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PubMed1997

[Role of myocardial contractile status and relaxation in ventricular dysfunction during the transition of heart hypertrophy to failure].

PURPOSE: To investigate the participation of contractile state and relaxation in cardiac muscle dysfunction during the transition from stable hypertrophy to cardiac decompensation in aging spontaneously hypertensive rats (SHR). METHODS: Isolated left ventricular papillary muscle function was studied in SHR with heart failure (SHR-F), in age-matched SHR without evidence of heart failure (SHR-NF), and in nonhypertensive controls Wistar-Kyoto rats (WKY). Muscles were analysed in isometric and isotonic contractions in Krebs-Henseleit solution with calcium concentration of 1.25 mM at 28 degrees C. RESULTS: Papillary muscles from SHR-F and SHR-NF demonstrated decreased active tension development and shortening velocity relative to normotensive WKY (p < 0.05). SHR-F and SHR-NF did not differ. Compared with SHR-NF and WKY, muscle passive stiffness was increased in the failing SHR (p < 0.05 versus WKY and SHR-NF). This parameter did not differ between SHR-NF and WKY (p > 0.05). CONCLUSION: These data suggest that the progression from stable hypertrophy to heart failure is associated with changes in the passive stiffness and is not related to depression of myocardial contractile function.

Animals↗
PubMed2002

High concentrations of KCl release noradrenaline from noradrenergic neurons in the rat anococcygeus muscle.

The aim of the present study was to investigate the effects of high concentrations of KCl in releasing noradrenaline from sympathetic nerves and its actions on postsynaptic alpha-adrenoceptors. We measured the isotonic contractions induced by KCl in the isolated rat anococcygeus muscle under different experimental conditions. The contractile responses induced by KCl were inhibited by alpha-adrenoceptor antagonists in 2.5 mM Ca2+ solution. Prazosin reduced the maximum effect from 100 to 53.9 +/- 10.2% (P<0.05) while the pD2 values were not changed. The contractile responses induced by KCl were abolished by prazosin in Ca2+-free solution (P<0.05). Treatment of the rats with reserpine reduced the maximum effect induced by KCl as compared to the contractile responses induced by acetylcholine from 339.5 +/- 157.8 to 167.3 +/- 65.5% (P<0.05), and increased the pD2 from 1.57 +/- 0.01 to 1.65 +/- 0.006 (P<0.05), but abolished the inhibitory effect of prazosin (P<0.05). In contrast, L-NAME increased the contractile responses induced by 120 mM KCl by 6.2 +/- 2.3% (P<0.05), indicating that KCl could stimulate the neurons that release nitric oxide, an inhibitory component of the contractile response induced by KCl. Our results indicate that high concentrations of KCl induce the release of noradrenaline from noradrenergic neurons, which interacts with alpha1-adrenoceptors in smooth muscle cells, producing a contractile response in 2.5 mM Ca2+ (100%) and in Ca2+-free solution, part of which is due to a direct effect of KCl on the rat anococcygeus muscle.

Adrenergic Agonists↗
PubMed2006

Effect of unsaturated fatty acids on myocardial performance, metabolism and morphology.

Diets rich in saturated fatty acids are one of the most important causes of atherosclerosis in men, and have been replaced with diets rich in unsaturated fatty acids (UFA) for the prevention of this disorder. However, the effect of UFA on myocardial performance, metabolism and morphology has not been completely characterized. The objective of the present investigation was to evaluate the effects of a UFA-rich diet on cardiac muscle function, oxidative stress, and morphology. Sixty-day-old male Wistar rats were fed a control (N = 8) or a UFA-rich diet (N = 8) for 60 days. Myocardial performance was studied in isolated papillary muscle by isometric and isotonic contractions under basal conditions after calcium chloride (5.2 mM) and ss-adrenergic stimulation with 1.0 microM isoproterenol. Fragments of the left ventricle free wall were used to study oxidative stress and were analyzed by light microscopy, and the myocardial ultrastructure was examined in left ventricle papillary muscle. After 60 days the UFA-rich diet did not change myocardial function. However, it caused high lipid hydroperoxide (176 +/- 5 vs 158 +/- 5, P < 0.0005) and low catalase (7 +/- 1 vs 9 +/- 1, P < 0.005) and superoxide-dismutase (18 +/- 2 vs 27 +/- 5, P < 0.005) levels, and discrete morphological changes in UFA-rich diet hearts such as lipid deposits and mitochondrial membrane alterations compared to control rats. These data show that a UFA-rich diet caused myocardial oxidative stress and mild structural alterations, but did not change mechanical function.

