In the oral ammonia liquid group, secretion of histamine was reduced, and after regiving of gastrin and muscarine, the secretion of histamine remained in an inhibitory state.
In Zollinger-Ellison syndrome, a tumor called gastrinoma secretes large amount of gastrin, that stimulates hydrochloric acid secretion in excess, and makes reflux even worse.
But coffee is a very complex beverage that affects all kinds of hormones and neurotransmitters like Adenosine, Dopamine, Cortisol, Adrenaline, Cholecystokinin, and Gastrin.
Most signals that increase stomach activity get the job done by increasing the secretion of gastrin, which then stimulates the release of other gastric fluids, as well as stomach-muscle activity.
At the same time, the secretion of gastrin is activated by other signals, like the rise in alkalinity caused by the stomach acid getting neutralized as it does its job.