Brain beta-hydroxybutyrate utilization in neonatal hypothyroidism in rats

The in vitro and in vivo utilization of 14C-beta-hydroxybutyrate (BOHB) by the brain in neonatal hypothyroidism was studied in rat pups made hypothyroid by feeding dams a diet containing 0.02% propylthiouracil during pregnancy and lactation. In the in vitro studies, the oxidation of BOHB to CO2 was lower at 14 and 21 days of age in hypothyroid pups than in pair-fed controls but higher at 35 days. The incorporation of BOHB into brain lipid was significantly higher in hypothyroid pups at 14, 21 and 35 days. In contrast, in the in vivo studies, incorporation of BOHB into lipid was significantly lower in hypothyroid pups at 14 and 21 days. These results suggest that hypothyroid pups may have a normal or increased capability to use BOHB for lipid synthesis, but were unable to achieve normal rates of utilization in vivo, possibly due to a decreased substrate availability. These findings may have implications for the decreased brain lipid content characteristic of neonatal hypothyroidism.