Animals↗
PubMed2005

Creatine supplementation and exercise performance: recent findings.

Creatine monohydrate (Cr) is perhaps one of the most widely used supplements taken in an attempt to improve athletic performance. The aim of this review is to update, summarise and evaluate the findings associated with Cr ingestion and sport and exercise performance with the most recent research available. Because of the large volume of scientific literature dealing with Cr supplementation and the recent efforts to delineate sport-specific effects, this paper focuses on research articles that have been published since 1999.Cr is produced endogenously by the liver or ingested from exogenous sources such as meat and fish. Almost all the Cr in the body is located in skeletal muscle in either the free (Cr: approximately 40%) or phosphorylated (PCr: approximately 60%) form and represents an average Cr pool of about 120-140 g for an average 70 kg person. It is hypothesised that Cr can act though a number of possible mechanisms as a potential ergogenic aid but it appears to be most effective for activities that involve repeated short bouts of high-intensity physical activity. Additionally, investigators have studied a number of different Cr loading programmes; the most common programme involves an initial loading phase of 20 g/day for 5-7 days, followed by a maintenance phase of 3-5 g/day for differing periods of time (1 week to 6 months). When maximal force or strength (dynamic or isotonic contractions) is the outcome measure following Cr ingestion, it generally appears that Cr does significantly impact force production regardless of sport, sex or age. The evidence is much more equivocal when investigating isokinetic force production and little evidence exists to support the use of Cr for isometric muscular performance. There is little benefit from Cr ingestion for the prevention or suppression of muscle damage or soreness following muscular activity. When performance is assessed based on intensity and duration of the exercises, there is contradictory evidence relative to both continuous and intermittent endurance activities. However, activities that involve jumping, sprinting or cycling generally show improved sport performance following Cr ingestion. With these concepts in mind, the focus of this paper is to summarise the effectiveness of Cr on specific performance outcomes rather than on proposed mechanisms of action. The last brief section of this review deals with the potential adverse effects of Cr supplementation. There appears to be no strong scientific evidence to support any adverse effects but it should be noted that there have been no studies to date that address the issue of long-term Cr usage.

Bicycling↗
PubMed1979

Effects of cadmium on the contractility of a frog cardiac muscle in relation to pH of external solution.

In order to examine the pH dependency of Cd effects on cardiac muscle, the electrical and mechanical activities in the bullfrog heart were investigated in relation to various external pHs and concentrations of Cd. The amplitude and duration of the action potential or the spontaneously beating frequency in the atrium were not significantly affected during the 3-min administration of various concentrations of Cd in a range from pH 6 to 10, but the isotonic contraction at the end of the same period was greatly altered: the lower the external pH the more Cd decreased the contractility of the atrium. This pH dependency of Cd effects was also observed in SO4-Ringer's solution whose anions, SO4, were more impermeable than Cl. Decrease in contractility in Cd-Ringer's solution was counteracted by excess Ca. The lower the pH of the Cd-Ringer's solution, the more Ca was necessary to counteract an equal amount of Cd. The amount of Cd-uptake into the atrium was analyzed after soaking the atrium in various concentrations of Cd-Ringer's solution. The higher the concentration of external Cd, the larger the Cd-uptake into the atrium. No pH dependency, however, was observed in this relationship. This suggests that probably only a small fraction of total Cd-uptake interacts with Ca-binding sites which is specific to contraction, and causes the Cd-induced decrease in contractility. This process is considered to be pH-dependent. However, most Cd-uptake into cardiac muscle is pH-independent and may be nonspecific to contraction.

