Expression Of Melatonin Receptors And 2-[125I]Iodomelatonin Binding Sites In The Pituitary of A Teleost Fish

2005 ◽  
pp. 61-72 ◽  
Author(s):  
Pascaline Gaildrat ◽  
Jack Falcón
Keyword(s):  
Teleost Fish ◽  
Binding Sites ◽  
Melatonin Receptors

scholarly journals Ontogeny of 2-[125I]iodomelatonin binding sites in the chicken (Gallus domesticus) kidney and spleen

1995 ◽  
Vol 73 (6) ◽  
pp. 685-692 ◽  
Author(s):  
Y. Song ◽  
S. F. Pang ◽  
A. M. S. Poon ◽  
G. M. Brown
Keyword(s):  
Binding Sites ◽  
Age Groups ◽  
Melatonin Receptors ◽  
Diurnal Rhythms ◽  
Immune Functions ◽  
Single Class ◽  
Age Related ◽  
Chicken Spleen ◽  
Chicken Kidney ◽  
Kidney Functions

To understand the possible role of melatonin receptors in the development of renal and immune functions, age-related variations of 2-[125I]iodomelatonin binding sites in the chicken kidney and spleen were investigated by radioreceptor assay. Chickens at embryonic day 20, as well as 2 days, 9 days, 2 weeks, 6 weeks, 12 weeks, and 16 weeks after hatching, were kept under a 12 h light: 12 h dark photoperiod and killed at the middle of the light period. Binding sites for 2-[125I]iodomelatonin in membrane preparations of the chicken kidney and spleen were present on embryonic day 20. The maximum binding densities (Bmax) in the kidney increased to a peak between 9 days and 2 weeks of age, then progressively decreased. Bmax values of 2-[125I]iodomelatonin binding sites in the chicken spleen were lower than in the kidney. The peak density in the chicken spleen was recorded at day 2 after hatching and decreased significantly after 6 weeks of age. There were no significant differences in binding affinities (Kd) in kidney and spleen of chicken in the different age groups studied. The unity of Hill coefficients of 2-[125I]iodomelatonin binding sites of the chicken kidney and spleen in all age groups tested suggested that only a single class of binding sites was present in these tissues during development. It is proposed that the developmental changes in 2-[125I]iodomelatonin binding sites in the chicken kidney and spleen may be pertinent to the development of diurnal rhythms of kidney functions and the post-pubertal decline in immune functions of the chicken.Key words: melatonin receptor, renal system, immune system, pineal gland, development, age-related change.

Cortisol decreases 2[125I]iodomelatonin binding sites in the duck thymu

1994 ◽  
Vol 130 (3) ◽  
pp. 320-324 ◽  
Author(s):  
AMS Poon ◽  
ZM Liu ◽  
F Tang ◽  
SF Pang
Keyword(s):  
Hong Kong ◽  
Binding Sites ◽  
Lymphoid Organs ◽  
The Body ◽  
Melatonin Receptors ◽  
Bursa Of Fabricius ◽  
Control Group ◽  
Lymphoid Tissues ◽  
Inhibitory Influence ◽  
Adrenal Steroids

Poon AMS, Liu ZM, Tang F, Pang SF. Cortisol decreases 2[125I]iodomelatonin binding sites in the duck thymus. Eur J Endocrinol 1994;130:320–4. ISSN 0804–4643 The immunosuppressive effect of chronic glucocorticoid treatment on 2[125I]iodomelatonin binding in the duck thymus was studied. Two-week-old ducks were injected intraperitoneally with either 1 mg of cortisol per day (experimental group) or an equivalent volume of vehicle (control group) in the middle of the light period for 7 days. 2[125I]Iodomelatonin binding assays were performed on thymic membranes. Cortisol injection reduced the body weight gain, size of the bursa of Fabricius and absolute weights of the primary lymphoid organs but had no effect on the spleen weights. The relative weights of the spleen were increased while those of the primary lymphoid organs were unchanged. The density of the thymus 2[125I]iodomelatonin binding sites was decreased while the affinity was not affected. The modulation of the thymic 2[125I]iodomelatonin binding sites by changes in the immune status of the duck suggests that these binding sites represent physiologically relevant melatonin receptors and that melatonin exerts its action on the lymphoid tissues directly. Our findings support the hypothesis that the thymus is the target site for the immunomodulatory interactions between the pineal melatonin and the adrenal steroids. A possible inhibitory influence of adrenal steroids on the immuno-enhancing effect of melatonin is also suggested. AMS Poon, University of Hong Kong, 5 Sassoon Rd, Hong Kong

Characterization of melatonin receptors in the ram pars tuberalis: influence of light

