Plasma arginine-vasotocin and hydroosmotic status of the terrestrial pit viper Bothrops jararaca.

Peaks corresponding to arg-vasotocin obtained by HPLC from Sep-Pak C18 column extracts of Bothrops jararaca plasma were identified by radioimmunoassay and amino acid analysis. Plasma vasotocin and protein levels, osmolality, and L-cystine-di-beta-naphthylamidase were also compared in snakes under normal hydration conditions with or without chronic administration of vasotocin or in the presence of chronic hydroosmotic challenges. Sep-Pak C18 and radioimmunoassay were validated for the extraction and determination of this peptide, respectively (about 80% recovery). EDTA presented a protective action on this recovery compared to the use of heparin as anticoagulant for snake blood. A reduction of vasotocin content related to the time of incubation of this peptide added to snake plasma was detected by radioimmunoassay. Snake plasma activity also on L-cystine-di-beta-naphthylamide indicated that this vasotocin-destroying effect was due to hydrolysis by a cystine-aminopeptidase-like activity. Plasma levels of vasotocin revealed an unexpected dispersion and absent correlation with plasma levels of osmolality. Measurable vasotocin in a large number of snakes associated with lower levels of l-cystine-di-beta-naphthylamidase in acute than in chronic salt loading suggested the role of this enzyme activity in long-term regulation of the vasotocin system in this snake.

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

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 evidenced 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.

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

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-ciruit current (SCC) and transepithelial potential difference (TPD) at a centrations of 1 and 10 mU/ml (to 50 per cent and 42 per cent 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, 50nM and 100 nM (to 85 per cent of control values), but increased these parameters at the concentration of 500 nM (to 115 per cent 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, reduced SCC and TPD. Should this hypothesis be correct, oxytocin would be important for freshwater adaptation, since it would increase absorption. The reduction of SCC and TPD in the posterior intestine A. anguilla induced by UII is evidence that this neurohormone is also important for freshwater adaptation in teleosts. Aldosterone did not show this effect probaly due to the lack of receptors in this organ.

L-cystine-di-beta-naphthylamidase activity in plasma of the snake Bothrops jararaca after chronic challenges of water balance.

Plasma protein, osmolality and L-cystine-di-beta-naphthylamidase activity were measured in Bothrops jararaca snakes submitted to normal hydration, water deprivation, water loading, salt loading or argvasotocin injections. Protein and osmolality were similar for male and female snakes in all treatments. Protein content was similar in all treatments, indicating the ability of the animals to maintain fluid balance between the vascular and extravascular compartment under osmotic challenges. Osmolality was increased in water-deprived and salt-loaded and was decreased in water-loaded animals compared with normally hydrated or argvasotocin-injected snakes. Enzymatic activity differed between males and females and was higher in salt-loaded females and in arg-vasotocin-injected females and males than in water-loaded snakes. A positive linear regression between osmolality and L-cystine-di-beta-naphthylamidase was obtained for female snakes (correlation coefficient = 0.6162, P < 0.01). The data show a role of arg-vasotocin in the consistent relationship between water balance and this sex-related aminopeptidase activity.

Effect of HCO-3 and pH on ion transport in the posterior intestine of the freshwater-adapted teleost Anguilla anguilla.

The intestinal mucosa may be exposed to acidic or alcaline solutions due to liberation of digestive secretions. In several situations blood pH may also change. Consequently, the effects of HCO-3, CO2, and pH variation of medium on the ion transport across the posterior intestine of the eel (Anguilla anguilla) adapted to freshwater were studied in terms of fractional values of short-circuit current (SCC), transepithelial potential difference (TPD) and conductance (G). Immature eels weighing 100-200 g were used. The control physiological solution contained: 118.5 mM NaCl, 25.0 mM NaHCO3, 3.0 mM CaCl2.2H2O, 4.7 mM KCl, 1.0 mM MgCl2.6H2O, 5.0 mM D-glucose, 10.0 mM D-mannitol, pH 7.80, ans was gassed with 98% O2-2% CO2. Control values (N = 21) were: SCC = 51.90 +/- 2.8 microA.cm-2, TPD = 2.33 +/- 0.1 mV, G = 22.43 +/- 0.6 mS.cm-2. At constant pH, the reduction of HCO-3 concentration to 50% and 10% did not alter the values of SCC and TPD, but G increased with HCO-3 reduction to 10%. In the absence of HCO-3, SCC, TPD and G (slightly) decreased, but 1.5 mM HCO-3 still maintained the ion transport within control values, at constant pH. Comparing pH values from 6.65 to 8.61, higher values of SCC and TPD were observed at pH 7.45, but were little affected below and above this pH. There was a significant correlation between pH and SCC and TPD values; from the regression equations (1) SCC was zero at pHs below 6.62 and above 8.78 and (2) TPD was zero below 6.50 and above 8.71.

Effect of HCO3 and pH on ion transport in the posterior intestine of the freshwater-adapted teleost Anguilla anguilla

The intestinal mucosa may be exposed to acidic or alcaline solutions due to liberation of digestive secretions. In several situations blood pH may also change. Consequently, the effects of HCO-3, CO2, and pH variation of medium on the ion transport acrross the posterior intestine of the eel (Anguilla anguilla) adapted to freshwater were studied in terms of fractional values of short-circuit current (SCC), transepithelial potential difference (TPD) and conductance (G). Immature eels weighing 100-200 g were used. The control physiological solution contained: 118.5 mM NaCl, 25.0 mM NaHCO3, 3.0 mM CaCl2.2H2O, 4.7 mM KCl, 1.0 mM MgCl2.6H2O, 5.0 mMD-glucose, 10.0 mM D-mannitol, pH 7.80, and was gassed with 98 percent O2-2 percent CO2. Control values(N = 21) were: SCC = 51.90 + or - 51.90 + or - 2.8 µA.cm-2, TPD = 2.33 + or - 0.1 mV, G = 22.43 + or - 0.6 mS.cm-2. At constant pH, the reduction of HCO-3 concentration to 50 percent and 10 percent did not alter the values of SCC and TPD, but G increased with HCO-3 reduction to 10 percent. In the absence of HCO-3, SCC, TPD and G (slightly) decreased, but 1.5 mM HCO-3 still maintained the ion transport within control values, at constant pH. Comparing PH values from 6.65 to 8.61, higher values of SCC and TPD were observed at PH 7.45, but were little affected below and above this pH. There was a significant correlation between pH and SCC and TPD values; from the regression equations (1) SCC was zero at pHs below 6.62 and above 8.78 and (2) TPD was zero below 6.50 and above 8.71

Ion transport across the isolated intestinal mucosa of Anguilla anguilla (Pisces).

The posterior intestine of freshwater-adapted Anguilla anguilla has a serosa negative transepithelial potential difference (TPD), and a current corresponding to the flow of negative current towards serosa. The TPD and the short-circuit current (SCC) were inhibited by Na+ and K+ withdrawal, and Cl- substitution or BA2+ addition inverts TPD and SCC, suggesting a Cl- and Na+ current mucosa-serosa, a K(+)-Cl- cotransport and a K+ channel in the mucosal side. The TPD and SCC were inhibited by ouabain, DIDS, furosemide and amiloride, indicating the presence of a Na(+)-K(+)-ATPase, and Cl-/HCO3-,Na(+)-K(+)-Cl- and Na+/H+ cotransporters.