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 a relative deficiency of muscle phospholipid arachidonate, and skelet al muscle arachidonate in humans is positively correlated with insulin sensitivity. To assess the hypothesis that the positive effects of ex ercise training on insulin sensitivity are mediated by increased muscl e arachidonate, we randomized 20 lean and 20 obese weanling male Zucke r rats to sedentary or treadmill exercise groups. After 9 wk, fasting serum, three skeletal muscles (white gastrocnemius, soleus, and extens or digitorum longus), and heart were obtained. Fasting insulin was hal ved by exercise training in the obese rat. In white gastrocnemius and extensor digitorum longus (fast-twitch muscles), but not in soleus (a slow-twitch muscle) or heart, phospholipid arachidonate was lower in o bese than in lean rats (P < 0.001). In all muscles, exercise in the ob ese rats reduced arachidonate (P < 0.03, by ANOVA contrast). We conclu de that improved insulin sensitivity with exercise in the obese genoty pe is not mediated by increased muscle arachidonate and that reduced m uscle arachidonate in obese Zucker rats is unique to fast-twitch muscl es.