A cytotoxin of pseudomonas aeruginosa acts directly on the cortical thick ascending limb of henle's loop of rabbit kidney

The present study examines directly the effect of a cytotoxin of Pseudomonas aeruginosa on the in vitro perfused rabbit cortical thick ascending limb of the loop of Henle (cTAL). 25 cTAL segments were perfused at high rate. The open circuit transepithelial electrical PD (PD_te) and the specific electrical transepithelial resistance (R_t) were recorded continuously. From PD_te/R_t the equivalent short circuit current (Isc) was calculated. The Isc was 214±30 A·cm^–2 under control conditions, and decreased significantly to 74±34 A·cm^–2 60 s after the addition of toxin (2 mg·l^–1) to the lumen perfusate. Microscopic observation and photographs taken at that time clearly indicated swelling of the cTAL cells. Thereafter inhibition of active transport proceeded further, R_t fell progressively, and cells started to desquamate from the basement membrane. This effect of the toxin was dose dependent, and was half maximal at approximately 1.2 mg·l^–1. From the bath side the effect was less marked and higher doses of toxin had to be used (half maximal effect at 5 mg·l^–1). We conclude that this toxin of Pseudomonas aeruginosa exerts its toxic effect on the cTAL segment by increasing primarily the permeability of the lumen membrane.Part of this study has been presented at Spring meering Dt. Pharmakol. Ges., Mainz, 1982. This work has been supported by the Schutzkommission beim Bundesminister des Inneren, Bonn-Bad Godesberg, and by Deutsche Forschungsgemeinschaft, Gr 480/5-7     

Molecular specificity of the tubular resorption of “acidic” amino acids

Single sections of superficial proximal convolutions of rat kidney were microperfused in vivo and in situ. The perfusion fluids contained radioactively labelledl- ord-aspartate,l-glutamate,l-pyroglutamate, or N-methyl-d-aspartate.l--Carboxyglutamate as well as the other amino acids were added in the unlabelled from. Results.l- andd-Aspartate (0.073 mmol·1^–1) are quickly resorbed at about the same rate.d-Aspartate resorption was blocked byl-aspartate (5 mmol·1^–1) but not by -alanine (5 mmol·1^–1).l-Aspartate resorption was inhibited byl-glutamate (2 mmol·1^–1) but not byd-glutamate,l-asparagine,l-phenylalanine or by succinate (2 mmol·1^–1, each). The fast resorption ofl-glutamate (0.073 mmol·1^–1) was blocked byd-aspartate,l-cysteate (2 mmol·1^–1), but not by 3-mercaptopicolinic acid (0.15 mmol·1^–1),l-glutamine, 2-oxoglutarate, taurine, N-methyl-l-glutamate or kainic acid (2 mmol·1^–1, each).l--Carboxyglutamate (0.66 mmol·1^–1) and N-methyl-d-aspartate (2mol·1^–1) were found to be resorbed only at an extremely small rate.l-pyroglutamate (0.076 mmol·1^–1) resorption was not influenced byl-glutamate (1 mmol·1^–1). Fractional excretion of -carboxyglutamate was 7–25% (l-from) or 45–70% (d-form) at an artificially elevated plasma level of 12mol·1^–1.It is concluded thatl- andd-aspartate,l-glutamate,l-cysteate and, to a much smaller extent,l--carboxyglutamate, are accepted by the tubular resorption mechanism highly specific for acidic amino acids. N-Substitution, the amidation of the - or -carboxyl group, or the removal of the -amino moiety almost completely abolish the ability of such compounds to be resorbed via this carrier; N-methylated or -carboxylated derivatives of acidic amino acids are not resorbed at all from the proximal tubule. The resorption of glutamate, but not of aspartate, is highly stereospecific.Parts of this work were presented at meetings of the German Physiological Society in 1978 [28] and of the Gesellschaft für Nephrologie in 1980 [29] as well as at the VIIIth International Congress of Nephrology in Athens in 1981 [26]with technical assistance of Angelika Ascher and Gertaud Vetter     