Action Potentials↗
PubMed1988

Effects of insulin on vasoconstrictive responses to norepinephrine and angiotensin II in rabbit femoral artery and vein.

To determine whether insulin has a vasodilator action on the artery and vein, the effects of insulin at varying concentrations (120 microU/ml, 1.2 mU/ml, 12 mU/ml, and 120 mU/ml) on vasoconstriction by norepinephrine (NE) and angiotensin II (ANG II) were studied in the isolated rabbit femoral artery and vein. Helical strips were suspended in an organ bath filled with modified Krebs solution (pH 7.4), were gassed with 95% O2/5% CO2 at 36 degrees C, and isotonic contractions were measured. Insulin significantly and dose dependently inhibited the vasoconstriction induced by NE (10(-8) M for the artery and 10(-7) M for the vein) at greater than or equal to 1.2 mU/ml for both the artery and vein and the vasoconstriction induced by ANG II (3 x 10(-10) M for the artery and 3 x 10(-9) M for the vein) at greater than or equal to 1.2 mU/ml for the artery and greater than or equal to 12 mU/ml for the vein. The results indicate that insulin has an inhibitory effect on NE- and ANG II-induced contraction in both the artery and vein, and this appeared to be a contributory factor in the hypotensive effect observed in diabetic patients treated with insulin.

Angiotensin II↗
PubMed1994

Electromyographic analysis of knee rehabilitation exercises.

Many exercises are used to strengthen the knee muscles, yet limited studies that evaluate the exercises exist. The purpose of this study was to describe and compare the muscle firing patterns in five knee muscles during five rehabilitative exercises, which were presumed either to strengthen a specific muscle group or to elicit a cocontraction. During short-arc knee extension, the medial and lateral vasti were significantly more active during the last 15 degrees of extension than during other arcs (p < .05). The short-arc knee extension with hamstring cocontraction demonstrated significantly more activity in the rectus femoris, vastus medialis oblique, and vastus lateralis than the biceps femoris and semimembranosus in the final 15 degrees of extension (p < .05). With isometric knee cocontractions, no significant difference in muscle activity occurred in any of the arcs tested. During squatting, the rectus femoris, vastus medialis oblique, and vastus lateralis were significantly more active than the biceps femoris and semimembranosus during the descending, holding, and arising phases (p < .05). This information offers suggestions in selecting optimal knee rehabilitation exercises.

Adult↗
PubMed1997

Postoperative eccentric and concentric isokinetic strength for the shoulder rotators in the scapular and neutral planes.

Considerable variability exists for isokinetic testing of the shoulder rotators, leaving the clinician in a quandry concerning the most appropriate method for patient evaluation. The purpose of this study was to evaluate concentric and eccentric rotational strength in the scapular and neutral planes for the surgical and nonsurgical shoulders. Fifteen males consented to be tested during a 90-minute isokinetic session. Both shoulders for each patient were tested concentrically (240 degrees/sec) and eccentrically (120 degrees/sec) in the scapular and neutral planes. Patient positioning was maintained through the use of a goniometer, plumb line, and floor grid system. Following a warmup, five maximal effort reciprocal internal and external rotation concentric and eccentric contractions were evaluated using multiple two-way analyses of variance (shoulder x plane) with repeated measures. Results indicated no statistically significant differences between the surgical or nonsurgical shoulders for either concentric (p = .063-.247) or eccentric (p = .460-.840) modes, regardless of test plane. No statistically significant differences were observed eccentrically between test planes (p = .06-.470), but the scapular plane produced significantly higher (p = .005) peak torques concentrically. Generally, the external rotators were 53.0% (concentrically) and 63.0% (eccentrically) of the internal rotator strength for either shoulder. Clinically, concentric and eccentric testing of the postoperative shoulder patient can occur in either the scapular or the neutral plane. However, the scapular plane may be preferred since it is more functionally relevant and less injurious to the rotator cuff. A full, functional recovery may be expected for the rotator cuff repair patient.

Adult↗
PubMed1997

Relationship between isokinetic concentric and eccentric contraction modes in the knee flexor and extensor muscle groups.

