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J Coombes

Publications and source records attributed to J Coombes.

9 recordsLinked to original sources
PubMed2001

Short-term exercise improves myocardial tolerance to in vivo ischemia-reperfusion in the rat.

These experiments examined the independent effects of short-term exercise and heat stress on myocardial responses during in vivo ischemia-reperfusion (I/R). Female Sprague-Dawley rats (4 mo old) were randomly assigned to one of four experimental groups: 1) control, 2) 3 consecutive days of treadmill exercise [60 min/day at 60-70% maximal O2 uptake (VO2 max)], 3) 5 consecutive days of treadmill exercise (60 min/day at 60-70% VO2 max), and 4) whole body heat stress (15 min at 42 degrees C). Twenty-four hours after heat stress or exercise, animals were anesthetized and mechanically ventilated, and the chest was opened by thoracotomy. Coronary occlusion was maintained for 30-min followed by a 30-min period of reperfusion. Compared with control, both heat-stressed animals and exercised animals (3 and 5 days) maintained higher (P < 0.05) left ventricular developed pressure (LVDP), maximum rate of left ventricular pressure development (+dP/dt), and maximum rate of left ventricular pressure decline (-dP/dt) at all measurement periods during both ischemia and reperfusion. No differences existed between heat-stressed and exercise groups in LVDP, +dP/dt, and -dP/dt at any time during ischemia or reperfusion. Both heat stress and exercise resulted in an increase (P < 0.05) in the relative levels of left ventricular heat shock protein 72 (HSP72). Furthermore, exercise (3 and 5 days) increased (P < 0.05) myocardial glutathione levels and manganese superoxide dismutase activity. These data indicate that 3-5 consecutive days of exercise improves myocardial contractile performance during in vivo I/R and that this exercise-induced myocardial protection is associated with an increase in both myocardial HSP72 and cardiac antioxidant defenses.

Animals↗
PubMed1999

Endurance training reduces the rate of diaphragm fatigue in vitro.

PURPOSE: The present study examined the effects of endurance training on the contractile and biochemical properties of the rat costal diaphragm in vitro. METHODS: Sixty-four rats were divided into two groups: exercise trained (T) and control (C). Training consisted of treadmill running 5 d x wk(-1), 60 min x d(-1) at approximately 70% of VO2max, over a 10-wk period. RESULTS: Control diaphragm strips produced an average of 12% less force from minute 15 to 50 of a 60-min in vitro fatigue protocol, compared with the T diaphragm strips (P < 0.01). T diaphragms had 10.1% higher citrate synthase (CS) and 12.1% higher superoxide dismutase (SOD) activities compared with the C (P < 0.05). Despite a significant decrease (P < 0.05) in Type IIb myosin heavy chains (MHC) and an increase (P < 0.05) in Type I MHC in T diaphragms, maximal shortening velocity (Vmax) in the diaphragm was not different between T and C animals. No differences were observed in specific force or the relative proportions of myosin light chains between groups. CONCLUSIONS: These findings suggest that endurance training reduces the rate of diaphragm fatigue in vitro but has no effect on Vmax or specific force.

Animals↗
PubMed1997

Bioenergetic characteristics of the costal and crural diaphragm in mammals.

These experiments compared oxidative and glycolytic enzyme activity in the costal and crural diaphragm in seven adult mammals (mouse, rat, rabbit, ferret, sheep, pig, cow) ranging in body mass from approximately 0.03 to 422 kg. Segments of the costal and crural diaphragm from the aforementioned species were homogenized to determine the activities of the glycolytic enzyme, lactate dehydrogenase (LDH), and the Krebs cycle enzyme, citrate synthase (CS). The results indicated that metabolic differences between the costal and crural diaphragm do not exist in all mammalian species. Specifically, CS activity differed (P < 0.05) between the costal and crural diaphragm (costal approximately 36% greater than crural) in only two species (rat and rabbit). Further, the oxidative capacity of the costal and crural diaphragm was significantly correlated with both breathing frequency and resting metabolic rate (r = 0.92 - 0.57; P < 0.05) across the species investigated. In contrast, glycolytic capacity was not significantly correlated (P > 0.05) with either breathing frequency or resting metabolic rate.

