Isotonic and hypertonic sodium loading in supine humans.

The hypothesis that hypertonic saline infusion induces a greater natriuresis than infusion of the same amount of sodium as isotonic saline was tested in 8 supine subjects on fixed sodium intake of 150 mmol NaCl day(-1). Sodium loads equivalent to the amount of sodium contained in 10% of measured extracellular volume were administered intravenously over 90 min either as isotonic saline or as hypertonic saline (850 mmol L(-1)). A third series without saline infusion served as time control. Experiments lasted 8 h. Water balance and sodium loads were maintained by replacing the excreted amounts every hour. Plasma sodium concentrations only increased following hypertonic saline infusion (by 2.7 +/- 0.3 mmol L(-1)). Oncotic pressure decreased significantly more with isotonic saline (4.1 +/- 0.3 mmHg) than with hypertonic saline (3.2 +/- 0.2 mmHg), indicating that isotonic saline induced a stronger volumetric stimulus. Renal sodium excretion increased more than a factor of four with isotonic and hypertonic saline but also increased during time control (factor of three). Cumulated sodium excretions following isotonic (131 +/- 13 mmol) and hypertonic saline (123 +/- 10 mmol) were statistically identical exceeding that of time control (81 +/- 9 mmol). Plasma angiotensin II decreased in all series but plasma ANP concentrations and urinary excretion rates of endothelin-1 remained unchanged. In conclusion, hypertonic saline did not produce excess natriuresis. However, as the two loading procedures induced similar natriureses during different volumetric stimuli, part of the natriuresis elicited by hypertonic saline could be mediated by stimulation of osmoreceptors involved in renal sodium excretion. The supine position does not provide stable time control conditions with regard to renal excretory function.     

Psychological stress and body temperature changes in humans.

We investigated the possible changes in body temperature, heart frequency, and blood pressure in 22 residents sitting for the yearly exam at the Specialty School of Psychiatry at Pisa University. All subjects were then evaluated 2 or 3 weeks later, in calm situations. In a subgroup, a specific plasmatic diazepam binding inhibitor (BBIA), previously described, was also measured. The results showed that all subjects underwent significant stress-related changes in the parameters studied, which suggest the involvement of different mechanisms in preexam stress.     

Effects of nedocromil sodium on allergen-induced rhinitis in humans.

Sixteen patients with allergic rhinitis were recruited into a double-blind crossover protocol studying the immediate effect of nedocromil sodium (NS) on the pattern of nasal symptoms and secretions after allergen challenge. After pretreatment with placebo or NS, allergen challenge resulted in pruritus, rhinorrhea, nasal congestion, and/or sneezing within 10 minutes in 12 of 16 subjects. Prostaglandin D2 (PGD2), a marker of mast cell degranulation, increased proportionately with symptom scores, remaining above the 95% confidence interval for 120 minutes after both pretreatments. No difference in PGD2 between the NS-treatment and placebo-treatment days was observed. Protein markers extravasated through the vasculature (albumin and IgG) or secreted by mucosal glands (lactoferrin) were assayed. Total protein, albumin, IgG, and lactoferrin all remained greater than 95% confidence interval for 100 minutes after allergen challenge in the placebo-pretreated group and 120 minutes in the NS-pretreated group. Although there appeared to be a trend for lower secretion of PGD2, albumin, and IgG in the NS-treated group, the overall differences did not achieve statistical significance. This protocol revealed that two topical 130 microliter doses of a 1% solution of NS failed to significantly reduce allergen-induced symptoms, PGD2 generation, or secretion of albumin, IgG, or lactoferrin when NS was compared with placebo. The anti-inflammatory and mast cell-stabilizing effects of NS may require more prolonged pretreatment before provocation to be effective.     

