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Biomedical subjects

Ryuichi Ajisaka

Publications and source records attributed to Ryuichi Ajisaka.

14 recordsLinked to original sources
PubMed2006

Vascular endothelium-derived factors and arterial stiffness in strength- and endurance-trained men.

Arterial stiffness is higher in strength-trained humans and lower in endurance-trained humans. However, the mechanisms underlying these different adaptations are unclear. Vascular endothelium-derived factors, such as endothelin-1 (ET-1) and nitric oxide (NO), play an important role in the regulation of vascular tonus. We hypothesized that endogenous ET-1 and NO participate in the adaptation of arterial stiffness in different types of exercise training. The purpose of this study was to investigate plasma ET-1 and NO concentrations and arterial stiffness in strength- and endurance-trained men. Young strength-trained athletes (SA; n = 11), endurance-trained athletes (EA; n = 12), and sedentary control men (C; n = 12) participated in this study. Maximal handgrip strength in SA and maximal oxygen uptake in EA were markedly greater than in C. Aortic pulse-wave velocity, which is an established index of arterial stiffness, was higher in SA and lower in EA than in C. Additionally, we measured systemic arterial compliance (SAC) using carotid artery applanation tonometry and Doppler echocardiography, because arterial stiffness is a primary determinant of the compliance. SAC was lower in SA and higher in EA compared with that in C. Plasma ET-1 concentrations were higher in SA compared with C and EA. We did not find significant differences in plasma NO concentrations (measured as the stable end product of NO, i.e., nitrite/nitrate). The relationships of plasma ET-1 concentrations to aortic pulse-wave velocity and SAC were linear. These results suggest that differences in endogenous ET-1 may partly participate in the mechanism underlying different adaptations of arterial stiffness in strength- and endurance-trained men.

Adaptation, Physiological↗
PubMed2006

Polymorphism in endothelin-related genes limits exercise-induced decreases in arterial stiffness in older subjects.

Increase in arterial stiffness is associated with aging, which is improved by regular exercise. Endothelin (ET) system has crucial roles in regulating vascular tone and in the progression of atherosclerosis. We hypothesized that molecular variations (ie, gene polymorphisms) in ET-related gene might affect exercise-induced improvement in arterial stiffness with age in human subjects. The present study provides a cross-sectional investigation of 191 healthy middle-aged and older (65+/-1 years) human subjects to clarify the relationship between the regular exercise-induced improvement of arterial stiffness and the gene polymorphisms of ET converting enzyme (ECE)-1, ECE-2, ET-A receptor (ET-A), and ET-B receptor (ET-B). The study subjects were divided into active and inactive groups based on the median value (186 kcal/d) of energy expenditure. Brachial-ankle arterial pulse wave velocity (baPWV) was used to evaluate arterial stiffness. All individuals were genotyped for 4 different polymorphisms of the ET system: 2013(+289)A/G in intron 17 of ECE-1, 669(+17)T/C in intron 5 of ECE-2, 958A/G in exon 6 of ET-A, and 831A/G in exon 4 of ET-B. The baseline baPWV was significantly lower in the active group without any change in blood pressure. Polymorphisms in ECE-1 influenced basal blood pressure. Polymorphisms in ECE-1 and ECE-2 had no effect on baPWV between active and inactive groups. However, polymorphisms in both ET-A and ET-B affected baPWV in the 2 groups. The present results suggest that differences in ET-A and ET-B polymorphisms may influence the response of the vascular wall to exercise whereas ECE-1 polymorphisms may affect basal blood pressure.

Aged↗
PubMed2006

Age-related reduction of systemic arterial compliance induces excessive myocardial oxygen consumption during sub-maximal exercise.