Facilitated diffusion of lactic acid in the guinea-pig placenta

In the guinea-pig placenta which was artificially perfused on the fetal side while maternal placental blood flow was controlled, the placental transfer per mean transplacental concentration difference (the transfer coefficient TC) was determined for lactate. TC forl-lactate (TC_LL) was compared to that ford-lactate (TC_DL) and measured for various concentrations ofl-lactate, bicarbonate, pyruvate and CO₂. Applying a closed circuit perfusion technique,l-lactate and proton concentrations on both sides of the placenta were followed during infusion of HCl and sodiuml-lactate into the fetal circulation.It was found that TC_LL is 3 times TC_DL. TC_LL is depressed by increasing concentrations ofl-lactate while TC for Cl-36 is not. TC_LL is also depressed by 50 mmol·l^–1 pyruvate. Concentration changes of glucose do not affect TC_LL. TC_LL rises with the proton concentration, independently of the concomitant changes of the bicarbonate concentration. Transplacentral proton concentration gradients producel-lactate concentration gradients and vice versa.It is concluded that (1) facilitated diffusion ofl-lactate occurs in the placenta and that (2)l-lactate transfer is coupled with proton transfer. Beside the well-known placental transport system for glucose this is the second passive transport system found in a placenta.Supported by the Deutsche Forschungsgemeinschaft (Mo 105/8)Partly presented at the Frühjahrstagung der Deutschen Physiologischen Gesellschaft, 1977     

The influence of work intensity on postexercise proteinuria

Summary Fifteen men were studied during 100 m, 400 m and 3,000 m runs at maximal speed to determine total urinary protein and albumin excretion rates in relation to different distances of running. Venous blood lactate rose to 7.5 mmol · l^–1 after the 100 m and 3,000 m events, while reaching 12 mmol · l^–1 after the 400 m dash. Total urinary protein excretion increased to 330, 1640 and 565 g · min^–1 after the 100 m, 400 m and 3,000 m runs respectively, as compared with basal values (70 g · min^–1). In the meantime, albumin excretion increased respectively by 5, 25 and 18 fold of the resting values. The renal clearance of albumin increased to 0.84, 5.62 and 3.35 l · min^–1 after the three runs, as compared with a mean value of 0.19 l · min^–1 at rest. Exponential relationships (r=0.85) were recorded between post-exercise venous lactate and albumin, and total protein excretion. The present work illustrates the major influence of the intensity of exercise (anaerobic glycolytic component), rather than its duration, on the excretion rate of urinary proteins.This work has been partially presented at the 1981 American College of Sports Medicine Annual Meeting (Miami Beach, USA)     

Renal tubular reabsorption of taurine,γ-aminobutyric acid (GABA) andβ-alanine studied by continuous microperfusion

Summary Renal tubular reabsorption of taurine, -aminobutyric acid (GABA), and -alanine was studied in vivo et situ by continuous microperfusion of single proximal tubules of the rat. In each case, reabsorption was much slower than that for other amino acids that have been studied. With a concentration of 0.1 mmol/l in initial perfusate, about 60% of initial load was reabsorbed over perfusion distance of 3 mm. Taurine reabsorption saturated with only 2.17 mmol/l in initial perfusate. Assuming simple two-parameter kinetics, upper limits for K _m of 0.54 mmol/l and forV _max of 0.59 pmol·cm^–1·s^–1 for tubular reabsorption of taurine were estimated. High (20 mmol/l) concentrations of taurine or -alanine in perfusate completely inhibited GABA reabsorption, butl-phenylalanine (20 mmol/l) had no significant effect. The results indicate that the three amino acids are reabsorbed slowly from the proximal tubule by what may be a common transport system. This system appears to have a high affinity but low capacity and to be different from other known renal tubular transport systems for amino acids.Supported by National Science Foundation Research Grant No. PCM 75-09918 and by grant No. 1740 of the Austrian Fonds zur Förderung der Wissenschaftlichen Forschung.     

