The role of venous valves in pressure shielding

Background

It is widely accepted that venous valves play an important role in reducing the pressure applied to the veins under dynamic load conditions, such as the act of standing up. This understanding is, however, qualitative and not quantitative. The purpose of this paper is to quantify the pressure shielding effect and its variation with a number of system parameters.

Methods

A one-dimensional mathematical model of a collapsible tube, with the facility to introduce valves at any position, was used. The model has been exercised to compute transient pressure and flow distributions along the vein under the action of an imposed gravity field (standing up).

Results

A quantitative evaluation of the effect of a valve, or valves, on the shielding of the vein from peak transient pressure effects was undertaken. The model used reported that a valve decreased the dynamic pressures applied to a vein when gravity is applied by a considerable amount.

Conclusion

The model has the potential to increase understanding of dynamic physical effects in venous physiology, and ultimately might be used as part of an interventional planning tool.     

Biaxial mechanical properties of bovine jugular venous valve leaflet tissues

Venous valve incompetence has been implicated in diseases ranging from chronic venous insufficiency (CVI) to intracranial venous hypertension. However, while the mechanical properties of venous valve leaflet tissues are central to CVI biomechanics and mechanobiology, neither stress–strain curves nor tangent moduli have been reported. Here, equibiaxial tensile mechanical tests were conducted to assess the tangent modulus, strength and anisotropy of venous valve leaflet tissues from bovine jugular veins. Valvular tissues were stretched to 60% strain in both the circumferential and radial directions, and leaflet tissue stress–strain curves were generated for proximal and distal valves (i.e., valves closest and furthest from the right heart, respectively). Toward linking mechanical properties to leaflet microstructure and composition, Masson’s trichrome and Verhoeff–Van Gieson staining and collagen assays were conducted. Results showed: (1) Proximal bovine jugular vein venous valves tended to be bicuspid (i.e., have two leaflets), while distal valves tended to be tricuspid; (2) leaflet tissues from proximal valves exhibited approximately threefold higher peak tangent moduli in the circumferential direction than in the orthogonal radial direction (i.e., proximal valve leaflet tissues were anisotropic; \(p<0.01\)); (3) individual leaflets excised from the same valve apparatus appeared to exhibit different mechanical properties (i.e., intra-valve variability); and (4) leaflets from distal valves exhibited a trend of higher soluble collagen concentrations than proximal ones (i.e., inter-valve variability). To the best of the authors’ knowledge, this is the first study reporting biaxial mechanical properties of venous valve leaflet tissues. These results provide a baseline for studying venous valve incompetence at the tissue level and a quantitative basis for prosthetic venous valve design.     

A method for studying social and reproductive behaviour of subterranean rodents in captivity

A methodology for studying the social and reproductive behaviour of solitary subterranean rodents under laboratory conditions is proposed. A first account ofCtenomys talarum (Thomas, 1898) behaviour is also provided with the aim of evaluating the proposed methodology and to advance presently unknown information on its social behaviour and mating system. The device is a seminatural enclosure, departing from traditional test cages with respect to increased: (1) size, (2) structural complexity, (3) social complexity, and (4) resemblance to natural conditions. It consists of artificial burrows each comprising 3.5 m of tunnel, a resource cage and a nest box, resembling the structural complexity described forC. talarum burrows. Burrows are connected to a common space, which allows social interaction among various individuals. Animals were observed in the seminatural enclosure — 3 females and 2 males, in accordance with sex ratios found in natural populations — for a period of 6 months. We obtained data related to reproductive and social behaviour: marking, aggression, vocalization, courtship and copulation, pregnancy, pup development, and parental care. The proposed system enables the collection of behavioural data as yet unavailable due to the secretive habits and aggressiveness that characterize this group of rodents, coupled with the difficulties associated with simulating subterranean conditions.     

On the number of steady states in a multiple futile cycle

The multisite phosphorylation-dephosphorylation cycle is a motif repeatedly used in cell signaling. This motif itself can generate a variety of dynamic behaviors like bistability and ultrasensitivity without direct positive feedbacks. In this paper, we study the number of positive steady states of a general multisite phosphorylation–dephosphorylation cycle, and how the number of positive steady states varies by changing the biological parameters. We show analytically that (1) for some parameter ranges, there are at least n + 1 (if n is even) or n (if n is odd) steady states; (2) there never are more than 2n − 1 steady states (in particular, this implies that for n = 2, including single levels of MAPK cascades, there are at most three steady states); (3) for parameters near the standard Michaelis–Menten quasi-steady state conditions, there are at most n + 1 steady states; and (4) for parameters far from the standard Michaelis–Menten quasi-steady state conditions, there is at most one steady state.      

