Pancreatic peptides regulate C1<sup>−</sup> secretion in the marine teleost gill

Hormonal regulation of the ionoregulatory function of the branchial epithelium in marine teleosts has been investigated using an isolated gill preparation of the seawater-adapted flounder Platichthys flesus. Agents which are assumed to elevate the effective intracellular concentration of cyclic AMP caused a stimulation of C1− secretion as determined by measurement of the transepithelial electrical potential difference in the isolated gill. The pancreatic endocrine glucagon may act as an endogenous regulator of ion excretion in the gill as this peptide stimulated the transepithelial potential. Another islet peptide, somatostatin, inhibited branchial electrogenic ion transport. Attempts to investigate the mode of action of these peptides by measuring cyclic AMP levels in isolated gills were unsuccessful, since it appears that the pool of cyclic nucleotide which specifies the epithelial C1− transport rate is small compared to total cyclic AMP content. A second approach investigating the ability of somatostatin to inhibit the transepithelial potential in gills stimulated by different secretagogues suggested dual modes of action for this peptide.

利用海水适应型比目鱼（Platichthys flesus）的离体鳃制备物，对海水硬骨鱼鳃上皮离子调节功能的激素调节进行了研究。通过测量离体鳃的跨上皮电位差确定，那些被认为可提高细胞内环磷酸腺苷（cyclic AMP）有效细胞内浓度的物质会刺激Cl⁻分泌。胰腺内分泌的胰高血糖素可能作为鳃中离子排泄的内源性调节剂，因为这种肽刺激了跨上皮电位。另一种胰岛肽——生长抑素抑制鳃的生电离子转运。通过测量离体鳃中环磷酸腺苷水平来研究这些肽的作用方式的尝试未获成功，因为与环磷酸腺苷总含量相比，决定上皮Cl⁻转运速率的环核苷酸库似乎较小。第二种方法是研究生长抑素抑制由不同促分泌素刺激的鳃跨上皮电位的能力，结果表明该肽具有双重作用模式。