Different mechanisms underlie the long-term regulation of pyruvate dehydrogenase kinase (PDHK) by tri-iodothyronine in heart and liver.

Antibodies to purified recombinant PDHKII were used for ELISAs of PDHKII in mitochondrial extracts. In liver, hyperthyroidism elicited a 2.3-fold increase in PDHK activity (P < 0.01) which was accompanied by a significant 1.5-fold (P < 0.001) increase in the amount of mitochondrial immunoreactive PDHKII. In contrast, despite a stable 2.0-fold increase in cardiac PDHK activity (P < 0.001), the amount of mitochondrial immunoreactive PDHKII in heart was unaffected by hyperthyroidism. The mechanisms for long-term regulation of PDHK activity by thyroid hormones therefore differ fundamentally between heart and liver.