Allograft semilunar cardiac valves processing and cryopreservation – morphology in scanning electron microscope

Objective: The most important factors of long term clinical performance of biological heart valve prostheses are methods of processing and cryopreservation. That is why we decided to evaluate the impact of current Allograft Heart Valves (AHV) Bank protocol on valve tissue morphology. Scanning electron microscope (SEM) is a valuable tool for investigation of biological surfaces. In case of cardiac valves it is especially suitable for detection of fine changes in endothelial covering and underlying layers. Material and methods: “Fresh” aortic and pulmonary AHV samples, harvested from “heart-beating” cadaveric donors, were compared with (1) tissue from AHV obtained from non heart-beating donors, (2) samples stored in 4 °C saline for 24 h, (3) antibiotic treated tissue for 24 h at 37 °C and finally (4) cryopreserved valves, stored in liquid nitrogen (−196 °C) for 6–38 months. All samples were dissected, dried with hexamethyldisilazane (HMDS), gold coated, studied and photographed by SEM (Tesla BS 301). Results: Our alternative method of drying samples by the HMDS method proved to be suitable for thin membranes of human semilunar valves. We were able to detect early changes in the endothelium after harvesting, and denudation of the endothelial covering during preservation with and without freezing. Conclusion: SEM (using HMDS drying) along with other methods may be helpful for the morphological control of processing, cryopreservation and liquid nitrogen storage of AHV. According to the current findings we have to avoid washing of AHV in saline after harvesting.     

Role of temperature in quanta mechanisms of facilitation in the frog neuromuscular junction

The results of computer simulations on the Double Barrier Synapse (DBS) model are presented which quantify the relationship between the synapse parameters and the quanta transfer process. The DBS model is applicable to a variety of states of synaptic activity, and by changing the synapse parameters it is possible to simulate various conditions of quanta transmission. The influence of the bathing solution temperature change on the synaptic parameters under different conditions of transmitter release in the frog neuromuscular junction is investigated. Simulations demonstrate that several synaptic parameters, including the parameters of the presynaptic membrane, are not affected by the temperature change. It is shown that a stimulation frequency exists at which the steady-state level of facilitation during a long train of stimuli is the same for a wide range of temperatures. Received: 2 August 1996 / Accepted in revised form: 19 February 1998     

Olfactory learning and behaviour are ‘insulated’ against visual processing in larval Drosophila

We investigate the organization of behaviour across sensory modalities, using larval Drosophila melanogaster. We ask whether olfactory learning and behaviour are affected by visual processing. We find that: (1) Visual choice does not affect concomitant odour choice. (2) Visual context does not influence odour learning, nor do changes of visual context between training and test affect retrieval of odour memory. (3) Larvae cannot solve a biconditional discrimination task, despite generally permissive conditions. In this task, larvae are required to establish conditional associations: in light, one odour is rewarded and the other one is not, whereas in dark the opposite contingency is established. After such training, choice between the two odours is equal under light and dark testing conditions, suggesting that larvae do not establish odour memories specifically for one visual context only. Together, these data suggest that, in larval Drosophila, olfactory learning and behaviour are ‘insulated’ against visual processing.     

Apoptosis in fresh and cryopreserved cardiac valves of pig samples

To analyse the influence of cold ischemic time (CIT) (2–24 h) and of cryopreservation (liquid phase) on the viability of the valvular fibroblasts and in the presence of apoptosis. Cardiac valves from 10 pigs were evaluated by anatomo-pathological study of the wall, muscle and leaflet. At the same time, the presence of cellular death due to apoptosis was investigated in two ways; directly on tissue by Apodetec system and by two-colour flow cytometry assay analyzing a suspension of fibroblast from valve leaflets using Anexina V and propidium iodure (PI). We established three groups of samples to compare different experimental conditions: 2 h of ischemia (group 1), 24 h of ischemia (group 2), and a programme of cryopreservation (−1°C/min) after 2 h of ischemia, followed by storage in liquid nitrogen during a week and thawing was performed (group 3). The analysis of viabilities showed slight differences between all three groups. The results indicated CIT of 24 h undergoing more structural affectation than CIT of 2 h. Flow cytometry analysis did not show important differences between groups; however cryopreserved samples (group 3) slightly less viability and a higher percentage of death by apoptosis than group 1 and 2 using flow cytometry. Apoptosis was confirmed on tissue from all valves but mainly in samples of group 2 and group 3. In summary, the viability of the valves in the case of ischemic times of 2 h, 24 h or after cryopreservation/thawing differs slightly. The death of the cells is mainly mediated by necrosis and not by apoptosis.     