Vascular endothelial growth factor in exercising humans under different environmental conditions

It was the aim of this study to investigate the time course of changes in the serum concentrations of vascular endothelial growth factor (VEGF) during a regular survival training programme combined with food and fluid deprivation and during a high altitude marathon run. We studied soldiers of the Austrian Special Forces performing survival training at sea-level and marathon runners of the Posta Atletica who crossed the border between Chile and Argentina at altitudes up to 4722?m. Baseline data collected before the 1-week of survival training showed that the soldiers had normal VEGF [n=8, 246.7?(SD 118.5)?pg?·?ml^?1] serum concentrations which remained unchanged during the course of the study. Before the high altitude marathon the subjects showed normal VEGF serum concentrations [178?(SD 84.5)?pg?·?ml^?1]. After the run VEGF concentrations were found to be significantly decreased [41.0?(SD 41.6)?pg?·?ml^?1, P?相似文献   

Renomedullary and intestinal hyaluronan content during body water excess: a study in rats and gerbils

Our previous studies in rats have suggested a role for renomedullary hyaluronan (HA) in water homeostasis. The gerbil is known for its unique ability to conserve water. In the present study renal papillary and intestinal HA were compared between groups of anaesthetized gerbils and rats before and after up to 6 h of i.v. water loading. Baseline papillary HA in gerbils was only 37 % of that in the rat. Water loading in rats increased the papillary HA content. Elevation was maximal (+27 %,   P < 0.05  ) after 2 h of water loading and then declined to control levels after 6 h of water loading (+3 %, n.s.). In contrast, the gerbil responded with a decreased papillary HA content during water loading. The depression was maximal after 2 h (-49 %,   P < 0.05  ) and was still 41 % below the control values after 6 h (   P < 0.05  ). The urine flow rate increased rapidly in the rat and its maximum, 21 times above the control level (   P < 0.05  ), occurred at the HA peak, i.e. after 2 h of water loading while in the gerbil, the urine flow rate increased slowly and slightly and was only six times above control values after 6 h of water loading (   P < 0.05  ). The HA content along the intestine was similar in the two species: lowest in the duodenum and jejunum and highest in the distal colon. To conclude, in the rat, the elevation of papillary interstitial HA during acute water loading would counteract water reabsorption by changing the physico-chemical characteristics of the interstitial matrix favouring rapid water diuresis. This would work as a complement to the powerful regulation by ADH. The gerbil has a diametrically different regulation of papillary HA turnover during water loading. The decreased papillary HA level during water loading and the slow and small diuretic response may represent a genetic difference in adaptation to enhance the ability to conserve water in an arid environment.     

Output of bile and pancreatic enzymes after test meals with different fat content. Influence of body weight on pancreatic enzyme composition

The output of bile and pancreatic enzymes after two mixed meals with different fat content was studied in 16 healthy volunteers of normal body-weight. A quantitative multiple indicator dilution method was used. The delivery of more fat per time to the duodenum after the fat rich compared to the low fat meal was followed by the emptying of more bile but did not significantly increase the pancreatic response. The ratio between amylase and lipase was constant throughout the course of a single experiment but differed between the subjects. The ratio decreased with an increasing body weight, indicating a relative dominance of amylase over lipase in the lighter and the reverse in the heavy subjects. The same correlation was found when results from a previously reported series with a glucose containing mixed meal were reexamined. It is proposed that long time dietary differences might influence the enzyme composition of the postprandial pancreatic secretion.     

Effects of dietary sodium on body and muscle potassium content during heat acclimation

Summary It has been suggested that renal conversion of sodium (Na⁺) during training in hot environments results in potassium (K⁺) deficiencies. This investigation examined the influence of two levels of dietary Na⁺ intake (399 vs 98 mmol · d⁻¹) on intramuscular, urinary, sweat, and whole body K⁺ homeostasis. Nine unacclimated, untrained males underwent heat acclimation during two 8 day dietary-exercise regimens (40.1±0.1‡ C, 23.5±0.4%RH). Both diets resulted in depressed urinary K⁺ excretion. Sweat K⁺ and muscle K⁺ concentrations were not altered by diets or acclimation. The whole body stores of Na⁺ increased 31.1% (+ 916.8 mmol) during the high Na⁺ diet and decreased 7.8% (−230.4 mmol) during the low Na⁺ diet; whole body stores of K⁺ increased 4.1% (+ 137.6 mmol) during the high Na⁺ diet and increased 3.4% (+ 113.6 mmol) during the low Na⁺ diet. This dietary-acclimation protocol did not result in whole-body or intramuscular K⁺ deficits and offers no evidence to support previous claims that dietary sodium levels affect K⁺ balance.     

