Dietary fish oil protects skeletal muscle from hypoxic stress during a bout of contractile fatigue in the rat in vivo hindlimb

Transcription

1 Identifying the primary site(s) of skeletal muscle fatigue Dietary fish oil protects skeletal muscle from hypoxic stress during a bout of contractile fatigue in the rat in vivo hindlimb an inability to generate the required or expected force (Edwards, 1981) Gregory E Peoples & Peter L McLennan. a reduction in the maximum generating force capacity School of Health Sciences Graduate School of Medicine (Bigland-Ritchie, et al., 1984)

2 Hypoxia and Exercise Capacity Reduced PaO2 / Oxygen Delivery Impact on work capacity / exercise tolerance Strategies (acclimation / acclimatisation)

3 Oxygen efficiency is a key determinant of force production in mammalian skeletal muscle during hypoxic stress. Exercise Muscle function Fulco et al., 1990 J. Appl. Physiol

4 Hypoxia and Membrane Fatty Acids Author / Year Study Findings Tissot et al., 2009 Human placental tissue 3,100m v sea level Oxidative preconditioning of placenta Jezkova et al., 2002 Chronic hypoxia and myocardial tissue Increased LC n-3 PUFA in the direction of cardio protection Guezennec et al., 1989 MaxEPA supplementation / RBC deformability at 3,000m Protected against loss of deformability

5 Direct effect of LC n-3 DHA Incorporation Heart and Skeletal muscle Heart Improved efficiency of oxygen consumption (Pepe and McLennan, 2002) Skeletal muscle Increased recovery (Peoples and McLennan, 2010) Time for Twitch Tension to Fall to 80% and 50% of Peak Tension Increased time to 50% fatigue (Peoples and McLennan, accepted 2013) Time (seconds) n-3 n-6 SF 0 80% 50% Percentage of peak twitch tension p<0.05 ANOVA

6 Therefore we examined the protective effects of a fish oil diet on skeletal muscle fatigue under the stress of hypoxia using the rat in vivo autologous perfused hindlimb. Whereby the provision of fish oil in the diet would; i) Attenuate muscle fatigue represented by sustained force. ii) Alter the efficiency of oxygen consumption.

7 Study Design 30 male wistar rats 3 weeks washout diet (Olive Oil) Saturated Fat Diet SF Safflower Oil Diet n-6 Fish Oil Diet n-3 8 weeks 8 weeks 8 weeks 10% by weight: SF as beef tallow; n-6 PUFA as safflower oil; n-3 PUFA as high-dha tuna fish oil (28 9% DHA and 9% EPA)

8 Muscle fatigue using the rat auto-perfused hindlimb Mean art. pressure HL arterial pressure 4 Flow direction in the rat hindlimb setup for the auto-perfused blood flow and fatigue protocol.1. artificial ventilator 2. carotid artery; 3. fluid filled polyethylene tube (cannula) of known volume 4. roller pump; 5. femoral arteries; 6. femoral veins; 7. fluid filled polyethylene tube (cannula) of known volume; 8. Abdominal vena cava. C % v 14% O2 S 7-12V, 0.05ms, 2Hz (Peoples et al., 2013 Mircocirculation)

9 Contractile Fatigue 30 minutes rest Flow: 1ml/minute 30 minutes contraction Flow: 2ml/minute 7-12V, 2Hz, 0.05ms

10 Muscle Twitch 90% 10% LATENT RT CD FT 10% 90% Stimulus 2-5 ms TIME (ms)

11 Oxygen consumption at Rest n-3 n-6 SF Weight (grams) 466±53 419±13 369±22 Min. Vent (ml/min) 140±19 140±9 117±19 Hb (g/100ml) 13.8± ± ±0.7 Normoxic Conditions Oxygen % SaO2 (%) CaO2 (umol/ml) 8.0± ± ±0.5 HL VO2 (umol/g/min) 0.3± ± ±0.06 Art. Glucose (mm) 6.6± ± ±0.8 Art. Lactate (mm) 1.7± ± ±0.17

12 Oxygen consumption at Rest n-3 n-6 SF Weight (grams) 466±53 419±13 369±22 Min. Vent (ml/min) 138±20 146±8 132±20 Hb (g/100ml) 13.8± ± ±0.7 Hypoxic Conditions Oxygen % SaO2 (%) CaO2 (umol/ml) 7.0± ± ±0.4 HL VO 2 (umol/g/min) 0.33± ± ±0.06 Art. Glucose (mm) 6.6± ± ±0.8 Art. Lactate (mm) 4.6± ± ±0.9

13 Relative Isometric Twitch Contraction During Hypoxia Isometric Twitch Force (grams/gram ww) n-3 n-6 SF Time (minutes) p<0.05 repeat measures ANOVA

14 Time (seconds) Time for Twitch tension to Fall to 80% and 50% of Peak Tension n-3 n-6 SF 0 80% 50% Percnetage of Peak Twitch Tension p<0.05 ANOVA

15 Oxygen Consumption During 30 minutes Isometric Twitch Contraction with Mild Hypoxia Oxygen Consumption (umol/g/minute) n-3 n-6 SF 0 Rest Time (minutes) p<0.05 repeat measures ANOVA

16 Blood Lactate Response to 30 Minutes Isometric Twitch Contraction During Mild Hypoxia Blood Lactate (mmol/l) n-3: Arterial n-6: Arterial SF: Arterial n-3: Venous n-6: Venous SF: Venous Rest Time (minutes) Venous ph During 30 minutes Isometric Twitch Contraction with M ild Hypoxia 7.45 n n-6 SF Time (minutes) p<0.05 repeat measures ANOVA

17 Rate of contraction and relaxation p<0.05 n-3 v n-6/sf repeat measures ANOVA Indirectly supports improved calcium handling by the skeletal muscle and attenuation of fatigue

18 Conclusion Under the challenge of hypoxia dietary fish oil and subsequent incorporation of DHA into the skeletal muscle membranes; No effect on resting oxygen consumption Improved repetitive contractile force Attenuate the rate of fatigue Delayed the fall in peak rate of contraction Thus, further supporting the role of membrane DHA in optimal skeletal muscle function.