Abstract 118 Poster Session II, Sunday, 5/2 (poster 254)

Introduction: CHD with high pulmonary blood flow produces early anatomic and functional changes in the pulmonary vasculature. The mechanisms producing these changes in vascular reactivity are not well understood. We studied the natriuretic peptide system in the pulmonary vasculature of an ovine model of CHD with high pulmonary blood flow. Natriuretic peptides are potent stimulants of cGMP production by particulate guanylyl cyclase (pGC). Atrial natriuretic peptide (ANP) is of cardiac origin, while C-type natriuretic peptide (CNP) has been recently localized to the vascular endothelium. These peptides activate pGC by distinct NPR-A and NPR-B receptors, which have high affinity for ANP and CNP respectively. A third receptor, NPR-C binds ANP and CNP with equal affinity, but does not activate pGC. The function of the NPR-C receptor is not well characterized, but it has been implicated as playing a role in vascular remodeling. Methods: 8 mm Gortex aorto-pulmonary vascular shunts were placed in fetal lambs at 139 days gestation, and lambs were allowed to deliver spontaneously. Shunted lambs (n=10) and age matched controls (n=13) were sacrificed at six weeks of age. Fifth generation pulmonary arteries (PA) and veins (PV) were isolated and studied using conventional tissue bath techniques. Rings were preconstricted with norepinephrine following pretreatment with propranolol, indomethacin, and L-NA to block cGMP production by NO-soluble guanylyl cyclase. Concentration response curves were generated for ANP and CNP (10-10 to 3 × 10-7 M). Repeated measures ANOVA was used for statistical comparisons. Using immunohistochemistry, we examined the localization for CNP (anti-CNP 22, 53, Peninsula Laboratories) and NPR-B (anti-rat NPR-B Z657 from D Garbers and K Hamra) in lung parenchyma. Results: PA from shunted lambs displayed a significant blunting in relaxations to CNP compared to PA from control lambs (EC50 8.0 ± 1.33 vs. 24.56 ± 8.21 nM, p<0.05). PV relaxations to CNP were similar in shunted and control lambs. There were no significant differences in relaxation responses of PA or PV to ANP. Immunohistochemical staining revealed a striking increase in CNP immunoreactivity in shunted lambs compared to controls, which localized to vascular smooth muscle cells of the entire arterial tree as well as PV at the bronchial and septal levels. There was no significant difference in quantity or localization of the NPR-B receptor in the pulmonary vasculature of shunt and control lambs. Conclusions: CNP relaxations are significantly blunted in PA isolated from shunted lambs. Despite increased CNP immunolocalization in the pulmonary arterial smooth muscle cells of the shunt lamb, no significant change in NPR-B receptors was noted. Speculation: We speculate that the changes in relaxation response and immunolocalization of CNP in the pulmonary vasculature of lambs with CHD with high pulmonary blood flow may be secondary to increases in NPR-C density in the shunt PA.

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