Interrelation between long-chain fatty acid oxidation rate and carnitine palmitoyltransferase 1 activity with different isoforms in rat tissues

This study examined the interrelation between the long-chain fatty acid (LCFA) oxidation rate and the carnitine palmitoyltransferase (CPT) 1 activity in various tissues containing L-CPT1 or M-CPT1. The Liver, kidney, heart, white and red gastrocnemius muscles, and white and brown adipose tissues obtained from Sprague-Dawley rats were examined. In the tissues containing L-CPT1 the liver showed a significantly higher (P<0.01) palmitate oxidation rate and CPT1 activity than the kidney. Among the tissues containing M-CPT1, the brown adipose tissue showed the highest palmitate oxidation rate and CPT1 activity. The tissues containing M-CPT1 (r2=0.907, p<0.001) showed a strong positive correlation between the palmitate oxidation rate and the CPT1 activity. The ratios of the palmitate oxidation rate to the CPT1 activity were calculated. The ratio in the liver was highest and the ratio in the kidney was lowest among the tissues. The ratios of the tissues containing M-CPT1 were similar. These results showed that the LCFA oxidation rates in the tissues containing M-CPT1 were directly proportional to the CPT1 activity, but not similarly proportional to the CPT1 activity in the tissues containing L-CPT1. In conclusion, CPT1 activity seems very important factor for LCFA oxidation, but it might be not the only rate-limiting step in LCFA oxidation.