ACCELERATED POSTNATAL DEVELOPMENT OF d (‐)‐β‐ HYDROXYBUTYRATE DEHYDROGENASE (EC 1.1.1.30) ACTIVITY IN THE BRAIN IN HYPERTHYROIDISM

The activity of d(‐)‐β‐hydroxybutyrate dehydrogenase, a mitochondrial enzyme involved in ketone body metabolism, was found to be low in rat brain at birth, to rise. progressively to a peak during the first 3 weeks of postnatal life, and to decline after weaning to the low levels characteristic of the mature brain. Hyperthyroidism, induced from birth by administration of exogenous thyroxine, accelerated the postnatal development of the enzymic activity in brain and shifted the entire pattern of maturation to approximately 2 days earlier. The effects on the activity of the enzyme were the same with excessive doses of thyroxine which exaggerated the catabolic effects of the hormone and retarded brain and body growth or with lesser doses which had no apparent effects on brain and body growth or on the contents of nucleic acids and proteins in the brain. The accumulation of proteolipid protein in brain was also enhanced in hyperthyroidism. These results suggest that biochemical maturation of the brain is accelerated in hyperthyroidism.