Mechanisms Controlling Stomach Volume of the Atlantic Cod (gadus Morhua) following Gastric Distension

1. Inflation of the cardiac stomach of the cod induced rhythmic contractions of the muscles and a slow increase in stomach volume towards a maximum. After deflation, the stomach remained relaxed and easily distensible for one or more hours. Section of the vagal tracts to the stomach did not change the response. 2. Inflation in vitro produced a somewhat faster relaxation and a much faster recovery to the pre-distended state than occurred in vivo. Stimulation of the cut ends of the vagus raised gastric tone and increased resistance to distension, an effect mediated by cholinergic nerves. 3. Tetrodotoxin and atropine relaxed the stomach so that distension was rapid and the maximal volume increased, revealing slower, possibly myogenic, contractions. 4. The 5-hydroxytryptamine (5-HT) antagonist methysergide, vasoactive intestinal polypeptide (VIP), met-enkephalin and neurotensin did not affect the responses to distension. Somatostatin abolished spontaneous contractions in the resting stomach and lowered gastric tone, but did not further affect the responses to distension. 5. In conclusion, cholinergic nerves maintain gastric tone in the cod. 5-HT neurones are absent in the cod stomach, and there are no indications of a 5-HT/VIP-controlled mechanism operating during distension. The effect of somatostatin differs from that in rainbow trout. 6. For comparison with trout and cod, responses to in vivo gastric distension are also described for the flatfish Scophthalmus maximus, Scophthalmus rhombus, Limanda limanda and Pleuronectes platessa.