Aims: Sympathetic nervous system (SNS) is essential for the blood pressure (BP) control. SNS development is accompanied by considerable changes in the regulation of vascular smooth muscle contraction, in particular, by smaller abundance of Rho-kinase (RhoK), an important regulator of contractile machinery sensitivity to calcium. Present study was designed to compare the role of RhoK in BP control in rats with different SNS maturity. A set of experiments was carried out on neonatally sympathectomized (SX) rats to test the hypothesis that decrease of the RhoK participation is associated with the SNS maturation. Methods: Effects of RhoK inhibitor fasudil (FAS, 3 mg/kg) on the responses to a₁-adrenoceptor agonist methoxamine (MX) were studied. Experiments were performed on Wistar rats. BP was recorded in 1- week-old and 4-5-week-old anesthetized (urethane 1.2 g/kg) rats after ganglionic blockade with chlorisondamine (2.5 mg/kg). Sympathectomy was provided by subcutaneous injection of guanethidine on postnatal days 1-42; BP was recorded in non-anesthetized free-moving 7-8- week-old rats. Results: FAS reduced duration of the response to MX bolus injection (200 mg/kg) 3- fold in 4-5-week-old and almost 30-fold in newborn rats. The pressor response to MX infusion (400 mg/kg/80s) decreased by 65% in 1- week-old and by only 13% in 4-5-week-old rats. In SX rats FAS diminished response to MX infusion (200mg/kg/80s) almost twice but did not change it in controls. In addition, FAS lowered BP level more considerably in SX rats than in controls. Conclusion: RhoK plays substantial role in adrenergic vasopressor response in newborn rats. Decrease of RhoK participation in BP control is associated with SNS maturation during postnatal development. This work was supported by RFBR (grant 07-04-01527).