Responsiveness of the ANP providing system to volume load in conscious dogs

We examined in detail changes in arterial plasma ANP concentration in response to volume load in conscious dogs. In a 5-min volume load experiment, 18 ml/kg of isosmotic and isooncotic 3% Dextran 40 in saline was infused over a period of 5 min. Mean left atrial pressure (MLAP) increased transiently by 7.6±0.9 mm Hg. Plasma ANP level (P-ANP) did not significantly increase. Assayed P-ANP levels were corrected for hemodilution. Corrected P-ANP (C-ANP) significantly increased from 206±17 to 348±34 pg/ml. However, the level of C-ANP did not reach a steady state. No significant linear correlation was found between increases in MLAP and normalized C-ANP. In a 45-min volume load experiment, the elevated level of MLAP caused by the 5-min volume load was maintained for 40 min by supplemental infusion. C-ANP significantly increased from 196±18 pg/ml to 435±73 ng/ml. The level of C-ANP reached a steady state. A close linear correlation was observed between increases in MLAP and normalized C-ANP. However, the peak time of C-ANP lagged 10 min behind MLAP. These results indicate that it takes 10 min for P-ANP to reach a steady state in fully responding to a volume load, and that the long-term volume load is a prerequisite to the response of the ANP providing system.     

Diagnosis of Polistes wasp hypersensitivity

Patients referred from the Houston, Texas, metropolitan area were evaluated for allergic reactions to insect stings. Forty-eight persons reported at least one systemic reaction caused by a Polistes paper-nest wasp sting. Honey bees, imported fire ants, and other types of Hymenoptera were identified in that order by 19 other subjects with systemic allergic reactions. Life-threatening airway obstruction and/or hypotension were noted by most of our patients. Wasp venom skin testing was positive in 65% of subjects reporting sensitivity to this insect. Skin testing was correlated quantitatively with basophil histamine release, and qualitatively with RAST assays using Polistes wasp venom. Venoms from common species of Polistes were highly cross-reactive as shown by RAST and basophil histamine release. Patients having a positive history and laboratory response (by skin testing, histamine release, or RAST) to Polistes wasp venom also were positive to bee venom about 20% of the time and to another vespid (hornet or yellow jacket) over 50% of the time.     

Polarized ion transport during migration of transformed Madin-Darby canine kidney cells

Epithelial cells lose their usual polarization during carcinogenesis. Although most malignant tumours are of epithelial origin little is known about ion channels in carcinoma cells. Previously, we observed that migration of transformed Madin-Darby canine kidney (MDCK-F) cells depended on oscillating K⁺ channel activity. In the present study we examined whether periodic K⁺ channel activity may cause changes of cell volume, and whether K⁺ channel activity is distributed in a uniform way in MDCK-F cells. After determining the average volume of MDCK-F cells (2013±270 m³; n=8) by means of atomic force microscopy we deduced volume changes by calculating the K⁺ efflux during bursts of K⁺ channel activity. Therefore, we measured the membrane conductance of MDCK-F cells which periodically rose by 22.3±2.5 nS from a resting level of 6.5±1.4 nS (n=12), and we measured the membrane potential which hyperpolarized in parallel from –35.4±1.2 mV to –71.6±1.8 mV (n=11). The distribution of K⁺ channel activity was assessed by locally superfusing the front or rear end of migrating MDCK-F cells with the K⁺ channel blocker charybdotoxin (CTX). Only exposure of the rear end to CTX inhibited migration providing evidence for horizontal polarization of K⁺ channel activity in transformed MDCK-F cells. This is in contrast to the vertical polarization in parent MDCK cells. We propose that the asymmetrical distribution of K⁺ channel activity is a prerequisite for migration of MDCK-F cells.     

Regulatory volume decrease in a renal distal tubular cell line (A6) II. Effect of Na+ transport rate

A6 epithelia, a cell line originating from the distal tubular part of the kidney ofXenopus laevis, were cultured on permeable supports and mounted in an Ussing-type chamber. Cell thickness (T _c), short-circuit current (I _sc) and transepithelial conductance (G _t) were recorded while tissues were bilaterally incubated in NaCl solutions and the transepithelial potential was clamped to zero. Effects of inhibition and stimulation of transepithelial Na⁺ transport on cell volume and on its regulation during a hyposmotic challenge were investigated. Under control conditions a slow spontaneous decrease ofT _c described by a linear baseline was recorded. The reduction of the apical osmolality from 260 to 140 mosmol/kg did not alter cell volume significantly, demonstrating a negligible water permeability of the apical barrier. The inhibition of Na⁺ uptake by replacing apical Na⁺ byN-methyl-d-glucamine (NMDG⁺) did not affect cell volume under isotonic conditions. An increase ofT _c by 12.1% above the control baseline was recorded after blocking active transport with ouabain for 60 min. The activation of Na⁺ transport with insulin or oxytocin, which is known to activate the apical water permeability in other epithelia, did not alter cell volume significantly. The insensitivity of cell volume to alterations in apical Na⁺ uptake or Na⁺ pump rate confirms the close coupling between apical and basolateral transport processes. The blockage of basolateral K⁺ channels by 5 mM Ba²⁺ elicited a significant increase inT _c of 16.3% above control. Quinine, a potent blocker of volume-activated K⁺ channels, did not changeT _c significantly. Basolateral hypotonicity elicited a rapid rise inT _c followed by a regulatory volume decrease (RVD). An RVD was also recorded after blocking apical Na⁺ uptake as well as after stimulating apical Na⁺ uptake with oxytocin or insulin. Inhibition of active transport with ouabain as well as blocking K⁺ efflux at the basolateral side with Ba²⁺ or quinine abolished the RVD. The inhibition of the RVD by ouabain seems to be caused by a depletion of cellular K⁺, whereas the effects of Ba²⁺ and quinine are most likely due to the blockage of the basolateral K⁺ pathway.     