Effect of anaerobic and aerobic exercise of equal duration and work expenditure on plasma growth hormone levels

Summary Growth hormone (GH) and lactic acid levels were measured in five normal males before, during and after two different types of exercise of nearly equal total duration and work expenditure. Exercise I (aerobic) consisted of continuous cycling at 100 W for 20 min. Exercise II (anaerobic) was intermittent cycling for one minute at 285 W followed by two minutes of rest, this cycle being repeated seven times. Significant differences (P<0.01) were observed in lactic acid levels at the end of exercise protocols (20 min) between the aerobic (I) and anaerobic (II) exercises (1.96±0.33 mM·l^–1 vs 9.22±0.41 mM·l^–1, respectively). GH levels were higher in anaerobic exercise (II) than in aerobic (I) at the end of the exercise (20 min) (2.65±0.95 g·l^–1 vs 0.8±0.4 g·l^–1;P<0.10) and into the recovery period (30 min) (7.25±6.20 g·l^–1 vs 2.5±2.9 g·l^–1;P<0.05, respectively).     

Effects of calcium channel blockers on the contractility of the filariidAcanthocheilonema viteae

The role of calcium in muscle contractility was explored in the filarial nematodeAcanthocheilonema viteae (Dipetalonema viteae). The parasite was slit open longitudinally and mounted in a smooth-muscle chamber that had been filled with aerated (95% N₂/5% CO₂) physiological solution at 37°C. Nifedipine (10^–6 m) and cadmium (3×10^–5 m) reduced the spontaneous isotonic contractions ofA. viteae, whereas verapamil (10^–5 m) and diltiazem (10^–5 m) enhanced them. The effects of nifedipine and verapamil did not appear to be due to the solvent ethanol. All of the drugs reduced the maximal contraction induced by acetylcholine (ACh, 10^–5 m), although nifedipine was the most potent. After the exposure of worm preparations to a calcium-free medium containing ethyleneglycol-bis-(-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA, 10^–4 m) for 1 h, application of ACh (10^–5 m) induced a small, transient contraction. Subsequent applications of ACh in this medium had no effect. Thus, the nematode muscle contraction appears to depend on extracellular calcium. Nifedipine, diltiazem, and verapamil could act by reducing the calcium influx across the muscle membrane.     

Adjustment of metabolism,catecholamines and β-adrenoceptors to 90 min of cycle ergometry

Adrenaline infusion of 0.1 g · kg^–1 · min^–1 in healthy volunteers results in an increase of hepatic glucose production, an increase of the absolute number of occupied -adrenoceptors and specific changes in metabolism. To compare these effects with the changes induced by an endogenous catecholamine release, we investigated healthy volunteers during cycle ergometry. After fasting at least 14 h seven healthy subjects exercised for 90 min at an intensity of 20% below their individual anaerobic threshold. The rate of glucose production as well as the turnover rates of alanine and leucine were calculated using stable isotope tracers. High and low affinity -adrenergic binding sites on lymphocytes were determined by an equilibrium binding assay with (–)¹²⁵ Iodocyanopindolol. After 90 min of cycling the rate of appearance of glucose increased significantly from means of 2.0 (SD 0.2) to 2.65 (SD 0.50) mg · kg^–1 · min^–1 with unchanged blood concentrations of glucose and lactate. The flux of the amino acids alanine and leucine decreased significantly from means of 0.91 (SD 0.21) to 0.62 (SD 0.14) mg · kg^–1 · min^–1 and from 0.40 (SD 0.05) to 0.32(SD 0.04) mg · kg^–1 · min^–1, respectively. The mean free fatty acid concentration increased significantly from 0.65 (SD 0.33) to 1.27 (SD 0.45) mmol · l^–1 during the endurance trial. The increase of glucose turnover and the decrease of amino acid flux point to a metabolic shift towards enhanced utilization of free fatty acids. Adrenaline and noradrenaline concentrations showed a moderate but significant increase from means of 0.61 (SD 0.20) to 0.99 (SD 0.36) nmol · l^–1 and from 2.27 (SD 0.75) to 3.46 (SD 0.38) nmol · 1^–1, respectively. The number of high affinity -adrenergic binding sites per cell (-adrenoceptors) nearly doubled from 770 (SD 130) to 1490 (SD 150) during 90 min of cycling. The observed endogenous plasma catecholamine concentrations were not sufficient to change significantly the relative receptor occupancy. This would seem to indicate that the aerobic exercise induced effects depended more on the absolute number of occupied -adrenoceptors than on their relative receptor occupancy. When compared to the results of the adrenaline infusion experiment the increases of the hepatic glucose production and the increase of -adrenoceptors were very similar in both groups despite ten times higher adrenaline plasma concentrations in the infusion group. This would seem to indicate that -adrenoceptors mediated effects do not correlate with catecholamine plasma concentrations.     

