The effect of urotensis II (UII) on the flow of water and ions (Na+, K+, Ca2+ and Mg2+) 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 Mg2+ 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.
This study analyzed the effect of the injection of urotensin I (UI) and urotensis II (UII) on the stabilization of the transepithelial potential difference (TPD) of the medium intestine, rectum, and gallbladder of Hoplias malabaricus to investigate if the transport of ions in these organs is affected "in vivo" by these neurohormones. The TPD of the medium intestine, rectum and gallbladder was serosa positive, and remained constant since the first measurement. The injection of both urotensins did not alter the stabilization of the TPD of the medium intestine and rectum when compared with saline-injected group. The injection of UI increased the TPD of the gallbladder in the beginning (0-10 min) of the stabilization period and in the interval of 20-30 min of the stabilization period when fishes were killed 2h and 4h after the injection, respectively, in relation to saline-injected group. The UII injection increased the TPD of the gallbladder only in the beginning (time 0) of the stabilization period in relation to saline when fishes were killed 2h after the injection. No changes in the TPD of the studied organs were detected when fishes were killed 4h after the injection of UII. This study confirms the hypothesis that UI and UII can participate in the regulation of the composition of the bile of fishes, since the injection of both hormones altered the TPD of the gallbladder of H. malabaricus.
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 (10-8M) 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.
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