Summary: Preterm infants have a significantly higher incidence of brain damage as a consequence of immature cerebralblood flow (CBF) autoregulation. In contrast to term neonates preterm neonates are not able to reduce CBF in response toincreased systemic BP. In preterm neonates exposure of fragile cerebral vessels to an increased amount of blood flow atelevated systemic pressure leads to their rupture and brain damage. Our preliminary studies demonstrate that near-termfetuses and term-newborn lambs can constrict carotid arteries and reduce CBF when systemic BP rises; however thiscapability is not developed in the preterm fetus. Also we observed that following the removal of sympathetic control in thenear-term fetus by severing the superior cervical ganglion made them lose their ability to restrict carotid blood flow to thebrain with the rise in systemic BP. We also observed that the constriction of carotid arteries to reduce CBF is regulated bythe sympathetic nervous system specifically by the activity of alpha-1 adrenergic receptors (1-ARs). These receptors areexpressed at a significantly lower number in preterm carotid arteries. Thus we concluded that reduced activity of 1-ARsplays a fundamental role in regulating carotid blood flow with the rise in systemic BP. Furthermore we present evidencethat differential DNA methylation regulates 1-ARs promoter activity and expression. Thus we will test the hypothesis thatDNA methylation and demethylation regulate the expression and function of 1-AR subtypes (1A- 1B- 1D) in the carotidarteries and play a crucial role in the maturation of CAR from preterm to term fetus. We will collect data from both sexesto identify any sex-related changes. The studies will be conducted in-vivo in chronically catheterized fetal sheep and ex-vivoon isolated carotid arteries. The hypothesis will be tested with two specific aims. Aim 1: From preterm to term fetus in asex-specific manner we will conduct an in-depth mechanistic analysis of promoter DNA methylation on differentialexpression of 1-AR subtypes in carotid arteries. Aim 2: In a sex-specific manner we will determine the functionalsignificance of differential 1-AR subtypes promoter methylation and expression on carotid artery contractility and bloodflow. The measurements will be conducted in real-time in-vivo with in-utero fetal maturation. This will provide valuableinformation regarding the role of 1-AR subtypes and the epigenetic mechanisms involved in the maturation of CAR.