EFFECTS OF CHANGES IN DIETARY FATTY-ACIDS ON ISOLATED SKELETAL-MUSCLEFUNCTION IN RATS

The effects of manipulating dietary levels of essential polyunsaturate d fatty acids on the function of isolated skeletal muscles in male Wis tar rats were examined. Three isoenergetic diets were used: an essenti al fatty acid-deficient diet (EFAD), a diet high in essential (n-6) fa tty acids [High (n-6)], and a diet enriched with essential(n-3) fatty acids [High (n-3)]. After 9 wk, groups of rats on each test diet were fed a stock diet of laboratory chow for a further 6 wk. Muscle functio n was examined by using a battery of five tests for soleus (slow twitc h) and extensor digitorum longus (EDL; fast twitch). Tests included si ngle muscle twitches, sustained tetanic contractions, posttetanic pote ntiation, sustained high-frequency stimulation, and intermittent low-f requency stimulation. Results for muscles from the High (n-6) and High (n-3) groups were very similar. However, the EFAD diet resulted in si gnificantly lower muscular tensions and reduced response times compare d with the High (n-6) and High (n-3) diets. Peak twitch tension in sol eus muscles was 16-21% less in the EFAD group than in the High (n-6) a nd High (n-3) groups, respectively [analysis of variance (ANOVA), P < 0.01)]. Also, twitch contraction and half-relaxation times were signif icantly 5-7% reduced in the EFAD group (ANOVA, P < 0.01). During high- frequency stimulation, EDL muscles from the EFAD rats fatigued 32% mor e quickly (ANOVA, P < 0.01). During intermittent low-frequency stimula tion, soleus muscles from the EFAD group generated 25-28% less tension than did the other groups (ANOVA, P < 0.01), but in EDL muscles from the EFAD group, endurance was 20% greater than in the High (n-6) group (ANOVA, P < 0.05). After 6 wk on the stock diet, there were no longer any differences between the dietary groups. Manipulation of dietary f atty acids results in significant, but reversible, effects in muscles of rats fed an EFAD diet.