mg/dL), medium > 0.91 < 1.30 mmol/L (> 35 < 50 mg/dL), and high > or = 1.30 mmol/L (> or = 50 mg/dL) groups. Plasma triglycerides and insulin levels were in the normal range, but subjects with low HDL-C levels had higher concentrations of plasma triglycerides and insulin than subjects with medium or high HDL-C concentrations. The absolute concentration (mg/dL) of apoA-I in the largest alpha-migrating HDL subpopulation (alpha 1) was (P < .01) lower in the low HDL-C subjects compared with the medium and high HDL-C groups. The relative concentration (percent distribution) of apoA-I was decreased (P < .01) in alpha 1 and increased (P < .01) in alpha 3 subpopulations. A positive correlation between HDL-C and alpha 1 (P < .001) and a negative correlation between HDL-C and alpha 3 were observed. The inverse correlation of apoA-I distribution (relative concentration) between alpha 1 and alpha 3 suggests an interconversion of alpha 1 and alpha 3 subpopulations, possibly by cholesteryl ester transfer protein. Pre-beta subpopulations showed an inverse trend with HDL-C, while the pre-alpha subpopulation behaved similarly to the alpha-migrating subpopulation. Colocalization of apoA-I and apoA-II particles in the different HDL subpopulations demonstrated that alpha 1, pre-beta 1, and pre-beta 2 subpopulations are apoA-I-only particles rather than apoA-I:A-II particles.

How to organize continuing education workshops and seminars.

Although required in only four states at present, continuing education for lab professionals is necessary for job survival. With this growing need for CE events, here's how one lab uses these seminars to establish a leadership position in the lab community and reaps numerous professional benefits for its employees.

Does vegetable oil attenuate the beneficial effects of fish oil in reducing risk factors for cardiovascular disease?

Contradictory reports on the protective effect of fish consumption on cardiovascular disease (CVD) risk could be due to variations in the intake of n-3 and n-6 polyunsaturated fatty acids (PUFAs). Metabolic competition between n-3 and n-6 PUFAs suggests that n-6 PUFAs in vegetable oils could attenuate the efficacy of n-3 PUFAs in fish oil to favorably alter endpoints relevant to CVD risk. We determined the effects of varying dietary amounts of fish oil on lipid and thrombotic endpoints relevant to risk factors for CVD and whether these effects were attenuated by vegetable oils. Two randomized, double-blind, placebo-controlled, parallel studies were conducted in human subjects fed varying amounts of n-3 and n-6 PUFAs; n-3 PUFA intake was varied by using fish or placebo oil capsules, and n-6 PUFA intake was modified by incorporating varying amounts of safflower oil into the diet. Endpoints included changes in membrane fatty acid composition, blood lipids, and thrombotic profile. The results indicated that absolute amounts of fish oil, and not the relative amounts of fish and vegetable oil (ratios of n-3 to n-6 PUFAs), determined the magnitude of the reduction of arachidonic acid and increase in eicosapentaenoic acid in phospholipids of plasma and platelets. The suppression of plasma triacylglycerols by fish oil was not affected by varying amounts of dietary n-6 PUFAs. Fibrinogen concentrations decreased with 15 g but not with 9 g fish oil/d fed at the same ratio of n-3 to n-6 PUFAs. The efficacy of fish oil in favorably modifying certain risk factors for CVD was not attenuated by vegetable oil.

A paradigm of experimentally induced mild hyperthyroidism: effects on nitrogen balance, body composition, and energy expenditure in healthy young men.

