Influence of polycythemia on blood volume and thermoregulation during exercise-heat stress

We studied the effects of autologous erythrocyte infusion on blood volume and thermoregulation during exercise in the heat. By use of a double-blind design, nine unacclimated male subjects were infused with either 600 ml of a NaCl-glucose-phosphate solution containing a approximately 50% hematocrit (n = 6, reinfusion) or 600 ml of this solution only (n = 3, saline). A heat stress test (HST) was attempted approximately 2-wk pre- and 48-h postinfusion during the late spring months. After 30 min of rest in a 20 degrees C antechamber, the HST consisted of a 120-min exposure (2 repeats of 15 min rest and 45 min treadmill walking) in a hot (35 degrees C, 45% rh) environment while euhydrated. Erythrocyte volume (RCV, 51Cr) and plasma volume (PV, 125I) were measured 24 h before each HST, and maximal O2 uptake (VO2max) was measured 24 h after each HST. Generally, no significant effects were found for the saline group. For the reinfusion group, RCV (11%, P less than 0.01) and VO2max (11%, P less than 0.05) increased after infusion, and the following observations were made: 1) the increased RCV was associated with a reduction in PV to maintain the same blood volume as during the preinfusion measurements; 2) polycythemia reduced total circulating protein but did not alter F-cell ratio, plasma osmolality, plasma protein content, or plasma lactate at rest or during exercise-heat stress; 3) polycythemia did not change the volume of fluid entering the intravascular space from rest to exercise-heat stress; and 4) polycythemia tended to reduce the rate of heat storage during exercise-heat stress.     

Plasma hormonal responses at graded hypohydration levels during exercise-heat stress

The effects of graded levels of hypohydration (3, 5, and 7% of body weight) on hormonal responses to exercise in the heat were examined in six heat-acclimated male volunteers. On the day following dehydration, subjects performed light (approximately 25% maximal O2 consumption, 1.03 1 X min-1) exercise in a hot (49 degrees C, 20% relative humidity) environment for four consecutive 25-min intervals interspaced by 10-min rests; blood was obtained before exercise and at approximately 10 min before completion of each exercise period. During euhydration, plasma cortisol (PC) levels manifested significant decrements over time (e.g., time 0, 14.2 micrograms X 100 ml-1 vs. time 2, 8.9 micrograms X 100 ml-1), probably related to its diurnal periodicity. However, during hypohydration, levels of PC were increased and correlated with hypohydration intensity (e.g., time 0, 0, 3, 5, and 7% hypohydration, 14.2, 16.5, 19.8, and 36.2 micrograms X 100 ml-1, respectively). Plasma renin activity (PRA) was increased significantly by hypohydration (e.g., time 0, euhydrated vs. 3%, 3.7 vs. 6.2 units) but was unaffected by exercise in the heat. Plasma aldosterone (ALD) levels were generally increased by exercise in the heat (e.g., time 0 vs. time 4, 3% hypohydration, 12.1 vs. 18.7 ng X 100 ml-1). Regression analysis illustrated that graded intensities of hypohydration were correlated with incremented PRA and ALD through 5% hypohydration. Conversely, PC was incrementally elevated through 7% hypohydration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamics of mating success in experimental groups ofDrosophila melanogaster (Diptera: Drosophilidae)

Determinants of male courtship success in Drosophila melanogasterwere examined in groups of five males sequentially presented with five individual females. Thirty-three percent of males never mated, while approximately half of the males mated two or three times. Rapid courtship initiation was associated with male success in early matings only. Male size was important for courtship outcome, but the size distributions of mating and nonmating males and their progeny numbers indicate balancing rather than directional selection on size- dependent courtship success.     

Glycerol hyperhydration: physiological responses during cold-air exposure.

Hypohydration occurs during cold-air exposure (CAE) through combined effects of reduced fluid intake and increased fluid losses. Because hypohydration is associated with reduced physical performance, strategies for maintaining hydration during CAE are important. Glycerol ingestion (GI) can induce hyperhydration in hot and temperate environments, resulting in greater fluid retention compared with water (WI) alone, but it is not effective during cold-water immersion. Water immersion induces a greater natriuresis and diuresis than cold exposure; therefore, whether GI might be effective for hyperhydration during CAE remains unknown. This study examined physiological responses, i.e., thermoregulatory, cardiovascular, renal, vascular fluid, and fluid-regulating hormonal responses, to GI in seven men during 4 h CAE (15 degrees C, 30% relative humidity). Subjects completed three separate, double-blind, and counterbalanced trials including WI (37 ml water/l total body water), GI (37 ml water/l total body water plus 1.5 g glycerol/l total body water), and no fluid. Fluids were ingested 30 min before CAE. Thermoregulatory responses to cold were similar during each trial. Urine flow rates were higher (P = 0.0001) with WI (peak 11.8 ml/min, SD 1.9) than GI (5.0 ml/min, SD 1.8), and fluid retention was greater (P = 0.0001) with GI (34%, SD 7) than WI (18%, SD 5) at the end of CAE. Differences in urine flow rate and fluid retention were the result of a greater free water clearance with WI. These data indicate glycerol can be an effective hyperhydrating agent during CAE.     