Some conditions for sustained oscillations in biochemical chains with feedback inhibition

A chain ofn reactions is considered in which the last substance inhibits the production of the first with degreep, p being the order of the inhibition. Maintained oscillations are possible for certain values of the parameters under the following conditions: (1) If there is no time delay, then there must be at least three compartments (n=3) and either the degree of inhibition is sufficiently large (p>8 forn=3) or there must be enzymatic removal from the first compartment, in which casep≥1. (2) If there are time delays, but there is no enzymatic removal, the degree of the inhibition must be greater than or equal to 2 for any value ofn. (3) If there is a time delay in addition to enzymatic removal, one compartment with simple first order inhibition is sufficient. Conditions on the parameters necessary for maintained oscillations are given for many of the cases discussed.     

Detecting and quantifying global instability during a dynamic task using kinetic and kinematic gait parameters

ObjectivesInstability during gait can be identified in many different ways. Recent studies have suggested utilizing spatiotemporal parameters to detect instability during gait. Detecting instability using kinetic and kinematic gait parameters has not yet been examined fully. In addition, these studies have not yet identified measures that are capable of assessing the magnitude of instability. The objective of the present study was to identify kinetic and kinematic gait parameters that can best identify instability and quantify its magnitude.MethodsTen healthy men underwent successive gait analysis testing under three controlled settings: (1) Stage 0 instability (control setting), (2) Stage 1 instability and (3) Stage 2 instability. The levels of instability were precisely applied with the use of a controlled perturbation device (AposTherapy System). Differences between all stages and between stages were identified using Friedman and Wilcoxon tests.ResultsStride-to-stride variability (STSV) in kinetic and kinematic measures increased significantly between stages 0 and 1 or between stages 0 and 2 for almost all parameters (all P<0.05). A significant increase between stage 0 and both stages 1 and 2 was found for knee flexion moment, knee varus moment, knee flexion angle and hip adduction angle. The increase between stages 1 and 2 was variable. Only the knee varus moment parameter showed a significant increase in STSV between stages 1 and 2 (P=0.026).ConclusionsAlmost all kinetic and kinematic gait parameters are sensitive to changes in global instability in a dynamic task. The most sensitive are parameters measured at the knee. Of these, STSV in knee varus moment can be used to quantify the magnitude of dynamic instability.     

“Chelatable iron pool”: inositol 1,2,3-trisphosphate fulfils the conditions required to be a safe cellular iron ligand

Mammalian cells contain a pool of iron that is not strongly bound to proteins, which can be detected with fluorescent chelating probes. The cellular ligands of this biologically important “chelatable”, “labile” or “transit” iron are not known. Proposed ligands are problematic, because they are saturated by magnesium under cellular conditions and/or because they are not “safe”, i.e. they allow iron to catalyse hydroxyl radical formation. Among small cellular molecules, certain inositol phosphates (InsPs) excel at complexing Fe³⁺ in such a “safe” manner in vitro. However, we previously calculated that the most abundant InsP, inositol hexakisphosphate, cannot interact with Fe³⁺ in the presence of cellular concentrations of Mg²⁺. In this work, we study the metal complexation behaviour of inositol 1,2,3-trisphosphate [Ins(1,2,3)P ₃], a cellular constituent of unknown function and the simplest InsP to display high-affinity, “safe”, iron complexation. We report thermodynamic constants for the interaction of Ins(1,2,3)P ₃ with Na⁺, K⁺, Mg²⁺, Ca²⁺, Cu²⁺, Fe²⁺ and Fe³⁺. Our calculations indicate that Ins(1,2,3)P ₃ can be expected to complex all available Fe³⁺ in a quantitative, 1:1 reaction, both in cytosol/nucleus and in acidic compartments, in which an important labile iron subpool is thought to exist. In addition, we calculate that the fluorescent iron probe calcein would strip Fe³⁺ from Ins(1,2,3)P ₃ under cellular conditions, and hence labile iron detected using this probe may include iron bound to Ins(1,2,3)P ₃. Therefore Ins(1,2,3)P ₃ is the first viable proposal for a transit iron ligand. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The 12 cc Penn State pulsatile pediatric ventricular assist device: fluid dynamics associated with valve selection

