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Increasing evidence indicates that fetal metabolic stress may result in a variety of post-natal perturbations during brain development. The goal of the study was to determine the duration of hypoxia/ischemia that would elicit a demonstrable regional depression of metabolism in the fetal brain and further to examine several end-points to determine if the metabolic stress affects the developing brain. The uterine artery and uterine branch of the ovarian artery were occluded with aneurysm clamps for a period of 45 min, the clips removed and the metabolites in five regions of the perinatal brain were measured at 0, 2 and 6 h of reflow. Regional P-creatine, ATP and glucose levels were significantly depleted at the end of the 45 min occlusion. The levels of glycogen and glutamate at the end of the occlusion indicated a decreasing trend which was not significant. The concentration of citrate remained essentially unchanged at the end of the occlusion. To ensure that the insult was not lethal to the tissue, the recovery of the metabolites was examined at 2 and 6 h of reflow and generally the concentrations of the high-energy phosphates and glucose were normal or near-normal by 6 h of reperfusion in the five regions of the brain examined. The changes in the metabolites indicate that 45 min of hypoxia/ischemia is an appropriate model for studying neonatal development after fetal metabolic stress.

The regional energy status and the availability of metabolic substrates during brain development are important, since a variety of fetal metabolic insults have been increasingly implicated in the evolution of neonatal brain disorders. The response of the brain to a metabolic insult is determined, in large part, by the ability to utilize the various substrates for intermediary metabolism in order to maintain energy stores within the tissue. To ascertain if metabolic conditions of the fetal brain make it more or less vulnerable to a stress, the high-energy phosphates and glucose-related compounds were examined in five regions of the embryonic day 18 (E-18) fetal brain. Glucose and glycogen levels in the E-18 fetal brain were generally higher in the cerebellum and its neuroepithelium than in the hippocampus, cerebral cortex, and its neuroepithelium. Regional lactate and high-energy phosphate concentrations were essentially the same in the five regions. Subsequently, the metabolic profile was examined in the cerebral cortex and striatum from E-18, postpartum day 7 (P-7) and adult rats. At the various stages of development, there were only minimal differences in the high-energy phosphate levels in the striatum and cortex. Glucose levels, the primary substrate in the adult brain, were essentially unchanged throughout development. In contrast, lactate was significantly elevated by 6- and 2-fold over those in the adult brain in the E-18 and P-7 striatum and cortex, respectively. Another alternative substrate, beta-hydroxybutyrate, was also significantly elevated at E-18 and increased more than 2-fold at P-7, but was barely detectable in the adult cortex and striatum. Finally, glucose and lactate levels were examined in cerebrospinal fluid, blood, and brain from the E-18 brain to determine if a gradient among the compartments exists. The levels of both lactate and glucose exhibited a concentration gradient in the E-18 fetus: blood > cerebrospinal fluid > brain parenchyma. The results indicate that energy state in the fetal brain is comparable to that in the neonates and the adults, but that the availability of alternative substrates for intermediary metabolism change markedly with development. The age-dependent substrate specificity for intermediary metabolism could affect the response of the fetal brain to a metabolic insult.

Experimental thermal brain injury leads to significant reduction of glucose utilization in the damaged hemisphere particularly evident in the cortex 3 days after the injury. The rate of development of these changes is not parallel with the observed damage to the blood-brain barrier, coexistent brain oedema and slight disturbances of cerebral blood flow. In a series of experiments it was possible to demonstrate significant accumulation of glucose, high-energy phosphate compounds and their metabolites in the areas of the brain near the damaged part. The authors think that this is an evidence of reduced glucose uptake by the brain resulting from reduced energy needs of the damaged brain tissue despite sufficient supply of energy-yielding substances. Since cerebral metabolism and functions are in close interrelationship reduced glucose metabolism in the damaged tissue leads to reduced activity of the cortex, which contributes to transient (or permanent) functional neurological deficits observed after cranio-cerebral trauma in humans. The knowledge and understanding of these processes regulating the development of local depression of cerebral metabolic processes may help in better results of treatment in such cases.