Effect of urotensin II on water and ion fluxes in the intestine, Gallbladder and urinary bladder of the freshwater teleost, Hoplias malabaricus

The effect of urotensis II (UII) on the flow of water and ions (Na + , K + , Ca 2+ and Mg 2+ ) in the medium intestine, rectum, gallbladder and urinary bladder of the freshwater teleost Hoplias malabaricus was investigated. The flow of water of all the studied organs of H. malabaricus is from mucosa to serosa (absorption). UII increased the flow of water in the medium intestine, gallbladder and urinary bladder. The medium intestine, gallbladder and urinary bladder also absorb Na + . K + is absorbed in the rectum and secreted in the urinary bladder. UII did not affect the flow of Na + and K + in the studied portions. All studied portions secreted Ca2+, and UII reduced the fow of this ion in the medium intestine and urinary bladder. The flow of Ca2+ in the rectum and gallbladder was not altered by UII. There is no significant flow of Mg 2+ in the studied portions, and UII stimulated the absorption of this ion in the medium intestine and urinary bladder. This study indicates that UII participates in the controlo f osmoregulatory organs of H. malabaricus . This study also raises the possibility that UII may be involved in the regulation of the composition of the bile fishesm, since it alters water and Ca2+ fluxes in the gallbladder of H. malabaricus .