The mortality rate for infants awaiting a heart transplant is 40% because of the extremely limited number of donor organs. Ventricular assist devices (VADs), a common bridge-to-transplant solution in adults, are becoming a viable option for pediatric patients. A major obstacle faced by VAD designers is thromboembolism. Previous studies have shown that the interrelated flow characteristics necessary for the prevention of thrombosis in a pulsatile VAD are a strong inlet jet, a late diastolic recirculating flow, and a wall shear rate greater than 500 s(-1). Particle image velocimetry was used to compare the flow fields in the chamber of the 12 cc Penn State pediatric pulsatile VAD using two mechanical heart valves: Bjork-Shiley monostrut (BSM) tilting disk valves and CarboMedics (CM) bileaflet valves. In conjunction with the flow evaluation, wall shear data were calculated and analyzed to help quantify wall washing. The major orifice inlet jet of the device containing BSM valves was more intense, which led to better recirculation and wall washing than the three jets produced by the CM valves. Regurgitation through the CM valve served as a significant hindrance to the development of the rotational flow.     

Photorespiratory 2-phosphoglycolate metabolism and photoreduction of O<Subscript>2</Subscript> cooperate in high-light acclimation of <Emphasis Type="Italic">Synechocystis</Emphasis> sp. strain PCC 6803

In cyanobacteria, photorespiratory 2-phosphoglycolate (2PG) metabolism is mediated by three different routes, including one route involving the glycine decarboxylase complex (Gcv). It has been suggested that, in addition to conversion of 2PG into non-toxic intermediates, this pathway is important for acclimation to high-light. The photoreduction of O₂ (Mehler reaction), which is mediated by two flavoproteins Flv1 and Flv3 in cyanobacteria, dissipates excess reductants under high-light by the four electron-reduction of oxygen to water. Single and double mutants defective in these processes were constructed to investigate the relation between photorespiratory 2PG-metabolism and the photoreduction of O₂ in the cyanobacterium Synechocystis sp. PCC 6803. The single mutants Δflv1, Δflv3, and ΔgcvT, as well as the double mutant Δflv1/ΔgcvT, were completely segregated but not the double mutant Δflv3/ΔgcvT, suggesting that the T-protein subunit of the Gcv (GcvT) and Flv3 proteins cooperate in an essential process. This assumption is supported by the following results: (1) The mutant Δflv3/ΔgcvT showed a considerable longer lag phase and sometimes bleached after shifts from slow (low light, air CO₂) to rapid (standard light, 5% CO₂) growing conditions. (2) Photoinhibition experiments indicated a decreased ability of the mutant Δflv3/ΔgcvT to cope with high-light. (3) Fluorescence measurements showed that the photosynthetic electron chain is reduced in this mutant. Our data suggest that the photorespiratory 2PG-metabolism and the photoreduction of O₂, particularly that catalyzed by Flv3, cooperate during acclimation to high-light stress in cyanobacteria. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Initiation of humoral and cellular immune responses in patients with refractory Hodgkin's disease by treatment with an anti-CD16/CD30 bispecific antibody

