Calcitonin Directly Inhibits Luteinizing Hormone-Stimulated Progesterone Production in Granulosa Cells of the Largest Follicle of Hen

Functional Analysis and Tissue-Specific Expression of Calcitonin and CGRP with RAMP-Modulated Receptors CTR and CLR in Chickens

Calcitonin (CT) and calcitonin gene-related peptide (CGRP) are critical regulators of calcium balance and have extensive implications for vertebrate physiological processes. This study explores the CT and CGRP signaling systems in chickens through cloning and characterization of the chicken calcitonin receptor (CTR) and calcitonin receptor-like receptor (CLR), together with three receptor activity-modifying proteins (RAMPs). We illuminated the functional roles for chickens between the receptors examined alone and in RAMP-associated complexes using luciferase reporter assays. Chicken CTRs and CLRs stimulated the cAMP/PKA and MAPK/ERK signaling pathways, signifying their functional receptor status, with CT showing appreciable ligand activity at nanomolar concentrations across receptor combinations. Notably, it is revealed that chicken CLR can act as a functional receptor for CT without or with RAMPs. Furthermore, we uncovered a tissue-specific expression profile for CT, CGRP, CTR, CLR, and RAMPs in chickens, indicating the different physiological roles across various tissues. In conclusion, our data establish a clear molecular basis to reveal information on CT, CGRP, CTR, CLR, and RAMPs in chickens and contribute to understanding the conserved or divergent functions of this family in vertebrates.

Melatonin Does Not Affect Progesterone Basal Secretion but Suppresses the Luteinizing Hormone Receptor Expression in Granulosa Cells of the Japanese Quail

The aim of this study was to evaluate the potential effect of melatonin on progesterone production by granulosa cells of the Japanese quail. For in vitro experiments, granulosa cells were isolated from pre-ovulatory follicles (F1–F3) when the F1 follicles were predicted to be either immature or mature (at 3–6 or 18–21 h after oviposition, respectively). Granulosa cells were cultured for 12 hwithor without melatonin concentration gradients of 0.0001–100 µg/mL, thereby averting luteinizing hormone (LH) stimulation. The concentration of progesterone in culture medium was measured using an enzyme immunoassay. The expression of melatonin receptor subtypes in granulosa cells from F1 follicles was detected by reverse transcription-PCR. The LH receptor (LHCGR) mRNA level in cultured granulosa cells of the F1 follicles was analyzed using quantitative real-time PCR. Six quails were used in each of four groups for in vivo experiments. Eachgroup received intraperitoneal injection of melatonin (0.67 mg/kg body weight) or mock-vehicle at 3 or 18 h after oviposition, respectively. The birds were decapitated to collect serum 3 hlater (at 6 or 21 h after oviposition, respectively). The serum progesterone level was also measured using an enzyme immunoassay. We observed that melatonin receptor subtypes (Mel-1a, 1b, and 1c) were expressed in the granulosa cells of the F1 follicles of the Japanese quail. Melatonin suppresses the LHCGR mRNA expression in granulosa cells of F1 follicles but does not affect the basal secretion of progesterone in cultured granulosa cells of the F1–F3 follicles. In addition, melatonin treatment has no influence on the serum progesterone concentration at 6 h post-oviposition, but suppresses progesterone level 21 h after oviposition in the Japanese quail.

Changes in angiotensin II receptor bindings in the hen neurohypophysis before and after oviposition

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.

Effect of calcitonin on adrenocorticotropic hormone secretion stimulated by corticotropin-releasing hormone in the hen anterior pituitary

The presence of a receptor for calcitonin (CT) and the effect of chicken CT (cCT) on adrenocorticotropic hormone (ACTH) secretion stimulated by rat/human corticotropin-releasing hormone (rhCRH) in the hen anterior pituitary were studied. The specific [(125)I]cCT binding component was present in the plasma membrane of hen anterior pituitary and this binding component had properties of a receptor which has binding specificity to cCT, reversibility, saturable binding, high affinity and limited capacity. When anterior pituitary cells were incubated in vitro, cCT increased the maximal secretion of chicken ACTH stimulated by rhCRH. These results suggest that CT may act directly on the anterior pituitary via its receptor binding and enhances the ACTH secretion by CRH.

Calcitonin receptor bindings in the hen hypothalamus before and after oviposition

To demonstrate the presence of a receptor for calcitonin (CT) in the hen hypothalamus and to determine when CT acts on this tissue during the oviposition cycle, bindings of (125)I labeled CT in the plasma membrane fraction of the hen hypothalamus were measured by radioligand binding assay. The specific CT binding component in the plasma membrane fraction of the hypothalamus containing the preoptic area (HPOA) possessed properties of a receptor: binding specificity to CT, saturable binding, high affinity, and limited capacity. As for the median eminence area, no specific binding component was found in the present study. Therefore, the binding component for CT in the plasma membrane fraction of HPOA is likely to be a receptor for CT. In laying hens, the binding affinity of CT receptor increased at 30 min before oviposition and the binding capacity was decreased at 30 min before oviposition but not changed in nonlaying hens during a 24-h period. These results suggest that the action of CT on the hen HPOA may increase 30 min before oviposition.

Effect of estradiol-17β on calcitonin receptor bindings in the hen neurohypophysis

The present study was performed to elucidate whether estradiol-17β (E₂) would affect calcitonin (CT) receptor binding in the hen neurohypophysis. The equilibrium dissociation constant (K(d)) and the maximum binding capacity (B(max)) of the CT receptor in the plasma membrane fraction of the hen neurohypophysis were examined by Scatchard analysis of specific binding of (125)I-labeled chicken CT. A single i.m. injection of E₂ into nonlaying hens caused a decrease in K(d) and B(max) values of the CT receptor. The K(d) and B(max) values of the CT receptor were smaller in laying hens than in nonlaying hens. The present study suggests that E₂ may increase the action of CT on the neurohypophysis in hens.