Dopamine as a possible neurotransmitter in gastric relaxation

In dogs with gastric fistulas, intragastric pressure was measured with a flaccid ballon containing 500 ml of water. Graded doses of dopamine caused graded decreases in intragastric pressure. The effect was blocked by pimozide or by metoclopramide but was not significantly affected by phenoxybenzamine, propranolol, guanethidine, or FLA-63 (a beta-hydroxylase inhibitor). Pretreatment with metoclopramide or with pimozide shifted the volume-pressure diagram of the stomach to the left; that is, at any given volume the pressure was greater after than before these drugs. In dogs with vagally innervated gastric pouches and gastric fistulas, feeding for 1 min (while allowing the food to leave the stomach through the gastric fistula) caused a prompt decrease in pressure in the pouch that lasted for about 5 min. Pretreatment with metoclopramide decreased the magnitude and duration of this receptive relaxation. It is concluded that these findings are consistent with (but do not establish) the hypothesis that dopamine is the neurotransmitter for receptive relaxation of the stomach, because dopamine mimics receptive relaxation, and dopamine antagonists partially block reflexly induced receptive relaxation.