Biochemical adaptation of cardiac and skeletal muscle to physical activity

Effect of antioxidant vitamin treatment on the time course of hematological and hemorheological alterations after an exhausting exercise episode in human subjects

This study examined the effects of a 2-mo antioxidant vitamin treatment on acute hematological and hemorheological alterations induced by exhausting exercise; both sedentary and trained individuals were employed. Eighteen young male, human subjects (9 sedentary, 9 trained by regular exercise) participated in the study and performed an initial maximal aerobic cycle ergometer exercise with frequent blood sampling over a 24-h period and analysis of hematological and hemorheological parameters. All subjects were treated with an antioxidant vitamin A, C, and E regimen, supplemented orally for 2 mo, and then subjected to a second exercise test and blood sampling at the end of this period. In the sedentary group during the first testing period (before vitamin treatment), white blood cell counts and granulocyte percentages were increased at 2 h after the exercise test and remained elevated for 4-12 h. Red blood cell (RBC) deformability and aggregation were also altered by exercise in the sedentary group before vitamin treatment. However, none of these parameters in the sedentary group were altered by exercise after the 2-mo period of antioxidant vitamin treatment. With the exception of a transient rise in granulocyte percentage, these parameters were also not affected in the trained subjects before the vitamin treatment. Significant increases of RBC lipid peroxidation observed 12 h after the exercise test in both sedentary and trained subjects were also totally prevented by vitamin treatment. Our results indicate that antioxidant vitamin treatment is effective in preventing the inflammation-like response and coincident adverse hemorheological changes after an episode of exhausting exercise, and suggest that such changes may be related to exercise-induced death events.

N-3 and n-6 fatty acids stimulate restitution by independent mechanisms in the IEC-6 model of intestinal wound healing

We have shown that intestinal epithelial restitution is stimulated by n-3 and n-6 fatty acids. The current studies were undertaken to elucidate the mechanistic pathway(s) involved in this fatty acid modulation of restitution. Inhibition of phospholipase A(2) and eicosanoid synthesis and its effect on fatty acid stimulation of cellular migration in confluent, wounded IEC-6 monolayers was examined. The production of prostaglandin E(2) and transforming growth factor beta(1) were also measured in fatty acid supplemented cultures. Inhibition of phospholipase A(2) attenuated the effect of fatty acid stimulation of restitution in both n-3 and n-6 supplemented cultures. The lipoxygenase inhibitor, nordihydorguaretic acid (2 &mgr;mol/L), had no effect on stimulation of migration by fatty acids. The cyclooxygenase inhibitor piroxicam (5 &mgr;mol/L) and cyclooxygenase-2 specific inhibitors dexamethasone (2 &mgr;mol/L) and NS-398 (10 &mgr;mol/L) all attenuated the fatty acid stimulation of migration by n-6 fatty acids but had no effect on n-3 stimulated restitution. Prostaglandin E(2) production in n-6 supplemented cultures was significantly greater than in control and n-3 supplemented cultures and was partially inhibited by dexamethasone and NS-398. Latent transforming growth factor beta(1) production in n-3 supplemented cultures was significantly higher than baseline and n-6 supplemented cultures. Docosapentaenoic acid supplementation significantly enhanced the restitution process and NS-398 treatment had no effect on this stimulation of cellular migration. The liberation of fatty acid from the sn-2 position of phospholipid appears to be necessary for both n-3 and n-6 fatty acid stimulation of restitution. N-6 fatty acid modulation of restitution appears to be mediated through the production of eicosanoid products, however, prostaglandin E(2) does not appear to be the sole prostanoid involved. N-3 supplementation elevates the production of latent transforming growth factor beta(1) and may be responsible for n-3 mediated stimulation of restitution. These results further emphasize that n-3 and n-6 fatty acids convey their effects through unique pathways.

Exercise training enhances glycolytic and oxidative enzymes in canine ventricular myocardium

Aerobic exercise training evokes adaptations in the myocardial contractile machinery that enhance cardiac functional capacity; in comparison, the effects of training on the myocardium's energy generating pathways are less well characterized. This study tested the hypothesis that aerobic exercise training can increase the capacities of the major pathways of intermediary metabolism in canine myocardium. Mongrel dogs were conditioned by a 9-week treadmill running program or cage rested for 4 weeks. Exercise conditioning was evidenced by 26% and 22% decreases (P<0.05) in respective heart rates at rest and during submaximal exercise and by a 40% increase (P<0.05) in citrate synthase (CS) activity of the vastus lateralis. Glycolytic, TCA cycle, and beta-oxidative enzymes were assayed in myocardial extracts at 37 degrees C. Relative to sedentary controls, training increased glyceraldehyde 3-phosphate dehydrogenase (GAPDH) activity by 49% in left and 33% in right ventricle, and pyruvate kinase, CS, and 3-hydroxyacyl CoA dehydrogenase (HADH) activities by 74%, 91%, and 77%, respectively, in left ventricle (P<0.05). Immunoblotting further confirmed that training increased left ventricular contents of CS and GAPDH. Other measured enzymes (hexokinase, phosphofructokinase, lactate dehydrogenase, alpha-ketoglutarate dehydrogenase, malate dehydrogenase) were not altered by training in either ventricle. Kinetic analyses revealed increased maximum rates but unaltered substrate affinities of GAPDH, CS and HADH following training. Thus, aerobic exercise training augments the intermediary metabolic capacity of canine myocardium by selectively increasing the concentrations of regulatory enzymes of glycolysis and oxidative metabolism.