Animals↗
PubMed1997

Exercise training-induced changes in respiratory muscles.

Interest in the adaptive strategies of respiratory muscles in response to exercise training has grown in recent years. Animal studies have clearly demonstrated that regular endurance exercise training results in small but significant increases in oxidative and antioxidant enzyme activities in both inspiratory and expiratory muscles. Further, exercise training has been shown to promote a shift in the fast myosin heavy chain isoforms (e.g. from type IIb to IId) within the costal diaphragm of endurance-trained rodents. Human studies using numerous respiratory muscle training programmes have shown that respiratory muscle training results in an increased work capacity of the ventilatory musculature. However, the issue of whatever respiratory muscle training improves whole body endurance capacity remains controversial. Although some authors have reported that ventilatory muscle training results in improved whole body exercise, many investigators argue that respiratory muscle performance does not limit high intensity exercise tolerance or influence maximum oxygen table uptake (VO2max). The explanation for the divergent findings is unclear but may be due to variance in the exercise tasks used to evaluate exercise endurance. This is an interesting area for future research.

Adaptation, Physiological↗
PubMed1996

Effects of aging and obesity on respiratory muscle phenotype in Zucker rats.

Because obesity results in an increased work of breathing, we tested the hypothesis that the oxidative properties and myosin heavy chain (MHC) isoform profiles in respiratory muscles would differ between lean and obese animals. Furthermore, we postulated that obesity-related changes in respiratory muscles would be independent of age. To test these hypothesis, samples of the costal diaphragm, crural diaphragm, and parasternal intercostal muscles were removed from three age groups (young, adult, and old) of obese and lean Zucker rats. Citrate synthase (CS) activity was measured as a marker of oxidative capacity, and MHC isoforms were identified with gel electrophoresis. Analysis revealed that CS activity was significantly higher in the crural and costal diaphragms and parasternal intercostal of obese animals compared with lean animals (P < 0.05); this obesity-related increased in CS activity was related independent of age. Furthermore, respiratory muscle percent type IIb MHC was lower and percent type I MHC isoforms were higher in obese animals compared with lean animals. These data support the notion that obesity results in a fast-to-slow shift in MHC phenotype and an increase in oxidative capacity in major inspiratory muscles. The shift in MHC isoforms in obese animals is also age related, whereas the obesity-mediated increase in oxidative capacity is relatively independent of age.

Aging↗
PubMed1996

A comparison of maximal bioenergetic enzyme activities obtained with commonly used homogenization techniques.

Homogenization of tissue for analysis of bioenergetic enzyme activities is a common practice in studies examining metabolic properties of skeletal muscle adaptation to disease, aging, inactivity or exercise. While numerous homogenization techniques are in use today, limited information exists concerning the efficacy of specific homogenization protocols. Therefore, the purpose of this study was to compare the efficacy of four commonly used approaches to homogenizing skeletal muscle for analysis of bioenergetic enzyme activity. The maximal enzyme activity (Vmax) of citrate synthase (CS) and lactate dehydrogenase (LDH) were measured from homogenous muscle samples (N = 48 per homogenization technique) and used as indicators to determine which protocol had the highest efficacy. The homogenization techniques were: (1) glass-on-glass pestle; (2) a combination of a mechanical blender and a teflon pestle (Potter-Elvehjem); (3) a combination of the mechanical blender and a biological detergent; and (4) the combined use of a mechanical blender and a sonicator. The glass-on-glass pestle homogenization protocol produced significantly higher (P < 0.05) enzyme activities compared to all other protocols for both enzymes. Of the four protocols examined, the data demonstrate that the glass-on-glass pestle homogenization protocol is the technique of choice for studying bioenergetic enzyme activity in skeletal muscle.

Adaptation, Physiological↗