We aimed to establish whether gastric mucosal mast cells undergo degranulation during normal postnatal development and to correlate this with gastric electrical parameters, paracellular permeability, and macromolecular absorption. Sprague-Dawley rats were studied between 10 and 30 days after birth. Gastric mucosal mast cell degranulation occurred and was maximal on days 15 and 17, measured by histology and gastric and serum levels of rat mast cell protease II. Short-circuit current, transepithelial conductance, and permeability of voltage-clamped glandular stomach were elevated in younger animals, falling with age except for a transient but significant increase in conductance and permeability at 17 days, closely correlated with maximal mast cell degranulation. Macromolecular uptake was significantly increased in animals aged 10-15 days. Concanavalin A and antigen-induced mast cell degranulation increased conductance and permeability in vitro in younger animals. We conclude that 1) gastric mucosal mast cells degranulate during development, 2) the neonatal stomach has increased permeability and uptake of macromolecules, and 3) gastric mucosal mast cell degranulation during development may affect mucosal permeability.