Both (n-3) and (n-6) fatty acids stimulate wound healing in the rat intestinal epithelial cell line, IEC-6

The control of proliferation and epithelial restitution are processes that are poorly understood. The effects of (n-3), (n-6) and trans fatty acids on proliferation of subconfluent IEC-6 cultures and restitution of wounded IEC-6 monolayers were investigated. Incorporation of supplemented fatty acids into cellular phospholipid was also assessed. Sulforhodamine B protein dye binding assay was utilized to assess the proliferative effects of fatty acids on growth of IEC-6 cultures. Incorporation of supplemental fatty acids into cellular phospholipid was examined by thin-layer chromatography combined with gas chromatography. The modulation of epithelial restitution was examined by razor blade wounding confluent IEC-6 monolayers grown in media supplemented with various fatty acids. Inhibition of eicosanoid synthesis by indomethacin during the wounding assay was also assessed. Both (n-3) and (n-6) fatty acids significantly inhibited growth of this intestinal epithelial cell model at concentrations above 125 micromol/L. The trans fatty acid, linoelaidate 18:2(n-6)trans, inhibited growth of IEC-6 cells at concentrations above 250 micromol/L. Another trans fatty acid, elaidate 18:1(n-9)trans, was well-tolerated at concentrations as high as 500 micromol/L. Eicosapentanoic 20:5(n-3), linoleic 18:2(n-6), alpha-linolenic 18:3(n-3), gamma-linolenic 18:3(n-6) and arachidonic 20:4(n-6) acids all significantly enhanced cellular migration in the IEC-6 model of wound healing. Eicosapentanoate, linoleate, alpha-linolenate, gamma-linolenate and arachidonate are all capable of improving reconstitution of epithelial integrity following mucosal injury. Inhibition of eicosanoid synthesis reduced the enhancement of restitution by n-6 fatty acids back to control levels.

Regulation of hexokinase II activity and expression in human muscle by moderate exercise

A single bout of exercise increases the rate of insulin-stimulated glucose uptake and metabolism in skeletal muscle. Exercise also increases insulin-stimulated glucose 6-phosphate in skeletal muscle, suggesting that exercise increases hexokinase activity. Within 3 h, exercise increases hexokinase II (HK II) mRNA and activity in skeletal muscle from rats. It is not known, however, if a single bout of moderate-intensity exercise increases HK II expression in humans. The present study was undertaken to answer this question. Six subjects had percutaneous biopsies of the vastus lateralis muscle before and 3 h after a single 3-h session of moderate-intensity aerobic (60% of maximal oxygen consumption) exercise. Glycogen synthase, HK I, and HK II activities as well as HK I and HK II mRNA content were determined from the muscle biopsy specimens. The fractional velocity of glycogen synthase was increased by 446 +/- 84% after exercise (P < 0.005). Hexokinase II activity in the soluble fraction of the homogenates increased from 1.2 +/- 0.4 to 4.5 +/- 1.6 pmol.min-1.microgram-1 (P < 0.05) but was unchanged in the particulate fraction (4.3 +/- 1.3 vs. 5.3 +/- 1.5). HK I activity in neither the soluble nor particulate fraction changed after exercise. Relative to a 28S rRNA control signal, HK II mRNA increased from 0.091 +/- 0.02 to 0.195 +/- 0.037 (P < 0.05), whereas HK I mRNA was unchanged (0.414 +/- 0.061 vs. 0.498 +/- 0.134, P < 0.20). The increase in HK II activity after moderate exercise in healthy subjects could be one factor responsible for the enhanced rate of insulin-stimulated glucose uptake seen after exercise.

Metabolic capacity, fibre type area and capillarization of rat plantaris muscle. Effects of age, overload and training and relationship with fatigue resistance

1. The influences of age (5, 13 and 25-month-old rats), overload as obtained by denervation of synergists, and training on the metabolic capacity, relative muscle cross-sectional area occupied by each fibre type, capillarization and fatigue resistance of the rat m. plantaris were investigated. 2. Creatine kinase, phosphorylase and citrate synthase activities were lower in muscles of 25 than in those of 13-month-old rats (P < 0.001). 3. Overload resulted in an increased relative area of type I and IIa fibres at all ages (P = 0.001). 4. Capillary density decreased with overload and increasing age (P < 0.001). 5. Fatigue resistance was higher in muscles of 13 than in those of 5-month-old rats (P < 0.05), and increased with overload (P < 0.05) at all ages. 6. Fatigue resistance of the whole muscle was not closely related to its oxidative capacity in contrast to what is generally found for single fibres or motor units.