Influence of charge density on bilayer bending rigidity in lipid vesicles: a combined dynamic light scattering and neutron spin-echo study.

We report a combined dynamic light scattering and neutron spin-echo study on vesicles composed of the uncharged stabilizing lipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) and the cationic lipid 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). Mechanical properties of a model membrane and thus the corresponding bilayer undulation dynamics can be specifically tuned by changing its composition through lipid headgroup or acyl chain properties. We compare the undulation dynamics in lipid vesicles composed of DMPC/DOTAP to vesicles composed of a mixture of the uncharged helper lipid DMPC with the also uncharged reference lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). We have performed dynamic light scattering on the lipid mixtures to investigate changes in lipid vesicle size and the corresponding center-of-mass diffusion. We study lipid translational diffusion in the membrane plane and local bilayer undulations using neutron spin-echo spectroscopy, on two distinct time scales, namely around 25 ns and around 150 ns. Finally, we calculate the respective bilayer bending rigidities κ for both types of lipid vesicles. We find that on the local length scale inserting lipid headgroup charge into the membrane influences the bilayer undulation dynamics and bilayer bending rigidity κ less than inserting lipid acyl chain unsaturation: We observe a bilayer softening with increasing inhomogenity of the lipid mixture, which could be caused by a hydrophobic mismatch between the acyl chains of the respective lipid components, causing a lateral phase segregation (domain formation) in the membrane plane.

Mechanical properties of sarcomeres during cardiac myofibrillar relaxation: stretch-induced cross-bridge detachment contributes to early diastolic filling.

Sudden Ca2+ removal from isometrically contracting cardiac myofibrils induces a biphasic relaxation: first a slow, linear force decline during which sarcomeres remain isometric and then a rapid, exponential decay originating from sequential lengthening, i.e., successive mechanical relaxation, of individual sarcomeres (Stehle et al. 2002; Biophys J 83:2152-2162). Step-stretches were applied to the myofibrils, in order to study the mechanical properties of sarcomeres during this dynamic relaxation process. Stretch applied soon (approximately 10 ms) after Ca2+ removal accelerated the initiation of the rapid, exponential force decay and of the sequential sarcomere lengthening. After the stretch, a short, transient period (approximately 24 ms) remained, during which time force was enhanced and sarcomeres were homogenously elongated by the stretch. This period was similar to the duration of the switching-off of troponin C in myofibrils, as measured by stopped-flow. In contrast, when the stretch was applied during the rapid, exponential relaxation phase, force quickly decayed after stretch, back to the force level of isometric controls or even lower. Smaller stretches lengthened only those sarcomeres that were located at the wave front of the sequential sarcomere relaxation. The more the stretch-size was increased, the more of the contracting sarcomeres became lengthened by the stretch; those sarcomeres that were relaxed prior to stretch were barely elongated. These results indicate that the stretch accelerates myofibrillar relaxation by forcing the cross-bridges in contracting sarcomeres to detach. Subsequent rapid cross-bridge reattachment occurs during a short period after Ca2+ removal until troponin C is switched off. However, this switch off occurs approximately 5 times too fast to directly rate-limit the force relaxation under the isometric condition. After troponin C is switched off, stretching induces cross-bridge detachment without subsequent reattachment, and force rapidly decays below the isometric level. This may explain the rapid distention of the ventricular myocardium during early diastolic filling.

Dynamic behaviour of half-sarcomeres during and after stretch in activated rabbit psoas myofibrils: sarcomere asymmetry but no 'sarcomere popping'.

