A new approach for functions of classical osmoregulatory hormones in fishes

在海水（SW）驯化的广盐鱼类中，胃肠道的离子/水渗透性通常大于淡水（FW）驯化的鱼类。SW鱼的食管上皮呈单柱状，FW鱼的食管上皮呈分层状。我们之前的研究表明，广盐虾虎鱼和罗非鱼的食管上皮细胞在FW鱼中增殖升高，但在SW驯化过程中发生凋亡(1)。虾虎鱼体内皮质醇处理不仅刺激了细胞凋亡，还刺激了食管上皮细胞增殖，而11-脱氧皮质酮，假定的骨矿皮质激素(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道细胞更新可能的双重作用模式，我们开发了一种培养食道组织外植体的方法，该方法来自大叶菜（Oryzias latipes）。寡核苷酸检测法和氧化还原指示剂分别作为细胞凋亡和细胞增殖的指示剂。将皮质醇（10 nM）添加到培养基中8天，刺激medaka食道细胞凋亡，这是一种公认的糖皮质激素功能。在更高剂量（100和1000 nM）下未见影响。另一方面，添加皮质醇（1000 nM） 8天可诱导细胞增殖。在生理范围（10 ~ 1000 nM）内，细胞增殖反应呈剂量依赖性。因此，皮质醇很可能不仅直接诱导了广盐鱼食道细胞的凋亡，而且还直接诱导了细胞的增殖，可能是通过糖皮质激素受体，因为糖皮质激素受体对皮质醇的敏感性低于矿皮质激素受体(2)。参考文献(1)Takahashi等人（2006）。J.比较物理。B, 176, 463-468。(2) Prunet et al. （2006）内分泌激素。， 147, 17-23。(3) Takahashi等人（2006）。生命科学。， 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.