Endothelial nitric oxide synthase in hypoxic newborn porcine pulmonary vessels

Abstract

Aims: To determine if the failure of neonatal pulmonary arteries to dilate is due to a lack of nitric oxide synthase (NOS).

Methods: A monoclonal antibody to endothelial NOS was used to demonstrate the distribution and density of NOS in the developing porcine lung after a period in hypobaric hypoxia. Newborn piglets were made hypertensive by exposure to hypobaric hypoxia (50.8 kPa) from < 5 minutes of age to 2.5 days of age, 3-6 days of age or 14-17 days of age. A semiquantitative scoring system was used to assess the distribution of endothelial NOS by light microscopy.

Results: NOS was present in the arteries in all hypoxic animals. However, hypoxia from birth caused a reduction in NOS compared with those lungs normal at birth and those normal at 3 days. Hypoxia from 3-6 days led to a high density of NOS compared with normal lungs at 6 days. Hypoxia from 14-17 days had little effect on the amount of NOS. On recovery in room air after exposure to hypoxia from birth there was a transient increase in endothelial NOS after three days of recovery, mirroring that seen at three days in normal animals.

Conclusions: Suppression of NOS production in the first few days of life may contribute to pulmonary hypertension in neonates.

Figure 1

Mean (SD) percentage of arteries at bronchiolar level containing no endothelial NOS, containing up to 50%, or 51-100% in hypoxic and control piglets. *P<0.05 compared with controls of the same age.

Figure 2

NOS score (SD) for control and hypoxic animals in arteries at the level of the bronchioli, terminal bronchi, respiratory bronchioli, alveolar ducts, and alveoli. *P<0.05 compared with control 3 day olds; +P<0.05 compared with control 6 day olds.

Figure 3

NOS score (SD) for control (C), hypoxic (H), and recovery (R) animals at each arterial level in 0-2.5 day hypoxic group. *P<0.05 compared with control 3 day olds; +P<0.05 compared with 2.5 day hypoxic animals.

Figure 4

NOS score for control (C), hypoxic (H), and recovery (R) animals at respiratory bronchiolar level in (A) 3-6 day hypoxic group and in (B) 14-17 day hypoxic group. *P<0.05 compared with 6 day old controls; +P<0.05 compared with 6 day hypoxia.

Figure 5

Mean (SD) NOS score for the three hypoxic groups. *P<0.05 compared with controls of the same age; +P<0.05 compared with hypoxia.