Electrophysiological analysis of sodium-transport in the colon of the frog (Rana esculenta)

Sodium transport and apical bioelectrical membrane properties were investigated in frog colonic epithelium in the absence and presence of the antidiuretic hormone arginine-vasotocin (AVT). Apical Na-permeability and intracellular Na-activity were evaluated by analysis of current-voltage relationships in the serosally K-depolarized tissue. Tissue- and apical membrane capacitance were measured by voltages step analysis. The frog colon was found to be a tight epithelium with a transepithelial resistance of 2.63±0.25 k·F (n=17). 85–90% of short circuit current (11.2±1.1 A·F·l^–1;n=17) was related to electrogenic Na-transport from mucosa to serosa. Graded doses of amiloride (<50 mol·l^–1) induced Michaelis-Menten-type inhibition kinetics. Serosal addition of 10^–6 mol·l^–1 AVT induced a significant increase in sodium current (25%), apical sodium permeability (19%) and tissue capacitance (4.3%) whereas intracellular Na-activity remained unchanged. There was a good correlation between increased Na-current and apical Na-permeability. No correlation was found between Na-current and membrane capacitance. Our results demonstrate that in contrast to other species the amphibian colon shows a natriferic reaction to AVT. We suggest that the regulation of Na-transport in frog colon is similar to that in the toad urinary bladder. It is caused by an activation of preexisting apical Na-channels and not by fusion of subapical cytoplasmic vesicles with the apical membrane.     

Comparison of the buffer capacity of endocytotic vesicles,lysosomes and cytoplasm in cells derived from the proximal tubule of the kidney (opossum kidney cells)

During transepithelial acid-base transport cells of the proximal tubule of the kidney have to maintain a relative constant intracellular pH. Herein cellular buffer capacity plays an important role. We measured vesicular buffer capacity in proximal tubule-derived opossum kidney cells and compared it with cytoplasmic buffer capacity to determine the possible importance of vesicular buffer capacity for cellular pH homeostasis. Under HCO₃ ^–-free conditions endocytotic vesicular buffer capacity was 43±4 mmol·l^–1·pH-unit^–1 (n=7) and exceeded cytoplasmic buffer capacity (19±3 mmol·l^–1 ·pH-unit^–1; n=7) significantly. Lysosomal buffer capacity was 19±6 mmol·l^–1·pH-unit^–1; (n=5). Inhibition of vesicular H⁺-ATPase using bafilomycin A₁ led to a dramatic increase of vesicular pH but to a decrease of cytoplasmic pH indicating the importance of organellar buffer systems. We estimated that endocytotic buffer capacity accounts for 23% of cellular buffer capacity under our experimental condition and thus, impairment of endosomal acidification may affect cytoplasmic pH indeed. From our results we conclude that endocytotic vesicles have a large buffer capacity and might play a role in cellular pH homeostasis.     

