C-type natriuretic peptie as a paracrine and an endocrine hormone

1.鳗鱼从淡水（FW）转移到海水（SW）后，血浆心钠素（ANP）和心室钠素（VNP）水平短暂升高。注射高渗溶液可显著提高血浆ANP和VNP水平，但血容量扩张剂的促分泌作用要小得多。在离体灌流的鳗鱼心脏中，增加灌注液渗透压后，ANP和VNP的分泌增加。这些结果表明，鳗鱼ANP和VNP的分泌以渗透压调节为主，渗透压刺激由心肌细胞自身感受.全身放射自显影显示鳃中有大量的~ <125>1H-eel ANP。放射性配体结合分析表明，鳗鱼鳃中的大多数ANP受体是清除型NPR-C，然而，鸟苷酸环化酶偶联的CNP特异性NPR-B也仅存在于FW鳗鱼的鳃中。这与SW鳗中NPR-B信息的表达量远低于FW鳗是一致的。ANP抑制饮水和肠道吸收的水和钠在FW和鳗鱼。ANP还抑制皮质醇的分泌，皮质醇是一种对SW适应很重要的鱼类盐皮质激素，仅在SW鳗鱼中引起抗利尿和尿钠排泄。表明心钠素在SW鱼体内可能是一种排钠激素.从牛蛙心室中分离出B型利钠肽（BNP）。因此，半水生两栖动物似乎有terapod型BNP没有鱼型VNP在他们的Ventriles。

1. Plasma atrial and ventricular natriuretic peptide (ANP and VNP) levels increased transiently after transfer of eels from fresh water (FW) to seawater (SW). Injection of hypertonic solutions markedly increased plasma ANP and VNP levels, but blood volume expanasion was a much smaller secretagogue in the eel. ANP and VNP secretion increased in isolated, perfused eel heart after prefusate osmolality was increased These results show that osmotic requlation dominates volemic requlation for ANP and VNP secretion in the eel, and osmotic stimulus was perceived by cardiocytes themselves.2. Whole-body autoradiography revealed dense accumulation of ^<125>I-eel ANP in the gill. Radio-ligand binding assay showed that most ANP receptors in the eel gill are clearance type NPR-C ; however, guanylate cyclase-coupled, CNP-specific NPR-B was also present in the gill of only FW eels. This is consistent with much less expression of NPR-B message in SW eels than in FW eels.3. ANP inhibits drinking and intestinal absorption of water and sodium in both FW and eels. ANP also inhibits secretion of cortisol, a fish mineralocorticoid important for SW adaptation, and causes antidiuresis and natriuresis only in SW eels. It seems that ANP is a sodium extruding hormone in SW fish.4. B-type natriuretic peptide (BNP) was isolated from the cardiac ventricle of bullfrog. Thus semiaquatic amphibians seem to have terapod-type BNP not fish-type VNP in their Ventriles.