Reduction of systemic arterial compliance (SAC) with aging increases left ventricular afterload. The present study was designed to examine whether age-related reduction of SAC is related to excessive myocardial oxygen consumption during sub-maximal aerobic exercise. We studied elderly (60-69 years; n = 25) and senior (70-82 years; n = 25) subjects. We measured SAC immediately before the start of the ramp-fashion exercise (i.e., at the end of the 20 W warm-up exercise) and the double product (DP: systolic blood pressure x heart rate) during the ramp-fashion exercise (20-50 W). SAC was significantly lower in senior subjects (0.76 +/- 0.25 ml mmHg(-1) m(-2)) compared with elderly subjects (0.95 +/- 0.22 ml mmHg(-1) m(-2)). DP was higher in senior subjects (20 W: 14.3 +/- 3.1; 30 W: 15.9 +/- 4.2; 40 W: 17.7 +/- 4.9; 50 W: 20.6 +/- 5.6 [x 10(3) mmHg bpm]) than in elderly subjects (12.8 +/- 3.0, 14.0 +/- 3.5, 15.1 +/- 4.0, 17.1 +/- 4.3 [x 10(3) mmHg bpm]). In total subjects, SAC correlated significantly with DP (r = -0.64, r = -0.64, r = -0.64, r = -0.64). In senior subjects, SAC was related significantly to DP (r = -0.83, r = -0.78, r = -0.76, r = -0.74). In elderly subjects, SAC tended to correlate with DP although its relationships were not statistically significant (r = -0.34, r = -0.36, r = -0.33, r = -0.31). Correlation coefficients at each respective exercise intensity were significantly higher in senior subjects compared with elderly subjects. These results suggest that the age-related reduction of SAC is related to excessive myocardial oxygen consumption during sub-maximal aerobic exercise in older humans, but this relation does not become significant until the SAC reduction becomes pronounced.

Age Factors↗
PubMed2006

The effect of exercise training on adiponectin receptor expression in KKAy obese/diabetic mice.

Adiponectin is an adipocyte-derived factor that plays a pivotal role in lipid and glucose metabolism. Recently, two types of adiponectin receptors (AdipoR1 and AdipoR2) were identified. We investigated whether exercise training (ET) or dietary restriction (DR) affects the expression of adiponectin receptors in skeletal muscle and liver, thereby improving glucose and lipid metabolism in KKAy mice. KKAy mice were subjected to 8 weeks of exercise training or food restriction. Following the experimental protocol, an intravenous glucose tolerance test and an intraperitoneal insulin tolerance test were performed in addition to the measurement of blood lipid and adiponectin concentrations. The mRNA levels of adiponectin, adiponectin receptors and genes that are putatively regulated by the adiponectin receptors were also analyzed. Both the 8-week exercise training and food restriction protocol improved insulin resistance in KKAy mice but did not alter plasma adiponectin concentration nor its mRNA expression. In comparison with C57BL/6 mice, AdipoR1 expression level was significantly decreased in skeletal muscle and AdipoR2 expression level was significantly increased in the liver in KKAy mice. After the 8-week experimental protocol, the expression level of AdipoR1 mRNA was approximately 1.8-fold greater in the skeletal muscle and 1.3-fold greater in the liver, and the level of AdipoR2 mRNA was 30% less in the liver of the ET group as compared with the control group. Additionally, in the ET group, mRNA expression of acyl coenzyme A-oxidase and carnitine palmitoyl transferase 1 (CPT1) was greater in the liver but not in skeletal muscle. In contrast, no significant changes were observed in the expression of genes encoding the adiponectin receptors in addition to other genes except for CPT1 in the DR group. These findings suggest that chronic exercise training affects the expression level of adiponectin receptors thereby improving insulin resistance in KKAy mice.

Adiponectin↗
PubMed2006

Effects of athletic strength and endurance exercise training in young humans on plasma endothelin-1 concentration and arterial distensibility.

