Sauna, sweat and science II - do we sweat what we drink?

Inspired by a previous 'Sauna, sweat and science' study [Zech et al. Isot Environ Health Stud. 2015;51(3):439-447] and out of curiosity and enthusiasm for stable isotope and sauna research we aimed at answering the question 'do we sweat (isotopically) what we drink'? We, therefore, pulse-labelled five test persons in a sauna experiment with beverages that were 2H-enriched at about +25,600 ‰. Sweat samples were collected during six sauna rounds and the hydrogen isotope composition δ2Hsweat was determined using an isotope ratio mass spectrometer. Before pulse labelling, δ2Hsweat - reflecting by approximation body water - ranged from -32 to -22 ‰. This is ∼35 ‰ enriched compared to usual mid-European drinking water and can be explained with hydrogen-bearing food as well as with the respiratory loss of 2H-depleted vapour. The absence of a clearly detectable 2H pulse in sweat after pulse labelling and δ2Hsweat results of ≤+250 ‰ due to a fast 2H equilibration with body water are moreover a clearly negative answer to our research question also in a short-term consideration. Given that the recovery of the tracer based on an isotope mass balance calculation is clearly below 100 %, we finally answer the question 'where did the rest of the tracer go?'

pH-Dependent Piecewise Linear Correlation of 1H,31P Chemical Shifts: Application in NMR Identification of Nerve Agent Metabolites in Urine Samples.

The NMR-observable nuclei of the acidic and basic compounds experience pH dependence in chemical shift. This phenomenon can be exploited in NMR titrations to determine p Ka values of compounds, or in pH measurement of solutions using dedicated pH reference compounds. On the other hand, this sensitivity can also cause problems in, for example, metabolomics, where slight changes in pH result in significant difficulties for peak alignment between spectra of set of samples for comparative analysis. In worst case, the pH sensitivity of chemical shifts can prevent unambiguous identification of compounds. Here, we propose an alternative approach for NMR identification of pH-sensitive analytes. The 1H and X (13C, 15N, 31P, ...) chemical shifts in close proximity to the acidic or basic functional group should, when presented as ordered pairs, express piecewise linear correlation with distinct slope, intercept, and range. We have studied the pH dependence of 1H and 31P chemical shifts of the CH3-P moiety in urinary metabolites of nerve agents sarin, soman and VX using 2D 1H-31P fast-HMQC spectroscopy. The 1H and 31P chemical shifts of these chemicals appear in very narrow range, and due to subtle changes in sample pH the identification on either 1H or 31P chemical shift alone is uncertain. However, if the observed 1H and 31P chemical shifts of the CH3-P moiety of individual compounds are presented as ordered pairs, they fall into distinct linear spaces, thus, facilitating identification with high confidence.

Kidney Response to the Spectrum of Diet-Induced Acid Stress.

Chronic ingestion of the acid (H⁺)-producing diets that are typical of developed societies appears to pose a long-term threat to kidney health. Mechanisms employed by kidneys to excrete this high dietary H⁺ load appear to cause long-term kidney injury when deployed over many years. In addition, cumulative urine H⁺ excretion is less than the cumulative increment in dietary H⁺, consistent with H⁺ retention. This H⁺ retention associated with the described high dietary H⁺ worsens as the glomerular filtration rate (GFR) declines which further exacerbates kidney injury. Modest H⁺ retention does not measurably change plasma acid⁻base parameters but, nevertheless, causes kidney injury and might contribute to progressive nephropathy. Current clinical methods do not detect H⁺ retention in its early stages but the condition manifests as metabolic acidosis as it worsens, with progressive decline of the glomerular filtration rate. We discuss this spectrum of H⁺ injury, which we characterize as “H⁺ stress”, and the emerging evidence that high dietary H⁺ constitutes a threat to long-term kidney health.

Effects of 1,5-anhydroglucitol on postprandial blood glucose and insulin levels and hydrogen excretion in rats and healthy humans.