Interrelations between age and plasma renin,aldosterone and cortisol,urinary catecholamines,and the body sodium/volume state in normal man

Summary Interrelations between age and plasma renin, aldosterone and cortisol levels, urinary catecholamines, plasma and blood volumes, exchangeable body sodium and blood pressure were studied in 28 young (19 to 29 years), 16 middle-aged (32 to 58 years) and 15 elderly (60 to 74 years) healthy subjects. Supine and upright plasma renin and supine aldosterone levels decreased while urinary noradrenaline excretion rate increased progressively with aging (r0.34;p<0.05), with significant differences in mean values between young and elderly subjects (p<0.02). There was also an age-related decrease in upright plasma aldosterone concentration, although this was not statistically significant. Furthermore, mean plasma cortisol concentrations increased in response to upright posture in elderly (+50%;p<0.02), but not in young (–10%) or middle-aged (–8%) subjects. Blood pressure correlated with age (r=0.35;p<0.05) or noradrenaline excretion rate (r=0.34) in the entire study population and with blood volume in the elderly (r=0.68), but not in the young or middle-aged study groups. There were no significant age-related differences in the body sodium/volume state, basal plasma cortisol levels or urinary adrenaline excretion rate, and plasma renin or aldosterone levels did not correlate with these parameters or with blood pressure. It is concluded that the influence of age on plasma renin or aldosterone levels, plasma cortisol responsiveness to upright posture, and urinary noradrenaline excretion should be taken into consideration, whenever these factors have to be interpreted in patients with arterial hypertension or other clinical disorders. Furthermore, these data are consistent with the possibility that in normal man increases in supine blood pressure with aging may be related at least partly to concomitant changes in free peripheral noradrenaline.This investigation was supported by the Swiss National Science Foundation     

A volume-activated anion conductance in insulin-secreting cells

The whole-cell patch-clamp recording technique was used to measure volume-activated currents in K⁺-free solutions in RINm5F and HIT-T15 insulinoma cells and in dispersed rat islet cells. Cell swelling, induced by intracellular hypertonicity or extracellular hypotonicity, caused activation of an outwardly rectifying conductance which could be subsequently inactivated by hypertonic extracellular solutions. The conductance required adenosine 5-triphosphate (ATP) in the pipette solution but was Ca²⁺ independent. Na⁺ and Cl^– substitution studies suggested that the swelling-activated current is Cl^– selective with a halide permeability sequence of Br > Cl > 1. The conductance was reversibly inhibited by the anion channel inhibitors 4,4-diisothiocyanatostilbene-2,2-disulphonic acid (DIDS) and by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB). Further evidence for a volume-activated anion conductance was provided by studies of volume regulation in insulin-secreting cells. When RINm5F cells were exposed to a hypotonic medium, the initial cell swelling was followed by a regulatory volume decrease (RVD). This RVD response was also inhibited by DIDS and by NPPB. These data therefore provide evidence for a volume-activated anion conductance in insulin-secreting cells which could be involved in the RVD following osmotic stress. A possible role for the conductance in hypotonically induced insulin release is also discussed.     

High-intensity intermittent running training improves pulmonary function and alters exercise breathing pattern in children

We investigated the effects of short duration running training on resting and exercise lung function in healthy prepubescent children. One trained group (TrG) (n = 9; three girls and six boys; age = 9.7 ± 0.9 year) participated in 8 weeks of high-intensity intermittent running training and was compared to a control group (ContG) (n = 9; four girls and five boys; age = 10.3 ± 0.7 year). Before and after the 8-week period, the children performed pulmonary function tests and an incremental exercise test on a cycle ergometer. After the 8-week period, no change was found in pulmonary function in ContG. Conversely, an increase in forced vital capacity (FVC) (+7 ± 4% ; P = 0.026), forced expiratory volume in one second (+11 ± 6% ; P = 0.025), peak expiratory flows (+17 ± 4% ; P = 0.005), maximal expiratory flows at 50% (+16 ± 10% ; P = 0.019) and 75% (+15 ± 8% ; P = 0.006) of FVC were reported in TrG. At peak exercise, TrG displayed higher values of peak oxygen consumption (+15 ± 4% ; P<0.001), minute ventilation (+16 ± 5% ; P = 0.033) and tidal volume (+15 ± 5% ; P = 0.019) after training. At sub-maximal exercise, ventilatory response to exercise was lower (P = 0.017) in TrG after training, associated with reduced end-tidal partial oxygen pressure (P<0.05) and higher end-tidal partial carbon dioxide pressure (P = 0.026). Lower deadspace volume relative to tidal volume was found at each stage of exercise in TrG after training (P<0.05). Eight weeks of high-intensity intermittent running training enhanced resting pulmonary function and led to deeper exercise ventilation reflecting a better effectiveness in prepubescent children.     

