Fatty acids inhibit intramyocellular triglyceride synthesis and turnover acutely in high fat-fed obese rats

Obesity is associated with hyperlipidemia and enlarged intramyocellular triglyceride (imcTG) stores. The latter is strongly correlated with muscle insulin resistance. However, whether hyperlipidemia plays a role in imcTG accumulation is unknown. In the present study, the effects of plasma fatty acids on imcTG fractional turnover rate (FTR) and synthesis in skeletal muscle of high fat-fed obese rats have been examined using pulse-chase technique. imcTG was prelabeled (pulse) by continuous infusion of [U-¹⁴C]glycerol and then the loss of ¹⁴C-labels from imcTG was chased while exogenous fatty acids were infused at 0 (saline), 1 (L) or 3 (H) μmol/kg/min. imcTG synthesis was determined using [2-³H]glycerol during the chase. L and H fatty acid infusions raised plasma fatty acids by 14% (p = 0.02) and 30% (p = 0.001), respectively, while plasma insulin and glycerol and the rate of glycerol appearance remained unchanged (p > 0.05). imcTG FTR was suppressed by 36-40% and 48% in gastrocnemius and tibialis anterior, respectively (both p < 0.05), and imcTG synthesis was suppressed by 50-60% in the same muscles (both p < 0.05). In contrast, neither turnover nor synthesis of imcTG in soleus was affected by fatty acid infusion (p > 0.05). imcTG content and the activities of diglyceride acyltransferase and hormone sensitive lipase were not affected by fatty acid infusion. The findings suggested that elevated plasma fatty acids suppress imcTG turnover and synthesis simultaneously and thus do not appear to promote imcTG accumulation in this obesity model at least in short term.