Preferential labeling of brain cholesterol by {3-14C}D(?)-3-hydroxybutyrate

{3-¹⁴C}D(−)-3-hydroxybutyrate or {2-¹⁴C}glucose was injected subcutaneously into 15-day old suckling rats. The animals were killed 3, 6 and 24 hr later by decapitation. Brain proteins, cholesterol, glycolipids, and phospholipids were extracted and prepared for counting. The {3-¹⁴C}D(−)-3-hydroxybutyrate injected animals showed ca. twofold greater labeling (p<.001) of brain cholesterol compared to {2-¹⁴C}glucose; whereas the {2-¹⁴C}glucose injected animals showed ca. fourfold greater labeling (p<.001) of brain proteins than {3-¹⁴C}D(−)-3-hydroxybutyrate at all time points. The difference in labeling of brain glycolipids and phospholipids was less striking, but greater labeling was apparent at each time point in the {2-¹⁴C}glucose injected animals compared to the {3-¹⁴C}D(−)-3-hydroxybutyrate injected animals. These data suggest that D(−)-3-hydroxybutyrate behaves differently than glucose, being a more direct precursor for brain cholesterol biosynthesis and a less effective precursor for brain protein synthesis. Further studies ascertaining the specific activities of the precursors are necessary to quantitatite the respective contributions of D(−)-3-hydroxybutyrate and glucose to lipid and protein synthesis in the rat brain during development.