The development of ketogenesis at birth in the rat

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Abstract
In the suckling newborn rat, blood ketone bodies begin to increase slowly 4 h after birth and then rise sharply between 12 and 16h, whereas the major increase in plasma non-esterified fatty acids and liver carnitine occurs during the 1st 2 h of life, parallel with the onset of suckling. In the starved newborn rat, which shows no increase in liver carnitine unless it is fed with a carnitine solution, the developmental pattern of the ketogenic capacity (tested by feeding a triacylglycerol emulsion, which increases plasma non-esterified fatty acids by 3-fold) is the same as in the suckling animal. This suggests that the increases in plasma non-esterified fatty acids and liver carnitine seen 2 h after birth in the suckling animal are not the predominant factors inducing the switch-on of ketogenesis. Injection of butyrate to starved newborn pups resulted in a pattern of blood ketone bodies which was similar to that found after administration of triacylglycerols, but at all time points studied, the hyperketonemia was more pronounced with butyrate. Even if the entry of long-chain fatty acids into the mitochondria is a rate-limiting step, it may not be the only factor controlling ketogenesis after birth in the rat. As in the adult rat, there is a reciprocal correlation between the liver glycogen content and the concentration of ketone bodies in the blood.