lung: light and electron microscopic study

Calcitonin gene related peptide immunoreactivity was investigated in the rat lung. Immunoreactive material was observed in nerve fibres surrounding bronchi, bronchioli, and blood vessels, and also in neuroendocrine cells and neuroepithelial bodies. In addition, the peptide was identified by immunoelectron microscopy in dense cored vesicles of granulated cells of the neuroepithelial bodies. These observations suggest that calcitonin gene related peptide plays a part in the regulatory function of the rat respiratory tract, exerting its influence by endocrine, paracrine, neurosecretory pathways, or a combination of these. Calcitonin gene related peptide (CGRP) is a peptide of 37 amino acids encoded on the calcitonin gene.' It depends for its expression on specific RNA processing, which gives rise to a messenger RNA different from the mRNA for calcitonin.2 It is found in thyroid parafollicular cells and in nuclei and nerve fibres of the central and peripheral nervous systems, 3-9 and may act as an extracellular modulator.9 Human CGRP differs from rat CGRP in four positions of its amino acid sequence.1' A second calcitonin-CGRP gene has recently been identified in rat and human tissue." 12 In the rat this gene produces a CGRP like peptide differing from the originally analysed CGRP by only one amino acid. The respiratory mucosa of several mammalian species contains cells of the APUD series, occurring either as single neuroendocrine cells or in corpuscular aggregates-the neuroepithelial bodies.13 '5 Since calcitonin has been identified in rat neuroendocrine cells and neuroepithelial bodies,'6 we undertook an investigation to find out whether CGRP is also present in these structures.