Chronic hypercapnia downregulates arginase expression and activity and increases pulmonary arterial smooth muscle relaxation in the newborn rat

Abstract

In rats, chronic hypercapnia has been reported to ameliorate hypoxia-induced pulmonary hypertension in newborn and adult and to enhance endothelium-dependent vasorelaxation in adult pulmonary arteries. The underlying mechanisms accounting for chronic hypercapnia-induced improvements in pulmonary vascular function are not understood. Hypothesizing that downregulation of arginase activity may be contributory, we examined relaxation responses and arginase activity and expression in pulmonary arteries from newborn rats that were exposed (from birth to 14 days) to either mild-to-moderate (5.5% inhaled CO(2)) or severe (10% CO(2)) hypercapnia with either normoxia or hypoxia (13% O(2)). Pulmonary arteries from pups exposed to normoxia and chronic hypercapnia (5.5 or 10% CO(2)) contracted less in response to a thromboxane A(2) analog, U-46619, and showed enhanced endothelium-dependent (but not independent) relaxation compared with arteries from normocapnic pups (P < 0.01). Parallel with these changes, arginase activity and arginase I (but not II) expression in lung and pulmonary arterial tissue were significantly decreased (P < 0.05). Exposure to 10% CO(2) significantly increased (P < 0.01) pulmonary arterial tissue nitric oxide (nitrite) generation. In pups chronically exposed to hypoxia (13% O(2)), severe hypercapnia (10% CO(2)) significantly (P < 0.05) enhanced endothelium-dependent relaxation, increased nitric oxide generation, and decreased arginase activity but not expression. We conclude that chronic hypercapnia-induced downregulation of lung arginase expression and/or activity may reduce pulmonary vascular resistance by enhancing nitric oxide generation and thus endothelium-dependent relaxation. This mechanism may explain some of the beneficial effects of chronic hypercapnia on experimental pulmonary hypertension.

Sustained therapeutic hypercapnia attenuates pulmonary arterial Rho-kinase activity and ameliorates chronic hypoxic pulmonary hypertension in juvenile rats

“…idative/nitrative stress (28,30,33,39) and GPCR signaling (33), as well as increased NO bioavailability and signaling (5). Given recent evidence of a critical role for ROCK signaling downstream and upstream of these pathways (41, 74), we were interested to determine the effects of hypercapnia on ROCK signaling in the setting of rescue therapy.…”

“…Isometric contraction of ex vivo intralobar pulmonary arteries, or mesenteric arteries (4 arteries from 4 pups representing 2 litters/group), in response to a thromboxane analog, U-46619, or relaxation responses to an eNOS stimulator (acetylcholine; ACh) were measured (8 arteries from 8 pups representing 4 litters/group) as previously described (5,28).…”

Multitracer Stable Isotope Quantification of Arginase and Nitric Oxide Synthase Activity in a Mouse Model of Pseudomonas Lung Infection

“…NO metabolite (nitrate + nitrite) concentrations were expressed as nmol/mg protein. Immunoblotting was performed as previously described, and bands on imaging film were quantified by densitometry and expressed as a ratio to the corresponding GAPDH densities [18, 21]. Antibodies for immunoblotting were purchased from Santa Cruz Biotechnology (Dallas, TX).…”

Increased Arginase Expression and Decreased Nitric Oxide in Pig Donor Lungs after Normothermic Ex Vivo Lung Perfusion

“…Total nitric oxide metabolite (nitrate+nitrite, NOx) concentrations were measured in lung tissue homogenates using chemiluminescent NO-analyzer techniques (NOA280, Eco Physics, Durnten, Switzerland) as previously reported [35]. l-arginine, l-ornithine, l-citrulline and asymmetric dimethylarginine (ADMA) were quantified in lung tissue homogenate supernatant using liquid chromatography-mass spectrometry (LC-MS/MS) similarly to previously reported [36].…”