Cardiopulmonary Effects of Chronic Administration of the NO Synthase Inhibitor L-NAME in the Chick Embryo

Abstract

Background: Experimental observations in mammalian models suggest that endothelial nitric oxide (NO) synthase (NOS) content and activity are decreased in persistent pulmonary hypertension of the newborn. Objectives: To test the hypothesis that disruption of NO signaling in the developing chick embryo lung may contribute to pulmonary hypertension. Methods: We analyzed pulmonary arterial reactivity and structure and heart morphology of 19-day chick embryos (incubation time 21 days) that received a daily injection of the NOS inhibitor Nω-nitro-L-arginine methyl ester (L-NAME, 20 µg per gram egg) or vehicle from day 12 until day 18. Results: Exposure to L-NAME did not affect embryonic survival or body mass of the embryos. The contractile responses to KCl, endothelin-1, the thromboxane A₂ mimetic U46619, noradrenaline, and electrical-field stimulation were not affected by exposure to L-NAME. In contrast, in ovo L-NAME exposure reduced the sensitivity of pulmonary arteries to acetylcholine (pD₂: 6.53 ± 0.14 vs. 6.96 ± 0.13; p < 0.05) and this effect was reversed by the NOS substrate L-arginine. Relaxations induced by sodium nitroprusside or forskolin were not altered by chronic L-NAME. Pulmonary vessel density was not different, but the percentage medial wall area of small pulmonary arteries (external diameter 10–50 µm) was slightly but significantly increased in the embryos exposed to L-NAME. In addition, hearts of L-NAME-exposed embryos showed an increase in right and left ventricular wall area. Conclusions: Chronic inhibition of NOS produced, in the chick embryo, impairment of endothelium-dependent relaxation, structural remodeling of the pulmonary vascular bed and biventricular cardiac enlargement.

Pulmonary Vascular Endothelial Growth Factor Expression and Disaturated Phospholipid Content in a Chicken Model of Hypoxia-Induced Fetal Growth Restriction

“…The chicken fetus is an excellent model for the study of the developmental consequences of hypoxia and other prenatal insults [16][17][18][19][20] . Hypoxia is easily induced by incubating the egg in a low-oxygen environment, and its effects can be studied without interferences of maternal hormonal, metabolic, or hemodynamic alterations.…”

The chicken embryo as a model for ductus arteriosus developmental developmental biology

“…Preliminary results of our laboratory also indicate that premature exposure to hyperoxia induces significant alterations in the developmental trajectory of the chicken DA. Other prenatal insults that we demonstrated to induce alterations in chicken perinatal vascular homeostasis are malnutrition (Ruijtenbeek et al 2003b), exposure to cigarette smoke extract or inhibition of NOS (Villamor et al 2005). Injection of drugs Villamor et al 2005) or gene transfer (Williams et al 2006) during incubation open a new territory for the investigation of the pathways involved in the developmental vascular biology of the DA.…”

“…During the last years, our group has analyzed the developmental changes in the reactivity of chicken embryo systemic and PAs and the influence of prenatal insults, such as chronic hypoxia or malnutrition, on chicken cardiovascular development (van Golde et al 1996;Mulder et al 1997;van Golde et al 1997;Mulder et al 1998;van Golde et al 1999;Mulder et al 2001;Mulder et al 2002;Ruijtenbeek et al 2002a;Ruijtenbeek et al 2002b;Ruijtenbeek et al 2003a;Ruijtenbeek et al 2003b;Villamor et al 2005).…”

“…In the last years, our group has accumulated a broad experience in the study of developmental circulation of chicken embryos and in the effects of adverse stimuli, such as hypoxia or malnutrition, on pulmonary and systemic vascular function and structure Ruijtenbeek et al 2002a;Ruijtenbeek et al 2002b;Ruijtenbeek et al 2003a;Ruijtenbeek et al 2003b;Villamor et al 2005).…”