Thermoregulation during prolonged exercise in heat: alterations with beta-adrenergic blockade

Thermoregulation and cardiovascular drift were studied under conditions of prolonged exercise in a warm environment (dry bulb temperature 31.7 +/- 0.3 degrees C, rh 44.7 +/- 4.7%) during beta-adrenergic blockade. Fourteen subjects performed 90-min rides on a cycle ergometer at a work rate equivalent to 40% of their control maximal O2 uptake under each of three treatments provided in a randomized double-blind manner: atenolol (100 mg/day), propranolol (160 mg/day), and a placebo. Exercise during the propranolol trial resulted in significantly higher forearm vascular resistance values and significantly lower forearm blood flows (FBF) compared with the placebo trial. However, the significantly lower FBF during propranolol did not significantly alter the rectal temperature (Tre) response to prolonged exercise. In addition, both beta-blockers produced lower FBF for any given Tre, suggesting that beta-adrenergic blockade affects FBF through nonthermal factors. The slight differences in Tre, despite the large differences in FBF between the various treatments, are apparently the result of an enhanced sweat loss and a lower mean skin temperature during exercise with beta-blockade. The uncoupling of FBF and sweat loss provides evidence of independent regulation. The reduction in FBF at any given Tre was concomitant to lower blood pressure values during beta-blockade and suggests that baroreflexes provide significant input to the control of skin blood flow when both pressure and temperature maintenance are simultaneously challenged.     

Trees on networks: resolving statistical patterns of phylogenetic similarities among interacting proteins

Background  

Phylogenies capture the evolutionary ancestry linking extant species. Correlations and similarities among a set of species are mediated by and need to be understood in terms of the phylogenic tree. In a similar way it has been argued that biological networks also induce correlations among sets of interacting genes or their protein products.     

The Unique Chemistry of Eastern Mediterranean Water Masses Selects for Distinct Microbial Communities by Depth

The waters of the Eastern Mediterranean are characterized by unique physical and chemical properties within separate water masses occupying different depths. Distinct water masses are present throughout the oceans, which drive thermohaline circulation. These water masses may contain specific microbial assemblages. The goal of this study was to examine the effect of physical and geological phenomena on the microbial community of the Eastern Mediterranean water column. Chemical measurements were combined with phospholipid fatty acid (PLFA) analysis and high-throughput 16S rRNA sequencing to characterize the microbial community in the water column at five sites. We demonstrate that the chemistry and microbial community of the water column were stratified into three distinct water masses. The salinity and nutrient concentrations vary between these water masses. Nutrient concentrations increased with depth, and salinity was highest in the intermediate water mass. Our PLFA analysis indicated different lipid classes were abundant in each water mass, suggesting that distinct groups of microbes inhabit these water masses. 16S rRNA gene sequencing confirmed the presence of distinct microbial communities in each water mass. Taxa involved in autotrophic nitrogen cycling were enriched in the intermediate water mass suggesting that microbes in this water mass may be important to the nitrogen cycle of the Eastern Mediterranean. The Eastern Mediterranean also contains numerous active hydrocarbon seeps. We sampled above the North Alex Mud Volcano, in order to test the effect of these geological features on the microbial community in the adjacent water column. The community in the waters overlaying the mud volcano was distinct from other communities collected at similar depths and was enriched in known hydrocarbon degrading taxa. Our results demonstrate that physical phenomena such stratification as well as geological phenomena such as mud volcanoes strongly affect microbial community structure in the Eastern Mediterranean water column.     

Reductions in blood pressure after acute exercise by hypertensive rats

Postexercise reductions in blood pressure at rest have been reported for hypertensive subjects. To determine whether post-exercise hypotension would occur in spontaneously hypertensive rats and to test the hypothesis that any reductions would result because of decreases in regional vascular resistances, hypertensive rats (n = 19) were instrumented with indwelling arterial catheters and Doppler probes to measure regional blood flows from the iliac, superior mesenteric, and renal arteries. Data were collected from animals who performed a 20- and a 40-min treadmill test at between 60 and 70% of their maximum O2 uptake. When the animals ran for 20 min, there was a pre- to postexercise drop in mean arterial pressure (MAP) from 158 +/- 3.6 to 150 +/- 3.6 mmHg (P less than 0.05), which was recorded 30 min after the exercise had ceased. The pre- to postexercise reduction in MAP after 40 min of treadmill running was from 154 +/- 3.1 to 138 +/- 3.0 mmHg (P less than 0.05) as recorded 30 min postexercise. Postexercise heart rate was significantly lower after the 40-min exercise bout, from a preexercise mean of 351 +/- 3 beats/min to 324 +/- 5 beats/min 30 min after the treadmill had stopped. Surprisingly, marked pre- to postexercise reductions in regional vascular resistance were not observed in either the iliac, superior mesenteric, or renal vascular beds. These data demonstrated the existence of postexercise hypotension in genetic hypertensive rats and suggested that reductions in cardiac output were the primary hemodynamic mechanism for this finding.     

