摘要:

In‐vitrovasoreactivity to extracellular potassium (Ko+) was tested in isolated human pial and mesenteric arteries as well as basilar and mesenteric arteries from rabbits and rats. Contractions were induced by stepwise increases in [K‐]oand were measured isometrically with a force‐displacement transducer, in small‐volume organ baths. Significant differences between species as well as between regions were found. The threshold of [K+]ofor eliciting contraction in human cerebral arteries in hyperosmotic solutions was 10 mM, in rabbit cerebral arteries 17 mM and in rat cerebral arteries 27 mM. The threshold concentration for contraction in mesenteric arteries was significantly higher compared to cerebral arteries in humans and rabbits, but lower in rats: 20 mM in humans, 26 mM in rabbits and 25 mM in rats. In all species the contractile amplitudes were significantly higher in both cerebral and mesenteric arteries when [K+]owas increased under isotonic conditions in the buffer solution than when hyper‐osomolality was created. This difference increased with increasing hyperosmolalitv. In hyperosmotic solutions, the EC50for [K+]owas lower in cerebral and mesenteric arteries from man than in vessels from rabbit and rat. When the solutions were isotonic, this pattern was seen only in mesenteric arteries. It is concluded that significant species and regional differences in vascular responses to [K+]oexist. Considering that [K+]ois increased in cerebral ischaemia, the observed significantly lower threshold for K+‐induced contractions in human cerebral arteries may be of importance, especially in human cerebral ischa

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08647.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Ring segments (1 mm in diameter) of the pulmonary artery obtained from 16 patients undergoing thoracic surgery were mounted in tissue baths. Cumulative concentration‐response curves of some prostanoids and amines were obtained, and Emaxand pEC50values calculated. Noradrenaline, phenylephrine, clonidine and serotonin (5‐HT) showed low intrinsic activities. Prostaglandin F2α(PGF2α) induced strong contractions with an Emaxof 126% of the preceding K+(124 mM)‐induced contraction, but its potency was low (pEC50= 5.70). The thromboxane receptor agonists U‐46619 and U‐44069 induced strong contractions (Emax= 139% and 133% respectively) and were significantly more potent than the other drugs used (pEC50= 8.43 and 8.30 respectively). The thromboxane receptor antagonist BM‐13.505 (10‐8to 10‐6M) caused rightward parallel shifts of the U‐46619 concentration‐response curves without reduction of Emax, indicating c

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08648.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The left ventricular pressure, arterial blood pressure and heart rate were studied in three series of pentobarbital‐anaesthetized rats exposed to 5‐bar normoxic (Po2= 0.2 bar) environments: nitrogen‐oxygen (15 and 60 min) and helium‐oxygen (15 min). The maximal left ventricular pressure (LVP max) and the maximal velocities of LVP rise (+ dP/dtmax) and fall (‐ dP/dt) were significantly (P<0.01) increased immediately after reaching normoxic 5 bar (He, 13–28%; N2, 13–23%) and during the exposure at 5 bar (He, 22–44%; N2, 13–18%). The pulse pressure increased significantly (He, 50–62%; N2, 30–34%;P0.01) during the hyperbaric exposure. No changes in heart rate or end‐diastolic and mean arterial pressure were detected.The present findings indicate an enhanced cardiac contractility (+ dP/dtmax) at 5 bar, with the greatest increase found when He was used as inert gas. The increased contractility was of significant duration (at least 60 min), and was not completely‐reversed until 5

