Effect of Urotensin I on the ionic content of the plasma and the Gallbladder bile of Hoplias malabaricus (Bloch, 1974) (Teleostei, Characiformes, Erythrinidae)

In this study the urotensin I (UI) effect on the ionic content of the plasma and the gallbladder bile (GB) of Hoplias malabaricus , a freshwater teleost, was investigated, and action of this hormone on the water trasnport in the gallbladder was analyzed. Fishes were captured in ponds situated on the campus of the Federal University of Santa Maria (UFSM), Santa Maria, Southern Brazil. Blood was collected by puncture of caudal artery and GB was drained by the cystic duct. The intraperitoneal injection of UI (500 ng/kg) in H. malabaricus increased the Na + levels in the plasma and in the GB in relation to the saline-injected group. However, no change was observed in the levels of K + , Ca ++ and Mg ++ in the plasma and in the GB when UI was injected. The gallbladder of H. malabaricus has a mucosa-serosa water flow. On incubation of the serosa of the gallbladder sacs with UI (10 -8 M) there was a significant increase in water flow. Due to the fact that UI alters the GB Na + levels and the water flow in the gallbladder, it is possible that UI can be involved in the regulation of the bile composition on fishes.