Involvement of Drinking and Intestinal Sodium Absorption in Hyponatremic Effect of Atrial Natriuretic Peptide in Seawater Eels
Involvement of Drinking and Intestinal Sodium Absorption in Hyponatremic Effect of Atrial Natriuretic Peptide in Seawater Eels
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DOI：
10.2108/zsj.22.77
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
T. Tsukada;J. Cliff Rankin;Y. Takei
中科院分区：
文献类型：
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作者：
T. Tsukada;J. Cliff Rankin;Y. Takei
心房利钠肽（ANP）降低鳗鱼血浆钠浓度，促进海水适应。低钠血症很可能是由于鳃对Na+的排出增加所致，但其机制尚未明确。本研究利用同位素~（22）Na初步研究了ANP对鳃钠离子流出的影响。然而，输注低钠剂量的ANP（5 pmol·kg-1·min-1）不会改变外排率。因此，我们试图研究ANP介导的低钠血症是否是由环境中Na+摄取减少引起的。由于饮酒量的减少与一定程度的低钠血症高度相关，因此清醒的SW鳗鱼以正常的饮酒速率将稀释的SW注入胃中，以抵消ANP的抗渴作用。在此方案下，ANP的低钠血症效应被消除。然后，我们通过测量沿着消化道的腔内液体的离子组成的变化来检查消化道中Na+吸收的部位。由于Na+在食管和前/中肠吸收，因此在每个部位制备囊，并在清醒的SW鳗鱼中原位检查ANP的影响。ANP输注没有改变Na+在食管的吸收，但它大大减少了在肠道的吸收。与我们以前的发现，ANP不改变肾脏Na+排泄，我们建议，ANP降低血浆Na+浓度SW鳗鱼抑制饮水和随后的吸收Na+的肠道。
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.