Although the inducible (type II) Nitric Oxide synthase isoform (iNOS) has been identified in the normal fetal lung, little is known about changes in iNOS expression in the lung during fetal and postnatal development. We studied qualitative and quantitative changes in iNOS mRNA expression in the lungs of fetal, newborn and adult sheep. We performed northern blot analysis with pooled poly(A+) mRNA from the lungs of normal 92 day (d), 114d, and 136d fetuses, 1 and 5d lambs, and maternal (adult). Total RNA from the lungs of a rat injected with bacterial lipopolysaccharide (LPS) was used as a positive control for iNOS mRNA. Hybridization was performed with mouse and human iNOS cDNA probes. Stringent washing conditions were used (0.4×SSC, 0.1%SDS, 65°C). Probe signals were detected and quantitated with a phosphorimager. Whereas one iNOS mRNA transcript of 4.1Kb was detected in the LPS-treated rat lung, two mRNA transcripts of 4.1 and 2.6 Kb were present at all ages in the fetal, newborn, and adult ovine lung. The relative abundance of the two mRNA transcripts changed after birth. In conclusion, two iNOS mRNA transcripts were detected at all ages of ovine lung. The ratio of abundance of the two transcripts changed after birth. We speculate that the 2.6 Kb iNOS mRNA transcript results from alternate splicing of the primary transcript for iNOS. Figure

figure 1

Figure 1