Intraduodenal fat and amino acids activate gallbladder motility in the rainbow trout, Oncorhynchus mykiss.

The effects on gall bladder motility of intraduodenal injections of fat (cod liver oil) and amino acids were investigated in rainbow trout, Onchorhynchus mykiss, in vivo. Fat (1 ml/kg, 15 min) increased basic tonus of the gallbladder by 79% and frequency of contractions by 53%; both effects were antagonized by pretreatment with atropine (1.2 mg/kg). The amino acid mixture similarly increased tonus and frequency of contractions of the gallbladder smooth muscle by 63 and 109%, respectively. The effects were mimicked by intraarterial infusion of cholecystokinin (100 pmol-1 nmol/kg-hr). It is concluded that the presence of oil and amino acids in the duodenum stimulates rainbow trout gallbladder motility and tension, possibly by a release of cholecystokinin, and that the effect of oil, as for cholecystokinin, involves a cholinergic pathway.