ORIGINAL ARTICLE Nitric oxide synthase and renin–angiotensin gene expression and NOS function in the postnatal renal resistance vasculature Brian Ratliff & Justin Rodebaugh & Miroslav Sekulic & Ke-Wen Dong & Michael Solhaug Received: 7 July 2007 / Revised: 15 July 2008 / Accepted: 16 July 2008 / Published online: 3 October 2008 # IPNA 2008 Abstract Nitric oxide (NO), produced by nitric oxide synthase (NOS), critically counteracts angiotensin-II- enhanced vascular resistance in the immature kidney, per- haps due to the developmental regulation of NOS expression and function in the postnatal preglomerular resistance vessels (PRV). Our experiments measured the messenger ribonucleic acid (mRNA) gene expression of neuronal NOS (nNOS), endothelial NOS (eNOS), and components of the renin– angiotensin system (renin, AT1 and AT2 receptors), by real- time RT-PCR, as well as NOS enzymatic activity by citrulline assay in PRVs (afferent, interlobular, and arcuate arterioles) obtained from swine ages newborn, 7 and 21 days, and adult. NOS enzymatic activity was upregulated in PRVs immediately after birth but decreased to adult levels with maturation. Neuronal NOS, renin, and AT2 receptor expres- sion in PRVs were upregulated in the newborn and decreased with age to lowest levels in the adult. In contrast, eNOS and AT1 receptor expression were downregulated at birth but increased to the highest levels in the adult. Upregulated NOS enzymatic activity in newborn PRVs supports the critical neonatal role for NO renal vascular vasodilation. Upregu- lated nNOS gene expression, concomitant with downregu- lated eNOS gene expression in neonatal PRVs, suggests that the nNOS isoform may be responsible for counteracting angiotensin II increased vascular resistance in immature porcine PRVs. Keywords Nitric oxide synthase . Renin–angiotensin system . Preglomerular resistance vessels . Developmental . Renal hemodynamics Introduction The neonate’ s unique renal hemodynamic state impacts newborn clinical management and predisposes the imma- ture kidney to development of vasomotor-mediated acute renal failure due to a variety of perinatal pathologies [1–6]. Newborn renal blood flow (RBF), initially low after birth, progressively increases during postnatal maturation to adult levels [7–17]. The predominant factor contributing to the newborn’ s low RBF is high renal vascular resistance (RVR) [8, 10]. The increase in RBF during maturation is caused by reduction of RVR [8, 9, 14, 18, 19]. The major factor that regulates neonatal RVR, at birth and during maturation, is the modulation of vasoactive factors [9, 20]. Previous studies have indicated the primary vasoactive factor that effects neonate RVR is the renin–angiotensin system (RAS) [17, 21–27]. The major components of the RAS, including renin, angiotensin II (ATII), and both ATII receptor subtypes (AT1 and AT2), are highly present in the immature kidney, but their anatomical distribution and activities are quite different than those seen in the adult kidney [21, 28–34]. In the neonate, nitric oxide (NO) vasodilation counterbalances the highly activated RAS and protects the immature kidney from the deleterious effects of adverse perinatal events that lead to vasomotor acute renal failure (ARF) [20, 35–37]. NO production is mediated by the isoforms of nitric oxide synthase (NOS), neuronal NOS (nNOS), and endothelial NOS (eNOS), all of which are constitutively expressed and are within the immature kidney [38–40]. Pediatr Nephrol (2009) 24:355–365 DOI 10.1007/s00467-008-0977-9 B. Ratliff : J. Rodebaugh : M. Sekulic : K.-W. Dong : M. Solhaug (*) Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23501-1980, USA e-mail: solhaumj@evms.edu