Does high intraspecific variability of two genome fragments indicate a recent speciation process of Paramecium dodecaurelia (P. aurelia species complex,Ciliophora, Protozoa)?

Species of the Paramecium aurelia complex show different levels of intraspecific polymorphism, with P. dodecaurelia revealing a high level of intraspecific variation. Paramecium dodecaurelia strains originating from distant localities in the Palaearctic, North America (USA), and Oceania (Hawaii) were studied in terms of intraspecific differentiation and the degree of speciation. Sequences of genes encoding the ITS1–5.8S-ITS2–5’ end of LSU rDNA (1063–1097 bp) and cytochrome c oxidase subunit I mtDNA (638–644 bp) were obtained from 33 strains of P. dodecaurelia, other P. aurelia species, and another species of the genus Paramecium, with Tetrahymena sp. used as an outgroup. In phylograms, the majority of P. dodecaurelia strains from the Palaearctic appear in one cluster, while strains from Japan, Hawaii and the USA are grouped in another cluster, together with some strains from Italy and representatives of the P. aurelia species complex. Our results tend to support the hypothesis that P. dodecaurelia seems to be a polyphyletic species with several haplotypes similar to or even shared with other members of the P. aurelia species complex. However, it is still an open question whether the revealed intraspecific differences within P. dodecaurelia are the result of ongoing speciation, or perhaps they just indicate genetic differentiation within a species that has a wide geographic distribution.     

Sweat rate prediction equations for outdoor exercise with transient solar radiation

We investigated the validity of employing a fuzzy piecewise prediction equation (PW) [Gonzalez et al. J Appl Physiol 107: 379-388, 2009] defined by sweat rate (m(sw), g·m(-2)·h(-1)) = 147 + 1.527·(E(req)) - 0.87·(E(max)), which integrates evaporation required (E(req)) and the maximum evaporative capacity of the environment (E(max)). Heat exchange and physiological responses were determined throughout the trials. Environmental conditions were ambient temperature (T(a)) = 16-26°C, relative humidity (RH) = 51-55%, and wind speed (V) = 0.5-1.5 m/s. Volunteers wore military fatigues [clothing evaporative potential (i(m)/clo) = 0.33] and carried loads (15-31 kg) while marching 14-37 km over variable terrains either at night (N = 77, trials 1-5) or night with increasing daylight (N = 33, trials 6 and 7). PW was modified (Pw,sol) for transient solar radiation (R(sol), W) determined from measured solar loads and verified in trials 6 and 7. PW provided a valid m(sw) prediction during night trials (1-5) matching previous laboratory values and verified by bootstrap correlation (r(bs) of 0.81, SE ± 0.014, SEE = ± 69.2 g·m(-2)·h(-1)). For trials 6 and 7, E(req) and E(max) components included R(sol) applying a modified equation Pw,sol, in which m(sw) = 147 + 1.527·(E(req,sol)) - 0.87·(E(max)). Linear prediction of m(sw) = 0.72·Pw,sol + 135 (N = 33) was validated (R(2) = 0.92; SEE = ±33.8 g·m(-2)·h(-1)) with PW β-coefficients unaltered during field marches between 16°C and 26°C T(a) for m(sw) ≤ 700 g·m(-2)·h(-1). PW was additionally derived for cool laboratory/night conditions (T(a) < 20°C) in which E(req) is low but E(max) is high, as: PW,cool (g·m(-2)·h(-1)) = 350 + 1.527·E(req) - 0.87·E(max). These sweat prediction equations allow valid tools for civilian, sports, and military medicine communities to predict water needs during a variety of heat stress/exercise conditions.     

Bioassay-guided discovery of antibacterial agents: in vitro screening of Peperomia vulcanica, Peperomia fernandopoioana and Scleria striatinux

Background

The global burden of bacterial infections is high and has been further aggravated by increasing resistance to antibiotics. In the search for novel antibacterials, three medicinal plants: Peperomia vulcanica, Peperomia fernandopoioana (Piperaceae) and Scleria striatinux (Cyperaceae), were investigated for antibacterial activity and toxicity.

Methods

Crude extracts of these plants were tested by the disc diffusion method against six bacterial test organisms followed by bio-assay guided fractionation, isolation and testing of pure compounds. The minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations were measured by the microdilution method. The acute toxicity of the active extracts and cytotoxicity of the active compound were performed in mice and mammalian cells, respectively.

Results

The diameter of the zones of inhibition (DZI) of the extracts ranged from 7?C13?mm on Escherichia coli and Staphylococcus aureus of which the methylene chloride:methanol [1:1] extract of Scleria striatinux recorded the highest activity (DZI?=?13?mm). Twenty-nine pure compounds were screened and one, Okundoperoxide, isolated from S. striatinux, recorded a DZI ranging from 10?C19?mm on S. aureus. The MICs and MBCs indicated that the Peperomias had broad-spectrum bacteriostatic activity. Toxicity tests showed that Okundoperoxide may have a low risk of toxicity with an LC₅₀ of 46.88???g/mL.

Conclusions

The antibacterial activity of these plants supports their use in traditional medicine. The pure compound, Okundoperoxide, may yield new antibacterial lead compounds following medicinal chemistry exploration.