The development of enzymes of energy metabolism in the brain of a precocial (guinea pig) and non-precocial (rat) species

Abstract

Key enzymes of ketone body metabolism (3-hydroxybutyrate dehydrogenase, 3-oxo-acid:CoA transferase, acetoacetyl-CoA thiolase) and glucose metabolism (hexokinase, lactate dehydrogenase, pyruvate dehydrogenase, citrate synthase) have been measured in the brains of foetal, neonatal, and adult guinea pigs and compared to those in the brains of neonatal and adult rats. The activities of the guinea pig brain ketone-body-metabolising enzymes remain relatively low in activity throughout the foetal and neonatal periods, with only slight increases occurring at birth. This contrasts with the rat brain, where three- to fourfold increases in activity occur during the suckling period (0-21 days post partum), followed by a corresponding decrease in the adult. The activities of the hexokinase (mitochondrial and cytosolic), pyruvate dehydrogenase, lactate dehydrogenase, and citrate synthase of guinea pig brain show marked increases in the last 10-15 days before birth, so that at birth the guinea pig possesses activities of these enzymes similar to the adult state. This contrasts with the rat brain where these enzymes develop during the late suckling period (10-15 days after birth). The development of the enzymes of aerobic glycolytic metabolism correlate with the onset of neurological competence in the two species, the guinea pig being a "precocial" species born neurologically competent and the rat being a "non-precocial" species born neurologically immature. The results are discussed with respect to the enzymatic activities required for the energy metabolism of a fully developed, neurologically competent mammalian brain and its relative sensitivity to hypoxia.