Variations of 3-hydroxybutyrate dehydrogenase activity in brain and liver mitochondria of the developing chick

Utilization of ketone bodies by chick brain and spinal cord during embryonic and postnatal development

Lipid synthesis from acetoacetate and 3-hydroxybutyrate was studied in chick embryo from 15 to 21 days and in chick neonate from 1 to 21 days. Embryonic spinal cord showed higher ability than brain to incorporate acetoacetate into total lipids, although a sharp decrease was found at hatching. 3-Hydroxybutyrate incorporation into total lipids was also higher in spinal cord than in brain, especially during the embryonic period. Phospholipids were the main lipids formed in both tissues from both precursors. An appreciable percentage of radioactivity was also recovered as free cholesterol, especially during the embryonic phase. The developmental patterns of amino acid synthesis from acetoacetate and 3-hydroxybutyrate were similar in both tissues: a clear increase after hatching was followed by a decrease at day 4 of neonatal life. Acetoacetate was a better substrate for amino acid synthesis than 3-hydroxybutyrate during the embryonic development in both tissues. Oxidation of both precursors to CO2 strongly decreased between 15 and 21 days of embryonic development both in brain and spinal cord.

Changes in ketone body utilization by chick liver, duodenal mucosa and kidney during embryonic and postnatal development

1. Lipid synthesis from acetoacetate and 3-hydroxybutyrate in chick kidney and duodenal mucosa showed a clear decrease between 15 and 19 days of the embryonic phase, followed by an increase at hatching and a new decrease during the first neonatal period. The hepatic synthesis of lipids presented a different profile: a peak at 19-day-old embryo and a new increase during postnatal development. 2. These changes would be related to those in 3-hydroxybutyrate concentration in chick plasma throughout the perinatal period. 3. Phospholipids were the main kind of lipid formed in the three tissues. An appreciable percentage of radioactivity was also recovered as free cholesterol, especially during the embryonic phase. Triglycerides were also formed from acetoacetate in a high proportion in liver from neonatal animals. 4. Chick kidney showed the maximal ability to incorporate both precursors into amino acids. The peak obtained around hatching time would be related to the availability of the substrates. 5. Ketone body oxidation to CO2 was also maximal in kidney. In this tissue, a drastic decrease was observed during the final embryonic period, followed by a strong increase at day 1 after hatching and a new decrease at 4 days.

In vivo utilization of D(-)-3-hydroxybutyrate by chick brain and spinal cord

The in vivo utilization of D-3-hydroxy[3-14C]butyrate for oxidation in the whole animal and for lipid and amino acid synthesis in brain and spinal cord of overnight-fasted 15-day-old chicks has been measured. Appreciable amounts of injected 3-hydroxy[3-14C]butyrate were expired as 14CO2 one hour after injection, the total amount of which increased with increasing dosages. Lipid synthesis was high in both brain and spinal cord. Free cholesterol and phospholipids were the main lipids labeled in both tissues, increasing with time after injection up to 120 min. The incorporation of radioactivity into triglycerides, esterified cholesterol and free fatty acids was not time-dependent. Increased concentrations of 3-hydroxybutyrate gave rise to higher synthetic rates both in brain and spinal cord. The rate of amino acid synthesis was slightly higher in brain than in spinal cord. Glutamate was always the major amino acid formed.

Ketogenesis in chick embryo isolated hepatocytes

Isolated hepatocytes from 17-day chick embryos exhibit high endogenous rates of ketogenesis. The addition of long-chain fatty acids stimulated ketogenesis with potency ordered as follows: palmitate greater than oleate greater than stearate. Octanoate produced a slight stimulation of ketogenesis when added at low concentrations (less than 0.25 mM). At higher concentrations the effect of octanoate was inhibitory. The addition of glucose to incubations failed to lessen endogenous ketogenesis whereas propionate, pyruvate and lactate produced inhibition. Ketogenesis from both endogenous sources and added fatty acids was not altered by the addition of glucagon, insulin, adrenalin or vasopresin.

Activity of acetoacetyl--CoA thiolase and regulation of ketone body metabolism in the brain of the developing chick

The acetoacetyl-CoA thiolase activity was estimated in subcellular fractions isolated from the cerebral hemispheres, the optic lobes and the cerebellum of the chick between the 20th day of embryonic life and the 30th day of postnatal maturation. Acetoacetyl-CoA thiolase is located both in mitochondria and microsomes of the chick brain. Mitochondrial enzyme activity remains high between the 20th day of embryonic life and the 2nd or the 4th day after hatching, depending on the considered brain area. It then decreases until 30 days after hatching. Cytoplasmic thiolase activity remains unchanged during pre- and postnatal development in the cerebral hemispheres; it increases during the same time in the optic lobes. In the cerebellum, cytoplasmic thiolase activity develops in the same way as in mitochondria. The regulation of ketone body utilization by the developing chick brain widely differs from that by the mammalian brain. In the chick, 3-hydroxybutyrate is nearly the single ketone body utilized by the brain. It is converted into acetyl-CoA in the mitochondria and cytoplasm of the chick brain through two exactly parallel pathways involving the participation of the same enzymes.

Activities of 3-oxo acid-CoA transferase and acetoacetyl-CoA synthetase in brain and liver of the developing chick

The 3-oxo acid-CoA transferase and acetoacetyl-CoA synthetase activities were estimated in subcellular fractions isolated from the cerebral hemispheres, the optic lobes, the cerebellum and the liver of the chick between the twentieth day of embryonic life and the thirtieth day of postnatal development. In the 3 areas of chick brain, the transferase activity increases during the whole postnatal development. Transferase is located both in mitochondria and microsomes unlike in the rat brain where this enzyme is specifically mitochondrial. There is no detectable activity of synthetase in the chick brain. These differences in enzyme localization imply that acetoacetate is converted into acetoacetyl-CoA only by 3-oxo acid-CoA transferase in the mitochondria and cytoplasm of the chick brain, whereas, in the rat brain, this reaction is performed by 3-oxo acid-CoA transferase in mitochondria and by acetoacetyl-CoA synthetase in the cytosol. There is no detectable activity either for transferase or for synthetase in the chick liver.