Tsukada T, Takei Y
Ocean Research Institute, University of Tokyo, Tokyo 164-8639, Japan.
Zoolog Sci. 2001 Dec;18(9):1253-8. doi: 10.2108/zsj.18.1253.
Evidence has accumulated that atrial natriuretic peptide (ANP) plays important roles in sea-water adaptation in eels. However, the roles of the other two natriuretic peptides (CNP and VNP) in osmoregulation have not been examined yet. In the present study, the effects of homologous ANP, CNP and VNP were compared on plasma Na+ concentration (an indicator of plasma osmolality), hematocrit (an approximate indicator of blood volume) and drinking rate in freshwater- and seawater-adapted eels. In seawater eels, ANP and VNP, but not CNP, infused at 5 pmol/kg/min decreased plasma Na+ concentration and drinking rate and increased hematocrit. In freshwater eels, ANP and VNP failed to decrease plasma Na+ concentration but increased hematocrit to the same extent as in seawater eels. Inhibition of drinking was not detectable in freshwater eels because of little drinking before NP infusions. These results show that the effects of NPs on plasma Na+ concentration, drinking rate and hematocrit are mediated by NPR-A, since only ANP and VNP that bind with higher affinity to NPR-A are effective in seawater eels. The mechanisms of regulation of plasma Na+ concentration and hematocrit are unknown, but NPR-A is present in the responsible tissues for regulation of hematocrit in both freshwater and seawater eels. However, NPR-A may be absent in the tissues of freshwater eels that are responsible for regulation of plasma Na+ concentration.
已有证据表明，心房利钠肽（ANP）在鳗鱼适应海水环境中发挥重要作用。然而，另外两种利钠肽（CNP和VNP）在渗透调节中的作用尚未得到研究。在本研究中，比较了同源ANP、CNP和VNP对淡水适应和海水适应鳗鱼的血浆Na⁺浓度（血浆渗透压的指标）、血细胞比容（血容量的近似指标）和饮水率的影响。在海水鳗鱼中，以5 pmol/kg/min的速度注入ANP和VNP（而非CNP）可降低血浆Na⁺浓度和饮水率，并增加血细胞比容。在淡水鳗鱼中，ANP和VNP未能降低血浆Na⁺浓度，但血细胞比容升高的程度与海水鳗鱼相同。由于在注入利钠肽之前淡水鳗鱼几乎不饮水，因此未检测到对饮水的抑制作用。这些结果表明，利钠肽对血浆Na⁺浓度、饮水率和血细胞比容的影响是由NPR - A介导的，因为只有与NPR - A具有较高亲和力的ANP和VNP在海水鳗鱼中有效。血浆Na⁺浓度和血细胞比容的调节机制尚不清楚，但NPR - A存在于淡水和海水鳗鱼中负责调节血细胞比容的组织中。然而，在淡水鳗鱼中负责调节血浆Na⁺浓度的组织中可能不存在NPR - A。
