**Abstract**

Endothelial function plays an important role in the extrauterine adaptation of newborn infants. Endothelium produces different biologically active mediators, which play the central role in physiological and pathological processes and also in the extrauterine adaptation of newborn infants. The imbalance between vasoconstrictive and vasodilatation factors results in impaired cardiovascular adaptation and microcirculation and also brain injury. Microcirculatory disturbances are observed very often in preterm babies, who have a serious risk for perinatal brain injury and further neurodevelopment disabilities. Present chapter presents the pathogenetic role of vascular tone regulators of endothelial genesis in the formation of microcirculatory changes in preterm babies with a high risk of perinatal hypoxic encephalopathy.

**Keywords:** microcirculation, hypoxic encephalopathy, preterm infants, endothelial function, nitric oxide