南瓜雌蕊与自花及远缘花粉的相互作用

南瓜柱头表面经去垢剂、蛋白酶及Con A处理后花粉不能萌发或花粉管生长受阻,Con A能专一地与柱头表面结合。柱头块加入培养液可促进花粉萌发。不同的远缘花粉授粉后在雌蕊不同部位受阻。在成熟南瓜雌蕊提取液中检测到血凝活性,凝集素可能参与雌蕊对远缘花粉的抑制。     

Differential control of forearm and calf vascular resistance during one-leg exercise

The purpose of this study was to determine whether blood flow (BF) and vascular resistance (VR) are controlled differently in the nonactive arm and leg during submaximal rhythmic exercise. In eight healthy men we simultaneously measured BF to the forearm and calf (venous occlusion plethysmography) and arterial blood pressure (sphygmomanometry) and calculated whole limb VR before (control) and during 3 min of cycling with the contralateral leg at 38, 56, and 75% of peak one-leg O2 uptake (VO2). During the initial phase of exercise (0-1.5 min) at all work loads, BF increased and VR decreased in the forearm (P less than 0.05), whereas calf BF and VR remained at control levels. Thereafter, BF decreased and VR increased in parallel and progressive fashion in both limbs. At end exercise, forearm BF and VR were not different from control values (P greater than 0.05); however, in the calf, BF tended to be lower (P less than 0.05 at 75% peak VO2 only) and VR was higher (23 +/- 9, 44 +/- 14, and 88 +/- 23% above control at 38, 56, and 75% of peak VO2, respectively, all P less than 0.05). In a second series of studies, forearm and calf skin blood flow (laser-Doppler velocimetry) and arterial pressure were measured during the same levels of exercise in six of the subjects. Compared with control, skin BF was unchanged and VR was increased (P less than 0.05) in the forearm by end exercise at all work loads, whereas calf skin BF increased (P less than 0.05) and VR decreased (P less than 0.05). The present findings indicate that skeletal muscle and skin VR are controlled differently in the nonactive forearm and calf during the initial phase of rhythmic exercise with the contralateral leg. Skeletal muscle vasodilation occurs in the forearm but not in the calf; forearm skin vasoconstricts, whereas calf skin vasodilates. Finally, during exercise a time-dependent vasoconstriction occurs in the skeletal muscle of both limbs.     

Action potential conduction between a ventricular cell model and an isolated ventricular cell.

We used the Luo and Rudy (LR) mathematical model of the guinea pig ventricular cell coupled to experimentally recorded guinea pig ventricular cells to investigate the effects of geometrical asymmetry on action potential propagation. The overall correspondence of the LR cell model with the recorded real cell action potentials was quite good, and the strength-duration curves for the real cells and for the LR model cell were in general correspondence. The experimental protocol allowed us to modify the effective size of either the simulation model or the real cell. 1) When we normalized real cell size to LR model cell size, required conductance for propagation between model cell and real cell was greater than that found for conduction between two LR model cells (5.4 nS), with a greater disparity when we stimulated the LR model cell (8.3 +/- 0.6 nS) than when we stimulated the real cell (7.0 +/- 0.2 nS). 2) Electrical loading of the action potential waveform was greater for real cell than for LR model cell even when real cell size was normalized to be equal to that of LR model cell. 3) When the size of the follower cell was doubled, required conductance for propagation was dramatically increased; but this increase was greatest for conduction from real cell to LR model cell, less for conduction from LR model cell to real cell, and least for conduction from LR model cell to LR model cell. The introduction of this "model clamp" technique allows testing of proposed membrane models of cardiac cells in terms of their source-sink behavior under conditions of extreme coupling by examining the symmetry of conduction of a cell pair composed of a model cell and a real cardiac cell. We have focused our experimental work with this technique on situations of extreme uncoupling that can lead to conduction block. In addition, the analysis of the geometrical factors that determine success or failure of conduction is important in the understanding of the process of discontinuous conduction, which occurs in myocardial infarction.