Involvement of Drinking and Intestinal Sodium Absorption in Hyponatremic Effect of Atrial Natriuretic Peptide in Seawater Eels
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Accession number;05A0211610
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| Title;Involvement of Drinking and Intestinal Sodium Absorption in Hyponatremic Effect of Atrial Natriuretic Peptide in Seawater Eels |
| Author;
TSUKADA T
(Univ. Tokyo, Tokyo, Jpn)
RANKIN J C
(Huddersfield Univ., Huddersfield, Gbr)
TAKEI Y
(Univ. Tokyo, Tokyo, Jpn)
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Journal Title;Zool Sci
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Journal Code:F0012B
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ISSN:0289-0003
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VOL.22;NO.1;PAGE.77-85(2005)
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| Figure&Table&Reference;FIG.8, TBL.1, REF.36 |
| Pub. Country;Japan |
| Language;English |
| Abstract;Atrial natriuretic peptide (ANP) decreases plasma Na+ concentration and promtes seawater (SW) adaptation in eels. The hyponatremia may most probably be caused by increased branchial extrusion of Na+, but the mechanism has not been determined yet. The present study examined initially the effects of ANP on branchial Na+ efflux in vivo using isotopic 22Na. However, the efflux rate was not altered by infusion of a hyponatremic dose of ANP (5 pmol kg-1 min-1). Therefore, we sought to examine whether the ANP-mediated hyponatremia is caused by a decrease in the uptake of Na+ from the environment. Since a decrease in drinking was highly correlated with a degree of hyponatremia, conscious SW eels were infused with dilute SW into the stomach at a normal drinking rate to offset the antidipsogenic effect of ANP. Under this regimen, the hyponatremic effect of ANP was abolished. Then, we examined the site of Na+ absorption in the alimentary tract by measuring the changes in ion composition of intraluminal fluid along the tract. Since Na+ was absorbed at the esophagus and anterior/middle intestine, a sac was prepared at each site and the effects of ANP were examined in situ in conscious SW eels. ANP infusion did not alter Na+ absorption at the esophagus, but it profoundly reduced the absorption at the intestine. Together with our previous finding that ANP does not alter renal Na+ excretion, we propose that ANP reduces plasma Na+ concentration in SW eels by inhibiting drinking and subsequent absorption of Na+ by the intestine. (author abst.) |
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