The oxidation of 3-hydroxybutyrate in developing rat jejunum

Ketone bodies and glutamine are the primary oxidative substrates in the intestine of fasting adult rats. Because suckling rats consume the majority of their calories in the form of lipid and as a result have elevated blood ketone concentrations similar to fasting adult rats, we examined the role of ketone oxidation as a source of energy in the intestine of suckling rats. In suckling rats the rate of [3-14C]DL-3-hydroxybutyrate oxidation in intestinal tissue slices, enterocytes, and intestinal mitochondria was 0.15 +/- 0.01 nmol/h/mg wet wt, 8.6 +/- 1.1 nmol/h/mg protein and 8.3 +/- 1.3 nmol/h/mg protein, respectively. In suckling rats the rate of intestinal oxidation of [3-14C]DL-3-hydroxybutyrate was 75% lower than the rate in weaned rats in intestinal tissue slices, 55% lower in enterocytes, and 50% lower in intestinal mitochondria. The activity of two enzymes involved in ketone oxidation, 3-hydroxybutyrate dehydrogenase, and acetoacetyl-CoA thiolase was 38% and 55% higher in intestinal homogenates of suckling rats compared with adult rats. In contrast, 3-oxoacid CoA-transferase activity, an enzyme also involved in 3-hydroxybutyrate oxidation, was one third that of adults. These studies indicate that intestinal oxidation of 3-HB occurs in suckling rat pups, but is lower than the rate of oxidation in the intestine of weaned rats.