Study of osmoregulation in birds

长期以来，渗透受体在渗透调节中的作用一直不清楚。近年来，水通道蛋白4（AQP4）被认为是一种潜在的渗透受体，但尚无明确的证据。我们克隆了鸡AQP4 cDNA并确定了其序列。我们分析了鸡下丘脑中与渗透刺激相关的AQP4基因表达。AQP4基因在鸡体内的表达因高渗而升高。因此，这些结果提示AQP4可能与鸡的渗透受体有关。由于在哺乳动物中没有观察到高渗引起AQP4基因表达的增加，因此这种增加是鸡特有的。比较断水后蛋鸡和肉鸡精氨酸缩宫素（AVT）基因表达，两种品系鸡体重下降，血浆渗透压升高。在AVT基因表达方面，蛋鸡AVT基因表达增加，肉鸡AVT基因表达不增加。结果表明，两种菌株的渗透调节机制存在一定差异。神经肽Y（NPY）一直被认为在摄食行为中起重要作用。但在缺水后，NPY基因在鸡体内的表达增加。因此，这些数据表明NPY在鸡体内水分平衡中起着关键作用。

For long time, it has been not clear about the osmoreceptor on the osmoregulation. Recently, aquaporin 4(AQP4) has been a candidate as an osmoreceptor, but there are no clear evidence about that. We cloned chicken AQP4 cDNA and determined its sequence. We analyzed the gene expression of AQP4 in the chicken hypothalamus in related with osmostimulation. AQP4 gene expression in the chicken increased by hyperosmolality. Threrefore, these results suggest that AQP4 may involve osmoreceptor in the chicken. Since there are no observations about the increase of AQP4 gene expression by hyperosmolality in the mammals, such increase is specific thing in the chicken.Comparing arginine vasotocin(AVT) gene expression between layer and broiler strain after water deprivation, both strains chick decreased body weights and increased plasma osmolality. On AVT gene expression, AVT gene expression increased in layer but not in broiler. These results suggested that there was some different mechanism of osmoregulation between two strains.It has been considered that neuropeptide Y(NPY) is a important role for feeding behavior. But, after water deprivation, NPY gene expression increased in the chicken. Therefore, these data suggest that NPY has a pivotal role on the water homeostasis in the chicken.