Gastric motor responses elicited by vagal stimulation and purine compounds in the atropine-treated rabbit.

1. The effects of vagal inhibitory stimulation and of purine compounds were studied in the rabbit stomach. 2. Gastric motility was assessed by the balloon method. Vagal nerves were electrically stimulated at the neck. Purine compounds were injected intra-arterially. 3. In the atropine-treated rabbit, vagal stimulation caused relaxant motor responses followed by a rebound contraction. 4. Among the purine compounds, only ADP and ATP caused relaxant motor responses similar to the effects of vagal inhibitory stimulation. However, the relaxation produced by ATP was more powerful than that due to ADP, especially at lower infusion rates. 5. Vagal inhibitory responses were recorded during and after infusion of ATP. When relaxation by ATP was fully developed, vagal inhibitory stimulation was ineffective. At the highest infusion rates of ATP, a depression of the vagal inhibitory motility was also observed after cessation of the infusion. 6. Relaxant responses to ATP and vagal inhibitory stimulation were not influenced by theophylline, scarcely affected by alpha,beta-methylene ATP, but were reduced or blocked by reactive blue 2. 7. The results are consistent with ATP being an inhibitory neurotransmitter in the stomach of the rabbit.