A new approach for functions of classical osmoregulatory hormones in fishes

在海水（SW）驯化的广盐性鱼类，胃肠道的离子/水的渗透性一般大于淡水（FW）驯化的鱼。SW鱼的食道上皮为单层柱状，而FW鱼的食道上皮为分层状。我们之前已经证明，广盐性虾虎鱼和罗非鱼的食管上皮细胞在FW鱼中显示出升高的细胞增殖，但在SW适应期间发生凋亡（1）。对虾虎鱼进行体内皮质醇处理不仅刺激了食管上皮细胞的凋亡，还刺激了细胞增殖，而11-脱氧皮质酮（推定的硬骨鱼盐皮质激素）（2）对细胞增殖或凋亡没有任何影响（3）。为了了解皮质醇对食管细胞周转可能的双重作用模式，我们开发了一种培养广盐性青鳉（Oryzias latipes）食管组织外植体的方法。寡核苷酸检测试验和氧化还原指示剂分别用作细胞凋亡和细胞增殖的指示剂。在培养基中加入皮质醇（10 nM）8天，刺激青鳉食道的细胞凋亡，这是一种公认的糖皮质激素功能。在较高剂量（100和1000 nM）下未观察到任何影响。另一方面，添加皮质醇（1000 nM）8天诱导细胞增殖。在生理范围内（10-1000 nM），细胞增殖反应呈剂量依赖性。因此，皮质醇可能不仅直接诱导细胞凋亡，而且可能通过糖皮质激素受体直接诱导广盐性鱼类食管处的细胞增殖，因为糖皮质激素受体对皮质醇的敏感性低于盐皮质激素受体（2）。参考文献（1）Takahashi et al.（2006）。J. Comp. Physiol. B，176，463-468. (2)Prunet等人（2006年）。内分泌综合征，147，17-23。(3)Takahashi等人（2006年）。生命科学，79，1873-1880.

In the seawater (SW)-acclimated euryhaline fishes, the ion/water permeability of the gastrointestinal tract is generally greater than that of freshwater (FW)-acclimated fish. The esophageal epithelium of SW fishes is simple columnar in form, whereas that of FW fishes is stratified. We have previously shown that esophageal epithelium of a euryhaline goby and tilapia displays elevated cell proliferation in FW fish, but undergoes apoptosis during SW acclimation (1). In-vivo cortisol treatment of the goby stimulated not only the apoptosis but also cell proliferation in the esophageal epithelium, whereas 11-deoxycorticosterone, the putative teleostean mineralocorticoid (2), did not have any impact on cell proliferation or apoptosis (3). To understand the possible dual mode of action of cortisol on the esophageal cell turnover, we have developed a method of culture tissue explants of the esophagus from euryhaline medaka (Oryzias latipes). Oligonucleotide detection assay and an oxidation-reduction indicator were used as indicators of apoptosis and cell proliferations, respectively. Addition of cortisol (10 nM) to the culture medium for 8 days stimulated apoptosis in the medaka esophagus, as a well-established glucocorticoid function. No effects were seen at higher doses (100 and 1000 nM). On the other hand, addition of cortisol (1000 nM) for 8 days induced the cell proliferation. The response of cell proliferation was dose-dependent within physiological range (10-1000 nM). Thus, it is likely that cortisol induces directly not only apoptosis but also cell proliferation at the esophagus in euryhaline fishes, possibly via glucocorticoid receptor, since glucocorticoid receptor shows lower sensitivity for cortisol than mineralocorticoid receptor (2).References(1) Takahashi et al. (2006). J. Comp. Physiol. B, 176, 463-468.(2) Prunet et al. (2006). Gen. Comp. Endocrinol., 147, 17-23.(3) Takahashi et al. (2006). Life Sci., 79, 1873-1880.