Effects of arterial hypotension on microvascular oxygen exchange in contracting skeletal muscle.

In healthy animals under normotensive conditions (N), contracting skeletal muscle perfusion is regulated to maintain microvascular O2 pressures (PmvO2) at levels commensurate with O2 demands. Hypovolemic hypotension (H) impairs muscle contractile function; we tested whether this condition would alter the matching of O2 delivery (Qo2) to O2 utilization (Vo2), as determined by PmvO2 at the onset of muscle contractions. PmvO2 in the spinotrapezius muscles of seven female Sprague-Dawley rats (280+/-6 g) was measured every 2 s across the transition from rest to 1-Hz twitch contractions. Measurements were made under N (mean arterial pressure, 97+/-4 mmHg) and H (induced by arterial section; mean arterial pressure, 58+/-3 mmHg, P<0.05) conditions; PmvO2 profiles were modeled using a multicomponent exponential fitted with independent time delays. Hypotension reduced muscle blood flow at rest (24+/-8 vs. 6+/-1 ml-1.min-1.100 g-1 for N and H, respectively; P<0.05) and during contractions (74+/-20 vs. 22+/-4 ml-1.min-1.100 g-1 for N and H, respectively; P<0.05). H significantly decreased resting PmvO2 and steady-state contracting PmvO2(19.4+/-2.4 vs. 8.7+/-1.6 Torr for N and H, respectively, P<0.05). At the onset of contractions, H reduced the time delay (11.8+/-1.7 vs. 5.9+/-0.9 s for N and H, respectively, P<0.05) before the fall in PmvO2 and accelerated the rate of PmvO2 decrease (time constant, 12.6+/-1.4 vs. 7.3+/-0.9 s for N and H, respectively, P<0.05). Muscle Vo2 was reduced by 71% at rest and 64% with contractions in H vs. N, and O2 extraction during H averaged 78% at rest and 94% during contractions vs. 51 and 78% in N. These results demonstrate that H constrains the increase of skeletal muscle Qo2 relative to that of Vo2 at the onset of contractions, leading to a decreased PmvO2. According to Fick's law, this scenario will decrease blood-myocyte O2 flux, thereby slowing Vo2 kinetics and exacerbating the O2 deficit generated at exercise onset.     

In situ SR function in postinfarction myocytes.

Previous studies have shown lower systolic intracellular Ca(2+) concentrations ([Ca(2+)](i)) and reduced sarcoplasmic reticulum (SR)-releasable Ca(2+) contents in myocytes isolated from rat hearts 3 wk after moderate myocardial infarction (MI). Ca(2+) entry via L-type Ca(2+) channels was normal, but that via reverse Na(+)/Ca(2+) exchange was depressed in 3-wk MI myocytes. To elucidate mechanisms of reduced SR Ca(2+) contents in MI myocytes, we measured SR Ca(2+) uptake and SR Ca(2+) leak in situ, i.e., in intact cardiac myocytes. For sham and MI myocytes, we first demonstrated that caffeine application to release SR Ca(2+) and inhibit SR Ca(2+) uptake resulted in a 10-fold prolongation of half-time (t(1/2)) of [Ca(2+)](i) transient decline compared with that measured during a normal twitch. These observations indicate that early decline of the [Ca(2+)](i) transient during a twitch in rat myocytes was primarily mediated by SR Ca(2+)-ATPase and that the t(1/2) of [Ca(2+)](i) decline is a measure of SR Ca(2+) uptake in situ. At 5.0 mM extracellular Ca(2+), systolic [Ca(2+)](i) was significantly (P 相似文献   

拟巫山淫羊藿的megastigmane糖苷和苯丙醇类成分

为了解拟巫山淫羊藿(Epimedium pseudowushaneseB. L. Guo)的化学成分,其从地上部分水提物中分离得到2个megastigmane糖苷和4个苯丙醇类化合物。通过波谱分析,分别鉴定为淫羊藿次苷B6(1)、megastigman-5-ene-3,9-diol 3-O-α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranoside (2)、丁香酚芸香糖苷(3)、2-羟基-1-(4-羟基-3,5-二甲氧基苯基)-1-丙酮(4)、2,3-二羟基-1-(4-羟基-3,5-二甲氧基苯基)-1-丙酮(5)、2,3-二羟基-1-(4-羟基-3-甲氧基苯基)-1-丙酮(6)、二氢松柏基醇γ-O-α-L-鼠李糖苷(7)。其中化合物2和7为新化合物,所有化合物均为首次从拟巫山淫羊藿中分离得到。     

