The oxygen delivery response to acute hypoxia during incremental knee extension exercise differs in active and trained males

Background

It is well known that hypoxic exercise in healthy individuals increases limb blood flow, leg oxygen extraction and limb vascular conductance during knee extension exercise. However, the effect of hypoxia on cardiac output, and total vascular conductance is less clear. Furthermore, the oxygen delivery response to hypoxic exercise in well trained individuals is not well known. Therefore our aim was to determine the cardiac output (Doppler echocardiography), vascular conductance, limb blood flow (Doppler echocardiography) and muscle oxygenation response during hypoxic knee extension in normally active and endurance-trained males.

Methods

Ten normally active and nine endurance-trained males (VO_2max = 46.1 and 65.5 mL/kg/min, respectively) performed 2 leg knee extension at 25, 50, 75 and 100% of their maximum intensity in both normoxic and hypoxic conditions (FIO₂ = 15%; randomized order). Results were analyzed with a 2-way mixed model ANOVA (group × intensity).

Results

The main finding was that in normally active individuals hypoxic sub-maximal exercise (25 – 75% of maximum intensity) brought about a 3 fold increase in limb blood flow but decreased stroke volume compared to normoxia. In the trained group there were no significant changes in stroke volume, cardiac output and limb blood flow at sub-maximal intensities (compared to normoxia). During maximal intensity hypoxic exercise limb blood flow increased approximately 300 mL/min compared to maximal intensity normoxic exercise.

Conclusion

Cardiorespiratory fitness likely influences the oxygen delivery response to hypoxic exercise both at a systemic and limb level. The increase in limb blood flow during maximal exercise in hypoxia (both active and trained individuals) suggests a hypoxic stimulus that is not present in normoxic conditions.

     

不同退化红砂荒漠草地的水分分配格局

研究了内蒙古阿拉善盟不同过牧退化红砂草地的土壤 植物 大气系统的水分分配格局、不同退化草地和主要植物种的水分利用效率 .2 0 0 1年降雨量 12 4 .3mm ,其中试验期 119.4mm .1m深土壤水分结果表明 ,10～ 4 0cm土层受蒸散影响最大 ;由于主要共存种红砂和无芒隐子草根系分布和蒸腾强度不同等 ,含水量在 10～ 2 0cm土层以中度退化区显著低于其它样区 (P <0 .0 5 ) ,而 2 0～ 4 0cm土层以轻度退化区较低 .样地年均蒸发量为 30 .6mm ,红砂种群的年均蒸腾量为 11.9mm .随着草地退化加剧 ,裸地的蒸发量和退化指示种匍根骆驼蓬种群的蒸腾量增加 ,而红砂种群的蒸腾量降低 .与较轻度退化区比 ,中度和重度退化区的水分利用率分别下降了 14 .6 %和 4 6 .1% ,红砂水分利用率分别下降了 37.8%和 73.8% .     

我国巴拉巴按蚊形态描述

白踝按蚊种团是由很多形态近似的蚊种组成,其中巴拉巴按蚊和白踝按蚊均为东南亚一带的重要传疟媒介。我国过去资料均记载为白踝按蚊,但未从形态上详细鉴定。为了确定该种的分类地位,1963年作者等在海南岛万宁县兴隆附近山林区采集“白踝按蚊”全套标本10批共150多套,1971年后从云南省采集少数标本进行形态鉴定,发现其与Colless(1956,1957)所描述的白踝按蚊Anopheles leucosphyrus leucosphyrus Donitz(1901)有很明显的差别,而与巴拉巴按蚊A.balabacensis balabacensis Balsas(1936)除某些特征略有差异外,余均完全一致。按Colless的分类法,过去我国记载的“白踝按蚊”,应鉴定为巴拉巴按蚊A.balabacensis balabacensis Baisas。     

Ghrelin在小鼠体内早期胚胎发育中的表达

为了探讨Ghrelin是否在昆明系小白鼠(Mus musculus)体内早期胚胎发育中发挥作用。运用激素超排卵技术及动物解剖学方法获取小鼠体内不同发育阶段的早期胚胎,应用实时定量PCR技术检测了Ghrelin mRNA的相对表达量。结果表明,Ghrelin mRNA在小鼠各期胚胎中均有表达;同时,GhrelinmRNA的表达量呈现一定规律性变化,2-细胞期表达量最低,8-细胞期表达量达到最高值,总体趋势是先降低后升高之后又降低。研究结果揭示,Ghrelin可能在小鼠早期胚胎发育中发挥一定的作用。     

Improvement on the competitive binding assay for the measurement of cyclic AMP by using ammonium sulphate precipitation.

The protein-binding assay developed by Brown, Albano, Ekins, Sgherzi & Tampion [(1971) Biochem. J. 121, 561-562] and Brown, Ekins & Albano [(1972) Adv. Cyclic Nucleotide Res. 2, 25-40] was modified by using precipitation with (NH4)2SO4 of the protein-cyclic AMP complex instead of adsorption of the free nucleotide on charcoal. The half-life of the protein-cyclic AMP complex obtained in the presence of charcoal was lower than that of the (NH4)2SO4-precipitated complex. In consequence, owing to the great stability of the precipitated protein-cyclic AMP complex, this method allows more accurate and reproducible determinations.     

Measurement of cystic fibrosis transmembrane conductance regulator activity using fluorescence spectrophotometry

Cystic fibrosis (CF) is a frequent autosomal recessive disease caused by mutations that impair the CF transmembrane conductance regulator (CFTR) protein function. CFTR is a chloride channel activated by cyclic AMP (cAMP) via protein kinase A (PKA) and ATP hydrolysis. We describe here a method to measure CFTR activity in a monolayer of cultured cells using a fluorescence spectrophotometer and the chloride-sensitive probe 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ). Modifying a slice holder, the spectrophotometer quartz cuvette was converted in a perfusion chamber, allowing measurement of CFTR activity in real time, in a monolayer of T84 colon carcinoma cells. The SPQ Stern–Volmer constant (K_Cl^-) for chloride in water solution was 115.0 ± 2.8 M⁻¹, whereas the intracellular K_Cl^- was 17.8 ± 0.8 M⁻¹, for T84 cells. A functional analysis was performed by measuring CFTR activity in T84 cells. The CFTR transport inhibitors CFTR(inh)-172 (5 μM) and glibenclamide (100 μM) showed a significant reduction (P < 0.05) in CFTR activity. This simple method allows measuring CFTR activity in a very simple, reproducible, and sensitive way.