Pulmonary NO synthase expression is attenuated in a fetal baboon model of chronic lung disease.

Nitric oxide (NO), produced by NO synthase (NOS), serves multiple functions in the perinatal lung. In fetal baboons, neuronal (nNOS), endothelial (eNOS), and inducible NOS (iNOS) are all primarily expressed in proximal respiratory epithelium. In the present study, NOS expression and activity in proximal lung and minute ventilation of NO standard temperature and pressure (VeNO(STP)) were evaluated in a model of chronic lung disease (CLD) in baboons delivered at 125 days (d) of gestation (term = 185 d) and ventilated for 14 d, obtaining control lung samples from fetuses at 125 or 140 d of gestation. In contrast to the normal 73% increase in total NOS activity from 125 to 140 d of gestation, there was an 83% decline with CLD. This was related to marked diminutions in both nNOS and eNOS expression and enzymatic activity. nNOS accounted for the vast majority of enzymatic activity in all groups. The normal 3.3-fold maturational rise in iNOS protein expression was blunted in CLD, yet iNOS activity was elevated in CLD compared with at birth. The contribution of iNOS to total NOS activity was minimal in all groups. VeNO(STP) remained stable in the range of 0.5-1.0 nl x kg(-1) x min(-1) from birth to day 7 of life, and it then rose by 2.5-fold. Thus the baboon model of CLD is characterized by deficiency of the principal pulmonary isoforms, nNOS and eNOS, and enhanced iNOS activity over the first 2 wk of postnatal life. It is postulated that these alterations in NOS expression and activity may contribute to the pathogenesis of CLD.

Developmental changes in nitric oxide synthase isoform expression and nitric oxide production in fetal baboon lung.

Nitric oxide (NO), produced by NO synthase (NOS), plays a critical role in multiple processes in the lung during the perinatal period. To better understand the regulation of pulmonary NO production in the developing primate, we determined the cell specificity and developmental changes in NOS isoform expression and action in the lungs of third-trimester fetal baboons. Immunohistochemistry in lungs obtained at 175 days (d) of gestation (term = 185 d) revealed that all three NOS isoforms, neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS), are primarily expressed in proximal airway epithelium. In proximal lung, there was a marked increase in total NOS enzymatic activity from 125 to 140 d gestation due to elevations in nNOS and eNOS, whereas iNOS expression and activity were minimal. Total NOS activity was constant from 140 to 175 d gestation, and during the latter stage (160-175 d gestation), a dramatic fall in nNOS and eNOS was replaced by a rise in iNOS. Studies done within 1 h of delivery at 125 or 140 d gestation revealed that the principal increase in NOS during the third trimester is associated with an elevation in exhaled NO levels, a decline in expiratory resistance, and greater pulmonary compliance. Thus, there are developmental increases in pulmonary NOS expression and NO production during the early third trimester in the primate that may enhance airway and parenchymal function in the immediate postnatal period.

Estrogen acutely activates prostacyclin synthesis in ovine fetal pulmonary artery endothelium.

Prostacyclin (PGI(2)) is a key mediator of pulmonary vasodilation during perinatal cardiopulmonary transition, at a time when fetal plasma estrogen levels are rising. We have previously shown that estradiol-17beta (E(2)) rapidly stimulates nitric oxide production by ovine fetal pulmonary artery endothelial cells (PAEC), and that this occurs through nongenomic mechanisms which are calcium- and tyrosine kinase-mitogen-activated protein (MAP) kinase-dependent. In the present study, we determined if E(2) acutely activates PGI(2) production in PAEC. E(2) (10(-8) M for 15 min) caused a 52% increase in PGI(2), the threshold concentration was 10(-10) M E(2), the effect occurred within 5 min, and it was not related to changes in cyclooxygenase type 1 (COX-1) or COX-2 abundance. Estrogen receptor (ER) alpha and ER beta proteins and mRNAs were found to be constitutively expressed in PAEC, and PGI(2) stimulation with E(2) was fully blocked by both ER antagonism with ICI 182,780, which is not selective for either ER isoform, and the ER beta-specific antagonist RR-tetrahydrochrysene. The rapid response to E(2) was also inhibited by calcium chelation, whereas genistein- or PD98059-induced inhibition of tyrosine kinase and MAP kinase kinase, respectively, had no effect. Thus, E(2) causes rapid stimulation of PGI(2) synthesis in fetal PAEC, this process is mediated by ER beta, and it is calcium-dependent and tyrosine kinase-MAP kinase-independent. These mechanisms may play a role in pulmonary vasodilation in the perinatal period.