The overall research objective is to determine those factors that influence the perinatal adjustment related to glucose homeostasis. The multiple causes of hypoglycemia in the neonate and the dire sequelae resulting, require that the pathogenesis of the low blood glucose be determined. This involves an investigation of the effect of those hormones (insulin, growth hormone, cortisol, catecholamines), substrates (fat, protein, ketones, glycerol) and enzymatic activities (rate- limiting reactions related to glucose uptake, production and gluconeogenesis) that have been implicated in maintaining normoglycemia. The use of the newborn piglet as a model system permits tissue analyses that may provide important leads in studying the human infant. The rapid development of resistance to starvation hypoglycemia in the pig by 4 days of age, provides a unique opportunity to determine critical factors in perinatal adaptation. The newborn rat is another model animal to be used in these studies since he develops starvation hypoglycemia during the neonatal period.