Abstract
The objective of this study was to observe possible interactions between the renin-angiotensin and nitrergic systems in chronic hypoxia-induced pulmonary hypertension in newborn piglets. Thirteen chronically instrumented newborn piglets (6.3 ± 0.9 days; 2369 ± 491 g) were randomly assigned to receive saline (placebo, P) or the AT1 receptor (AT1-R) blocker L-158,809 (L) during 6 days of hypoxia (FiO2 = 0.12). During hypoxia, pulmonary arterial pressure (Ppa; P < 0.0001), pulmonary vascular resistance (PVR; P < 0.02) and the pulmonary to systemic vascular resistance ratio (PVR/SVR; P < 0.05) were significantly attenuated in the L (N = 7) group compared to the P group (N = 6). Western blot analysis of lung proteins showed a significant decrease of endothelial NOS (eNOS) in both P and L animals, and of AT1-R in P animals during hypoxia compared to normoxic animals (C group, N = 5; P < 0.01 for all groups). AT1-R tended to decrease in L animals. Inducible NOS (iNOS) did not differ among P, L, and C animals and iNOS immunohistochemical staining in macrophages was significantly more intense in L than in P animals (P < 0.01). The vascular endothelium showed moderate or strong eNOS and AT1-R staining. Macrophages and pneumocytes showed moderate or strong iNOS and AT1-R staining, but C animals showed weak iNOS and AT1-R staining. Macrophages of L and P animals showed moderate and weak AT2-R staining, respectively, but the endothelium of all groups only showed weak staining. In conclusion, pulmonary hypertension induced by chronic hypoxia in newborn piglets is partially attenuated by AT1-R blockade. We suggest that AT1-R blockade might act through AT2-R and/or Mas receptors and the nitrergic system in the lungs of hypoxemic newborn piglets.
Highlights
Pulmonary hypertension induced by chronic hypoxia is a complex process of sustained elevation of pulmonary artery pressure involving vasoconstriction and pulmonary vessel remodeling
There were no significant differences in arterial blood gases (ABG) or acid-base values in room air/normoxia and hypoxia or in systemic hemodynamic responses (Psa, Systemic vascular (SVR), and cardiac output (CO)) between the P and L groups
Pulmonary hypertension induced by chronic hypoxia in newborn piglets was markedly attenuated by L-158,809, a highly potent and selective nonpeptide AT1 receptor (AT1-R) blocker [19]
Summary
Pulmonary hypertension induced by chronic hypoxia is a complex process of sustained elevation of pulmonary artery pressure involving vasoconstriction and pulmonary vessel remodeling. These events have been consistently observed in experimental animal models and in adult humans [1], but in newborns and in neonatal animal models, only one study showed involvement of the renin-angiotensin system (RAS) [2]. They are multifactorial processes involving different mediators such as endothelin and angiotensin II (Ang II) and nitric oxide.
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