The inhibition by 1,5-anhydro-d-glucitol (1,5-AG) was determined on disaccharidases of rats and humans. Then, the metabolism and fate of 1,5-AG was investigated in rats and humans. Although 1,5-AG inhibited about 50 % of sucrase activity in rat small intestine, the inhibition was less than half of d-sorbose. 1,5-AG strongly inhibited trehalase and lactase, whereas d-sorbose inhibited them very weakly. 1,5-AG noncompetitively inhibited sucrase. The inhibition of 1,5-AG on sucrase and maltase was similar between humans and rats. 1,5-AG in serum increased 30 min after oral administration of 1,5-AG (600 mg) in rats, and mostly 100 % of 1,5-AG was excreted into the urine 24 h after administration. 1,5-AG in serum showed a peak 30 min after ingestion of 1,5-AG (20 g) by healthy subjects, and decreased gradually over 180 min. About 60 % of 1,5-AG was excreted into the urine for 9 h following ingestion. Hydrogen was scarcely excreted in both rats and humans 24 h after administration of 1,5-AG. Furthermore, 1,5-AG significantly suppressed the blood glucose elevation, and hydrogen excretion was increased following the simultaneous ingestion of sucrose and 1,5-AG in healthy subjects. 1,5-AG also significantly suppressed the blood glucose elevation following the simultaneous ingestion of glucose and 1,5-AG; however, hydrogen excretion was negligible. The available energy of 1,5-AG, which is absorbed readily from the small intestine and excreted quickly into the urine, is 0 kJ/g (0 kcal/g). Furthermore, 1,5-AG might suppress the blood glucose elevation through the inhibition of sucrase, as well as intestinal glucose absorption.

Direct analysis of δ2H and δ18O in natural and enriched human urine using laser-based, off-axis integrated cavity output spectroscopy.

The stable isotopes of hydrogen (δ(2)H) and oxygen (δ(18)O) in human urine are measured during studies of total energy expenditure by the doubly labeled water method, measurement of total body water, and measurement of insulin resistance by glucose disposal among other applications. An ultrasensitive laser absorption spectrometer based on off-axis integrated cavity output spectroscopy was demonstrated for simple and inexpensive measurement of stable isotopes in natural isotopic abundance and isotopically enriched human urine. Preparation of urine for analysis was simple and rapid (approximately 25 samples per hour), requiring no decolorizing or distillation steps. Analysis schemes were demonstrated to address sample-to-sample memory while still allowing analysis of 45 natural or 30 enriched urine samples per day. The instrument was linear over a wide range of water isotopes (δ(2)H = -454 to +1702 ‰ and δ(18)O = -58.3 to +265 ‰). Measurements of human urine were precise to better than 0.65 ‰ 1σ for δ(2)H and 0.09 ‰ 1σ for δ(18)O for natural urines, 1.1 ‰ 1σ for δ(2)H and 0.13 ‰ 1σ for δ(18)O for low enriched urines, and 1.0 ‰ 1σ for δ(2)H and 0.08 ‰ 1σ for δ(18)O for high enriched urines. Furthermore, the accuracy of the isotope measurements of human urines was verified to better than ±0.81 ‰ in δ(2)H and ±0.13 ‰ in δ(18)O (average deviation) against three independent isotope-ratio mass spectrometry laboratories. The ability to immediately and inexpensively measure the stable isotopes of water in human urine is expected to increase the number and variety of experiments which can be undertaken.

Association of urinary pH with body weight in nephrolithiasis.

BACKGROUND: The prevalence of kidney stone disease in the United States is progressively increasing, paralleling the growing rate of obesity. Uric acid nephrolithiasis, a condition associated with a low urinary pH, has been linked to obesity and insulin resistance. Based on these observations, we hypothesized that urinary pH may be inversely associated to body weight in nephrolithiasis. METHODS: Data were retrieved from 4883 patients with nephrolithiasis who underwent ambulatory evaluation at two established stone clinics in Dallas and Chicago. The patients collected 24-hour urine samples on an outpatient basis, while avoiding any drug that could alter urinary pH. Patients were divided in increasing sextiles of body weight, and urinary pH was adjusted for urinary creatinine and for age. RESULTS: Urinary pH had a strong, graded inverse association with body weight. Urinary creatinine and age were both found to be significant covariates of urinary pH, while gender was not a significant independent variable after adjustment for urinary creatinine. Mean 24-hour urinary pH, adjusted for age and urinary creatinine, were 6.09, 6.04, 6.01, 5.99, 5.97, and 5.91 for sextiles of body weight in increasing order from Dallas (P for linear trend <0.0001), and 6.18, 6.10, 6.04, 6.02, 5.97, and 5.88 for the sextiles from Chicago (P for linear trend <0.0001). CONCLUSION: We conclude that urinary pH is inversely related to body weight among patients with stones. The results confirm the previously proposed scheme that obesity may sometimes cause uric acid nephrolithiasis by producing excessively acid urine due to insulin resistance.