Although T3 exerts major regulatory actions in both animals and humans, most clinical studies of T3 administration have been relatively short term. The present study examined the effects of more than 2 months (63 days) of low dose T3 treatment on nitrogen balance, body composition, 24-h energy expenditure (EE), and protein turnover in seven healthy men studied at an in-patient metabolic unit. Subjects were also randomly assigned to either high or low fat diets to determine the effects of diet composition. T3 treatment produced significant losses in both lean mass (1.5 +/- 0.3 kg) and fat mass (2.7 +/- 0.4 kg) by 6 weeks, with similar reductions in both at 9 weeks. The high fat diet somewhat attenuated the loss of body fat. Nitrogen balance was significantly negative for the first 3 weeks of T3 treatment, but tended to return to baseline thereafter. There were no significant effects of treatment on protein turnover at 9 weeks, although there was a slight increase in leucine oxidation (P = 0.07). Despite the apparent adaptation in nitrogen balance, total 24-h EE and sleeping EE were significantly increased at 9 weeks. We conclude that although healthy men are able to adapt to mild hyperthyroidism in terms of nitrogen balance, they exhibit significant and persistent changes in fat and fat-free mass as well as energy balance.

Comparison of bone density measurement techniques: DXA and Archimedes' principle.

The standard method for determination of density (g/cm3) of bones from small animals has been the application of Archimedes' principle. A recent development has been software for the determination of "density" (g/cm2) of small animal bones with dual-energy X-ray absorptiometry (DXA). We compared Archimedes' principle and DXA (Hologic QDR-2000) in the measurement of the densities of whole and hollowed femurs of 5- to 6-month-old retired female breeder rats. In an attempt to ensure detectable treatment differences, rats were used from a low-vitamin D Holtzman and a supplemental-vitamin D Sprague-Dawley colony. Whole femur densities were higher for supplemental-vitamin D colony rats than for low vitamin D rats using both techniques (Archimedes' principle, p < 0.002; DXA, p < 0.005), and the densities from the two techniques were highly correlated (r = 0.82, p < 0.0001). Actual density values were higher for Archimedes' principle than for DXA. Other variables such as femur ash weight and calcium content were also highly correlated to densities with both techniques. Hollowed femur density values were higher than whole femur values with Archimedes' principle but lower with DXA. Colony effects for hollowed femur densities were diminished with Archimedes' principle (p < 0.03) and eliminated with DXA (p < 0.53). Investigation of whole bones is more biologically relevant, and both techniques were effective in detecting differences between whole femurs from low-vitamin D and supplemental-vitamin D colony rats.

Effects of experimentally induced mild hyperthyroidism on growth hormone and insulin secretion and sex steroid levels in healthy young men.

Although triiodothyronine (T3) exerts major regulatory actions in both animals and humans, most clinical studies of T3 administration have been relatively short-term. The present study examined the effects of more than 2 months (63 days) of low-dose T3 treatment on overnight pulsatile growth hormone (GH) secretion, short-term insulin secretion, and of sex steroid levels in seven healthy, lean men studied at an inpatient metabolic unit. At baseline, there were strong correlations between sex hormone-binding globulin (SHBG) and several measures of GH production, including total GH production (r = .99), GH interburst interval (r = -.75), and GH mass (r = .82). SHBG was also inversely correlated with basal insulin secretion (r = -.74). There was a 42% increase in serum levels of total testosterone (18.5 +/- 1.3 to 26.3 +/- 1.8 nmol/L, P = .005) and a 150% increase in SHBG (18.0 +/- 2.2 to 44.9 +/- 7.0 nmol/L, P = .008) following T3 treatment. Estradiol and free testosterone levels were unchanged by treatment, although free testosterone decreased from 142.8 +/- 18.4 to 137.3 +/- 19.5 pmol/L. T3 treatment significantly reduced the GH interburst interval (P < .05) and produced slight increases in the measures of GH secretion. There were no statistically significant effects of T3 treatment on insulin secretion, although insulin peak amplitude, mass secreted per burst, and total production all decreased. We conclude that experimentally induced T3 excess in healthy men produces significant and sustained changes in sex hormone levels and GH secretion. Furthermore, there are strong associations between SHBG and both GH and insulin secretion independent of thyroid hormone excess that require additional study.

Race and physical activity: cardiovascular and renal response to sodium loading.