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08649.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Male and female Wistar rats were exercise‐trained for 6 or 11 weeks respectively, to examine the effects of acute exercise or exercise trainingper seon insulin‐stimulated glucose utilization in soleus muscles. isolated and incubatedin vitro.The maximal activities of hexokinase and 2‐oxoglutarate dehydrogenase were significantly elevated (by>50%) in gastrocnemius muscle of exercise‐trained male and female rats, indicating an adaptation to the training regime. No significant differences in any of the variables studied were observed between appropriately matched male and female rats. There were no significant differences in the sensitivity or responsiveness of the rates of lactate formation or glycogen synthesis in soleus muscles isolated from exercise‐trained and sedentary animals at rest (exercise‐trained animals were studied 40 h after the last exercise bout). On the other hand, acute exercise caused significant changes in soleus muscle glucose metabolism. Basal and insulin‐stimulated rates of glycogen synthesis were significantly elevated in soleus muscles incubated from both sedentary and exercise‐trained rats immediately after an exercise bout. In addition, the responsiveness of glucose utilization to insulin in soleus muscles from exercise‐trained rats was significantly increased after acute exercise. The results indicate that significant changes in the control of glucose metabolism by insulin in soleus muscle occur as a result of an acute exercise bout, while no adaptive changes in insulin sensitivity occur in soleus muscle after

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08650.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The aims were: (1) to investigate whether the 10–20% lower force during bilateral (BL) as compared to unilateral (UL) leg extension could be due to a general inability to activate fully a large number of muscles simultaneously, (2) to analyse the EMG signal of the quadriceps femoris during leg extensions, (3) to study the BL/UL force ratio in extension of the knee, and (4) to study the BL/UL leg extension force ratio in untrained and trained subjects. A 10% lower maximal voluntary isometric force was demonstrated during BL as compared to UL leg extension. This force discrepancy did not change when a total arm load of 250 N was applied simultaneously. Nor did the absolute force levels change, which indicates that the lower BL leg extension force is not due to a general mechanism of reduced activation with an increased number of muscles recruited in maximal voluntary contractions. Integrated EMG activity, mean power frequency and root mean square value of the EMG amplitude did not differ between UL and BL leg extensions. The knee extension force was slightly greater (4%) during BL than UL contractions. These findings are arguments against a reduced activation of the knee extensor muscles being the cause of the lower bilateral leg extension force. No differences in BL/UL force ratio were noted between groups of untrained and trained subjects despite the fact that several of the trained groups do different forms of BL leg extensions regularly. Thus, it does not appear that training readily affects the BL/UL leg extension force rati

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08651.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The influence of exercise intensity on the accumulation of inosine monophosphate (IMP) in human skeletal muscle has been investigated. Ten men cycled at workloads corresponding to 40%, 75% and 100% of their maximal oxygen uptake (Vo2max). Muscle IMP was below the detection limit (<0.01 mmol kg‐1dry wt) at rest and after exercise at 40% ofVo2max, but increased to 0.26 ± 0.06(mean ± SEM) and 3.50 ± 0.51 mmol kg‐1dry wt after exercise at 75% and 100% ofVo2max respectively. Accumulation of IMP corresponded to a similar decrease in the total adenine nucleotide content. The muscle content of IMP was positively related to lactate and negatively related to phosphocreatine (PCr). IMP was formed in both fibre types, but the IMP content at fatigue was about twice as high in type II fibres as in type I fibres. It was concluded that the IMP content of human skeletal muscle is very low at rest and after low‐intensity exercise, but increases after moderate and high‐intensity exercise. In contrast to rat muscle, where deamination of AMP predominantly occurs in the fast‐twitch muscle fibres, IMP is formed during exercise in both fibre types in human muscle. Accumulation of IMP appears to reflect an imbalance between the rate of utilization and the rate of regener

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08652.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The effect of hypoxaemia on the muscle content of inosine monophosphate (IMP) during short‐term, low‐intensity exercise has been investigated. Six men cycled twice for 5 min at 120 ± 6 W (mean ± SE), which corresponded to ˜ 50% of their maximal normoxic O2uptake, breathing air (N) on one occasion and 11% O2in N2(H) on the other. Oxygen uptake at the end of the exercise period was similar between treatments. No significant difference was observed between H and N in the muscle metabolite contents at rest. Muscle content of phosphocreatine (PCr) decreased and lactate increased during exercise. Post‐exercise PCr during H was 80% of the value during N (P>0.05) and post‐exercise muscle lactate was fourfold higher during H than during N (P<0.001). Post‐exercise muscle content of ADP was significantly higher during H than during N (P0.05 HvsN). IMP was not detectable in pre‐exercise muscle samples (<0.01 mmol kg‐1dry wt) but increased during N exercise (0.03 ± 0.01 mmol kg‐1dry wt,P<0.05) and even more during H exercise (0.16 ± 0.05 mmol kg‐1dry wt,P0.05, HvsN). Post‐exercise IMP was negatively related to PCr (r = ‐0.90) and positively related to lactate (r =0.88). It is concluded that hypoxaemia results in an enhanced accumulation of IMP during submaximal exercise and that the IMP level is related to the degree of an