We examined length changes of individual half-sarcomeres during and after stretch in actively contracting, single rabbit psoas myofibrils containing 10-30 sarcomeres. The myofibrils were fluorescently immunostained so that both Z-lines and M-bands of sarcomeres could be monitored by video microscopy simultaneously with the force measurement. Half-sarcomere lengths were determined by processing of video images and tracking the fluorescent Z-line and M-band signals. Upon Ca2+ activation, during the rise in force, active half-sarcomeres predominantly shorten but to different extents so that an active myofibril consists of half-sarcomeres of different lengths and thus asymmetric sarcomeres, i.e. shifted A-bands, indicating different amounts of filament overlap in the two halves. When force reached a plateau, the myofibril was stretched by 15-20% resting length (L0) at a velocity of approximately 0.2 L0 s(-1). The myofibril force response to a ramp stretch is similar to that reported from muscle fibres. Despite the approximately 2.5-fold increase in force due to the stretch, the variability in half-sarcomere length remained almost constant during the stretch and A-band shifts did not progress further, independent of whether half-sarcomeres shortened or lengthened during the initial Ca2+ activation. Moreover, albeit half-sarcomeres lengthened to different extents during a stretch, rapid elongation of individual sarcomeres beyond filament overlap ('popping') was not observed. Thus, in contrast to predictions of the 'popping sarcomere' hypothesis, a stretch rather stabilizes the uniformity of half-sarcomere lengths and sarcomere symmetry. In general, the half-sarcomere length changes (dynamics) before and after stretch were slow and the dynamics after stretch were not readily predictable on the basis of the steady-state force-sarcomere length relation.

Effects of the mutation R145G in human cardiac troponin I on the kinetics of the contraction-relaxation cycle in isolated cardiac myofibrils.

Familial hypertrophic cardiomyopathy (FHC) has been linked to mutations in sarcomeric proteins such as human cardiac troponin I (hcTnI). To elucidate the functional consequences of the mutation hcTnI(R145G) on crossbridge kinetics, force kinetics were analysed in murine cardiac myofibrils carrying either the mutant or the wild-type protein. The mutation was introduced into the myofibrils in two different ways: in the first approach, the endogenous Tn was replaced by incubation of the myofibrils with an excess of reconstituted recombinant hcTn containing either hcTnI(WT) or hcTnI(R145G). Alternatively, myofibrils were isolated either from non-transgenic or transgenic mice expressing the corresponding mcTnI(R146G) mutation. In myofibrils from both models, the mutation leads to a significant upward shift of the passive force-sarcomere length relation determined at pCa 7.5. Addition of 5 mm BDM (2,3-butandione-2-monoxime), an inhibitor of actomyosin ATPase partially reverses this shift, suggesting that the mutation impairs the normal function of cTnI to fully inhibit formation of force-generating crossbridges in the absence of Ca(2)(+). Maximum force development (F(max)) is significantly decreased by the mutation only in myofibrils exchanged with hcTnI(R145G) in vitro. Ca(2)(+) sensitivity of force development was reduced by the mutation in myofibrils from transgenic mice but not in exchanged myofibrils. In both models the rate constant of force development k(ACT) is reduced at maximal [Ca(2)(+)] but not at low [Ca(2)(+)] where it is rather increased. Force relaxation is significantly prolonged due to a reduction of the relaxation rate constant k(REL). We therefore assume that the impairment in the regulatory function of TnI by the mutation leads to modulations in crossbridge kinetics that significantly alter the dynamics of myofibrillar contraction and relaxation.

Force kinetics and individual sarcomere dynamics in cardiac myofibrils after rapid ca(2+) changes.

Kinetics of force development and relaxation after rapid application and removal of Ca(2+) were measured by atomic force cantilevers on subcellular bundles of myofibrils prepared from guinea pig left ventricles. Changes in the structure of individual sarcomeres were simultaneously recorded by video microscopy. Upon Ca(2+) application, force developed with an exponential rate constant k(ACT) almost identical to k(TR), the rate constant of force redevelopment measured during steady-state Ca(2+) activation; this indicates that k(ACT) reflects isometric cross-bridge turnover kinetics. The kinetics of force relaxation after sudden Ca(2+) removal were markedly biphasic. An initial slow linear decline (rate constant k(LIN)) lasting for a time t(LIN) was abruptly followed by an ~20 times faster exponential decay (rate constant k(REL)). k(LIN) is similar to k(TR) measured at low activating [Ca(2+)], indicating that k(LIN) reflects isometric cross-bridge turnover kinetics under relaxed-like conditions (see also. Biophys. J. 83:2142-2151). Video microscopy revealed the following: invariably at t(LIN) a single sarcomere suddenly lengthened and returned to a relaxed-type structure. Originating from this sarcomere, structural relaxation propagated from one sarcomere to the next. Propagated sarcomeric relaxation, along with effects of stretch and P(i) on relaxation kinetics, supports an intersarcomeric chemomechanical coupling mechanism for rapid striated muscle relaxation in which cross-bridges conserve chemical energy by strain-induced rebinding of P(i).