We investigated whether in normal subjects isokinetic concentric and eccentric strength variables were related in order to have a better picture in relation to rehabilitation and possible injury prevention. We studied the relationship between isokinetic concentric and eccentric peak torque, total work, and average power of knee extension and knee flexion at 60 degrees/sec and 120 degrees/sec in 42 young Chinese adults (22 males, age = 27 +/- 6.9 years; 20 females, age = 24.9 +/- 5.05 years) using the Cybex 6000 isokinetic dynamometer. Repeated analysis of covariance was used to compare the means between concentric and eccentric variables adjusted by limb dominance, speed of testing, and the muscle groups tested. A highly significant correlation was found between all concentric and eccentric variables, with correlation coefficients (r) ranging from 0.67 to 0.93. All but two of the eccentric variables were significantly greater than the concentric variables. Concentric and eccentric knee flexion to knee extension (H:Q) ratios were poorly correlated, with r ranging from 0.359 to 0.645. Although there is an acceptably high correlation between isokinetic concentric and eccentric strength variables of knee flexion and extension in young healthy individuals, we recommend measuring concentric and eccentric strength to plan a proper rehabilitation program and to assess muscle groups in a given contraction mode.

Adult↗
PubMed1999

Early changes in muscle strength after total knee arthroplasty. A 6-month follow-up of 30 knees.

We studied 30 patients with arthrosis in one knee operated on with a cemented (n 26) or an uncemented total knee arthroplasty (TKA) (n 4). Full weight-bearing from the first postoperative day was allowed in all patients, and they received standard postoperative physiotherapy. 1 week prior to surgery, and after 3 and 6 months, isokinetic and isometric muscle strength in both legs were measured, using a Cybex 6000 dynamometer. Isokinetic tests showed a bilateral, significant, and progressive increase (30-53%) in flexor muscle strength most pronounced in the operated legs. Isokinetic extensor strength increased significantly (14-18%) in the operated legs, while in the contralateral legs, a limited increase was found. Isometric flexion strength significantly decreased in the operated knees (17%). Isometric extension strength showed a temporary decrease at 3 months, which returned to the preoperative level. No significant change in isometric strength was observed in the contralateral legs. The knee pain during the muscle strength measurements decreased significantly from the preoperative level, which may indicate that the substantial pain relief within 3 months after a TKA is an important factor for evaluation of muscle strength.

Aged↗
PubMedDate not supplied

The regularizing effect of some active substances upon uterine smooth muscle contractile activity.

Our study concentrated upon the modifications of some parameters which characterize uterine smooth muscle contractile activity under the action of active substances. We studied the isotonic contractions of the uterine smooth muscle in a classical organ bath in which we introduced some contracting and relaxing substances. At the beginning, we introduced Oxytocin to determine uterine smooth muscle contractions. After that, we added relaxing substances (Papaverin, Diazepam, Terbutalin, Isoxuprin, Hexoprenalin) in the organ bath, and then, in another protocol, we added combinations of two relaxing substances. We determined for each wave some parameters: minimum, mean, maximum and net amplitude, wave area and duration, the interval between waves, the time while the curve increases from the minimal value of the amplitude to the maximum value, the frequency of contractile waves. For each parameter we determined the variance coefficient (C.V. %), which reflects the regularity of the uterine activity. We observed a regularizing effect of the uterine activity after administration of some active substances. The smallest variance coefficient (C.V. %) was found for HEXO + PAP combination (mean value for C.V. % is 4.71%).

Animals↗
PubMed2000

Human cortical muscle coherence is directly related to specific motor parameters.