Strength exercise training induces a decrease in arterial distensibility, whereas endurance exercise training causes an increase in arterial distensibility. Endothelin-1 (ET-1), which is produced by vascular endothelial cells, has potent vasoconstrictor and proliferative activity on vascular smooth muscle cells. We hypothesized that endogenous ET-1 participates in alteration of arterial distensibility by different exercise training types (i.e., strength and endurance exercise training). The purpose of the present study was to investigate plasma ET-1 concentration and arterial distensibility in strength- and endurance-trained athletes. Subjects were male strength-trained athletes (discus, hammer, or javelin throwers; 22.2 years; SA), male endurance-trained athletes (long- or middle-distance runners; 20.7 years; EA), and sedentary healthy men (20.6 years; sedentary control, SC). Maximum hand-grip strength was markedly greater in SA compared with EA and SC (55.3 vs. 41.1 vs. 40.5 kg, P < 0.05). Maximum oxygen uptake was markedly greater in EA than in SA and SC (60.9 vs. 43.1 vs. 43.6 ml/kg/min, P < 0.05). Arterial pulse wave velocity (PWV), which is an index of arterial distensibility, was significantly higher in SA than in EA and SC (688 vs. 529 vs. 601 cm/sec, P < 0.05). In EA, PWV was significantly lower in comparison to that in SC (P < 0.05). Thus arterial distensibility was lower in SA than in EA and SC and higher in EA than in SC. Plasma ET-1 concentration was significantly higher in SA compared with EA and SC (1.64 vs. 1.12 vs. 1.24 pg/ml, P < 0.05). Plasma ET-1 concentration tended to be lower in EA than in SC. These results suggest that the difference in plasma ET-1 level may participate in the mechanism underlying different adaptation of arterial distensibility between strength- and endurance-trained athletes.

Adult↗
PubMed2005

Assessing muscle vasodilation using near-infrared spectroscopy in cardiac patients.

BACKGROUND: In patients with chronic heart failure, an inadequate increase in muscle blood flow resulting from impaired vasodilation plays a key role in their exercise intolerance. However, no non-invasive methods to assess muscle vasodilation during dynamic exercise were available. We investigated whether the changes in tissue hemoglobin and myoglobin content (total-Hb + Mb) determined by non-invasive measurement using near-infrared spectroscopy (NIRS) reflect vessel conductance of working muscle during exercise. METHODS AND RESULTS: Sixteen patients (10 patients with normal cardiac systolic function, 6 with cardiac dysfunction) performed incremental bicycle exercise testing. Total-Hb + Mb from the right vastus lateralis muscle was monitored using NIRS. Leg blood flow (LBF) in the right femoral vein was measured using a thermodilution technique every 30-60 s. Leg vessel conductance was calculated as LBF/mean arterial pressure at each time of the measurement. In all cases except 1, the levels of total-Hb + Mb showed significant correlation with the leg vessel conductance (r=0.792 to 0.980). Intra-subject reproducibility of the NIRS measurement was also confirmed in 6 patients. CONCLUSIONS: Total-Hb + Mb from NIRS reflected muscle vasodilation during sub-maximal dynamic exercise in patients with and without cardiac dysfunction, indicating that NIRS provides a valuable method to assess the working muscle vasodilation.

Adult↗
PubMed2005

Effect of arterial lumen enlargement on carotid arterial compliance in normotensive postmenopausal women.

A reduction in central arterial compliance has been identified as an independent risk factor for future cardiovascular disease. The aim of the present study was to determine the influence of age-related carotid arterial enlargement on carotid arterial compliance in postmenopausal females, using a cross-sectional study design. Carotid arterial properties were measured with applanation tonometry and ultrasound system in 113 normotensive females (aged 50-78). Brachial-ankle pulse wave velocity (baPWV) measured by a plethysmographic technique was used as an index of arterial stiffness. In comparisons among the three age groups (50-59, 60-69, and 70-78 years old), baPWV (F=11.9, p<0.001) and carotid systolic (F=4.5, p<0.05) and pulse pressures (F=9.6, p<0.0001), and lumen diameter (F=5.6, p<0.01) increased with advancing age. Carotid arterial compliance gradually decreased with age, but not significantly. A stepwise regression analysis revealed that carotid systolic pressure and lumen diameter and age were independent correlates of carotid arterial compliance. After carotid lumen diameter was taken into account (ANCOVA), the differences in carotid arterial compliance among the three age groups became significant (F=3.8, p<0.05). These results suggest that an increase in arterial lumen diameter might compensate for the age-related increase in arterial stiffness and limit the deterioration of the buffering capacity of the central artery in normotensive postmenopausal females.

Adaptation, Physiological↗
PubMed2004

Effects of nitric oxide synthase inhibitor on decrease in peripheral arterial stiffness with acute low-intensity aerobic exercise.