Reabsorption of monocarboxylic acids in the proximal tubule of the rat kidney

The transport ofd-lactate across the epithelium of the late proximal convolution was investigated by two methods: 1. by measuring the zero net flux transtubular concentration difference (c _tt,45s) and the permeability (P) ofd-lactate and calculating from both the transtubular active transport rate (J _lac ^act ). 2. By measuring the 3.5 s efflux ofd-lactate from the tubular lumen, while blood was flowing through the capillaries. The 3.5 s efflux comprises two components, one going through the brush border (J _lac ^bb ) and one going the paracellular pathway (J _lac ^paracell =P _lac·c _{lac lumen}). Both,J _lac ^act andJ _lac ^bb ofd-lactate gave the sameK _m 1.9 and 1.7 mmol/l and the same maximal transport rate 3.2 and 2.9 pmol cm^–1 s^–1. TheK _i ofl-lactate tested againstJ _lac ^act andJ _lac ^bb ofd-lactate was also the same: 1.1 and 1.0 mmol/l. These data indicate that under our experimental conditions only the flux through the brush border seems to be rate limiting and thatd-lactate uses the same transport system asl-lactate.When Na⁺ was omitted from the perfusatesJ _lac ^act disappeared completely, whileJ _lac ^bb was reduced by 64%. These data reflect the Na⁺ dependence of thed-lactate transport through the brush border. Variation of intra-and extracellular pH by raisingpCO₂, omitting HCO ₃ ^– from the perfusates or adding acetazolamide had no effect on the transport ofd-lactate when -ketoglutarate was used as fuel. However, when acetate was used as fuel, intracellular acidosis brought the reducedJ _lac ^act back to the values obtained with -ketoglutarate as fuel. It is suggested that this is an effect on a contraluminal transport step.Probenecid (5 mmol/l) and phloretin (0.25 mmol/l) inhibitedJ _lac ^act significantly.J _lac ^bb , however, was only inhibited by probenecid when acetate was used as fuel. These data indicate that both compounds act on thed-lactate exit at the contraluminal cell side, but that probenecid acts in addition at the luminal cell side. SITS (1 mmol/l) augmentedJ _lac ^bb when acetate was used as fuel and is similar to the effect of lowering intracellular pH as described above. The SH reagents mersalyl (1.0 mmol/l) and maleolylglycine (1 mmol/l) did not influenceJ _lac ^bb .     

Effect of calcium,furosemide and chlorothiazide on net volume reabsorption and basolateral membrane potential of the distal tubule

In the distal tubule of the isolated kidney of Amphiuma net volume reabsorption (split-oil droplet method) and basolateral membrane potential ( _b ) were measured. Luminal perfusion solution could be changed rapidly from 108 mmol·l^–1 NaCl plus 0.1 mmol·l^–1 calcium to solutions containing 103 or 97 mmol·l^–1 NaCl plus 3.6 or plus 7.2 mmol·l^–1 calcium. Furthermore, 10^–4 mol·l^–1 furosemide or chlorothiazide were applied luminally. (1) Addition of 7.2 mmol·l^–1 calcium hyperpolarized _b from –73.4 mV to –108.3 mV and inhibited net volume reabsorption. (2) Similarly, when furosemide was injected, _b was hyperpolarized and net volume reabsorption reduced. Application of both high calcium and furosemide further inhibited volume reabsorption. (3) The effects of chlorothiazide were similar to those of furosemide. However, when both high calcium and chlorothiazide were administered _b and volume reabsorption were almost normalized. (4) The data are consistent with the hypothesis that calcium and the diuretics interfere primarly with chloride uptake across the luminal membrane and thus reduce sodium chloride transport. When chlorothiazide in the presence of high luminal calcium almost normalized chloride transport, it is likely that its effects were by stimulating calcium transport and thus increasing intracellular calcium activity.Supported by Deutsche Forschungsgemeinschaft (Wi 328)The paper was presented, in part, at the XXVIIth Int. Congr. Physiol. Sci., Paris 1977, Proc. Vol. 13:304     

