Study of osmoregulation in birds

长期以来，对渗透压调节上的渗透压感受器的研究一直不清楚。最近，水通道蛋白4(AQP4)被认为是渗透压受体的候选分子，但没有明确的证据表明这一点。我们克隆了鸡AQP4基因，并测定了其序列。我们分析了AQP4在鸡下丘脑中与渗透刺激相关的基因表达。高渗诱导鸡AQP4基因表达增强。这些结果提示，AQP4可能与鸡的渗透压感受器有关。由于没有观察到AQP4基因在哺乳动物中的表达增加，这种增加在鸡中是特有的。比较水分剥夺后蛋鸡和肉鸡品系的精氨酸血管催产素(AVT)基因的表达，两个品系的鸡都降低了体重，增加了血浆渗透压。在AVT基因表达上，蛋鸡AVT基因表达增加，肉鸡AVT基因表达不增加。这些结果表明，两个品系之间存在着不同的渗透调节机制。神经肽Y(NPY)被认为在摄食行为中起着重要作用。但是，缺水后，鸡的NPY基因表达增加。因此，这些数据表明NPY在鸡体内的水分动态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.