Coal face and stockpile ash analyser for the coal mining industry.

A portable nucleonic instrument was developed for the determination of coal ash on the coal face or the surface of coal stockpiles. The instrument employs the backscattered gamma-gamma technique. There are two gamma-ray sources used in this instrument: a 1.1 MBq 133Ba source as the primary source of radiation and a 37 kBq 137Cs for gain stabilization. The instrument is commercially available.

Generation of tension by skinned fibers and intact skeletal muscles from desmin-deficient mice.

We have investigated the physiological role of desmin in skeletal muscle by measuring isometric tension generated in skinned fibres and intact skeletal muscles from desmin knock-out (DES-KO) mice. About 80% of skinned single extensor digitorum longus (EDL) fibres from adult DES-KO mice generated tensions close to that of wild-type (WT) controls. Weights and maximum tensions of intact EDL but not of soleus (SOL) muscles were lowered in DES-KO mice. Repeated contractions with stretch did not affect subsequent isometric tension in EDL muscles of DES-KO mice. Tension during high frequency fatigue (HFF) declined faster and this deficiency was compensated in DES-KO EDL muscles by 5 mM caffeine which had no influence on HFF in WT EDL. Furthermore, caffeine evoked twitch potentiation was higher in DES-KO than in WT muscles. We conclude that desmin is not essential for acute tensile strength but rather for optimal activation of intact myofibres during E-C coupling.

Kinetics of the initial steps of rabbit psoas myofibrillar ATPases studied by tryptophan and pyrene fluorescence stopped-flow and rapid flow-quench. Evidence that cross-bridge detachment is slower than ATP binding.

The kinetics of the tryptophan fluorescence enhancement that occurs when myofibrils (rabbit psoas) are mixed with Mg-ATP were studied by stopped-flow in different solvents (water, 40% ethylene glycol, 20% methanol) at 4 degrees C. Under relaxing conditions (low Ca(2+)) in water (mu = 0.16 M, pH 7.4) and at high ATP concentrations, the transient was biphasic, giving a k(fast)(max) of 230 s(-)(1) and a k(slow)(max) of 15 s(-)(1). The kinetics of the two phases were compared with those obtained by chemical sampling using [gamma-(32)P]ATP and quenching in acid (P(i) burst experiments: these give unambiguously the ATP cleavage kinetics), or cold Mg-ATP (cold ATP chase: ATP binding kinetics). k(slow) is due to ATP cleavage, as with S1. Interestingly, k(fast) is slower than the ATP binding kinetics. Instead, this constant appears to report ATP-induced cross-bridge detachment from actin because (1) it was identical to the fluorescence transient obtained on addition of ATP to pyrene-labeled myofibrils; (2) when the initial filament overlap in the myofibrils was decreased, the amplitude of the fast phase decreased; (3) there was no fluorescent enhancement upon the addition of ADP to myofibrils. This is different from the situation with S1 or actoS1 where there was also a fast fluorescent ATP-induced transient but whose kinetics were identical to those of the tight ATP binding. To increase the time resolution and to confirm our results, we also carried out transient kinetics in ethylene glycol and methanol. We interpret our results by a scheme in which a rapid equilibrium between attached (AM.ATP) and detached (M.ATP) states is modulated by the fraction of myosin heads in rigor (AM) during the time of experiment.

