Studies of the long-term regulation of hepatic pyruvate dehydrogenase kinase.

The administration of a low-carbohydrate/high-saturated-fat (LC/HF) diet for 28 days or starvation for 48 h both increased pyruvate dehydrogenase kinase (PDHK) activity in extracts of rat hepatic mitochondria, by approx. 2.1-fold and 3.5-fold respectively. ELISAs of extracts of hepatic mitochondria, conducted over a range of pyruvate dehydrogenase (PDH) activities, revealed that mitochondrial immunoreactive PDHKII (the major PDHK isoform in rat liver) was significantly increased by approx. 1.4-fold after 28 days of LC/HF feeding and by approx. 2-fold after 48 h of starvation. The effect of LC/HF feeding to increase hepatic PDHK activity was retained through hepatocyte preparation, but was decreased on 21 h culture with insulin (100 micro-i.u./ml). A sustained (24 h) 2-4-fold elevation in plasma insulin concentration in vivo (achieved by insulin infusion via an osmotic pump) suppressed the effect of LC/HF feeding so that hepatic PDHK activities did not differ significantly from those of (insulin-infused) control rats. The increase in hepatic PDHK activity evoked by 28 days of LC/HF feeding was prevented and reversed (within 24 h) by the replacement of 7% of the dietary lipid with long-chain omega-3 fatty acids. Analysis of hepatic membrane lipid revealed a 1.9-fold increase in the ratio of total polyunsaturated omega-3 fatty acids to total mono-unsaturated fatty acids. The results indicate that the increased hepatic PDHK activities observed in livers of LC/HF-fed or 48 h-starved rats are associated with long-term actions to increase hepatic PDHKII concentrations. The long-term regulation of hepatic PDHK by LC/HF feeding might be achieved through an impaired action of insulin to suppress PDHK activity. In addition, the fatty acid composition of the diet, rather than the fat content, is a key influence.