Calcitonin, CGRP and helodermin in endocrine cells of the developing rat lung.

Calcitonin gene-related peptide (CGRP), calcitonin and immunoreactive helodermin occur in endocrine cells in the murine airways. In the lungs these cells form clusters, while they occur scattered in the larynx and trachea. In the present study of the developing rat CGRP-immunoreactive cells were more numerous at all stages than the calcitonin- and helodermin-containing ones. A subpopulation of the CGRP-containing cells contained either calcitonin or helodermin. Immunocytochemistry revealed a higher density of CGRP-containing endocrine cells in the lungs of fetal and newborn rats than in the lungs of older rats, while the density of calcitonin-containing cells was largely unchanged. The helodermin-containing cells were few at all developmental stages examined. The concentration and content of CGRP were highest in newborn rats; the levels decreased postnatally. The calcitonin concentration did not change during development while the content increased with age. The concentration and content of helodermin increased with age.