Cross-bridge attachment during high-speed active shortening of skinned fibers of the rabbit psoas muscle: implications for cross-bridge action during maximum velocity of filament sliding.

To characterize the kinetics of cross-bridge attachment to actin during unloaded contraction (maximum velocity of filament sliding), ramp-shaped stretches with different stretch-velocities (2-40,000 nm per half-sarcomere per s) were applied to actively contracting skinned fibers of the rabbit psoas muscle. Apparent fiber stiffness observed during such stretches was plotted versus the speed of the imposed stretch (stiffness-speed relation) to derive the rate constants for cross-bridge dissociation from actin. The stiffness-speed relation obtained for unloaded shortening conditions was shifted by about two orders of magnitude to faster stretch velocities compared to isometric conditions and was almost identical to the stiffness-speed relation observed in the presence of MgATPgammaS at high Ca(2+) concentrations, i.e., under conditions where cross-bridges are weakly attached to the fully Ca(2+) activated thin filaments. These data together with several control experiments suggest that, in contrast to previous assumptions, most of the fiber stiffness observed during high-speed shortening results from weak cross-bridge attachment to actin. The fraction of strongly attached cross-bridges during unloaded shortening appears to be as low as some 1-5% of the fraction present during isometric contraction. This is about an order of magnitude less than previous estimates in which contribution of weak cross-bridge attachment to observed fiber stiffness was not considered. Our findings imply that 1) the interaction distance of strongly attached cross-bridges during high-speed shortening is well within the range consistent with conventional cross-bridge models, i.e., that no repetitive power strokes need to be assumed, and 2) that a significant part of the negative forces that limit the maximum speed of filament sliding might originate from weak cross-bridge interactions with actin.

Cryoenzymic studies on an organized system: myofibrillar ATPases and shortening.

We have exploited cryoenzymology, first, to probe the product release steps of myofibrillar ATPase under relaxing conditions and, second, to define the conditions for studying the contractile process in slow motion. Cryoenzymology implies perturbation by temperature and by the antifreeze added to allow for work at subzero temperatures. Here, we studied myofibrillar shortening and ATPases by the rapid quench flow method over a wide temperature range (-15 to 30 degrees C) in two antifreezes, 40% ethylene glycol and 20% methanol. The choice of solvent and temperature was dictated by the purpose of the experiment. Ethylene glycol (40%) is suitable for investigating the kinetics of the products release steps which is difficult in water. In this cryosolvent, the myofibrillar ATPase is not activated by Ca2+ nor is there shortening, except under special conditions, i.e., Ca2+ plus strong rigor bridges [Stehle, R., Lionne, C., Travers, F., and Barman, T. (1998) J. Muscl. Res. Cell Motil. 19, 381-392]. By the use of the glycol, we show that at low Ca2+ the kinetics of the ADP release are much faster with myofibrils than with S1. On the other hand, the kinetics of the Pi release were very similar for the two materials. Therefore, we suggest that, upon Ca2+ activation, only the Pi release kinetics are accelerated. In 20% methanol, in the presence of Ca2+, myofibrils shortened at temperatures above -2 degrees C but not below. At a given temperature above -2 degrees C, both the shortening and ATPase rates were reduced by the methanol. The temperature dependences of the myofibrillar ATPases (+/-Ca2+) converged with a decrease in temperature: at 20 degrees C, Ca2+ activated 30-fold, but at -15 degrees C, only about 5-fold. We suggest that studies in methanol may open the way for an investigation of muscle contraction in slow motion and, further, to obtain thermodynamic information on the internal forces involved in the shortening process.

ATPase and shortening rates in frog fast skeletal myofibrils by time-resolved measurements of protein-bound and free Pi.

