[2006] [3875.4] Effects of Hyperoxia and Nitric Oxide on PDE5 Expression and Activity in Persistent Pulmonary Hypertension (PPHN)

Kathryn N. Farrow, Lyubov Czech, Satyan Lakshminrusimha, Sylvia F. Gugino, James A. Russell, Robin H. Steinhorn. Pediatrics, Northwestern University, Chicago, IL; Physiology, SUNY at Buffalo, Buffalo, NY.

BACKGROUND: In the pulmonary vasculature, endogenous NO increases cGMP, leading to vasorelaxation. This pathway is downregulated by a cGMP-dependent phosphodiesterase, PDE5. PDE5 expression has been studied in fetal lambs with PPHN, but little is known about changes following birth as well as changes in response to PPHN treatments.
OBJECTIVE: To determine if hyperoxia or inhaled NO (iNO) affect PDE5 expression in an ovine model of PPHN.
DESIGN/METHODS: The ductus arteriosus was ligated in fetal lambs at 126 days gestation. After delivery at 135 days, PPHN lambs or age-matched controls were ventilated with 100% O2 or 100% O2+ 20 ppm iNO for 24 hours. PDE5 protein expression was assayed in pulmonary arteries by Western blotting; controls included fetal lambs and spontaneously breathing 1-day lambs. PDE5 expression was localized in frozen lung sections by fluorescent immunohistochemistry (IHC). PDE5 activity in total lung was measured by a commercially available colorimetric assay.
RESULTS: PDE5 expression was decreased in PA from fetal PPHN lambs vs controls (29±7%, p<0.05). PDE5 protein expression was lower in 1-day spontaneously breathing lambs vs fetal controls (44±10%, p<0.05). Following ventilation with 100% O2, PDE5 expression dramatically increased in PPHN (403±65%), but not in control PA (p<0.05). Inhaled NO blunted this increase in PPHN PA (262%±163%), but had no effect in control PA. The increases in PDE5 protein expression in PPHN PA were localized primarily to vascular smooth muscle by IHC (197±26%, p<0.05). Lung PDE5 activity did not change in control ventilated lambs. In contrast, PDE5 activity increased in PPHN lambs following ventilation with 100%O2 (132%) and 100%O2+iNO (165%) relative to PPHN fetal controls.
CONCLUSIONS: In PPHN lambs, delivery and ventilation with 100% O2 is a potent activator of PDE5 expression and activity. NO inhalation decreased PDE5 expression, but not activity, in PPHN lambs. We suggest that elevations in PDE5 expression and activity increase contractility in the remodeled pulmonary vasculature, which may have important implications for clinical management.

E-PAS2006:59:3875.4