Race and level of physical activity may be important factors affecting cardiovascular responsiveness to acute sodium intake. We examined the effects of a 4-day sodium loading procedure on heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure, 24-hour electrolyte excretion, and extracellular fluid volume (ECF) in African-American (n = 16) and Caucasian (n = 16) adult males. All subjects were normotensive with either moderately high (> or = 3 day/wk; > or = 20 min/day) or low (< or = 3 day/wk; < or = 20 min/day) physical activity levels. Subjects ingested either placebo or NaCl (0.2 g/kg/day) during two 4-day periods. Sodium loading increased SBP and decreased HR in all high physical activity subjects but not in low physical activity subjects (p < 0.05). Na+ excretion did not differ among groups, although urine volume and K+ excretion were lower, and Na+/K+ excretion ratio was higher in African-American compared to Caucasian subjects (p < 0.05). ECF, as measured by NaBr dilution, was greater in high physical activity subjects compared to low physical activity subjects (p < 0.05). These data suggest that high physical activity levels do not attenuate but rather exaggerate SBP response to a sodium load.

Abdominal fat distribution and metabolic risk factors: effects of race.

Previous studies have shown differences between African-American and Caucasian populations in the prevalence of obesity and obesity-related diseases such as type IIoffabetes. The purpose of this study was (1) to compare the insulin sensitivity index (SI) from the minimal model in 37 African-American and 22 Caucasian women matched for age and obesity, and (2) to determine whether the relationship between intraabdominal fat distribution and SI (and other health risk factors) was similar in both races. To address the second question, intraabdominal fat distribution was assessed by computed tomographic (CT) scans in a subset of 23 African-American and 15 Caucasian women. Despite having a similar body mass index ([BMI] weight in kilograms divided by height in meters squared) and waist to hip ratio (WHR), African-American women had a mean SI value that was approximately 36% lower than in the Caucasian women (3.45 +/- 0.42 v 5.40 +/- 0.55 x 10(-5) min(-1) / pmol x L, P = .007). Visceral fat area was smaller in African-American women (98.0 +/- 8.5 CM2) than in Caucasian women (117.3 +/- 12.4 CM2) despite similar BMI and WHR. Visceral fat area was strongly correlated with WHR in the Caucasian women (r = .76, P < .001), as previously observed, but not in the African-American women (r = .24, NS). WHR was significantly correlated with fasting insulin and serum cholesterol in the Caucasian women but not in the African-Americans. Visceral fat was correlated with metabolic risk factors in both groups, but subcutaneous abdominal fat was significantly correlated with SI and fasting insulin only in the African-American women. These results suggest that the relationship between body fat distribution and health risk factors may be different in African-Americans and Caucasians. Additionally, reduced insulin sensitivity in African-American women may in part explain the high diabetes rate in this population.

Oral anabolic steroid treatment, but not parenteral androgen treatment, decreases abdominal fat in obese, older men.

OBJECTIVE: To compare the effects of testosterone enanthate (TE), anabolic steroid (AS) or placebo (PL) on regional fat distribution and health risk factors in obese middle-aged men undergoing weight loss by dietary means. DESIGN: Randomized, double-blind, placebo-controlled clinical trial, carried out for 9 months with primary assessments at 3 month intervals. Due to adverse blood lipid changes, the AS group was switched from oral oxandrolone (ASOX) to parenteral nandrolone decaoate (ASND) after the 3 month assessment point. SUBJECTS: Thirty healthy, obese men, aged 40-60 years, with serum testosterone (T) levels in the low-normal range (2-5 ng/mL). MAIN OUTCOME MEASURES: Abdominal fat distribution and thigh muscle volume by CT scan, body composition by dual energy X-ray absorptiometry (DEXA), insulin sensitivity by the Minimal Model method, blood lipids, blood chemistry, blood pressure, thyroid hormones and urological parameters. RESULTS: After 3 months, there was a significantly greater decrease in subcutaneous (SQ) abdominal fat in the ASOX group compared to the TE and PL groups although body weight changes did not differ by treatment group. There was also a tendency for the ASOX group to exhibit greater losses in visceral fat, and the absolute level of visceral fat in this group was significantly lower at 3 months than in the TE and PL groups. There were significant main effects of treatment at 3 months on serum T and free T (increased in the TE group and decreased in the ASOX group) and on thyroid hormone parameters (T4 and T3 resin uptake significantly decreased in the ASOX group compared with the other two groups). There was a significant decrease in HDL-C, and increase in LDL-C in the ASOX group, which led to their being switched to the parenteral nandrolone decanoate (ASND) after 3 months. ASND had opposite effects on visceral fat from ASOX, producing a significant increase from 3 to 9 months while continuing to decrease SQ abdominal fat. ASND treatment also decreased thigh muscle area, while ASOX treatment increased high muscle. ASND reversed the effects of ASOX on lipoproteins and thyroid hormones. The previously reported effect of T to decrease visceral fat was not observed, in fact, visceral fat in the TE group increased slightly from 3 to 9 months, although SQ fat continued to decrease. Neither TE nor AS treatment resulted in any change in urologic parameters. CONCLUSIONS: Oral oxandrolone decreased SQ abdominal fat more than TE or weight loss alone and also tended to produce favorable changes in visceral fat. TE and ASND injections given every 2 weeks had similar effects to weight loss alone on regional body fat. Most of the beneficial effects observed on metabolic and cardiovascular risk factors were due to weight loss per se. These results suggest that SQ and visceral abdominal fat can be independently modulated by androgens and that at least some anabolic steroids are capable of influencing abdominal fat.

