Karen A. Orfali

Long-term regulation of pyruvate dehydrogenase kinase by high-fat feeding: Experiments in vivo and in cultured cardiomyocytes

The provision of the high‐fat diet (47% of calories as fat) for 28 days evoked a significant decline in cardiac PDHa, activity, together with marked increases in the activity of PDH kinase measured in isolated mitochondria and freshly‐prepared cardiomyocytes from adult rats. Plasma insulin concentrations in fat‐fed rats were not significantly different from control, but plasma NEFA concentrations were elevated. PDH kinase activity in cardiomyocytes from fat‐fed rats fell substantially in culture (25 h). This decline was prevented by the inclusion of n‐octanoate and DBcAMP in combination, but not individually, in the culture medium. The results are discussed in relation to the role for fatty acids and insulin in the long‐term modulation of cardiac PDH kinase activity by high‐fat feeding.

Pyruvate inhibition of pyruvate dehydrogenase kinase: Effects of progressive starvation and hyperthyroidism in vivo, and of dibutyryl cyclic AMP and fatty acids in cultured cardiac myocytes

Both prolonged starvation and hyperthyroidism evoke stable increases in cardiac pyruvate dehydrogenase kinase (PDHK) activity. Pyruvate inhibits PDHK in rat heart mitochondria with activation of PDHC. The sensitivity of PDHK to inhibition by pyruvate declines after prolonged starvation. In the present study, pyruvate concentrations giving 50% active complex (PDHa) in mitochondria from fed, control and fed, hyperthyroid rats were 0.3 and 0.8 mM, respectively, compared with 1.0 and 2.8 mM, respectively in mitochondria from 24‐h‐starved and 48‐h‐starved rats. The results demonstrate that altered pyruvate sensitivity is not of necessity linked with altered PDHK activity. PDHK activities in mitochondria prepared from cardiac myocytes from fed rats were increased after culture for 24 h with dibutyryl cyclic AMP (50 μM) plus n‐octanoate (1 mM), with a concomitant decline in sensitivity of PDHK to pyruvate inhibition, suggesting that changes in sensitivity of PDHK to pyruvate inhibition in vivo may be secondary to increased fatty acid supply and cyclic AMP concentrations.

Increased hepatic pyruvate dehydrogenase kinase activity in fed hyperthyroid rats: studies in vivo and with cultured hepatocytes

Experimental hyperthyroidism induced by the administration of tri-iodothyronine (T3; 100 micrograms/100 g body wt; 3 days) increased plasma non-esterified fatty acids in the fed state in the rat. At the same time, hepatic PDH kinase responded with a persistent (1.6-fold) increase in activity. The exposure of hepatocytes from fed euthyroid rats to T3 (100 nM) in culture for 21 h increased PDH kinase activity to an extent comparable to that observed in vivo in response to hyperthyroidism. The in vitro increase in PDH kinase activity was suppressed by insulin (100 microU/ml) and by inhibition of mitochondrial fatty acid oxidation. The results demonstrate a direct hepatic action of T3 to increase PDH kinase activity, which is mediated by intramitochondrial fatty acyl-CoA or a product of beta-oxidation, and facilitated by hepatic insulin resistance.