Factors affecting renal hydrogen ion excretion capacity in healthy children.

In 560 healthy German children and adolescents aged 2.8-22.0 years from the DONALD (Dortmund Nutritional and Anthropometric Longitudinally Designed) study, the relationship between urine pH and renal net acid excretion (mmol/day/1.73 m2) was analysed. A quadratic model showed the best fit (r2 = 0.608). Using logistic regression analysis three parameters (urinary phosphorus excretion, total protein intake and urinary ratio of potassium and sodium) had a significant effect on renal hydrogen ion excretion capacity characterised by the probability of high or low net acid excretion with respect to the urine pH value. Urinary osmolality, in contrast to what has been seen in a previous experimental study with low birth weight infants, along with sex and age had no significant independent effects on renal net acid excretion with respect to the urine pH value over the range of osmolalities observed. In healthy children and adolescents a low fluid intake with high urinary osmolality does not at least substantially decrease the renal capacity of hydrogen ion excretion.

A comparison of 1H8- and 2H8-toluene toxicokinetics in men.

1. To examine the bioequivalence of an isotope-labelled tracer to study toxicant disposition, we conducted 33 controlled human exposures to a mixture of 50 ppm 1H8-toluene and 50 ppm 2H8-toluene for 2 h, and measured concentrations in blood and breath, and metabolite levels in urine for 100 h post-exposure. 2. A physiologically based kinetic (PBK) model found that compared with 1H8-toluene, 2H8-toluene had a 6.4+/-13% (mean+/-SD) lower AUC, a 6.5+/-13% higher systemic clearance (1.46+/-0.27 versus 1.38+/-0.25 l/h-kg), a 17+/-22% larger terminal volume of distribution (66.4+/-14 versus 57.2+/-10 l/kg) and a 9.7+/-26% longer terminal half-life (38+/-12 versus 34+/-10 h) (p < 0.05 for all comparisons). 3. The higher 2H8-toluene clearance may have been due to an increased rate of ring oxidation, consistent with the 17% higher observed fraction of 2H5- versus 1H5-cresol metabolites in urine. 4. The larger terminal volume and half-lives for 2H8-toluene suggested a higher adipose tissue/blood partition coefficient. 5. Observed isotope differences were small compared with interindividual differences in 1H8-toluene kinetics from previous studies. 6. The PBK model allowed us to ascribe observed isotope differences in solvent toxicokinetics to underlying physiologic mechanisms.

Physiological disposal of the potential alkali load in diet of the rat: steps to achieve acid-base balance.

The purpose of this study was to provide a better understanding of the physiological role of endogenous net organic acid production in rats consuming their usual diet. Balance studies were performed over 24 h, and urine was collected in the day and night portions of the diurnal cycle. A supplemented low-electrolyte diet(LED) was fed to determine whether urinary organic anions were identical to those in the diet. A titration procedure was developed to determine the pK of titratable groups in the urine of rats studied with and without an acid load. Although normal rats excreted net acid (NAE), the latter was inversely related to the amount of food consumed. The rates of excretion of bicarbonate (HCO3), citrate, unmeasured organic anions, and NH+4 were higher in the night portion of the diurnal cycle. NAE rose dramatically when alkali intake was decreased by consuming the LED. Dietary and urinary organic anions were not identical because rats fed the LED supplemented with potassium citrate excreted <10% of this alkali load as citrate and <25% as HCO3. In the 24 h after 3,000 ¿mol NH4Cl was given intraperitoneally, H+ did not appear to be retained, yet NAE rose by only close to 2,000 ¿eq. The rate of excretion of titratable groups with a pK in the 3 to 5 pH range fell by close to 1,000 ¿eq; most of these changes occurred in the first 7 h after NH4Cl was given. We conclude that rat chow provides a large net alkali load. There appear to be two types of endogenous acid production, a form associated with a rise in NAE (e.g., sulfuric acid) and dietary alkali-driven endogenous net acid production, which titrates this alkali. Renal excretion of organic anions makes these acids end products of metabolism.

