Changes in the electrophysiological parameters of the posterior intestine of Anguilla anguilla (Pisces) induced by oxytocin, urotensin II and aldosterone

Abstract

In view of the importance of the intestine in the osmoregulation of freshwater fishes, we determined the effects of oxytocin, urotensin II (UII), and aldosterone added to the serosal side of the isolated posterior intestine of the freshwater-adapted teleost Anguilla anguilla on electrophysiological parameters. Oxytocin decreased the short-circuit current (SCC) and transepithelial potential difference (TPD) at concentrations of 1 and 10 mU/ml (to 50% and 42% of control values, respectively), but did not alter these parameters at a concentration of 0.1 mU/ml. UII reduced SCC and TPD at concentrations of 10 nM, 50 nM and 100 nM (to 85% of control values), but increased these parameters at the concentration of 500 nM (to 115% of control values). Aldosterone did not alter SCC or TPD at the concentrations tested (10 nM and 100 nM). Oxytocin may open Na + channels in the apical membrane, allowing the flow of Na + to the serosa, reducing SCC and TPD. Should this hypothesis be correct, oxytocin would be important for freshwater adaptation, since it would increase Na + absorption. The reduction of SCC and TPD in the posterior intestine of A. anguilla induced by UII is evidence that this neurohormone is also important for freshwater adaptation in teleosts. Aldosterone did not show this effect probably due to the lack of receptors in this organ.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, Urotensin II–Related Peptide, and Their Receptor: From Structure to Function

“…Electrophysiological studies indicate that UII exerts a dual effect on the isolated posterior intestine of freshwater-adapted European eel Anguilla anguilla: UII reduces short-circuit current and transepithelial potential difference at concentrations ranging from 10 to 100 nM and increases these parameters at a concentration of 500 nM (Baldisserotto and Mimura, 1997). Altogether, these observations substantiate a role of UII in osmoregulation in fish.…”

Urotensin II and its receptor in the killifish gill: regulators of NaCl extrusion

“…In the same species, UII stimulated active Na + uptake by both the urinary bladder in animals acclimated to seawater (SW) (Loretz and Bern, 1981) and the posterior intestine in animals acclimated to 5% SW (Loretz et al, 1985). In contrast, UII inhibited the I sc across the posterior intestine of FW-acclimated Anguilla anguilla at concentrations of 10-100nmoll -1 , but stimulated the I sc at 500nmoll -1 (Baldisserotto and Mimura, 1997). Given the strategies of hyper-osmoregulation (Evans and Claiborne, 2009), these responses to UII appear to be adaptive for teleosts in FW.…”

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

“…A specific role for UII in freshwater adaptation was suggested, since the effects of this neurohormone on some osmoregulatory organs would led to an increase of plasma ion concentration (Loretz et aI., 1981;Baldisserotto, 1991). UII inhibited CIsecretion by the skin of Gillichthys mirabilis (Marshall and Bem, 1981) and opercular membrane of Oreochromis mossambicus (Foskett and Hubbard, 1981;Loretz et aI., 1981), change of water, and/or Na+ and CI-absorption in the intestine of G. mirabilis (Loretz et aI., 1983), O. mossambicus (Mainoya andBem, 1982, 1984) and Anguilla anguilla (Baldisserotto and Mimura, 1996), and increased diuresis in Aj7guilla japonica (Chan, 1975). In contrast, UII enhances the reabsorption of Na+ in the urinary bladder of G. mirabilis (as occurs in seawateradapted specimens) and inhibited prolactin secretion (the most important hormone in freshwater adaptation) (Rivas et aI., 1986).…”