Comparison of D2O and ethanol dilutions in total body water measurements in humans

Total body water was measured by ethanol dilution and D₂O stable isotope dilution in a group of 20 healthy volunteers (5 females and 15 males), predominantly 23- to 31-year-old students. Both indicator substances were given orally with an ethanol burden of 0.8 g/kg body weight and a D₂O burden of 0.1 g/kg body weight after 12-h food and fluid restriction. This first direct comparison of total body water (TBW) from ethanol and D₂O dilutions revealed the ethanol compartments to be smaller than those of D₂O. The quotient of TBW (ethanol)/TBW (D₂O) was 97.7% , which is the order of the quotient TBW (H₂ ¹⁸O)/TBW (D₂O) (=97%), well known from the literature and taken to represent relatively exactly the value of TBW overestimation (based on H/D exchange for acid protons) following D₂O dilution [36]. Thus the value of TBW (ethanol) is almost identical to that of H₂ ¹⁸O, which provides direct evidence that ethanol is distributed only in the body water.Abbreviations TBW total body water - BIW water content in whole blood - GC gas chromatography     

Urinary dopamine excretion in healthy volunteers: effect of sodium diet and acute water load

The present study was designed to investigate, in human subjects, urinary dopamine excretion under different conditions of sodium and water homeostasis. In a cross-over trial, ten healthy volunteers were subjected to low-salt (LS; dietary salt restriction, sodium chloride (NaCl) intake <5 g per day), normal-salt (NS; normal food ad libitum), and high-salt (HS; normal food plus NaCl 100 mg/kg per day) regimens for 8 days in a randomized order. On day 7, urine was collected for 24 h. The variations in urinary sodium excretion reflected the dietary salt intake (LS: 16.3+/-4.7; NS: 144.1+/-18.2; HS: 221.9+/-12.9 mmol 24 h(-1) 1.73 m(-2)), but were not accompanied by significant changes in urinary dopamine excretion. On day 8, clearance studies showed that an acute oral water load of 1500 ml did not alter glomerular filtration rate or renal plasma flow but significantly increased urinary flow rate without affecting dopamine excretion. Assuming that excreted dopamine is not metabolized or reabsorbed during the tubular passage, both the unchanged urinary dopamine output in spite of 14-fold variations in sodium excretion and its independence of an acute water load argue against the hypothesis that dopamine in the tubular lumen acts as a natriuretic and/or diuretic factor in humans.     

Regulation of body weight in humans

The mechanisms involved in body weight regulation in humans include genetic, physiological, and behavioral factors. Stability of body weight and body composition requires that energy intake matches energy expenditure and that nutrient balance is achieved. Human obesity is usually associated with high rates of energy expenditure. In adult individuals, protein and carbohydrate stores vary relatively little, whereas adipose tissue mass may change markedly. A feedback regulatory loop with three distinct steps has been recently identified in rodents: 1) a sensor that monitors the size of adipose tissue mass is represented by the amount of leptin synthesized by adipose cells (a protein encoded by the ob gene) which determines the plasma leptin levels; 2) hypothalamic centers, with specific leptin receptors, which receive and integrate the intensity of the signal; and 3) effector systems that influence the two determinants of energy balance, i.e., energy intake and energy expenditure. With the exception of a few very rare cases, the majority of obese human subjects have high plasma leptin levels that are related to the size of their adipose tissue mass. However, the expected regulatory responses (reduction in food intake and increase in energy expenditure) are not observed in obese individuals. Thus obese humans are resistant to the effect of endogenous leptin, despite unaltered hypothalamic leptin receptors. Whether defects in the leptin signaling cascade play a role in the development of human obesity is a field of great actual interest that needs further research. Present evidences suggest that genetic and environmental factors influence eating behavior of people prone to obesity and that diets that are high in fat or energy dense undermine body weight regulation by promoting an overconsumption of energy relative to need.     