Energy expenditure and fluid production in hyperbaric He-O2 environments using doubly labeled water.

Energy expenditure (EE), carbon dioxide production (rCO2), water turnover (rH2O), and urine production (UP) were measured to determine nutrient requirements of U.S. Navy divers during saturation dives. Parameters were measured in a normal surface environment (n = 10) and in 0.56 MPa (n = 9) and 3.17 MPa (n = 11) helium-oxygen environments. Daily EE, rCO2, and rH2O were measured with the doubly labeled water method for 10-14 days in each environment. Daily UP was determined by 24-h urine collection for 5- to 10-day periods in each environment. Divers consumed a mixed diet composed of 30% calories from fat, 15% protein, and 55% carbohydrate. Both EE and rCO2 increased significantly relative to surface conditions at 0.56 MPa (13 +/- 4% and 11 +/- 4%) and 3.17 MPa (14 +/- 4% and 11 +/- 3%), but there was no difference between dives. Water turnover was not significantly affected by the hyperbaric environment. UP was significantly greater than surface conditions at 0.56 MPa (53 +/- 19%) but not at 3.17 MPa (38 +/- 18%). Increased EE is attributed to thermal stress caused by the helium-oxygen environment. Increased UP may have been caused by decreased evaporative water loss.

Resistant starch decreases serum total cholesterol and triacylglycerol concentrations in rats.

Rats were meal-fed semipurified diets containing a low (0.8 g/MJ) and a high (9.6 g/MJ) amount of resistant starch (RS) or various amounts of RS (0.8 to 9.6 g/MJ) and guar gum (0 to 8.8 g/MJ). In one experiment, rats were fed the low and high RS diets in three dietary regimens (ad libitum consuming, 12 h ad libitum/12 h food deprived, and meal fed). Effects of RS and guar gum on serum postprandial and postabsorptive concentrations of total cholesterol (TC) and triacylglycerol (TAG), growth, hydrogen excretion, tissue weights and contents of small intestine and cecum, and pH of cecal contents were investigated. In addition, effects of RS on food intake, de novo hepatic synthesis of fatty acids and neutral sterols, and on lipoprotein lipase activity and weight of epididymal fat pads were investigated. Compared with feeding the low RS diet, the high RS diet reduced the serum TC and TAG concentrations, with these effects observed after 1 and 2 wk of feeding, respectively. The dietary regimen did not influence the effect of RS on the serum TC and TAG concentrations, but it did affect the serum TAG concentration. Resistant starch had no effect on the hepatic synthesis of fatty acids and neutral sterols or on the lipoprotein lipase activity in epididymal fat pads. Guar gum also reduced the serum TC concentration, but it had no effect on serum TAG concentration. The tissue weights and contents of small intestine and cecum as well as hydrogen excretion increased with increasing amounts of dietary RS and guar gum, whereas the pH of cecal contents decreased. No effects of RS on food intake and total body weight gain were found, whereas guar gum decreased weight gain. Feeding the high RS diet also led to a lower weight of the epididymal fat pads. We conclude that dietary RS can reduce serum TC and TAG concentrations and fat accretion.

Prostaglandin regulation of H+ secretion in amphibian epithelia.

