Pilocarpine stimulation of the bronchiolar Clara cell secretion.

Fasted rats were given a single cholinergic subcutaneous injection of pilocarpine and sacrificed from 30 minutes to 24 hours later. Secretory granules were extruded by Clara cells as early as 30 minutes 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 to 2 hours, new secretory granules reached the cell surface and were discharged into the bronchiolar lumen by exocytosis. At 4 hours the Clara cell organelles appeared quiescent. Complete cell recovery apparently occurred by 12 to 24 hours 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.