应用RNA干扰技术调节大鼠c-jun基因的表达

目的:应用RNA干扰(RNAi)技术调节大鼠c-jun基因在Cos-7细胞中的表达.方法:分别构建大鼠c-jun基因的RNA干扰载体和真核表达GFP(绿色荧光蛋白)载体,将两者共转染Cos-7细胞,镜下观察大鼠C-Jun-GFP融合蛋白的表达,应用Western blot方法检测抑制效率.结果:酶切和测序结果表明,大鼠c-jun基因的RNA干扰载体和真核表达GFP载体构建成功,镜下及Western blot共转染结果均显示随着RNA干扰载体浓度的增加C-Jun-GFP融合蛋白表达量逐渐减少.结论:在Cos-7细胞中应用RNAi技术成功调节大鼠c-jun基因的表达.     

Genome-wide association study and meta-analysis of intraocular pressure

Elevated intraocular pressure (IOP) is a major risk factor for glaucoma and is influenced by genetic and environmental factors. Recent genome-wide association studies (GWAS) reported associations with IOP at TMCO1 and GAS7, and with primary open-angle glaucoma (POAG) at CDKN2B-AS1, CAV1/CAV2, and SIX1/SIX6. To identify novel genetic variants and replicate the published findings, we performed GWAS and meta-analysis of IOP in >6,000 subjects of European ancestry collected in three datasets: the NEI Glaucoma Human genetics collaBORation, GLAUcoma Genes and ENvironment study, and a subset of the Age-related Macular Degeneration-Michigan, Mayo, AREDS and Pennsylvania study. While no signal achieved genome-wide significance in individual datasets, a meta-analysis identified significant associations with IOP at TMCO1 (rs7518099-G, p = 8.0 × 10^?8). Focused analyses of five loci previously reported for IOP and/or POAG, i.e., TMCO1, CDKN2B-AS1, GAS7, CAV1/CAV2, and SIX1/SIX6, revealed associations with IOP that were largely consistent across our three datasets, and replicated the previously reported associations in both effect size and direction. These results confirm the involvement of common variants in multiple genomic regions in regulating IOP and/or glaucoma risk.     

Chronic acid water feeding protects mice against lethal gut-derived sepsis due to Pseudomonas aeruginosa

Acidified feeding formulas have been proposed as a method of controlling gastrointestinal colonization and nosocomial infection in critically ill patients. We examined possible mechanisms by which chronic acid water feeding might protect the host against lethal gut derived sepsis by assessing its effect on both local intestinal epithelial barrier function to bacteria as well as on local and systemic heat shock protein expression. Heat shock protein expression measured by immunoblot demonstrated that HSP25 was increased in the stomach, aorta and kidney of mice chronically fed acid water (8 weeks) compared to tap water fed controls. HSP72 expression was also increased in the aorta of mice drinking acid water. The protein content of cecum and its barrier function were enhanced in mice ingesting acidified water. The direct effect of an acid environment on intestinal epithelial barrier function was tested in cultured human intestinal epithelial cells. An acidified environment protected against bacterial mediated disruption of the intestinal epithelial barrier. Finally, the protective effect of chronic acid water feeding on gut-derived sepsis due to P. aeruginosa was tested in mice. Chronic acid water feeding protected mice from the lethal gut derived sepsis due to P. aeruginosa.     

Aldosterone regulation of intestinal Na absorption involves SGK-mediated changes in NHE3 and Na+ pump activity

Aldosterone-induced intestinal Na(+) absorption is mediated by increased activities of apical membrane Na(+)/H(+) exchange (aNHE3) and basolateral membrane Na(+)-K(+)-ATPase (BLM-Na(+)-K(+)-ATPase) activities. Because the processes coordinating these events were not well understood, we investigated human intestinal Caco-2BBE cells where aldosterone increases within 2-4 h of aNHE3 and alpha-subunit of BLM-Na(+)-K(+)-ATPase, but not total abundance of these proteins. Although aldosterone activated Akt2 and serum glucorticoid kinase-1 (SGK-1), the latter through stimulation of phosphatidylinositol 3-kinase (PI3K), only the SGK-1 pathway mediated its effects on Na(+)-K(+)-ATPase. Ouabain inhibition of the early increase in aldosterone-induced Na(+)-K(+)-ATPase activation blocked most of the apical NHE3 insertion, possibly by inhibiting Na(+)-K(+)-ATPase-induced changes in intracellular sodium concentration ([Na](i)). Over the next 6-48 h, further increases in aNHE3 and BLM-Na(+)-K(+)-ATPase activity and total protein expression were observed to be largely mediated by aldosterone-activated SGK-1 pathway. Aldosterone-induced increases in NHE3 mRNA, for instance, could be inhibited by RNA silencing of SGK-1, but not Akt2. Additionally, aldosterone-induced increases in NHE3 promoter activity were blocked by silencing SGK-1 as well as pharmacological inhibition of PI3K. In conclusion, aldosterone-stimulated intestinal Na(+) absorption involves two phases. The first phase involves stimulation of PI3K, which increases SGK-dependent insertion and function of BLM-Na(+)-K(+)-ATPase and subsequent increased membrane insertion of aNHE3. The latter may be caused by Na(+)-K(+)-ATPase-induced changes in [Na] or transcellular Na flux. The second phase involves SGK-dependent increases in total NHE3 and Na(+)-K(+)-ATPase protein expression and activities. The coordination of apical and BLM transporters after aldosterone stimulation is therefore a complex process that requires multiple time- and interdependent cellular processes.     