The role of prostaglandins in regulating H+ excretion in amphibian epithelia was investigated. The abdominal skin of the southern leopard frog Rana pipiens and the urinary bladder of the toad Bufo marinus were used to measure proton excretion across their mucosal surface. Prostaglandin F2 alpha (PGF2 alpha) produced a dose-dependent inhibition of H+ excretion across the frog skin. Frogs pretreated with ibuprofen (30 mg.kg-1.day-1 for 3 days) showed an enhanced proton excretion similar to that observed when frogs are placed in chronic metabolic acidosis. The number of mitochondria-rich cells, the cells responsible for proton excretion, was also increased in frog skins after chronic metabolic acidosis or ibuprofen treatment. Mezerein and the phorbol ester 4 beta-phorbol 12-myristate 13-acetate (4 beta-PMA), activators of protein kinase C (PCK), decreased H+ excretion in frog skin, whereas the inactive phorbol 4 alpha-PMA was without an effect. The inhibition of proton excretion was similar to that observed with PGF2 alpha and suggested that the effects of PGF2 alpha and activation of PKC were mediated through a common pathway. Frogs pretreated with ibuprofen not only had an enhanced proton excretion rate but also had a decrease in cytosolic PKC activity. In another amphibian tissue, the toad urinary bladder, PGE2 inhibited proton excretion at low doses but enhanced H+ excretion at higher doses. Toads maintained under chronic metabolic acidosis had enhanced proton excretion rates and also had a threefold increase in cellular PGE2 concentration, which was consistent with the observation that PGE2 enhanced proton excretion at high doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Nephrotoxic effects of diethylene glycol (DEG) in rats.

Diethylene glycol (DEG) is a widely used substance with various risks of intoxication. In adult rats influences of DEG on functional parameters are characterized, indicating early signs of nephrotoxicity. A dose dependent proteinuria, an oliguric effect, an increased excretion of free hydrogen ions and a compensated impairment of renal tubular transport processes can be stated (0.25, 0.5 and 0.75 ml DEG/100 g b.m. i.p.). Following a single dose of 0.5 ml DEG/100 g b.m. i.p. the maximally expressed nephrotoxic effect is measurable 4 to 8 days after administration.

Renal acidification during chronic hypercapnia in the conscious dog.

Enhanced renal acidification during chronic hypercapnia (CH) results in transient augmentation in net acid excretion (NAE) (adaptation phase) and persistent acceleration in renal bicarbonate reclamation (adaptation and steady-state phases). The mechanisms responsible for the return of NAE to control values despite persistent acidemia during the steady state phase of CH remain undefined. In addition, it remains unsettled whether the enhancement of renal ammoniagenesis known to occur during the adaptation phase of CH persists during the steady-state phase. Furthermore it is uncertain if the alteration in whole-kidney acidification observed in CH originates from augmentation in the acidification of both proximal and distal nephronal segments. To shed further light on these issues, observations on the profile of the urine acid-base moieties during the adaptive and steady-state phases of CH were carried out in dogs chronically exposed to hypercapnia (10% FiCO2) in an environmental chamber (13 days). Additionally, collecting duct hydrogen ion secretion (CDH+S) was evaluated by employing the U-B PCO2 in alkaline urine in intact unanesthetized dogs with either CH (10% FiCO2) or eucapnia. The balance studies demonstrated that NAE increased in early hypercapnia (4.84 meq/kg body weight, control 3.27 meq/kg body weight, p less than 0.05) and returned to baseline thereafter; by contrast, urine NH+4 which was augmented during the adaptation phase (3.71 meq/kg body weight, control 1.97 meq/kg body weight, p less than 0.05) remained elevated throughout (3.25 meq/kg body weight).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of urinary pH on the behavioral responses of squirrel monkeys to nicotine.

The present study evaluated the behavioral effects of nicotine under conditions that manipulated urinary pH. The effects of nicotine were examined on the responding of squirrel monkeys under a multiple fixed-interval, fixed-ratio schedule of stimulus-shock termination when nicotine was administered alone or together with the gastric administration of an acidifier (ammonium chloride) or an alkalinizer (sodium bicarbonate). Responding under the FI schedule was increased markedly across a range of doses of nicotine (0.02-0.20 mg/kg). Responding under the FR was increased to a lesser extent by the lower doses of nicotine (0.02-0.05 mg/kg) and was decreased by doses of nicotine that increased responding under the FI (0.10-0.20 mg/kg). Generally, administration of the acidifier attenuated the effects of nicotine while administration of the alkalinizer potentiated those effects. These findings support the argument that changes in cigarette smoking under conditions that alter urinary pH involve nicotine per se. In addition, a new interpretation of the relationship between urinary pH and cigarette smoking is offered.