Abstract 1879 Poster Session I, Saturday, 5/1 (poster 84)

The nitric oxide (NO)/cGMP signal transduction system plays a critical role in the mammalian pulmonary vascular adaptation to extrauterine life. PDE5 modulates nitric oxide responsiveness in the lung by decreasing intracellular cGMP concentrations. We previously reported attenuated expression of endothelial nitric oxide synthase (NOS III) and soluble guanylate cyclase (sGC) in newborn lambs with PPHN following antenatal ligation of the ductus arteriosus, as well as attenuated pulmonary vascular responses and cGMP accumulation to exogenous NO. In addition, fifth-generation pulmonary arteries isolated from fetal lambs with pulmonary hypertension exhibited depressed relaxation to selective PDE5 inhibitors compared to controls. To further investigate the role of PDE5 in regulating NO responsiveness in this ovine model of PPHN, PDE5 mRNA levels, total pulmonary cGMP PDE activity, Zaprinast-inhibitable cGMP PDE activity and PDE5 immunoreactive protein levels were measured in total lung homogenates obtained from late gestation fetal lambs with PPHN (n=6) and age-matched controls (n=6). EGTA was added to cGMP PDE assay samples to inhibit PDE1 enzyme activity. Total pulmonary cGMP PDE enzyme activity was decreased by 27% and Zaprinast-inhibitable cGMP PDE enzyme activity, an estimate of PDE5 enzyme activity, was decreased by 39% in lambs with PPHN compared to twin controls (p<0.05). Pulmonary PDE5 gene expression, as well as PDE5 immunoreactive protein levels were similarly decreased in lambs with PPHN compared to controls. These results are analogous to those previously reported for NOS III and sGC, and indicate the gene encoding PDE5 is also modulated in this model of pulmonary hypertension. We speculate that antenatal pulmonary hypertension, as exhibited in this model, disrupts the increases in NOS III, sGC and PDE5 which normally occur during late gestation.

Funded by the Robert Wood Johnson Foundation, NIH 54705 and AHA (R.H.S. is an Established Investigator of the AHA).