Shortening and ATPase rates were measured in Ca2+-activated myofibrils from frog fast muscles in unloaded conditions at 4 degrees C. ATPase rates were determined using the phosphate-binding protein method (free phosphate) and quench flow (total phosphate). Shortening rates at near zero load (V0) were estimated by quenching reaction mixtures 50 ms to 10 s old at pH 3.5 and measuring sarcomere lengths under the optical microscope. As with the rabbit psoas myofibrils (C. Lionne, F. Travers, and T. Barman, 1996, Biophys. J. 70:887-895), the ATPase progress curves had three phases: a transient Pi burst, a fast linear phase (kF), and a deceleration to a slow phase (kS). Evidence is given that kF is the ATPase rate of shortening myofibrils. V0 is in good agreement with mechanical measurements in myofibrils and fibers. Under the same conditions and at saturation in ATP, V0 and kF are 2.4 microm half-sarcomere(-1) s(-1) and 4.6 s(-1), and their Km values are 33 and 200 microM, respectively. These parameters are higher than found with rabbit psoas myofibrils. The myofibrillar kF is higher than the fiber ATPase rates obtained previously in frog fast muscles but considerably lower than obtained in skinned fibers by the phosphate-binding protein method (Z. H. He, R. K. Chillingworth, M. Brune, J. E. T. Corrie, D. R. Trentham, M. R. Webb, and M. R. Ferenczi, 1997, J. Physiol. 50:125-148). We show that, with frog as with rabbit myofibrillar ATPase, phosphate release is the rate-limiting step.

Probing the coupling of Ca2+ and rigor activation of rabbit psoas myofibrillar ATPase with ethylene glycol.

We have exploited solvent perturbation to probe the coupling of Ca2+ and rigor activation of the ATPase of myofibrils from rabbit psoas. Three techniques were used: overall myofibrillar ATPases by the rapid-flow quench method; kinetics of the interaction of ATP with myofibrils by fluorescence stopped-flow; and myofibrillar shortening by optical microscopy. Because of its extensive use with muscle systems, ranging from myosin subfragment-1 to muscle fibres, we chose 40% ethylene glycol as the relaxing agent. At 4 degrees C, the glycol had little effect on the myofibrillar ATPase at low [Ca2+], but at high [Ca2+] the activity was reduced 50-fold, close to the level found under relaxing conditions, and there was no shortening. However, the ATPase of chemically cross-linked myofibrils (permanently activated even without Ca2+) was reduced only 3-4-fold. The lesser reduction of the ATPase of permanently activated myofibrils was also observed in single turnover experiments in which activation occurs by a few heads in the rigor state activating the remaining heads. The addition of ADP, which also promotes strong head-thin filament interactions, also activated the ATPase but only in the presence of Ca2+. Further experiments revealed that in 40% ethylene glycol, Ca2+ does initiate shortening but only with the aid of strong interactions and at temperatures above 15 degrees C. This confirms that in the organized and intact myofibril, Ca2+ and rigor activation are coupled, as proposed previously for regulated actomyosin subfragment-1.

Targeting delavirdine/atevirdine resistant HIV-1: identification of (alkylamino)piperidine-containing bis(heteroaryl)piperazines as broad spectrum HIV-1 reverse transcriptase inhibitors.

A novel class of bis(heteroaryl)piperazine (BHAP) analogs which possesses the ability to inhibit NNRTI (non-nucleoside reverse transcriptase inhibitor) resistant recombinant HIV-1 reverse transcriptase (RT) and NNRTI resistant variants of HIV-1 has been identified via targeted screening. Further investigation of the structure-activity relationships of close congeners of these novel (alkylamino)piperidine BHAPs (AAP-BHAPs) led to the synthesis of several compounds possessing the desired phenotype (e.g., activity against recombinant RTs carrying the Y181C and P236L substitutions). Further structural modifications were required to inhibit metabolism and modulate solubility in order to obtain compounds with the desired biological profile as well as appropriate pharmaceutical properties. The AAP-BHAPs with the most suitable characteristics were compounds 7, 15, and 36.