Cortical oscillations have been the target of many recent investigations, because it has been proposed that they could function to solve the "binding" problem. In the motor cortex, oscillatory activity has been reported at a variety of frequencies between approximately 4 and approximately 60 Hz. Previous research has shown that 15-30 Hz oscillatory activity in the primary motor cortex is coherent or phase locked to activity in contralateral hand and forearm muscles during isometric contractions. However, the function of this oscillatory activity remains unclear. Is it simply an epiphenomenon or is it related to specific motor parameters? In this study, we investigated task-dependent modulation in coherence between motor cortex and hand muscles during precision grip tasks. Twelve right-handed subjects used index finger and thumb to grip two levers that were under robotic control. Each lever was fitted with a sensitive force gauge. Subjects received visual feedback of lever force levels and were instructed to keep them within target boxes throughout each trial. Surface EMGs were recorded from four hand and forearm muscles, and magnetoencephalography (MEG) was recorded using a 306 channel neuromagnetometer. All subjects showed significant levels of coherence (0.086-0.599) between MEG and muscle in the 15-30 Hz range. Coherence was significantly smaller when the task was performed under an isometric condition (levers fixed) compared with a compliant condition in which subjects moved the levers against a spring-like load. Furthermore, there was a positive, significant relationship between the level of coherence and the degree of lever compliance. These results argue in favor of coherence between cortex and muscle being related to specific parameters of hand motor function.

Adult↗
PubMedDate not supplied

Hyperresponsiveness of airway muscle to acetylcholine in asthmatic and non-asthmatic subjects.

BACKGROUND: Despite a long-standing recognition, the bronchial hyperresponsiveness (BHR) of airway smooth muscle, in asthmatic and non-asthmatic subjects is still under investigation. OBJECTIVE: In order to better understand the mechanism regulating the airway function, some results obtained with cellular physiology techniques are compared, for some non-asthmatic without BHR subjects and other subjects suffering from real bronchial asthma. SUBJECTS: Eighteen subjects without chronic or acute bronchopathy and seven patients with a typical history of bronchial asthma were considered. All of them were non-smokers, with a wide range of in vivo hyperresponsiveness to Acetylcholine (ACh). Owing to neoplastic lesions, all patients underwent a thoracic surgery. MEASUREMENTS AND RESULTS: In vitro hyperresponsiveness of airway-smooth-muscle chains was assessed with isotonic contractions to incremental doses of ACh, in accordance with a non-cumulative dose-response technique. Regression between muscle contractions and ACh doses was studied for both groups, and it turned out to be linear in both cases. The slopes and elevations of the regression lines of the two groups were statically identical. There was no correlation between in vivo hyperresponsiveness (as PD20-ACh-FEV1) and in vitro responses (as EC50), for both asthmatic and non-asthmatic group. CONCLUSIONS: (i) in vitro, the same BHR of smooth-muscle resulted, for both asthmatic and non-asthmatic subjects, (ii) in vivo, a different BHR of the former group resulted. This can be explained with the peculiarity of the micro-environmental surrounding the bronchial tissue, not with an intrinsic defect of the isolated bronchial tissue.

Acetylcholine↗
PubMed2001

Effects of ACE-I on diabetic cardiovascular complications: anti-hypertensive and non-antihypertensive doses.

To evaluate the effects of angiotensin converting enzyme inhibitor (ACE-I) on diabetic cardiovascular complications, a streptozotozin (STZ, i.p., 70 mg/kg BW) induced diabetes rat model was used. The animals were separated into four major groups including: control (NSS), STZ-treated rats, STZ-treated rats received daily oral feeding of cilazapril starting one day after STZ injection (STZ-C1), and STZ-treated rats received daily oral feeding of cilazapril eight weeks after the STZ injection (STZ-C8). Within the groups of STZ-C1 and STZ-C8, the animals were also divided into three subgroups of six rats that received different doses of cilazapril treatment, 0.01 mg/Kg BW, 1 mg/Kg BW, and 10 mg/Kg BW. By using the modified isolated heart model, the parameters of mean arterial pressure (MAP), heart rate (HR), left ventricular isotonic contraction (LVIC), aortic flow rate (AFR), coronary flow rate (CFR), and ratio of heart weight per body weight (R) were assessed for each groups 8 and 20 weeks after the STZ injections. Moreover, the changes of wall thickness of the left ventricular wall (LV), right ventricular wall (RV), and interventricular septal wall (IVS) were monitored from the scanning electron micrographs of each heart. The results indicated that in both STZ-C1 and STZ-C8, the diabetic hypertension could be prevented or treated by anti-hypertensive doses of cilazaprils. Besides, the values of AFR, CFR, and LVIC were significantly increased when comparing between the STZ and STZ-C1 or STZ-C8. The results of morphological examinations indicated that: (1) left ventricular walls of the three hearts of STZ-rats had increased significantly more than controls. (2) Right ventricular walls and interventricular septal walls were not significantly different among STZ-rats, cilazapril treated STZ-rats and age matched controls. Therefore, it is concluded that ACE-I could act either as a cardioprotective or therapeutic agent for diabetic hearts. Both major anti-hypertension and anti-trophic effects of ACE-I have already been elucidated.