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08653.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Tension and stiffness of tetanically activated skeletal muscle fibres of the frog were studied at varied tonicity of the extracellular medium (1.7–3.2 °C; sarcomere length, 2.13–2.22 μm). The stiffness was measured from the change in peak tension in response to fast (0.2 ms) stretches and releases of small amplitude (0.11–0.15% of the fibre length). The bathing solution was made hypotonic by reduction of NaCl and hypertonic by addition of sucrose. The osmotic strength of the solutions tested varied from 81 to 168% of the isotonic value. Maximum tetanic tension decreased markedly with increased tonicity. The active stiffness, on the other hand, increased as the tonicity was raised, and the tension/stiffness ratio (the total extension of the undamped fibre elasticity) was thus greatly reduced under these conditions. Evidence is presented to show that the change in the tension/stiffness ratio is due neither to the development of rigor cross‐bridges nor to the recruitment of passive parallel‐elastic elements in response to increased tonicity. Neither are viscous‐like components important for explaining the effect. A change in the tension/stiffness ratio, similar to that seen in response to increased tonicity, did not occur as fibre width was reduced by increasing the sarcomere length. This suggests that the changes in the fibre volume affect this ratio mainly by mechanisms that are unrelated to changes in lateral spacing between the

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08654.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

In this study the variation in ground reaction force parameters was investigated with respect to adaptations to speed and mode of progression, and to type of foot‐strike. Twelve healthy male subjects were studied during walking (1.0–3.0 m s‐1) and running (1.5–6.0 m s‐1). The subjects were selected with respect to foot‐strike pattern during running. Six subjects were classified as rearfoot strikers and six as forefoot strikers. Constant speeds were accomplished by pacer lights beside an indoor straightway and controlled by means of a photo‐electronic device. The vertical, anteroposterior and mediolateral force components were recorded with a force platform. Computer software was used to calculate durations, amplitudes and impulses of the reaction forces. The amplitudes were normalized with respect to body weight (b.w.). Increased speed was accompanied by shorter force periods and larger peak forces. The peak amplitude of the vertical reaction force in walking and running increased with speed from approximately 1.0 to 1.5 b.w. and 2.0 to 2.9 b.w. respectively. The anteroposterior peak force and mediolateral peak‐to‐peak force increased about 2 times with speed in walking and about 2–4 times in running (the absolute values were on average about 10 times smaller than the vertical). The transition from walking to running resulted in a shorter support phase duration and a change in the shape of the vertical reaction force curve. The vertical peak force increased whereas the vertical impulse and the anteroposterior impulses and peak forces decreased. In running the vertical force showed an impact peak at touch‐down among the rearfoot strikers but generally not among the forefoot strikers. The first mediolateral force peak was laterally directed (as in walking) for the rearfoot strikers but medially for the forefoot strikers.Thus, there is a change with speed in the complex interaction between vertical and horizontal forces needed for propulsion and equilibrium during human locomotion. The differences present between walking and running are consequences of fundamental differences in motor strategies between the two major forms

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08655.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The effect of adrenaline infusion on glycogen breakdown in different muscle fibres types in resting extensor digitorum longus (EDL) and soleus was investigated with histochemical methods. During adrenaline infusion the glycogen content in type IIB and type HA fibres in EDL, as measured in PAS‐stained sections, decreased 24.5 % and 11.5% respectively. The glycogen content in type I fibres in EDL and in type I, type IIA and T‐fibres in soleus did not change during adrenaline infusion. The present study shows that adrenaline infusion has different effects on glycogen breakdown in the different fibre types in EDL and a different effect on type IIA fibres in EDL and soleus. So far, the reason for these differences is unkn

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08656.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY