Calcium and ionophore A23187 lower calcitonin gene-related peptide-like immunoreactivity in endocrine cells of organ cultured fetal rat lungs

The pulmonary neuroendocrine system: the past decade

The pulmonary neuroendocrine system consists of specialized airway endocrine epithelial cells, associated with nerve fibres. The epithelial cells, the pulmonary neuroendocrine cells (PNEC), can be solitary or clustered to form neuroepithelial bodies (NEB). During the last thirty years, the pulmonary neuroendocrine system has been intensively investigated and much knowledge of its function has been obtained. This text reviews work which dates from the last ten years. In this period, the picture of the pulmonary neuroendocrine system we previously had, has not fundamentally changed. The pulmonary neuroendocrine system is still regarded as an oxygen sensitive chemoreceptor with local and reflex-mediated regulatory functions, and as a regulator of airway growth and development. Continuing research has much more refined this picture. This text reviews several aspects of the pulmonary neuroendocrine system: phylogeny, the amine and peptide content of its epithelial cells, ontogeny and influence on lung development, the influence of hypoxia and nonhypoxic stimuli, immunomodulatory function, innervation and pathology. Among the discoveries of the past decade, three stand out prominently because of their great significance: additional proof that the neural component of the pulmonary neuroendocrine system is sensory, sound experimental evidence that PNEC stimulate airway epithelial cell differentiation and the discovery of a specific membrane oxygen receptor in the PNEC.

Calcitonin gene-related peptide expression is altered in pulmonary neuroendocrine cells in developing lungs of rats with congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is associated with high neonatal mortality from lung hypoplasia and persistent pulmonary hypertension. Pulmonary neuroendocrine cells (PNEC) produce calcitonin gene-related peptide (CGRP), a potent vasodilator. We previously reported altered distribution of CGRP-positive PNEC in full-term rats with CDH, that may lead to an imbalance in vasoactive mediators. In the present study we examined the expression of CGRP-positive PNEC during lung development in rats with CDH induced by 2,4-dichlorophenyl-p-nitrophenylether (Nitrofen). Cesarean sections were performed on Days 16, 18, 20, or 22, and the lungs were immunostained for CGRP and immunoreactive cells were quantitated through image analysis. On Day 16, CGRP-immunoreactive staining was negative; on Day 18, CGRP-immunoreactive cells were found in all controls (not exposed to Nitrofen), whereas in CDH pups, CGRP-positive cells were present in only four of six cases. On Day 20, CGRP immunoreactivity was similar in CDH pups, Nitrofen-exposed pups without CDH, and controls. On Day 22 (term), significantly more CGRP-positive cells (i.e., number of positive cells per surface area [mm2] or lung volume [mm3]) were found in ipsilateral lungs of CDH pups than in controls (P < 0.05). The difference was even more striking in contralateral lungs of CDH pups (P < 0.001), ruling out nonspecific effects of Nitrofen. In CDH lungs, the proportion of immunostained epithelium and the size of the neuroendocrine cell clusters (neuroepithelial bodies [NEB]) were not significantly different from those of controls. On Day 22, supraoptimal dilution immunocytochemistry yielded similar results in CDH pups and controls. We conclude that in CDH, CGRP expression in PNEC and NEB is delayed during early stages of lung development. Because CGRP also exhibits growth factor-like properties for endothelium and epithelial cells, the lack of this factor during a crucial developmental stage (canalicular period) may be causally related to lung hypoplasia.

Pulmonary Neuroendocrine Cells and Lung Development

Pulmonary neuroendocrine cells produce bioactive peptides such as gastrin-releasing peptide (GRP) at high levels in developing fetal lung. The role of GRP and other peptides in promoting branching morphogenesis, cell proliferation, and cell differentiation during lung organogenesis is reviewed. Possible roles for bioactive peptides derived from these cells in the pathophysiology of perinatal lung disorders are discussed.

Development of PGP 9.5- and calcitonin gene-related peptide-like immunoreactivity in organ cultured fetal rat lungs

Knowing that small-granule endocrine cells develop in organ cultured fetal lungs, we investigated whether the cells produce regulatory peptides in vitro, and if sufficient amounts appear to permit using the cultures as an experimental system for physiological study of secretory mechanisms. The paired lungs from 14-day and 15-day fetal rats were organ cultured for 1-8 days and examined daily for development of immunoreactivity against marker proteins and regulatory peptides associated with small-granule endocrine cells and nerves. They proved reactive against protein gene product 9.5 (PGP) and calcitonin-gene related peptide (CGRP) but not against calcitonin or neurofilament protein 200 K, although positive controls were obtained for these substances in lungs from postnatal animals. Initially PGP-like immunoreactivity is associated with cell bodies and processes of neuroblasts which run medial to the bronchial axis on day 14 and are increasingly prevalent on day 15. In 15-day explants PGP becomes detectable after a day in vitro in rare "clear cell" precursors of small-granule cells located in the epithelium lining proximate parts of the lungs, although in 14-day explants comparable reactivity is not seen until the third day (14 + 3 days). In culture PGP-positive neuroblasts increase in number, and nerve processes gradually extend down the airway to encircle the sleeve of smooth muscle that develops as the bronchial tree expands. Concurrently, the initially small clusters of small-granule cells increase in size, and new ones appear in the airway lining. By 15 + 5 days they extend to the boundary between a taller, more proximal epithelium and a glycogen-rich cuboidal layer that lines one or two most-distal generations of branches. Thereafter, the trachea and central, cartilage-bound segments of the primary bronchi mainly contain solitary endocrine cells and the more peripheral lung a mixture of single cells and clusters, much as in near-term lungs in vivo. At this stage PGP-positive nerves extend as far as the entrances of the terminal sacs, and most are distributed to the airway muscle plexus. Exceptionally, they may innervate a small-granule cell cluster, converting it into a neuroepithelial body. CGRP-like immunoreactivity initially appears in small-granule cells of 15 + 2-day cultures but does not develop in ganglion cells or nerves. It localizes to endocrine cells at all conducting airway levels, increasing in staining intensity and accounting for most if not all of the PGP-positive population between 15 + 4 - 15 + 8 days.(ABSTRACT TRUNCATED AT 400 WORDS)