Gastric glands were isolated from rabbit gastric mucosa and incubated in the presence of secretin, cholecystokinin octapeptide (CCK-8), and in hyperosmolar medium. These agents all elicited a compound exocytotic response from the chief cells observed by electron microscopy. Responses to secretagogues yielded significantly higher values than controls at 2.5 min after exposure, and were essentially complete within 30 min. The response to hyperosmolarity was more gradual and continued over a 60 min period. Glands incubated in hyperosmolar medium were still capable of responding to secretagogues, and the combination was additive. The results indicate that both secretagogues, which initiate specific receptor mediated events, and hyperosmolarity, which causes a more generalized change in the cells, result in pepsinogen-granule release by compound exocytosis.
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