Potassium channel conductance: a mechanism affecting hair growth both in vitro and in vivo.

The opening of intracellular potassium channels has been suggested as a mechanism regulating hair growth. Enhancing the flux of potassium ions is a mechanism shared by several structurally diverse antihypertensive agents including minoxidil sulfate (the active metabolite of minoxidil), pinacidil, P-1075 (a potent pinacidil analog), RP-49,356, diazoxide, cromakalim, and nicorandil. Of these drugs, minoxidil, pinacidil, and diazoxide have been reported to elicit hypertrichosis in humans. This potassium channel hypothesis was examined by testing these drugs for effects on hair growth both in vitro and in vivo. For the in vitro studies, mouse vibrissae follicles were cultured for 3 d with drug and the effects on hair growth were measured by metabolic labeling. All drugs, except diazoxide, enhanced cysteine incorporation into the hair shafts of the cultured vibrissae. Diazoxide was poorly soluble and thus was tested only at low doses. Minoxidil, P-1075, cromakalim, and RP-49,356 were also evaluated in vivo by measuring hair growth effects in balding stumptail macaque monkeys. The drugs were administered topically to defined sites on balding scalps once per day for 4-5 months and the amount of hair grown was determined by monthly measurements of shaved hair weight. Three of the drugs produced significant increases in hair weight whereas, the RP-49,356 had no effect. These studies provide correlative evidence that the opening of potassium channels is an important regulatory mechanism for hair growth. This provides the impetus for further studies on this potentially important mechanism affecting hair biology.

Immunoreactive insulin-like growth factor binding protein-3 in the culture of human luteinized granulosa cells.

Granulosa cells from human preovulatory follicles were cultured under serum-free conditions to investigate the presence of immunoreactive insulin-like growth factor binding protein-3 (IGFBP-3). IGFBP-3 levels were measured by a radioimmunoassay developed against the acid-stable subunit of the protein. The antiserum had no cross-reactivity to the low molecular weight GH-independent IGFBP-1. Granulosa luteal cells exhibited a continuous release of IGFBP-3 into the culture medium during the whole time (6 days) of the incubation. A dose-dependent increase in IGFBP-3 was observed when the cells were treated by dibutyryl cAMP. Cycloheximide suppressed almost completely both the basal and the stimulated production of IGFBP-3. The smallest effective dose of dibutyryl cAMP enhancing the progesterone release was lower than that for IGFBP-3. The different time course of IGFBP-3 and progesterone secretion to dibutyryl cAMP treatment, as well as the failure of progesterone to elicit IGFBP-3 increase alone, do not support the participation of progesterone in the IGFBP-3 production of granulosa cells. It is concluded that 1. immunoreactive IGFBP-3 is produced by cultured granulosa luteal cells; 2. its synthesis is regulated by physiological intracellular mechanisms.

Insulin-like growth factors and their binding proteins in human follicular fluid.

Increasing evidence suggests that insulin-like growth factors I and II (IGF-I, IGF-II) have a regulatory role in animal granulosa cells. This study was undertaken to investigate the presence of IGF-I and IGF-II, as well as that of their binding proteins (BP), IGFBP-1 and IGFBP-3 in human serum and follicular fluid (FF). Preovulatory FF was obtained from 51 patients undergoing in-vitro fertilization. The IGFBP-1 level was found to be significantly higher (P less than 0.01) in FF than in serum, whereas IGF-I and IGFBP-3 values remained markedly lower (P less than 0.01) in FF. Serum IGF-II levels were slightly but not significantly elevated compared to values obtained in the FF of patients. A positive correlation (P less than 0.001) between individual serum and FF levels was observed only for IGF-I. When a group of poor responders was compared to patients with normal stimulation characteristics, no significant difference was found in either IGF or IGFBP levels in the FF. It is concluded that IGFBP-1 is produced locally, whereas the serum may possibly be the major source of IGF-I. No clear conclusions can be drawn regarding the source of FF IGF-II and IGFBP-3. Neither the absolute level nor the relationship of IGFs to their transport proteins could explain the poor response to ovarian stimulation.

