Involvement of drinking and intestinal sodium absorption in hyponatremic effect of atrial natriuretic peptide in seawater eels.

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.

• Authors: Takehiro Tsukada, J Cliff Rankin, Yoshio Takei
• Journal: Zoological science (Zoolog Sci) Vol. 22 Issue 1 Pg. 77-85 (Jan 2005) ISSN: 0289-0003 [Print] Japan
• PMID: 15684587 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Sodium Radioisotopes
• Atrial Natriuretic Factor

Topics

• Analysis of Variance
• Anguilla (metabolism, physiology)
• Animals
• Atrial Natriuretic Factor (metabolism)
• Biological Transport, Active
• Drinking (physiology)
• Hyponatremia (metabolism)
• Intestinal Mucosa (metabolism)
• Ion Transport
• Japan
• Seawater
• Sodium Radioisotopes (blood, metabolism)
• Water-Electrolyte Balance (physiology)