Uphill transport of pyrimidine nucleosides in renal brush border vesicles

The uptake of cytidine, of thymidine and of uridine in brush border vesicles prepared from the cortex of rat kidney has been studied by the technique of rapid filtration. The nucleosides were not metabolized in the vesicles. The time-courses of uptake in the presence of inwardly directed gradients of Na⁺ and of K⁺ showed an overshoot, indicating uphill transport. The overshoot was much more pronounced with Na⁺ than with K⁺; it was not observed when Na⁺ was at equilibrium across the membrane. The uptake of the nucleosides was stimulated by an inside negative potential in the presence of Na⁺. These results provide evidence for a cotransport of pyrimidine nucleosides with Na⁺. The apparentK _m's for the uptake of cytidine, of thymidine and of uridine were 3.76 mol · l^–1, 4.18 mol · l^–1 and 7.21 mol · l^–1 respectively. The uptake of the pyrimidine nucleosides was insensitive to 6-nitrobenzylthioinosine. This insensitivity as well as the high affinity for the nucleosides and the capacity for uphill transport indicate that the nucleoside carrier(s) is renal brush border is (are) different from the carriers found in most other cell types.Abbreviations HEPES N-2-hydroxymethylpiperazine-N-2-ethanesulfonic acid - MES 2-(N-morpholino)ethanesulfonic acid - NBMPR 6-nitrobenzylthioinosine - Tris tris(hydroxymethyl)-aminomethane     

Desensitization in denervated mouse muscles

In denervated mouse soleus (DSOL) muscle preparations washed in Na methanesulfonate solutions containing 30 mmol · l^–1 K⁺, bath-applied ACh (55 mol · l^–1) caused the resting potential to decrease from about –36 to –3.2 mV within 2–4s; the potential remained stable or became slightly more negative when ACh was applied for 1–2 min. Two components of the membrane current change (ACh current) were found in DSOL when using a point voltage clamp, and initial current component declining to 1/2 the initial amplitude in 11–15 s (desensitization) and a steady late current comprising 16–47% of the maximum ACh current. Membrane conductance (in s · cm^–2) was 0.35 in the absence of ACh, 20.3 at the peak of the initial current, and 1.57 during late current. The late current saturated a 0.55 to 5.5 mol · l^–1 ACh, whereas the initial current required 55 or more mol · l^–1 ACh to saturate. The null (reversal) potential was 6–13 mV more positive for the late current than for the initial current. The late current was masked when Na⁺ was replaced by Tris⁺, sucrose, or K⁺. An initial and a late current could also be distinguished in non-denervated endplates. The late current was more sensitive to ACh than the initial current, but the null potenital was more negative than that for the initial current in endplates. In denervated membrane, the half time of desensitization was increased when Mg²⁺ was replaced by Ca²⁺ but the changes were on the average less than 15% the control values. It was concluded that desensitizing and non-desensitizing receptors may exist in extrajunctional membranes of denervated muscles and in endplates, the two being attached to different ionic channels.     

Plasma levels of beta-endorphin,prolactin and gonadotropins in male athletes after an international nordic ski race

Summary Plasma -endorphin, prolactin (PRL), FSH and LH were measured in 17 volunteer male subjects at rest and under the stress caused by a long-distance nordic ski race. The race induced increased levels of -endorphin and PRL in all skiers. The changes in PRL with exercise were significantly related to the changes in -endorphin (r=0.69, p<0.001). Furthermore, the highly trained skiers training over 150 km·week^–1 of nordic ski showed consistently higher post-exercise -endorphin and PRL levels than the moderately trained skiers who trained for 20 km·week^–1. In addition the race induced slight falls in FSH and LH; however plasma gonadotropin levels did not show any correlation with plasma -endorphin concentrations and did not differ between the two groups of skiers. These results suggest that endogenous opioid peptides may modulate PRL secretion in heavy exercise, since they are of minor importance in the release of FSH and LH in such a situation. The observations also suggest that the degree of previous training and the exercise intensity do seem to be responsible for the hormonal changes.     

Presence of luminal K+, a prerequisite for active NaCl transport in the cortical thick ascending limb of Henle's loop of rabbit kidney

