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Whole Body Arginine Metabolism and Nitric Oxide Synthesis in Newborns with Persistent Pulmonary Hypertension

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Whole Body Arginine Metabolism and Nitric Oxide Synthesis in Newborns with Persistent Pulmonary Hypertension 0031-3998/95/3801-0017$03.00/0 PEDIATRIC RESEARCH Vol. 38, No. 1, 1995 Copyright O 1995 International Pediatric Research Foundation, Inc. Printed in U.S.A. Whole Body Arginine Metabolism and Nitric Oxide Synthesis in Newborns with Persistent Pulmonary Hypertension L. CASTILLO, T. DEROJAS-WALKER, Y. M. YU, M. SANCHEZ, T. E. CHAPMAN, D. SHANNON, S. TANNENBAUM, J. F. BURKE, AND V. R. YOUNG Laboratory of Human Nutrition, Clinical Research Center [L.C., Y.M. Y., M.S., T.E. C., V.R.Y.], and Division of Toxicology [T.D.R.-W., S.T.], Massachusetts Institute of Technology, Boston, Massachusetts 02139; Shriners Burns Institute, Boston Massachusetts 02114 [L.C., Y.M.Y., T.E.C., V.R.Y.]; and Pediatric and Neonatal Intensive Care Units and Children's Service, Departments of Pediatrics [L.C., M.S.], Pediatric Pulmonary Care [D.S.], and Surgery [J.F.B.], Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114 R ACT Despite the potential relevance of the L-arginine-nitric oxide lescence, whereas leucine fluxes were unchanged (168.5 ? 15 (NO) pathway in the pathophysiology of pulmonary hyperten- versus 178.8 ? 10.2 prnol.kg.-'h-l), and comparable to those sion, no in vivo studies of the kinetics of arginine and NO have reported in healthy newborns. During convalescence total urinary been conducted previously in this population. The terminal gua- nitrate excreted increased by 66% (p < 0.05), urinary "NO,- nidino N-atom of L-arginine is the precursor for NO, which is increased from 0.29 ? 0.07 to 0.74 ? 0.15 pmo1.d-' (p < oxidized to the stable inorganic nitrogen oxides, nitrite (NO,-) 0.05), and the rate of plasma arginine conversion to NO in- and nitrate (NO,-). Thus, synthesized NO is detected in serum or creased from 10.3 ? 2.2 to 45.6 + 13 pmol.d-' (p< 0.05). This urine as NO,- and NO,-. The purpose of this investigation was study indicates a decreased plasma arginine utilization for whole to compare studies of whole body arginine metabolism twice in body NO synthesis during the acute vasoconstrictive state of nine patients with persistent pulmonary hypertension of the PPHN and suggests that arginine availability may become an newborn (PPHN), using a primed constant i.v. infusion of important factor in NO formation. (Pediatr Res 38: 17-24,1995) ~-[~uanidino-~~N,,5,5~H,]ar~inineand L-[5,5,52~,]leucine, first during acute pulmonary vasoconstriction and again during con- Abbreviations valescence, and thereby to characterize quantitative aspects of PPHN, persistent pulmonary hypertension of the newborn whole body arginine kinetics and NO production, as estimated NO, nitric oxide from the rate of transfer of the '5~-guanidino-labelof arginine to eNOS, nitric oxide synthase urinary nitrate (ISNO,-). Arginine flux rates were 84.1 ? 8.6 AaDO,, alveolo-arterial oxygen gradient prn~l-k~.-~h-~(mean ? SEM) during acute pulmonary hyper- ECMO, extracorporeal membrane oxygenation tension and increased to 125 ? 13.2 (p < 0.05) during conva- A.P.E., atom percent excess PPHN is an acute vascular maladaptation to extrauterine life, must be considered. NO is produced in the pulmonary and characterized by reactive pulmonary vasoconstriction, causing systemic arteries of newborn animals (5) and contributes to the extrapulmonary shunting of blood across fetal channels and postnatal vasodilation of the pulmonary circulation (6, 7). NO critical hypoxemia. Remodeling of the pulmonary arteries has is synthesized in the endothelial cells, through the action of been observed in some patients with PPHN (1). The etiology of eNOS, and diffuses into subjacent vascular smooth muscle, this disorder is uncertain, but a role for altered NO production, where it binds to its molecular target, the prosthetic heme a recently discovered key regulator of vascular tone (2-4), group of soluble guanylyl cyclase, forming nitrosyl proteins (8). This process activates guanylyl cyclase, augmenting levels of the second messenger, cGMP (8). Intracellular elevation of Received October 10, 1994; accepted February 27, 1995. Correspondence and reprint requests: Leticia Castillo, M.D., Pediatric and Neonatal cGMP levels activates cGMP-dependent protein kinases, lead- Intensive Care Units, Massachusetts General Hospital, Ellison 317, Fruit Street, Boston, ing to phosphorylation of proteins and inhibition of intracellu- MA 02114. lar calcium release and/or influx through calcium channels. Supported by a Research Grant from the American Lung Association, with additional This mechanism is for No-induced va- support.. from NIH Grants DK 15856, RR88 (CRC Core Grant), and (2.4-26731 and the Shriners Hospital for Crippled Children Grants No. 15897 and 15843. sorelaxation (8). 