Fifteen patients with refractory Hodgkin's disease were treated in a dose-escalation trial with the bispecific monoclonal antibody (bi-mAb) HRS-3/A9, which is directed against the Fcγ receptor III (CD16 antigen) and the Hodgkin's-associated CD30 antigen. Treatment consisted of four cycles of four bi-mAb infusions given over 1 h every 3–4 days at different dose levels ranging from 1 mg/m² to 64 mg/m². Measurable serum levels (above 0.1 μg/ml) of circulating bi-mAb could be detected in patients treated with doses above 4 mg/m², reaching peak levels of 9.5 μg/ml immediately after the end of antibody infusion on the highest dose level. Bi-mAb elimination corresponded to second-order kinetics with a terminal half-life time (t _1/2,β) of 28–32 h. Bi-mAb treatment induced the occurrence of human anti-(mouse Ig) antibodies (HAMA) in 6 out of 13 patients initially testing negative. All 6 patients not only developed anti-isotypic anti-(mouse Ig) but also anti-idiotypic and anti-anti-idiotypic antibodies. While no consistent changes of peripheral blood cell counts, or of any lymphocyte subpopulation including natural killer (NK) cells, has been observed, 4 out of 6 evaluable patients treated with doses of at least 4 mg/m² showed an increase of NK cell activity within 2 weeks after treatment, which lasted for a maximum of 12 weeks. Circulating amounts of soluble CD30 antigen could be detected in the serum of 6 patients. However, like the results and time courses of all the other immunological parameters evaluated, this was not predictive for treatment outcome. Received: 16 September 1999 / Accepted: 6 January 2000     

ASSOCIATIONS OF METABOLIC PARAMETERS AND ETHANOL CONSUMPTION WITH MESSENGER RNA EXPRESSION OF CLOCK GENES IN HEALTHY MEN

Recent studies suggest that the impairment of circadian clock function causes various pathological conditions, such as obesity, diabetes, and alcoholism, and an altered mRNA expression of clock genes was found under these conditions. However, it remains to be determined whether clock gene expression varies depending on metabolic conditions even in healthy people. To address this issue, we investigated the associations of metabolic parameters and alcohol consumption with mRNA expression of clock genes (CLOCK, BMAL1, PER1, PER2, and PER3) in peripheral blood cells obtained from 29 healthy non-obese elderly men (age 51–78 yrs) who adhered to a regular sleep-wake routine, through a single time-of-day venous blood sampling at ～09:00?h. There were significant correlations between (1) waist circumference and mRNA level of PER1 (r?=?0.43), (2) plasma glucose concentration and PER2 (r?=?0.50), (3) ethanol consumption and BMAL1 (r?=?0.43), and (4) serum γ-GTP concentration (a sensitive marker of alcohol consumption) and PER2 (r?=?0.40). These results suggest mRNA expression of clock genes is associated with obesity, glucose tolerance, and ethanol consumption even in healthy people. (Author correspondence: akiofuji@jichi.ac.jp)     

Kinetic comparisons of mesophilic and thermophilic aerobic biomass

Kinetic parameters describing growth and decay of mesophilic (30°C) and thermophilic (55°C) aerobic biomass were determined in continuous and batch experiments by using oxygen uptake rate measurements. Biomass was cultivated on a single soluble substrate (acetate) in a mineral medium. The intrinsic maximum growth rate (μ _max) at 55°C was 0.71±0.09 h⁻¹, which is 1.5 times higher than the μ _max at 30°C (0.48±0.11 h⁻¹). The biomass decay rates increased from 0.004 h⁻¹ at 30°C to 0.017 h⁻¹ at 55°C. Monod constants were very low for both types of biomass: 9±2 mg chemical oxygen demand (COD) l⁻¹at 30°C and 3±2 mg COD l⁻¹at 55°C. Theoretical biomass yields were similar at 30 and 55°C: 0.5 g biomass COD (g acetate COD)⁻¹. The observed biomass yields decreased under both temperature conditions as a function of the cell residence time. Under thermophilic conditions, this effect was more pronounced due to the higher decay rates, resulting in lower biomass production at 55°C compared to 30°C. Electronic Publication     

A simple device for measuring a vertical jump: description and results

A simple and cheap device has been designed which makes it possible to quantify a vertical jump. The parameters which can be measured or calculated with this device include: height of the jump, duration of thrust, maximal velocity and thus the corresponding maximal power output. The device was tested on 22 young soccer players for whom the height of the jump (0.47 m, SEM 0.015) and maximal power output (34.9 W. kg-1, SEM 1.04) were considered. The device is proposed for assessing training methods and sports aptitude.     