Muscle hypertrophy following 5‐week resistance training using a non‐gravity‐dependent exercise system

Aim: The efficacy of a mechanical, gravity‐independent resistance exercise (RE) system to induce strength gains and muscle hypertrophy was validated. Designed for space crew in orbit, this technique offers resistance during coupled concentric and eccentric actions by utilizing the inertia of a rotating flywheel(s), set in motion by the trainee. Methods: Ten middle‐aged (30–53 years) men and women performed four sets of seven maximal, unilateral (left limb) knee extensions two or three times weekly for 5 weeks. Knee extensor force and electromyographic (EMG) activity of the three superficial quadriceps muscles were measured before and after this intervention. In addition, with the use of magnetic resonance imaging (MRI), volume of individual knee extensor and ankle plantar flexor muscles was assessed. Results: Over the 12 training sessions, the average concentric (CON) and eccentric (ECC) force generated during exercise increased by 11% (P < 0.05). Likewise, maximal isometric strength (maximal voluntary contraction, MVC) at 90 and 120° knee angle increased by (P < 0.05) 11 and 12% respectively, after training. Neither individual quadriceps muscle showed a change (P > 0.05) in maximal integrated EMG (iEMG) activity. Quadriceps muscle volume increased by 6.1% (P < 0.05). Although the magnitude of response varied, all individual quadriceps muscles showed increased (P < 0.05) volume after training. As expected, ankle plantar flexor volume of the trained limb was unchanged (P > 0.05). Likewise, MVC, CON and ECC force, iEMG and knee extensor and plantar flexor muscle volume were unaltered (P > 0.05) in the right, non‐trained limb. Conclusion: The results of this study show that the present RE regimen produces marked muscle hypertrophy and important increases in maximal voluntary strength and appears equally effective as RE paradigms using gravity‐dependent weights, in this regard.     

Glomerular structure in lithium-induced chronic renal failure in rats

The effects of long-term lithium administration on glomerular structure and intervention with angiotensin converting enzyme inhibitor (ACEI) were studied in rats. Male Wistar rats were fed a lithium-containing diet (Li) or control diet (C) for 16 weeks postnatally. Li-treated rats developed renal failure, hypertension and proteinuria. During the subsequent 24 weeks, subgroups were treated with ACEI. The kidneys were fixed by perfusion, and tissue blocks were serially cut for estimation of glomerular volume and glomerular characteristics by light microscopy. Mesangial and mesangial matrix volume fractions, surface density of capillary walls, basement membrane thickness and foot process width (FPW) were measured by electron microscopy. Glomerular volume was decreased in Li-rats, with increased intra-individual variation. In all Li-rats, some glomeruli (mean 27%) were abnormal, with severe changes in only three rats. Ultrastructural parameters obtained by systematic sampling of three glomeruli in each rat showed no differences among groups. Among Li-treated animals there was a significant correlation between FPW and albumin excretion per unit filtration surface, and between filtration surface per glomerulus and inulin clearance. In conclusion, long-term lithium administration to newborn rats caused marked changes in glomerular volume which were not associated with measurable changes in structural parameters. No effect of ACEI-treatment was detectable.     

The cellular structure and lipid/protein composition of adipose tissue surrounding chronically stimulated lymph nodes in rats

To test the hypothesis that chronic immune stimulation of a peripheral lymph node induces the formation of additional mature adipocytes in adjacent adipose tissue, one popliteal lymph node of large male rats was stimulated by local injection of 10 microg or 20 microg lipopolysaccharide three times a week for 6 weeks. Adipocyte volumes in sites defined by their anatomical relations to the stimulated and homologous unstimulated popliteal lymph nodes were measured, plus adipocyte complement of the popliteal depot, and the lipid and protein content of adipocytes and adipose stroma. The higher dose of lipopolysaccharide doubled the mass of the locally stimulated lymph node and the surrounding adipose tissue enlarged by the appearance of additional mature adipocytes. Similar but smaller changes were observed in the popliteal adipose depot of the unstimulated leg and in a nodeless depot. The lipid content of the adipocytes decreased and that of the stroma increased dose-dependently in all samples measured but the changes were consistently greater in the depot surrounding the stimulated lymph node. The protein content of both adipocytes and stroma increased in samples surrounding the stimulated node. We conclude that chronic immune stimulation of lymphoid tissues induces the formation of more adipocytes in the adjacent adipose tissue. These findings suggest a mechanism for the selective hypertrophy of lymphoid-containing adipose depots in the HIV-associated adipose redistribution syndrome.