Previous data from our laboratory have shown that active transport in the cortical thick ascending limb of Henle's loop (cTAL), as measured by the short circuit current (I_SC, A · cm^–2), requires the presence of Na⁺ and Cl^–. The data were compatible with the model of secondarily active Cl^– reabsorption involving the cotransport of Na⁺ and Cl^– across the luminal membrane. The data suggested, furthermore, that 1 Na⁺ and 2 Cl^– interact with the luminal carrier. In the present study it was tested whether this reabsorptive mechanism also requires the presence of luminal K⁺. Isolated cTAL segments (n=40) were perfused at high flow rates with a modified Ringer's solution. Removal of K⁺ from the lumen reduced I_SC significantly from 215 to 133 A·cm^–2. Addition of Ba²⁺ (10^–3 mol·l^–1) which blocks the K⁺ conductance of the luminal membrane, to the K⁺-containing lumen perfusate decreased I_SC significantly from 234 to 141 A·cm^–2. Combination of both manoeuvres: perfusion with a K⁺-free and Ba²⁺-containing solution almost abolished I_SC from a control of 237 to 56 A · cm^–2. The results are compatible with the view that in rabbit cTAL the luminal carrier interacts with all 3 ions, possibly 1 Na⁺, 2 Cl^–, and 1 K⁺. K⁺ recycles across the luminal membrane through its conductive pathway.This study was supported by Deutsche Forschungsgemeinschaft Gr. 460/5-6-2     

Validity of the Wescor's sweat conductivity analyzer for the assessment of sweat electrolyte concentrations

The purpose of this study was to compare the NaCl equivalent values determined by the Wescor's sweat conductivity analyzer (Sweat-Chek) with the sweat Na⁺ and Cl^– concentration values measured by conventional methods. The sweat was induced by 60-min exercise and collected by a closed-pouch collector. The NaCl equivalent values determined by the sweat conductivity analyzer (mean: 75 mmol · L^–1, range: 38 – 122, n = 72) were significantly (P < 0.05) greater than Na⁺ concentration values (mean: 7I mmol · L^–1, range: 24 – 123, n = 72) measured by flame photometry and Cl^– concentration values (mean : 61 mmol· L^–1, range: 18 – 100, n = 48) measured by coulometric titration. The differences were most accen-tuated for low concentration values. The 95% confidence-agreement intervals around the mean differences between methods were 11 mmol· L^–1 (14%) for both Na⁺ and Cl^–. The SweatChek conductivity analyzer is a portable instrument which approximates the actual Na⁺ and Cl^– concentrations in sweat but with a positive bias probably due to the other unmeasured anions present in sweat.     

Gastric emptying and serum insulin levels after intake of glucose-polymer solutions

Summary To examine the gastric emptying characteristics of four drinks varying in carbohydrate composition and concentration, five men ingested 600 ml of one of the different drinks on four separate occasions. All drinks contained Na⁺ 71 mmol · l^–1, Cl^– 60 mmol · l^–1, Mg⁺² 5 mmol · l^–1 and citrate 7 mmol · l^–1; the carbohydrate component was either 3% glucose, 3% glucose-polymer (GP), 5% GP or 10% GP. With ^99mTc-diethylene-triaminepenta-acetic acid (DTPA) as a marker, a scintillation camera and computer were used to measure the rate of gastric emptying. The half-emptying times (T _1/2) were inversely related to the glucose content of the solutions. The T _1/2 for 3% PG was 22.4±4.4 min (mean±SE) and for 10% GP 50±3.3 min (p< 0.005). There was no significant difference in T_1/2 between the 3% glucose and 3% GP solutions. The increments in blood glucose (highest blood levels from 7.4±0.3 mmol · l^–1 to 8.9±0.8 mmol · l^–1), serum insulin (from 28±6 mU · l^–1 to 77±13 mU · l^–1) and C-peptide (from 3.6±0.4 g · l^–1 to 5.8±0.9 g · l^–1) were related to the amount of carbohydrate ingested. In all cases the serum insulin levels were high enough to inhibit the liberation of free fatty acids from the adipose tissue. It is concluded that the amount of carbohydrate in glucosyl units in the solution is a major determinant of gastric emptying. Furthermore, the inhibitory effect of glucose is not modified by replacing monomer glucose with glucose polymer or adding NaCl (about 70 mmol · l^–1) in the solution.     