Administration, Oral↗
PubMed2001

Effects of general, special, and specific resistance training on throwing velocity in baseball: a brief review.

Throwing velocity is a necessary requirement for success in baseball. All position players, including pitchers, may increase their defensive performance if their throwing velocity is improved. A review of the literature suggests that throwing velocity can be increased by resistance training and/or biomechanical improvement of the throwing motion. This paper reviews the 3 broad categories of resistance-training methods by which throwing velocity is increased. The results of research using general, special, and specific throwing resistance-training exercises are presented. The role and applications of these different exercises for baseball players of different ages are discussed.

Adaptation, Physiological↗
PubMed2002

Mechanism of the contractile effects of galantide and Galanin(1-14) [alpha-aminobutyric acid]scyliorhinin-I in rat isolated fundus strips.

BACKGROUND: The study was undertaken to establish the pharmacological basis of the stimulatory activity of galantide (M15) and galanin(1-14)-(a-aminobutyric acid8-[Abu8])scyliorhinin-I [Scy-I] in gastric smooth muscle. MATERIAL/METHODS: Isotonic contractions of the isolated, longitudinal rat gastric fundus strips were recorded. RESULTS: Galanin, galanin(1-15)-NH2, M15 and galanin(1-14)-[Abu8]Scy-I elicited concentration-dependent contractions. Their EC50s equaled 12.95, 174, 70.06 and 187 nM respectively. Hill's coefficients for galanin and galanin(1-15)-NH2 were not different from unity, indicating an interaction of one peptide molecule with one receptor according to the principles of classical receptor theory. Hill's coefficients were 0.73 and 1.56 for M15 and galanin (1-14)-[Abu8]Scy-I, respectively, a value significantly different from unity. Cold-storage denervation, tetrodotoxin-TTX (1 mM), spantide (100 mM) and NK1-3 receptor antagonists SR140333, 48968, 142801 (up to 10 mM) notably diminished M15, galanin(1-14)-[Abu8]Scy-I, SP(5-11) and [Abu8]-Scy-I evoked contractions without affecting activities of galanin and galanin(1-15)-NH2. Additionally, cross-desensitization experiments attenuated activity of M15 and galanin(1-14)-[Abu8]Scy-I without any noticeable action on galanin or galanin(1-15)-NH2. CONCLUSIONS: The action of chimeric peptides on the smooth muscle of the rat gastrointestinal tract depended not only on the myogenic interaction of those peptides with galanin binding sites, but also on the activation of tachykinin receptors or the release of endogenous mediators from the presynaptic terminals.

Animals↗
PubMed1999

[Measurement of strength of thigh muscles through arthroscope after reconstruction of anterior cruciate ligament].

OBJECTIVE: To observe the strength of thigh muscles after reconstruction of anterior cruciate ligament by autogenous bone-patellar tendon-bone graft. METHODS: Twenty-three patients, 9 males and 14 females, were followed up one year after reconstruction of the anterior cruciate ligament with autogenous bone-patellar tendon-bone graft. Through arthroscope, no intra-articular derangement was found. The strengths of isometric and isotonic contractions of the quadri ceps and the hamstrings muscles of the affected and contralateral thighs were recorded. RESULTS: The donor side for autogenous bone-patellar tendon-bone graft showed significant decrease (P < 0.01), but no effect on that of the hamstrings muscle(P > 0.05). CONCLUSION: To reconstruct the anterior cruciate ligament, harvest of the bone-patellar tendon-bone graft as a reparative material may markedly lower the strength of the quadriceps femoris muscle.

Adolescent↗