Department of Avian Endocrinology, Gifu University, Yanagido, Gifu, Japan.
Poult Sci. 2011 Nov;90(11):2565-72. doi: 10.3382/ps.2010-01328.
The present study was performed to elucidate whether the angiotensin II (ANG II) receptor exists in the plasma membrane fraction of the neurohypophysis in hens, to estimate the time of action of ANG II on the neurohypophysis before and after oviposition, and to examine relationships between the action of ANG II on the neurohypophysis and those of estrogen and prostaglandin F(2α) (PGF(2α)) in relation to arginine vasotocin (AVT) release. The specific binding had a binding specificity to chicken ANG II (cANG II), reversibility, and saturation in the [(125)I]cANG II binding assay. Scatchard analysis revealed that the binding sites are of a single class. The equilibrium dissociation constant (K(d)) obtained by kinetic analysis and Scatchard analysis suggested a high affinity, and the maximum binding capacity (B(max)) obtained by Scatchard analysis suggested a limited capacity. These results suggest that an ANG II receptor exists in the neurohypophysis of hens. The K(d) and the B(max) value was significantly smaller in laying hens than in nonlaying hens, which suggests that bindings of the cANG II receptor change, depending on the difference in laying condition. Values of the K(d) and the B(max) decreased approximately 15 min before oviposition in laying hens, and decreased 1 h after an intramuscular injection of estradiol-17β and 5 min after an intravenous injection of cANG II in nonlaying hens. The amount of specific binding of PGF(2α) receptor in the neurohypophysis also decreased and AVT concentration in blood increased after the cANG II injection. It seems likely that the action of cANG II in the neurohypophysis increases due to the effect of estrogen approximately 15 min before oviposition, and the cANG II action stimulates AVT release through the increase in the PGF(2α) action in this tissue.
本研究旨在阐明血管紧张素 II（ANG II）受体是否存在于母鸡神经垂体的质膜部分，估计 ANG II 在排卵前后作用于神经垂体的时间，并研究 ANG II 对神经垂体的作用与雌激素和前列腺素 F2α（PGF2α）之间的关系，以及它们与精氨酸加压素（AVT）释放的关系。在 [(125)I]cANG II 结合测定中，特异性结合具有结合特异性、可逆性和饱和性。Scatchard 分析表明，结合位点是单一类型的。通过动力学分析和 Scatchard 分析获得的平衡解离常数（Kd）表明具有高亲和力，通过 Scatchard 分析获得的最大结合容量（Bmax）表明具有有限的容量。这些结果表明，ANG II 受体存在于母鸡的神经垂体中。在产蛋母鸡中，Kd 和 Bmax 值明显小于非产蛋母鸡，这表明 cANG II 受体的结合随产蛋状态的差异而变化。在产蛋母鸡中，大约在排卵前 15 分钟，Kd 和 Bmax 值降低，在非产蛋母鸡中，静脉注射 cANG II 后 5 分钟，Kd 和 Bmax 值降低。在注射 cANG II 后，神经垂体中 PGF2α 受体的特异性结合量也减少，血液中 AVT 浓度增加。看来，大约在排卵前 15 分钟，由于雌激素的作用，cANG II 在神经垂体中的作用增加，而 cANG II 作用通过增加该组织中 PGF2α 的作用来刺激 AVT 释放。
