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Properties of estrogen binding components in the plasma membrane of neurohypophysis in hens and changes in its binding before and after oviposition

Department of Avian Endocrinology, Gifu University, Yanagido, Gifu 501-1193, Japan

¹ Corresponding author: kawasima{at}gifu-u.ac.jp

The present study was performed to elucidate whether the estrogen binding component regarded as a receptor exists in the plasma membrane fraction of neurohypophysis in hens and whether the binding of receptor changes with relation to oviposition. The specific binding for estradiol-17β (E₂) in the neurohypophysis of hens was demonstrated by the use of radioligand binding assays on the plasma membrane fraction of the tissue. The binding to [³H]E₂ had a binding specificity to E₂ and diethylstilbestrol, reversibility, and saturation. Scatchard analysis revealed that the binding sites are of a single class. The equilibrium dissociation constant obtained by Scatchard analysis and kinetic analysis suggested a high affinity, and the maximum binding capacity obtained by Scatchard analysis suggested a limited capacity. These properties are characteristics of a receptor, which suggests that an estrogen receptor exists in the plasma membrane of hen neurohypophysis. The equilibrium dissociation constant value of estrogen receptor of the neurohypophysis was not significantly different between laying hens and nonlaying hens, but the maximum binding capacity value was statistically smaller (the binding affinity is higher) in laying hens than in nonlaying hens. The specific binding of estrogen receptor showed a decrease at 1 h after an injection of diethylstilbestrol in nonlaying hens. The specific binding also decreased 3 h before oviposition in laying hens and maintained low value until just after oviposition. The present study suggests that estrogen may act directly on the neurohypophysis during 3 h before oviposition in hens.

Key Words: hen neurohypophysis • estrogen receptor binding • plasma membrane • arginine vasotocin release • oviposition cycle