IMPAIRED FFA OXIDATION AND INCREASED TRIACYLGLYCEROL SYNTHESIS IN CONTRACTING SOLEUS MUSCLE IN OBESE ZUCKER RATS.

Abstract

1369 We examined the effect of obesity on the synthesis and degradation of muscle lipid pools (TG, triacylglycerol; DG, diacylglycerol; MG, monoacylglycerol; PL, phospholipid) and exogenous palmitate oxidation, in resting and contracting soleus muscles. Isolated soleus strips from 10 lean (162 ± 2 g) and 10 obese (250 ± 7 g) Zucker rats were incubated in Kreb's-Henseleit buffer (4% BSA, 2 mM pyruvate, 1.0 mM palmitic acid), using the previously defined pulse-chase procedure. Lipid metabolism was monitored either at rest (60 min) or during electrically induced contraction (20 tetani per min, 30 min). Plasma FFA, TG and insulin concentrations were significantly elevated in the obese rats. At rest, incorporation of palmitate into PL was significantly lower in the obese condition (0.6 vs. 1.0 nmol/min/g). Palmitate esterification into TG tended to be greater in the obese condition (4.7 vs. 4.2 nmol/g/min), but this difference was not significant (p=0.26). Degradation of the lipid pools at rest was unaffected by obesity. During contraction, palmitate oxidation and incorporation into all lipid pools was significantly increased. However, during contraction in the obese state, there was a repartitioning of palmitate towards storage in TG (5.9 vs. 4.8 nmol/g/min), and away from oxidation (5.5 vs. 9.4 nmol/g/min). Triacylglycerol degradation was significantly increased with contraction in muscle from both lean and obese rats, but this increase was blunted by 38% in the obese condition. In summary, in contracting oxidative muscle, obesity decreases palmitate oxidation, and increases TG storage by increasing esterification and decreasing hydrolysis. Supported by the NSERC of Canada.