18 CASTILLO ET AL. The terminal guanidino N-atom of t-arginine is the precur- therefore pulmonary vasoconstriction. We wished to address sor of NO, which is synthesized in cells by a cytokine-induced, the following questions. I) Is whole body arginine and protein high output L-arginine-NO pathway as well as a constitutive metabolism different during the acute phase of PPHN when low output pathway (3). NO formed by either pathway under- compared to convalescence? 2) Is the utilization of plasma goes oxidative degradation to the stable inorganic nitrogen arginine for whole body NO synthesis altered during PPHN? oxides, nitrite (NO2-) and nitrate (NO3-). In the in vivo system NO2- is oxidized to NO3- via hemoglobin, thus NO can be METHODS eventually detected in serum or urine as NO3- (9, 10). Despite the biochemical importance of arginine as the pre- Patients. Nine sequential critically ill newborns with a cursor for NO, little is known about the in vivo regulation of diagnosis of PPHN confirmed by echocardiogram were inves- arginine metabolism or how it varies during human pathophys- tigated. The echocardiogram showed right to left shunting in iology. It has been shown that in some pathologic states, such all patients. Two patients (nos. 3 and 8) were shunting only as hypercholesterolemia (ll), intimal hyperplasia post-balloon through the ductus arteriosus, and the remaining seven patients catheterization injury (12), or hypoxia (13, 14), endothelial were shunting through the foramen ovale and the ductus dysfunction may be reversed or attenuated by administration of arteriosus. Pulmonary artery pressure was estimated by mea- L-arginine, the precursor of NO. surement of the doppler tricuspid regurgitation velocity jet and Arginine, via ornithine, is also the precursor for polyamines an assumed right atrial pressure of 10, in patients without (spermine, spermidine, and putrescine). These low molecular continuous right atrial pressure measurement. Seven patients weight cations play an important role in the pulmonary arter- had suprasystemic and two patients had systemic pulmonary ies' remodeling during chronic hypoxemia (15-17). It appears, artery pressure. The mean + SEM systolic pulmonary pressure then, that these two important metabolites of arginine (NO and was 46 + 1.8 with a range of 37 to 54 Torr. Seven patients also polyamines) are related to the main pathophysiologic events of had a diagnosis of meconium aspiration, one patient had blood PPHN: vasoconstriction and remodeling of the pulmonary aspiration, and one patient had primary PPHN. Patients with arteries. liver or renal failure, those treated with any nitrite-nitrate In this study, we examined whole body arginine and protein containing medication, or those with evidence of infection metabolism and NO production twice in infants with PPHN, were excluded. The clinical characteristics of the patients are first during acute pulmonary vasoconstriction and again during described in Table 1. All patients were outborn and transferred convalescence. We used a primed constant i.v. infusion of to the Neonatal Intensive Care Unit at the Massachusetts ~-['~~]~uanidino-labeledarginine and leucine cine to char- General Hospital. The patients were first studied within 24 h acterize quantitative aspects of arginine and protein kinetics in after admission, during acute hypoxemia with an AaDO, of 81 these patients. NO production was estimated by the rate of + 1.9 kPa (609 t- 7 Torr, mean + SEM), at 3.1 + 0.3 d of age, transfer of the ["~]~uanidinolabel of arginine to urinary and again during convalescence, AaDO, 19.5 f 0.9 kPa (146 15~0,-.Due to arginine7s precursor role for NO, we hypoth- + 4 Torr), at 6.9 + 0.7 d of age. We used the Neonatal esized that the L-arginine-NO metabolic pathway is altered Physiologic Stability Index (18) and the Therapeutic Interven- during PPHN, resulting in a decreased rate of NO synthesis and tion Score System (19) to assess the severity of disease and the Table 1. Clinical characteristics of patients with PPHN studied for arginine metabolism Age on AaDO, Gestational Weight Age on acute AaDO, acute convalescent convalescent Patient age (wk) (kg) Diagnosisa Treatment study (d) study (mm Hg) study (d) study (mm Hg) 1 40 2.7 PPHN ECMO 5 656 10 162 Mec Asp V-Ab 2 39 3.4 PPHN ECMO 5 625 10 172 Mec Asp V-A 3 40 2.9 PPHN Conventional 3 590 9 146 Blood Asp 4 39 4.2 PPHN ECMO 3 612 6 140 Mec Asp V-A 5 38 3.2 PPHN Conventional 2 605 6 137 Mec Asp 6 39 3.3 PPHN ECMO 3 620 7 147 Mec Asp V-A 7 37 2.9 PPHN Conventional 2 600 5 151 8 37 2.7 PPHN Conventional 3 578 7 124 Mec Asp 9 42 3.1 PPHN Conventional 2 603 6 142 Mec Asp Mean t SEM 38.9 t 0.5 3.2 ? 0.1 3.1 i 0.3 609 i 7 6.9 ? 0.7 146 rfi 4 " Mec, meconium; Asp, aspiration. V-A, veno-arterial. ARGININE METABOLISM IN PPHN 19 degree of therapeutic intervention required in these patients. Blood samples were obtained at 0, 120, 180,210, and 240 min, The Neonatal Physiologic Stability Index score for the acute to measure plasma isotopic enrichment of both amino acid state was 7.7 + 1.9 (mean + SEM) and for convalescence was tracers.
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