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，血浆心房和心室利钠肽（ANP和VNP）水平瞬间升高。注射高渗溶液可显著提高血浆ANP和VNP水平，但在鳗鲡中，血容量扩张的作用要小得多。在离体灌注的鳗鱼心脏中，预充液渗透压升高后，ANP和VNP的分泌增加，表明渗透调节主导了鳗鱼ANP和VNP分泌的容量调节，渗透刺激可被心肌细胞自身感知。全身放射自显像显示鳗鱼鳃内ANP密集积聚^<125 bb0。放射性配体结合试验表明，鳗鲡鳃中ANP受体多为清除率型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。这与西南鳗鲡的NPR-B信息表达量远低于西南鳗鲡的情况一致。ANP抑制FW和鳗鱼饮水和肠道对水和钠的吸收。ANP还抑制皮质醇的分泌，皮质醇是一种鱼类矿物质皮质激素，对SW适应很重要，仅在SW鳗鱼中引起抗利尿和尿钠。ANP可能是SW鱼体内的一种钠挤出激素。从牛蛙心室中分离到b型利钠肽（BNP）。因此，半水生两栖动物的腹部似乎有四足类BNP而不是鱼类VNP。

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.