Maintenance of iron status in healthy men during an extended period of stress and physical activity.

Body weight loss and iron status of 55 male soldiers were measured during 62 d of intense physical activity and sustained stress and sleep deprivation. Body weight declined from (mean +/- SD) 75.9 +/- 9.0 to 63.8 +/- 6.7 kg (P < 0.05). Serum iron fell from 13.7 +/- 5.6 to 8.3 +/- 3.6 mumol/L by 14 d (P < 0.05), but returned to baseline values by 8 wk. Total iron-binding capacity declined from 53.4 +/- 6.8 at baseline to 47.5 +/- 6.3 mumol/L at 8 wk (P < 0.05). During the study, hematocrit, serum hemoglobin, and erythrocyte count did not change, whereas ferritin increased from 116 +/- 84 to 202 +/- 106 micrograms/L (P > 0.05). Adequate dietary iron, initiation of training with adequate body iron stores, and physical activity not in excess of pretraining workloads contributed to the maintenance of iron status during prolonged physical activity and stress. Our results suggest that some acute phase-like disturbances in iron metabolism may be a normal component of adaptation to stress and physical activity in healthy men.

Fluid replacement beverages and maintenance of plasma volume during exercise: role of aldosterone and vasopressin.

Previous experiments have demonstrated that consumption of a glucose polymer-electrolyte (GP-E) beverage is superior to water in minimizing exercise-induced decreases in plasma volume (PV). We tested the hypothesis that elevated plasma concentrations of vasopressin and/or aldosterone above that seen with water ingestion may explain this observation. Six trained cyclists performed 115 min of constant-load exercise (approximately 65% of maximal oxygen consumption) on a cycle ergometer on two occasions with 7 days separating experiments. Ambient conditions were maintained relatively constant for both exercise tests (29-30 degrees C; 58-66% relative humidity). During each experiment, subjects consumed 400 ml of one of the following beverages 20 min prior to exercise and 275 ml immediately prior to and every 15 min during exercise: (1) distilled water or (2) GP-E drink contents = 7% carbohydrate (glucose polymers and fructose; 9 mmol.l-1 sodium; 5 mmol.l-1 potassium; osmolality 250 mosmol.l-1). No significant difference (P > 0.05) existed in mean skin temperature, rectal temperature, oxygen consumption, carbon dioxide production or the respiratory exchange ratio between treatments. Further, no significant differences existed in plasma osmolality and plasma concentrations of sodium, potassium, chloride or magnesium between treatments. Plasma volume was better maintained (P < 0.05) in the GP-E trial at 90 and 120 min of exercise when compared to the water treatment. No differences existed in plasma levels of vasopressin or aldosterone between treatments at any measurement period. Further, the correlation coefficients between plasma concentrations of vasopressin and aldosterone and change in PV during exercise were 0.42 (P < 0.05) and 0.16 (P > 0.05), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)