A convergence theorem for linear threshold elements

“Linear threshold element”, is the generic term for a device, natural or artificial, of the input-output type which (1) has a finite numberk of input lines and one output line; (2) forms a linear combinationa ₁ x ₁+a ₂ x ₂+...+a _k x _k of the inputk-tuple (x ₁,x ₂,...,x _k) and compares it with a threshold quantity θ; and (3) yields one of two outputs depending on whether the linear combination does or does not exceed the threshold θ. Such elements find wide use as means for realizing linear discriminant functions and as analogs for certain features characterizing neurons. Adaptive classification of inputs into one of two categories, as designated by the two outputs, can sometimes be achieved by the suitable adjustment, based on experience, of the parametersa ₁,a ₂,...,a _k and θ. One such adjustment rule having the characteristics of a steepest descent algorithm is here investigated. Established is a theorem giving the necessary and sufficient conditions that the mean values of the adjusted parameters converge to a solution of the equations required for minimizing the mean square error relative to a quantity associated with classification performance when the element is exposed to a stationary sequence of independent inputs.     

Kinetic analysis of the template effect in ribooligoguanylate elongation

We have undertaken a complete kinetic analysis of the template-directed oligoguanylate synthesis originated in Orgel's laboratory (Inoue and Orgel, 1982). The reaction of guanosine 5′-phospho-2-methylimidazolide, 2-MelmpG, with ribooligoguanylates all 3′–5′ linked, designatedn ³ withn=7−12, was studied in the presence/absence of the complementary template polycytidylic acid, poly(C). Conditions were chosen where poly(C) and 2-MelmpG are in large excess over the oligoguanylate. In the absence of the template at 37 °C the reaction leads to three isomeric oligomers that are elongated by one monomer unit. They are the 3′–5′ linked, (n+1)³, the 2′–5′ linked, (n+1)², and the pyrophosphate product, (n+1) ^p , formed in an approximate ratio 1:2:5. In the presence of the template the reaction is 20-fold faster and yields productsn+1,n+2,n+3 etc. as long as 2-MelmpG is available. Most importantly the formation of the natural, 3′–5′ linked isomer, is enhanced selectively by 140-fold at 37 °C. Qualitative observations allow the conclusion that this enhancement is temperature dependent and increases with decreasing temperature. For example, at 1 °C only the 3′–5′ linked isomers were detected. Initial rates for the disappearance of then ³ oligoguanylate were determined at 1, 23, and 37 °C. It was found that the pseudo-first order rate constant for oligoguanylate elongation was linearly proportional to the 2-MelmpG concentration. This implies that the reaction complex poly(C)·n ³·2-MelmpG does not accumulate under the reaction conditions, a conclusion which is also supported by infrared data (Miles and Frazier, 1982). The implication of the above results with respect to chemical evolution is that lower temperatures, i.e., close to freezing, enhance the regioselectivity of these template-directed reactions and that one way to improve replication models may be sought in finding conditions that favor stable reaction complexes. NASA — National Research Council Research Fellow.     

The effect of sodium balance on sweat sodium secretion and plasma aldosterone concentration

The effect of manipulating sodium intake upon sweat sodium secretion was investigated during heat acclimation. Twenty-five male subjects were confined to an environmental chamber at a temperature of 25°C for 3 days, and then acclimated to heat by a further 5 days at 40°C. The subjects' daily sodium intake was controlled throughout as follows: high (HNa), 348.4 (0.8) mmol · day⁻¹, n = 7; moderate (MNa), 174.1 (0.6) mmol · day⁻¹, n = 9; or low (LNa), 66.3 mmol · day⁻¹, n = 9. Sodium losses were estimated from urinary, faecal and sweat collections using a whole-body washdown method. Plasma aldosterone concentration was also measured from venous blood sampled each morning. Measurements of body temperature and heart rate during the heat exposure phase indicated a degree of heat acclimation. During this heat phase there was a reduction (P < 0.01) in sweat sodium secretion for all three conditions which was greatest for the LNa condition, although this finding was not significant (P < 0.1). In the LNa condition, plasma aldosterone concentration increased (P < 0.05) prior to heat exposure, and the secretion of aldosterone was potentiated (P < 0.01) during the heat exposure in comparison with the MNa condition. In contrast, the HNa diet produced a fall (P < 0.05) in plasma aldosterone concentration prior to heat exposure and an attenuation of aldosterone secretion thereafter. These findings are inconsistent with the hypothesis that retention of sweat sodium is dependent upon a net body sodium deficit, but demonstrate that aldosterone secretion is potentiated under such conditions. Accepted: 22 May 1988