Prostaglandin F2α receptor in the neurohypophysis of hens

To elucidate whether the receptor for prostaglandin (PG) F-2 alpha, one of PG, exists in the neurohypophysis in hens and whether the binding of receptor changes with relation to oviposition, the PGF(2 alpha) binding component in the membrane fraction of the neurohypophysis of laying hens was analyzed by radioligand binding assay using [5,6,8,9,11,12,14,15(n)-H-3] PGF(2 alpha). The binding component had characteristics of a receptor such as binding specificity, high affinity, and limited capacity for PGF(2 alpha). Scatchard analysis indicated that the binding site was of a single class. The binding capacity of the receptor was smaller in laying hens than in nonlaying hens, whereas the binding affinity was not significantly different between these hens. When nonlaying hens received an i.m. injection of estradiol-17 beta or progesterone (0.5 mg/hen), the specific binding of the PGF(2 alpha) receptor in the neurohypophysis was decreased. In laying hens, the specific binding decreased and the blood arginine vasotocin (AVT) concentration increased just after oviposition but did not change during a 24-h day in nonlaying hens. An i.v. injection of PGF(2 alpha) (2 mu g/hen) induced oviposition and caused an increase in the blood AVT concentration with a decrease in the specific binding of PGF(2 alpha) receptor. The present study suggests a possibility that PGF(2 alpha) may directly cause the AVT release from the neurohypophysis at oviposition time in hens.