We previously reported that even low-intensity, short-duration acute aerobic exercise decreases arterial stiffness. We aimed to test the hypothesis that the exercise-induced decrease in arterial stiffness is caused by the increased production of NO in vascular endothelium with exercise. Nine healthy men (age: approximately 22-28 yr) performed a 5-min single-leg cycling exercise (30 W) in the supine position under an intravenous infusion of NG-monomethyl-L-arginine (L-NMMA; 3 mg/kg during the initial 5 min and subsequent continuous infusion of 50 mug.kg(-1).min(-1) in saline) or vehicle (saline) in random order on separate days. The pulse wave velocity (PWV) from the femoral to posterior tibial artery was measured on both legs before and after the infusion at rest and 2 min after exercise. Under the control condition, exercised leg PWV significantly decreased after exercise (P <0.05), whereas nonexercised leg PWV did not show a significant change throughout the experiment. Under L-NMMA administration, exercised leg PWV was increased significantly by the infusion (P <0.05) but decreased significantly after the exercise (P <0.05). Nonexercised leg PWV increased with L-NMMA administration and maintained a significantly higher level during the administration compared with baseline (before the infusion, all P <0.05). The NO synthase blockade x time interaction on exercised leg PWV was not significant (P=0.706). These results suggest that increased production of NO is not a major factor in the decrease of regional arterial stiffness with low-intensity, short-duration aerobic exercise.

Adult↗
PubMed2004

Moderate regular exercise increases basal production of nitric oxide in elderly women.

Vascular endothelial cells produce nitric oxide (NO), which is a potent vasodilator substance and is thought to have antiatherosclerotic properties. Therefore, it has also been proposed that NO may be useful to regulate vascular tonus and prevent progression of atherosclerosis. On the other hand, NO activity reduces with aging. We previously reported that the plasma nitrite/nitrate (NOx: the stable end product of NO) concentration was significantly increased by intense aerobic exercise training in healthy young humans. We hypothesized that lifestyle modification (e.g., even mild regular exercise training) can increase NO production in previously sedentary older humans. We measured the plasma NOx concentration before and after a mild aerobic exercise training regimen (cycling on a leg ergometer at 80% ventilatory threshold for 30 min, 5 days/week) for 3 months in elderly women. In addition, we assessed the plasma concentration of cyclic guanosine monophosphate (cGMP), a second messenger of NO, in the same samples. The individual ventilatory threshold increased significantly after the 3-month exercise training. The blood pressure at rest significantly decreased after exercise training. These results suggest that the 3-month exercise training in the older women produced favorable physiological effects. The plasma concentration of NOx significantly increased by the exercise training, and the plasma concentration of cGMP also increased by the exercise training. The present study suggests that even a mild regular aerobic-endurance exercise increases NO production in previously sedentary older humans, which may have beneficial effects (i.e., antihypertensive and antiatherosclerotic effects by endogenous NO) on the cardiovascular system.

Aged↗
PubMed2003

Aerobic exercise training reduces plasma endothelin-1 concentration in older women.

Endothelial function deteriorates with aging. On the other hand, exercise training improves the function of vascular endothelial cells. Endothelin-1 (ET-1), which is produced by vascular endothelial cells, has potent constrictor and proliferative activity in vascular smooth muscle cells and, therefore, has been implicated in regulation of vascular tonus and progression of atherosclerosis. We previously reported significantly higher plasma ET-1 concentration in middle-aged than in young humans, and recently we showed that plasma ET-1 concentration was significantly decreased by aerobic exercise training in healthy young humans. We hypothesized that plasma ET-1 concentration increases with age, even in healthy adults, and that lifestyle modification (i.e., exercise) can reduce plasma ET-1 concentration in previously sedentary older adults. We measured plasma ET-1 concentration in healthy young women (21-28 yr old), healthy middle-aged women (31-47 yr old), and healthy older women (61-69 yr old). The plasma level of ET-1 significantly increased with aging (1.02 +/- 0.08, 1.33 +/- 0.11, and 2.90 +/- 0.20 pg/ml in young, middle-aged, and older women, respectively). Thus plasma ET-1 concentration was markedly higher in healthy older women than in healthy young or middle-aged women (by approximately 3- and 2-fold, respectively). In healthy older women, we also measured plasma ET-1 concentration after 3 mo of aerobic exercise (cycling on a leg ergometer at 80% of ventilatory threshold for 30 min, 5 days/wk). Regular exercise significantly decreased plasma ET-1 concentration in the healthy older women (2.22 +/- 0.16 pg/ml, P < 0.01) and also significantly reduced their blood pressure. The present study suggests that regular aerobic-endurance exercise reduces plasma ET-1 concentration in older humans, and this reduction in plasma ET-1 concentration may have beneficial effects on the cardiovascular system (i.e., prevention of progression of hypertension and/or atherosclerosis by endogenous ET-1).

