Metabolic Coupling and the Role Played By Astrocytes in Energy Distribution and Homeostasis

Abstract

The lactate accumulated during late gestation is actively oxidized within the first hours of extrauterine life (Medina et al., 1980; Persson and Tunell, 1971), indicating that neonatal tissues actively utilize blood lactate. It is noteworthy that gluconeogenesis is not yet induced in these circumstances (Fernandez et al., 1983; Medina et al., 1980), in agreement with the idea that lactate is utilized directly as a source of energy and carbon skeletons by some neonatal tissues (see: Medina et al., 1992). Since lactate removal takes place at a very high rate, it is likely that several tissues would be involved in lactate utilization. Thus, it has been reported that neonatal lung (Patterson et al., 1986), heart (Fernandez, E. and Medina, J. M., unpublished results), and liver (Almeida et al., 1992) utilize lactate for energy production and/or lipogenic purposes. However, special attention has been paid to lactate utilization by the brain, probably because this organ must continue its development even under the starvation that occurs during the presuckling period. Lactate utilization by the brain has been reported in fetal (Bolanos and Medina, 1993), early newborn (Arizmendi and Medina, 1983; Fernández and Medina, 1986; Vicario et al., 1991; Vicario and Medina, 1992) and suckling rats (Dombrowski et al., 1989; Itoh and Quastel, 1970), in newborn dogs (Hellmann et al., 1982) and in glucose-6-phosphatase-deficient human babies (Fernandes et al., 1984).