PILOCARPINE STIMULATION OF BRONCHIOLAR CLARA CELL SECRETION

Abstract

Fasted rats were given a single cholinergic subcutaneous injection of pilocarpine and sacrificed from 30 min to 24 h later. Secretory granules were extruded by Clara cells as early as 30 min after pilocarpine administration. Simultaneously and thereafter, Clara cells displayed dilated cisternae of endoplasmic reticulum and active assembly of secretory granules at the Golgi complex. After 1-2 h, new secretory granules reached the cell surface and were discharged into the bronchiolar lumen by exocytosis. At 4 h the Clara cell organelles appeared quiescent. Complete cell recovery apparently occurred by 12-24 h after pilocarpine administration. The accelerated secretion by Clara cells with pilocarpine provides an evidence of their exocrine character and the exocytotic secretory mechanism. The morphologic data indicate that the production and secretion by Clara cells may be controlled by neurohumoral mechanism.