Acute effects of hydrogen peroxide on skeletal muscle microvascular oxygenation from rest to contractions

Reactive oxygen species, such as hydrogen peroxide (H(2)O(2)), exert a critical regulatory role on skeletal muscle function. Whether acute increases in H(2)O(2) modulate muscle microvascular O(2) delivery-utilization (Qo(2)/Vo(2)) matching [i.e., microvascular partial pressure of O(2) (Pmv(O(2)))] at rest and following the onset of contractions is unknown. The hypothesis was tested that H(2)O(2) treatment (exogenous H(2)O(2)) would enhance Pmv(O(2)) and slow Pmv(O(2)) kinetics during contractions compared with control. Anesthetized, healthy young Sprague-Dawley rats had their spinotrapezius muscles either exposed for measurement of blood flow (and therefore QO(2)), VO(2), and Pmv(O(2)), or exteriorized for measurement of force production. Electrically stimulated twitch contractions (1 Hz, ~7 V, 2-ms pulse duration, 3 min) were evoked following acute superfusion with Krebs-Henseleit (control) and H(2)O(2) (100 μM). Relative to control, H(2)O(2) treatment elicited disproportionate increases in QO(2) and VO(2) that elevated Pmv(O(2)) at rest and throughout contractions and slowed overall Pmv(O(2)) kinetics (i.e., ~85% slower mean response time; P < 0.05). Accordingly, H(2)O(2) resulted in ~33% greater overall Pmv(O(2)), as assessed by the area under the Pmv(O(2)) curve (P < 0.05). Muscle force production was not altered with H(2)O(2) treatment (P > 0.05), evidencing reduced economy during contractions (~40% decrease in the force/VO(2) relationship; P < 0.05). These findings indicate that, although increasing the driving force for blood-myocyte O(2) flux (i.e., Pmv(O(2))), transient elevations in H(2)O(2) impair skeletal muscle function (i.e., reduced economy during contractions), which mechanistically may underlie, in part, the reduced exercise tolerance in conditions associated with oxidative stress.     

Aging alters the contribution of nitric oxide to regional muscle hemodynamic control at rest and during exercise in rats

Advanced age is associated with altered skeletal muscle hemodynamic control during the transition from rest to exercise. This study investigated the effects of aging on the functional role of nitric oxide (NO) in regulating total, inter-, and intramuscular hindlimb hemodynamic control at rest and during submaximal whole body exercise. We tested the hypothesis that NO synthase inhibition (N(G)-nitro-l-arginine methyl ester, l-NAME; 10 mg/kg) would result in attenuated reductions in vascular conductance (VC) primarily in oxidative muscles in old compared with young rats. Total and regional hindlimb muscle VCs were determined via radiolabeled microspheres at rest and during treadmill running (20 m/min, 5% grade) in nine young (6-8 mo) and seven old (27-29 mo) male Fisher 344 × Brown Norway rats. At rest, l-NAME increased mean arterial pressure (MAP) significantly by ～17% and 21% in young and old rats, respectively. During exercise, l-NAME increased MAP significantly by ～13% and 19% in young and old rats, respectively. Compared with young rats, l-NAME administration in old rats evoked attenuated reductions in 1) total hindlimb VC during exercise (i.e., down by ～23% in old vs. 43% in young rats; P < 0.05), and 2) VC in predominantly oxidative muscles both at rest and during exercise (P < 0.05). Our results indicate that the dependency of highly oxidative muscles on NO-mediated vasodilation is markedly diminished, and therefore mechanisms other than NO-mediated vasodilation control the bulk of the increase in skeletal muscle VC during the transition from rest to exercise in old rats. Reduced NO contribution to vasomotor control with advanced age is associated with blood flow redistribution from highly oxidative to glycolytic muscles during exercise.