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 t… Show more
“…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.…”
Section: Effect Of Urotensin Ii/urotensin Ii-related Peptide On Thmentioning
“…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.…”
Section: Effect Of Urotensin Ii/urotensin Ii-related Peptide On Thmentioning
“…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 10-100nmoll -1 , but stimulated the I sc at 500nmoll -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.…”
SUMMARYThe peptide urotensin II (UII) and its receptor (UT) mediate cardiovascular and renal effects in both mammals and fishes. In both groups, vasopressor and diuretic responses predominate, although, in mammals, some secondary vasodilatation is found, mediated by secondary release of nitric oxide or prostacyclin. In fishes, gill extrusion of NaCl is inhibited by UII, but a single study has determined that UT is expressed in gill vasculature, not on the epithelium that mediates the transport. To begin to clarify the pathways involved in UII inhibition of gill transport, we have cloned the cDNA encoding UII and UT from the euryhaline killifish (Fundulus heteroclitus L.) gill and spinal cord, quantified UT mRNA expression in various tissues and measured relative expression in gill tissue from fish acclimated to seawater (SW) vs fresh water (FW). We have also localized UT in the gill epithelium, and measured the effect of UII on ion transport across the opercular epithelium. We found that both UII and UT are synthesized in the gill of F. heteroclitus and that gill UT mRNA levels are ~80% higher in SW-vs FW-acclimated individuals. In addition, UII inhibits NaCl transport across the opercular epithelium in a concentration-dependent manner, and this inhibition is at least partially mediated by both nitric oxide and a prostanoid.
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“…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).…”
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.
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