Adult↗
PubMed2003

The effects of low-intensity single-leg exercise on regional arterial stiffness.

We examined the effect of low-intensity single-leg exercise (20 or 30 watt, 5 min) on pulse wave velocity from the femoral to the ankle arteries in 18 young men. After the exercise, the velocity significantly decreased in the exercised leg, but not in the counterpart, suggesting that the decrease in arterial stiffness in the exercised leg was induced mainly by exercise-related regional factors.

Adult↗
PubMed2002

Polymorphisms in control region of mtDNA relates to individual differences in endurance capacity or trainability.

The purpose of this study was to investigate whether the polymorphisms in the control region of mitochondrial DNA (mtDNA) related to individual difference in the endurance capacity or trainability. Fifty-five sedentary males participated in this study and were submitted to an 8-week endurance training program. The VO(2 max) was determined before and after training. Total DNA was extracted from the blood, and the sequence of the mtDNA control region was determined. The polymorphism in the mtDNA control region was decided based on the "Cambridge sequence." In 29 of the 55 subjects, vastus lateralis muscle biopsy samples were taken at rest before and after the training program. MtDNA content and CS (citrate synthase) activity in skeletal muscle was measured as the phenotype of the polymorphisms in the mtDNA control region. The VO(2 max) increased to 48.2 +/- 6.3 ml/min/kg from 42.1 +/- 6.0 as a result of the 8-week training (p < 0.05). The numbers of polymorphisms in determined 1,122 bp were 11.1 +/- 2.9 variable sites per person, and the total numbers of polymorphisms were 125 variable sites. The subjects were classified into two groups at each variable site, the Cambridge sequence (Cam) group and the non-Cambridge sequence (non-Cam) group. There were significant differences in pre-VO(2 max) between the two groups at each mtDNA nucleotide positions 16298, 16325, and 199, and in % Delta VO(2 max) at 16223 and 16362. Twenty-nine subjects who underwent the biopsy revealed significant differences in pre-CS activity at 194 and pre-mtDNA content at 514. Also, significant differences were found in the change rate of VO(2 max )and CS activity as a result of training between the two groups at 16519. In conclusion, it suggested that mtDNA polymorphisms in the control region might result in individual differences in endurance capacity or trainability.

Adult↗
PubMed2002

[Changes in blood volume in the muscles of the thigh and calf during exercise and recovery and their relationships to exercise tolerance in patients with cardiac disease].

OBJECTIVES: This study compared the blood-volume changes and recovery in the thigh and calf during leg exercise and evaluated the relationships to exercise tolerance. METHODS: The peak oxygen uptake and total hemoglobin level(blood-volume index), oxyhemoglobin level, and deoxyhemoglobin level in the thigh and calf were measured by near-infrared spectroscopy during leg ergometer exercise and recovery in 13 patients with cardiac disease(mean age: 66 +/- 6 years, left ventricular ejection fraction: 31-82%). RESULTS: There was no significant difference between the increase in blood-volume index during exercise in the thigh and that in the calf. The increase in the blood-volume index during recovery in the calf was significantly greater than that in the thigh, mainly due to the difference in deoxyhemoglobin levels. There were no positive relationships between the peak oxygen uptake and increases in blood-volume index except for the increase in blood-volume index in the thigh during exercise(r = 0.73). CONCLUSIONS: There was no significant difference between the increase in blood-volume index in the thigh and that in the calf during exercise, whereas the increase in blood-volume index during recovery in the calf was significantly greater than that in the thigh in patients with cardiac disease. Only the increase in the blood-volume index in the thigh during exercise is related to the leg-exercise tolerance in patients with cardiac disease.

Aged↗