Exercise training reduces skeletal muscle membrane arachidonate in the obese (fa/fa) Zucker rat

Compared with the lean(Fa/) genotype, obese(fa/fa) Zucker rats have arelative deficiency of muscle phospholipid arachidonate, and skeletalmuscle arachidonate in humans is positively correlated with insulinsensitivity. To assess the hypothesis that the positive effects ofexercise training on insulin sensitivity are mediated by increasedmuscle arachidonate, we randomized 20 lean and 20 obese weanling maleZucker rats to sedentary or treadmill exercise groups. After 9 wk,fasting serum, three skeletal muscles (white gastrocnemius, soleus, andextensor digitorum longus), and heart were obtained. Fasting insulinwas halved by exercise training in the obese rat. In whitegastrocnemius and extensor digitorum longus (fast-twitch muscles), butnot in soleus (a slow-twitch muscle) or heart, phospholipidarachidonate was lower in obese than in lean rats(P < 0.001). In all muscles,exercise in the obese rats reduced arachidonate(P < 0.03, by ANOVA contrast). Weconclude that improved insulin sensitivity with exercise in the obesegenotype is not mediated by increased muscle arachidonate and thatreduced muscle arachidonate in obese Zucker rats is unique tofast-twitch muscles.