ONTOGENY OF ENDOCRINE-CELLS IN THE RESPIRATORY SYSTEM OF SYRIAN GOLDEN-HAMSTERS .2. INTRAPULMONARY AIRWAYS AND ALVEOLI

Results of this and the preceding study reveal 3 patterns of endocrine cell development in hamster airway. The first, a prenatal wave, begin s in the larynx and sweeps down the extra- and intrapulmonary conducti ng airway to the bronchioloalveolar portals. Cells differentiate singl y and in groups (presumptive neuroepithelial bodies, pNEBs), colocaliz e immunoreactivity for seretonin (5-HT) and calcitonin gene-related pe ptide (CGRP), and persist throughout adulthood. Postnatally a few cell s also express calcitonin (CT). Appearance of 5-HT and CGRP staining c orrelates with the onset of local, NEB-associated mitogenesis in fetal hamster airway epithelium. The second pattern begins after birth and is unique to the larynx and cartilaginous trachea. It involves differe ntiation of single cells which stain for CGRP but not 5-HT. Later, a p roportion also stain for CT. This pattern seemingly accounts for the p redominance of single cells in laryngotracheal epithelium of adult ani mals. In the third pattern, cells immunoreactive for peptide YY (PYY) differentiate, singly at first and later among cells of tiny pNEBs. Th is begins postnatally in alveoli, spreading centripetally with retrogr ade differentiation of alveolar epithelium back into the bronchiolar t erminations. Restricted distribution and lack of immunoreactivity for 5-HT, CGRP, or CT suggest that the PYY-positive endocrine cells form a regional subset performing special roles in pulmonary homeostasis.