The in vitro effect of acetylcholine, pilocarpine, serotonina and adrenaline on gastric motility of the teleost Hoplias malabaricus was studied. The stomach of this specieshas spontaneous contractile activity, with no relationship between tension or frequency of contrations and fish weight. Acetylcholine reduced the frequency of contrations at higher concentrations, but had not effect at lower concentrations. The higher doses of this drug increased the tension and tonus of the contrations. Pilocarpine increased the frequency and tension of contractions at higher concentrations, but had not effect at lower concentrations, and increased tonus only at the concentration of 10-7 M. A significant correlation between the doses of acetylcholine and policarpine and tension of gastric contractions was found. Adrenaline and serotonina had not effect on the frequency, tension and tonus of the stomach contractions. The results obtained with acetylcholine and policarpine demonstrate that the stomach of H. malabaricus has muscarinic cholinoceptors. The results obtained with adrenaline and serptonin did not demonstrate the existence of adrenergic or serotonergic receptors in the stomach of this species.