Change in body mass accurately and reliably predicts change in body water after endurance exercise

This study tested the hypothesis that the change in body mass (ΔBM) accurately reflects the change in total body water (ΔTBW) after prolonged exercise. Subjects (4 men, 4 women; 22–36 year; 66 ± 10 kg) completed 2 h of interval running (70% VO_2max) in the heat (30°C), followed by a run to exhaustion (85% VO_2max), and then sat for a 1 h recovery period. During exercise and recovery, subjects drank fluid or no fluid to maintain their BM, increase BM by 2%, or decrease BM by 2 or 4% in separate trials. Pre- and post-experiment TBW were determined using the deuterium oxide (D₂O) dilution technique and corrected for D₂O lost in urine, sweat, breath vapor, and nonaqueous hydrogen exchange. The average difference between ΔBM and ΔTBW was 0.07 ± 1.07 kg (paired t test, P = 0.29). The slope and intercept of the relation between ΔBM and ΔTBW were not significantly different from 1 and 0, respectively. The intraclass correlation coefficient between ΔBM and ΔTBW was 0.76, which is indicative of excellent reliability between methods. Measuring pre- to post-exercise ΔBM is an accurate and reliable method to assess the ΔTBW.     

Effects of normobaric hyperoxia on water content in different organs in rats

Pulmonary oxygen toxicity is a dose-dependent effect on alveolar epithelial and endothelial cells resulting in pulmonary oedema. Any concomitant effects on systemic capillary endothelium would be expected to result in capillary leakage and an increase in the tissues' water content. Total tissue water (TTW) in different organs was therefore studied in freely moving rats exposed to 100% O2 at normobaric pressure for 24 or 48 h, and compared to air-breathing control rats. The TTW for the following tissues was measured: Trachea, left bronchus, left lung, left and right ventricle, left kidney, skin (left paw-hindlimb), skin (back of the rat), left brain, left eye and thigh muscle left side. There was a significant increase in TTW of the lung accompanied by pleural effusion after 48 h of oxygen exposure as expected in all exposed animals. There was a small increase in TTW of the paw only, and a small decrease or no change in other tissues after 24 and 48 h of exposure. We conclude that there is no evidence of systemic capillary dysfunction as measured by tissue water content after exposure to hyperoxia in a dosage causing pulmonary oedema.     

Plasma volume changes during and after acute variations of body hydration level in humans

This study examined plasma volume changes (ΔPV) in humans during periods with or without changes in body hydration: exercise-induced dehydration, heat-induced dehydration and glycerol hyperhydration. Repeated measurements of plasma volume were made after two injections of Evans blue. Results were compared to ΔPV calculated from haematocrit (Hct) and blood haemoglobin concentration ([Hb]). Eight well-trained men completed four trials in randomized order: euhydration (control test C), 2.8% dehydration of body mass by passive controlled hyperthermia (D) and by treadmill exercise (60% of their maximal oxygen uptake, V˙O_2max) (E), and hyperhydration (H) by glycerol ingestion. The Hct, [Hb], plasma protein concentrations and plasma osmolality were measured before, during and after the changes in body hydration. Different Hct and [Hb] reference values were obtained to allow for posture-induced variations between and during trials. The ΔPV values calculated after two Evans blue injections were in good agreement with ΔPV calculated from Hct and [Hb]. Compared to the control test, mean plasma volume declined markedly during heat-induced dehydration [?11.4 (SEM 1.7)%] and slightly during exercise-induced dehydration [?4.2 (SEM 0.9)%] (P?相似文献