Changes in parathyroid hormone receptor binding affinity during egg laying: Implications for calcium homeostasis in chicken

Abstract

Parathyroid hormone (PTH) receptor bindings were examined in the membrane fraction of the calvaria and the kidney of the hen by the use of [125I]PTH-related protein (PTHrP) binding assays. The binding specificity, reversibility, and saturation of the receptor were demonstrated. The equilibrium dissociation constant (Kd) and the maximum binding capacity (Bmax) were obtained by Scatchard analyses. In both calvaria and kidney, Kd and Bmax values decreased at 3 h before oviposition in egg-laying hens, but not in nonlaying hens. Administration of 17 beta-estradiol or progesterone in vivo caused a decrease in the Kd and Bmax values. Ionized calcium concentrations in the blood plasma showed a decrease at 13 h before oviposition. The results suggest that the PTH receptor binding in the calvaria and the kidney is affected by ovarian steroid hormones and may play a role in maintaining the calcium homeostasis in the egg-laying hen.

Calcitonin directly increases adrenocorticotropic hormone-stimulated corticosterone production in the hen adrenal gland

“…Chicken CT (cCT; Peninsula Laboratories Inc., Belmont, CA) was iodinated with Na-125 I (Amersham International plc, Buckinghamshire, UK) using iodogen (Pierce Biochemicals, Rockford, IL), and free Na-125 I was separated from radioiodinated cCT on a 1 × 100 cm Sephadex G-25 (Pharmacia LKB) column as described previously (Yasuoka et al, 1996). The specific activity of the radioligand was 369 ± 20 Ci/mmol (mean ± SEM, n = 12).…”

“…The ionized cCT was utilized in the experiment within 40 d after the radioiodination. The specific binding of [ 125 I]cCT was measured by the use of the method of Yasuoka et al (1996). Aliquots of the membrane fractions (40 µg of protein/tube) were incubated at 4°C for 1 h with [ 125 I]cCT (0.14 to 4.6 nM) in the absence (total binding) or presence (nonspecific binding) of 1 µM unlabeled cCT in a total volume of 300 µL.…”

“…Membrane fractions were prepared at 4°C using the method of Yasuoka et al (1996) with slight modification. Twenty adrenal glands were pooled, and cortical cells were washed with HEPES buffer and homogenized in Tris-EDTA (TE) buffer [50 mM Tris-HCl (Wako Pure Chemical Industries Ltd.), 1 mM EDTA (Wako Pure Chemical Industries Ltd.), pH 7.4].…”

Parathyroid hormone-related peptide directly increases adrenocorticotropic hormone secretion from the anterior pituitary in hens

“…All experiments were performed within 40 d. The specific binding of [ 125 I]cPTHrP was measured using a method reported earlier (Yasuoka et al, 1996;Kawashima et al, 2005). Aliquots of the plasma membrane fraction (150 μg of protein/tube) were incubated at 4°C for 2 h with [ 125 I]cPTHrP (0.1 to 3.2 nM) in the absence (for total binding) or presence (for nonspecific binding) of 1 μM unlabeled cPTHrP in a total volume of 300 μL.…”

“…The primary role of these hormones is to maintain calcium homeostasis (Yates et al, 1988) with calcitonin (Kenny, 1986) and vitamin D (Savaram et al, 2008;Bar, 2009). Parathyroid hormone-related peptide receptor has been found in the calvarial bone and kidney of the chicken (Yasuoka et al, 1996), shell glands of the chicken (Ieda et al, 2000) and the guinea fowl (Ogawa et al, 2000), and adrenocortical cells of the chicken (Kawashima et al, 2005). Parathyroid hormone-related peptide stimulates bone resorption and increases renal tubular reabsorption of calcium (Yates et al, 1988).…”