Objectives: To describe the cellular distribution and level of expression of certain hormones and opioid receptors during fetal development and in the lung of the healthy adult.
Method: We sampled lung tissue from fetuses at three stages of development (pseudoglandular, canalicular and saccular) (3 samples per stage), from newborn infants (3), from 10-month-old infants (2) and from adults (3) who had died without lung disease. After specific immunohistochemical staining for hormones (calcitonin, parathormone, serotonin and adrenocorticotropic hormone - ACTH) and opioid receptors, we assessed the percentage of positive cells for each cell type in each sample.
Results: Serotonin is the first to appear (pseudoglandular stage in isolated neuroendocrine cells) and it disappears later. Calcitonin appears in the canalicular stage in neuroendocrine and lung cells. Expression is at its peak at birth and is less in the adult lung. We found no ACTH or parathormone production. Opioid receptors appear in the canalicular stage and peak at birth. In adult lung, bronchiolar muscle and mesothelial cells, only delta-type opioid receptors are present.
Conclusions: Pulmonary hormone secretion is significant during fetal development and peaks at birth. Calcitonin is the main hormone produced in the fetal lung. Opioid receptors are present during fetal development in various types of cells and peak at birth. An understanding of the expression of active substances could have therapeutic relevance in certain conditions, such as bronchial asthma or respiratory distress syndrome in the child.