Effect of Estradiol-17β and Progesterone on Arginine Vasotocin in Nonlaying Hens

2009

To elucidate whether the receptor for prostaglandin (PG) F(2alpha), one of PG, exists in the neurohypophysis in hens and whether the binding of receptor changes with relation to oviposition, the PGF(2alpha) 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)-(3)H]PGF(2alpha). The binding component had characteristics of a receptor such as binding specificity, high affinity, and limited capacity for PGF(2alpha). 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 non-laying hens received an i.m. injection of estradiol-17beta or progesterone (0.5 mg/hen), the specific binding of the PGF(2alpha) 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(2alpha) (2 microg/hen) induced oviposition and caused an increase in the blood AVT concentration with a decrease in the specific binding of PGF(2alpha) receptor. The present study suggests a possibility that PGF(2alpha) may directly cause the AVT release from the neurohypophysis at oviposition time in hens.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Prostaglandin F2α receptor in the neurohypophysis of hens

2009

“…Accordingly, it seems likely that E 2 acts on the neu-rohypophysis through the membrane estrogen receptor regardless of the nuclear estrogen receptor. Estradiol-17β stimulates the action of prostaglandin F 2α in the neurohypophysis (Takahashi and Kawashima, 2009) and increases the AVT concentration in blood (Takahashi et al, 1994a). These facts imply that an administration of estrogen may induce oviposition theoretically.…”

Section: Discussionmentioning

confidence: 93%

“…In hens, an injection of E 2 increases the blood concentration of arginine vasotocin (AVT; Takahashi et al, 1994a), which is one of the avian neurohypophysial hormones (Munsick et al, 1960). The AVT is produced by neurons of the hypothalamus (Bons, 1980;Tennyson et al, 1985) extending to the neurohypophysis from where it is released into the blood vessels.…”

Section: Introductionmentioning

confidence: 99%

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

2009

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-17beta (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.

“…Blood was also collected from the nonlaying hens at a time corresponding to the time (0600, 0700, and 1800 h) of collecting blood of the laying hens (6 birds at each time). Mesotocin and AVT were extracted from 1 mL of the plasma using an octadecasilyl-silica cartridge (Sep Pak C18, Waters Corp., Milford, MA) as reported earlier (Takahashi et al, 1994a). Eluents from the cartridge were dried by a centrifugal evaporator (CVE-100, Tokyo Rikakikai Co. Ltd., Tokyo, Japan).…”

Section: Measurement Of Plasma Mt and Avt Concentrations Before And Amentioning

confidence: 99%

Mesotocin Increases the Sensitivity of the Hen Oviduct Uterus to Arginine Vasotocin

2008

The present study was performed to elucidate whether mesotocin (MT), one of avian neurohypophysial hormones, relates to the action of arginine vasotocin (AVT) on oviposition of hens. The ratio of AVT-induced oviposition was increased when 1 microg/hen of MT was injected together with AVT. An intravenous injection of 1 microg/hen of MT caused an increase in the binding affinity of the uterine AVT receptor and a decrease in the binding capacity. Blood MT concentrations measured by RIA increased approximately 1 min before oviposition during the period of the bearing-down behavior, but the AVT concentration did not change at this time. The blood AVT concentration dramatically increased within 1 min just after oviposition. The results suggest that MT may have an effect of enhancing the inducing oviposition by AVT through the increase in the sensitivity of the uterus to AVT at oviposition in hens.