Contraluminal transport of hexoses in the proximal convolution of the rat kidney in situ

In order to study contraluminal hexose transport, concentration and time-dependent influx of³H-2-deoxy-d-glucose from the interstitium into cortical tubular cells has been measured. The influx curves fit to a two parameter kinetics (K _m 1.3±0.2 mmol/l,J _max 0.67±0.16 pmol/s · cm) plus an additional diffusion term (withP=6·10^–8 cm²/s) and a distribution ratio extracellular to intracellular amount of 2-deoxy-d-glucose of 10.6. Since the extracellular to intracellular free water space as estimated from morphological data was 12, one must conclude that glucose has only free access to 1/3 of the cell water. The intracellularly accessible space was augmented when the tubules were preperfused for 10 s with hypotonic saline. Thereby an increase of the compartment into which diffusion occurs was revealed and a final rupture of this intracellular compartment at 1/4 isotonic solutions was observed. Total replacement of ions in the peritubular perfusate by mannitol did not change 2-deoxy-d-glucose influx, indicating that it is Na⁺-independent. By adding isotonic concentrations of the respective sugars to the capillary perfusate, three degrees of inhibition of 2-deoxy-d-glucose influx could be revealed: strong inhibition byd-glucose, methyl--d-glucoside,d-mannose, 3-O-methyl-d-glucose, 2-deoxy-d-galactose, methyl--d-galactoside and 6-deoxy-d-glucose, moderate inhibition byd-galactose,l-glucose,l-mannose andd-fructose, no or borderline inhibition by methyl -d-glucoside, 2-deoxy-methyl--d-galactoside, 1-thio--d-glucose, 1-thio--d-galactose, 5-thio--d-glucose, myo-inositol and mannitol. The contraluminal 2-deoxy-d-glucose influx was also inhibited by phloretin, chlormerodrin and preperfusion with cytochalasin B. Starvation as well as streptozotocin diabetes has no influence on contraluminal 2-deoxy-d-glucose transport. Thus, in contrast to the luminal hexose transport system the contraluminal system is Na⁺-independent, does not require on OH-group at C-atom 2, acceptsl-glucose and fructose, but not an -methyl group at C-atom 1.     

Einfluß von Aldosteron auf den Natriumtransport in den Sammelrohren der Säugetierniere

Zusammenfassung Durch Mikropunktion und -perfusion der Vasa recta an der freigelegten Nierenpapille von Wistarratten wurde es möglich, die schwankenden Harnstoff- und Natriumkonzentrationen im Interstitium des Nierenmarks zu beseitigen und definierte Versuchsbedingungen für die Sammelrohre zu schaffen.An diesen funktionell isolierten Sammelrohrabschnitten wurdenin situ sowohl die Gleichgewichtskonzentrationsdifferenz bei fehlendem Nettosubstanz-und -volumenfluß (C _Na) als auch der Nettonatriumtransport ( _Na) bei gleicher Natriumkonzentration auf beiden Seiten der Sammelrohrwand gemessen. Es konnte gezeigt werden, daß unter diesen Versuchsbedingungen, bei denen die Tiere in Antidiurese sind, die Natriumrückresorption aus den Sammelrohren isoton abläuft.Die Versuche wurden an vier Tiergruppen durchgeführt: an adrenalektomierten Tieren, an normal ernährten Tieren, an salzarm ernährten Tieren und an normal ernährten Tieren, die zusätzlich Aldosteron bekamen. _{Na iso} war bei adrenalektomierten Tieren 1,2·10^–5 bei normal ernährten Tieren 3,1·10^–5, bei salzarm ernährten Tieren 4,1·10^–5 und bei normal ernährten Tieren unter Aldosteronsubstitution 4,2·10^–5 Äq·mm^–2·sec^–1. Die entsprechenden C _Na werte waren 4, 31, 98, 93 mÄq/l.Unter der Annahme, daß _{Na iso} die Transportkapazität des Systems angibt und daß C _Na bei gegebenem _{Na iso} umgekehrt proportional der Leckpermeabilität für Natriumionen ist, kann man aus den vorliegenden Daten schließen, daß Aldosteron am Sammelrohr nicht nur die innere Transportkapazität für Na erhöht, sondern auch die Leckpermeabilität für Na herabsetzt.