Local topical delivery of drugs: a model incorporating simultaneous diffusion and metabolic interconversion between drug and a single metabolite in the skin.

A comprehensive biophysical model for the topical delivery of a drug and its single, locally active metabolite is proposed. This elaboration of the simpler case, in which the drug converts irreversibly to a pharmacologically active metabolite in the tissue, allows for enzymatic interconversion between drug and metabolite. Exact mathematical expressions give concentration-distance relationships of drug and metabolite as well as fluxes of the two molecules in terms of concentration of drug applied to the stratum corneum, permeability coefficient of drug in the stratum corneum, diffusion coefficients of drug and metabolite in the viable tissues (epidermis and dermis), rate constants for the two enzyme systems, and the thickness of the viable tissue. Constants included in the mathematical expressions can be evaluated independently by appropriate in vitro experiments with freshly excised animal skin. The model can then predict what physiochemical drug constants will lead to maximal levels of active metabolite at the site of activity within the skin.

Effects of temperature and water immersion on plasma catecholamines and circulation.

The effects of environmental air temperature of 6 degrees C and 26 degrees C on catecholamines (CA) and circulation were studied in eight male subjects during rest and during bicycle exercise at WOBLA for 45 min each. We found that resting at 6 degrees C increased the norepinephrine (NE) levels to the same levels as endurance exercises at 6 degrees C. The increase of CA levels was 2.5 to 3 times higher during work at 26 degrees C compared with 6 degrees C. During both rest and exercise at 6 degrees C we found a higher stroke volume of the heart and a reduced heart rate (HR) with no or only small effects on the oxygen uptake and blood lactate levels compared with 26 degrees C. Measurements of the skin temperatures showed large differences both at rest and during work; those of core temperature showed no changes at rest and a slightly more pronounced increase during work at 26 degrees C compared with 6 degrees C. The behavior of CA, plasma renin activity (PRA), plasma aldosterone (PA), and circulation were studied in 13 top class swimmers and 12 recreational swimmers during immersion into water of 27 degrees C for 10 min. The recreational swimmers were additionally immersed into water of 21 degrees C and 33 degrees C. Even immersion at 33 degrees C induced a small but significant increase of NE levels and of blood pressure (BP) values with no effect on the HR and blood lactate values. Epinephrine (EPI) showed a tendency to decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in sympathoadrenal, hormonal, and metabolic adaptation to submaximal and maximal arm and leg work compared with whole stroke in breast-style swimming.

During work on land adaptational reactions of circulation and hormones are influenced by the body position, the activated muscle mass, and the working extremities. The aim of this study was to explore the additional effect of water immersion during swimming on cardiocirculatory, metabolic, and hormonal regulation under different working conditions. Twelve young men not specifically trained in swimming underwent swimming tests on 3 different days. They had to swim breast stroke in total as well as isolated with legs or arms only each for 10 min at submaximal intensity and 150 m or 100 m at maximal intensity. This study was focused on changes of catecholamines (CA), heart rate (HR), blood pressure (BP), glucose, lactate, plasma renin activity (PRA), and plasma aldosterone (PA). Additionally, parameters of the electrolyte-volume homeostasis were investigated. Norepinephrine (NE) and epinephrine (EPI) increased during swimming under submaximal and maximal conditions. The augmentation of CA and HR was the highest after swimming whole stroke and the lowest after swimming arm stroke only. They were related to intensity within one type of swimming and showed a dependence on muscle mass independent from lactate or glucose levels when the different types of swimming were compared, although a positive correlation between CA and lactate levels was found. The BP was higher after leg work than after arm work, contrary to observations done on land regarding the comparable submaximal work loads. We suppose that this is an effect of water immersion and the horizontal body position whereby the central hemodynamic circulation becomes stabilized.(ABSTRACT TRUNCATED AT 250 WORDS)