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Department of Pediatrics, Medical College of Wisconsin, Milwaukee 53226; and Research Services, Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin 53295
Previously, our laboratory found that
pulmonary hypertension developed and lung nitric oxide (NO) production
was reduced when piglets were exposed to chronic hypoxia (Fike CD,
Kaplowitz MR, Thomas CJ, and Nelin LD. Am J Physiol Lung
Cell Mol Physiol 274: L517-L526, 1998).
The purposes of this study were to determine whether
L-arginine addition augments NO production and to evaluate whether L-arginine uptake is impaired in isolated lungs of
chronically hypoxic newborn piglets. Studies were performed by using 1- to 3-day-old piglets raised in room air (control) or 10%
O2 (chronic hypoxia) for 10-12 days. Lung NO
production was assessed in isolated lungs from both groups by measuring
the perfusate accumulation of nitrites and nitrates (collectively
termed NO
x) before and after
addition of L-arginine (10
2 M) to the
perfusate. The rate of perfusate
NO
x accumulation increased by
220% (from 0.8 ± 0.4 to 2.5 ± 0.5 nmol/min, P < 0.05)
after L-arginine addition to chronic hypoxic lungs but remained unchanged (3.2 ± 0.8 before vs. 3.3 ± 0.4 nmol/min after L-arginine) in control lungs. In the second series of
studies, L-arginine uptake was evaluated by measuring the
perfusate concentration of
L-[3H]arginine at fixed time
intervals. The perfusate concentration of
L-[3H]arginine at each time point
was less (P < 0.05) in control than in chronic hypoxic lungs.
Thus L-arginine uptake was impaired and may underlie in
part the reduction in lung NO production that occurs when piglets are
exposed to 10-12 days of chronic hypoxia. Moreover, these findings
in isolated lungs lead to the possibility that L-arginine
supplementation might increase in vivo lung NO production in piglets
with chronic hypoxia-induced pulmonary hypertension.
neonatal pulmonary hypertension; L-arginine uptake; nitrites; nitrates
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