Developmental expression of no synthase isoforms in fetal rat lung:
implications for transitional circulation and pulmonary
angiogenesis.
Johns, Roger A., Chun Xue, Paul R. Reynolds.
Department of Anesthesiology, Box 238, University of Virginia
Health Sciences Center, Charlottesville, VA 22908
APStracts 2:0136L, 1995.
To better understand the role of nitric oxide (NO) in fetal lung
development, specifically in the transition of the fetal circulation
at birth, we studied the timing of cell specific expression of NO
synthase (NOS) isoforms from formation of lung buds (13th day of
gestation) to 7 days postnatal. Expression of NOS was studied using
immunohistochemical labeling with antibodies against the three known
NOS isoforms and the NADPH diaphorase technique (NADPH-d).
Endothelial NOS (eNOS) immunoreactivity was found in the cells of the
14 day fetal lung. As gestation proceeded, the quantity of these
immuno-positive cells increased, and they coalesced to form an inner
(endothelial) layer of pulmonary vessels. This process of
angiogenesis marked by eNOS positive cells was seen from 15 days of
gestation to at least 7 days postnatal life. A majority of the eNOS
immunoreactivity appeared densely in one focal spot in the cytoplasm,
indicating that during development the eNOS may be primarily located
in a cytoplasmic organelle. Epithelial cells of the rat airway from
the same developmental period were positively stained with both brain
NOS antibody (bNOS) and NADPH-d at the beginning of 13 days of
gestation. Then the intensity of stainings began to decrease and
reached the lowest level in the 16-day fetal lung. However, the NOS
stainings of the epithelium, especially in small canalicular
structures of the airways, began to increase at 18 days of gestation
and was dramatically elevated at 20 days of gestation (term is 22
days). Postnatally, NOS in epithelium was decreased in distal airways
in conjunction with the formation of alveolar structure. Inducible
NOS (iNOS) immunoreactivity was also found in the epithelium of rat
lung airways after 16 days of gestation. Unlike the bNOS staining,
iNOS immunoreactivity exhibited a pattern of a small dot-like
staining within epithelial cytoplasm during gestation and the first
day of postnatal life, then changed to a pattern of diffuse
cytoplasmic staining by the 7th postnatal day. This study concludes
that 1) expression of three isoforms of NOS is present and regulated
during lung development; 2) markedly increased NOS in epithelium near
term supports a role for nitric oxide (NO) in mediating the pulmonary
transition from fetal to neonatal life; 3) eNOS immunohistochemistry
serves as an effective marker to follow the process of pulmonary
angiogenesis and suggests the concept of in situ formation of
endothelial vesicles in developing mesenchyme.
Received 12 January 1995; accepted in final form 24 July 1995.
APS Manuscript Number L10-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.