1990 ◽  
Vol 123 (5) ◽  
pp. 557-562 ◽  
Author(s):  
Jean Pelletier ◽  
Bertrand Castro ◽  
Georges Roblot ◽  
Renée Wylde ◽  
Marie-Madeleine de Reviers
Keyword(s):  
Median Eminence ◽  
Binding Sites ◽  
Melatonin Receptors ◽  
Scatchard Analysis ◽  
Pars Tuberalis

Abstract. The present study was conducted to assess the binding of [125I]melatonin to frozen unfixed sections of pars tuberalis/median eminence tissue from Ile-de-France rams exposed or not exposed to light before slaughter. The specificity of [125I]melatonin binding to the pars tuberalis tissue was revealed by autoradiography and the magnitude of binding as related to the pars tuberalis area was determined after incubation and counting of pars tuberalis/median eminence sections. Subsequent studies with sections incubated with [125I]melatonin indicated that 1. the binding sites were saturable; 2. binding was stable for 24 h at 20°C, but unstable at 28 or 37°C; 3. melatonin and [12 7I]melatonin had a similar potency to compete with [125I]melatonin for binding sites, whereas other ligands such as serotonin or N-acetylserotonin were devoid of activity, and 4. by Scatchard analysis, the constant affinity Ka was found to be high in the 1010 l/mol range. Rams exposed to light throughout the night prior to slaughter presented a significant increase in the apparent number of [125I]melatonin binding sites in comparison to animals maintained under darkness (2.25±0.30 vs 1.01±0.17 fmol/mm2 pars tuberalis, p<0.01), whereas Ka values were similar in both groups. These results indicate the presence of true melatonin receptors in the pars tuberalis of the ram. Furthermore, they suggest that their apparent number is light-dependent.

Melatonin receptors are present in adult rat Leydig cells and are coupled through a pertussis toxin-sensitive G-protein

1997 ◽  
Vol 136 (6) ◽  
pp. 633-639 ◽  
Author(s):  
Sandra Valenti ◽  
Massimo Giusti ◽  
Roberta Guido ◽  
Giulio Giordano
Keyword(s):  
G Protein ◽  
Pertussis Toxin ◽  
Binding Sites ◽  
Leydig Cells ◽  
Melatonin Receptors ◽  
Scatchard Analysis ◽  
Adult Rat ◽  
Testosterone Secretion ◽  
High Affinity Binding Site ◽  
17 Hydroxyprogesterone

Abstract Previous studies have suggested that melatonin (MLT) acts directly on rat Leydig cells by modulating androgen production. In the present study, the site of action of MLT was investigated. The binding of 2-[125I]iodomelatonin (125I-MLT; 7–240 pmol/l) to Leydig cell membrane fragments was tested in the presence or absence of guanosine 5′-O-(3-thiotriphosphate) (GTP-γ-S; 50 μmol/l). Saturation studies and Scatchard analysis revealed the existence of a high-affinity binding site with a Bmax of 46·70± 3·50 fmol/mg protein and a Kd of 88·70±6·20 pmol/l; treatment with GTP-γ-S reduced the concentration of 125I-MLT binding sites (Bmax 34·03±4·50), while increasing the Kd to 106·5± 2·61 pmol/l. Pretreatment of the cells with pertussis toxin (PTX; 10 ng/ml for 16 h) resulted in a decreased binding of I-MLT and a lack of effect of GTP-γ-S. Moreover, the effect of MLT on testosterone secretion induced by LH (30 mIU/ml), forskolin (1 μmol/l) and LHRH (100 nmol/l) was studied after 3-h incubation of cells which had been precultured with or without PTX. The inhibition of testosterone secretion due to MLT administration was eliminated by PTX pretreatment during forskolin and LH, but not during LHRH administration. However, 17-hydroxyprogesterone levels were higher in all groups incubated in the presence of MLT, irrespective of PTX pretreatment. Our data suggest that: (a) MLT receptors are present on the membranes of adult rat Leydig cells; (b) they couple through PTX-sensitive G-protein-coupled binding sites; (c) the mechanism by which MLT blocks 17–20 desmolase enzymatic activity (thus leading to increased 17-hydroxyprogesterone levels), and testosterone secretion during LHRH stimulation is likely to depend on one or more different mechanism(s) of action. European Journal of Endocrinology 136 633–639

Daily Rhythms of Melatonin Binding Sites in the Rat Pars tuberalis and Suprachiasmatic Nuclei; Evidence for a Regulation of Melatonin Receptors by Melatonin Itself

1993 ◽  
Vol 57 (1) ◽  
pp. 120-126 ◽  
Author(s):  
François Gauer ◽  
Mireille Masson-Pévet ◽  
Debra Jean Skene ◽  
Berthe Vivien-Roels ◽  
Paul Pévet
Keyword(s):  
Binding Sites ◽  
Melatonin Receptors ◽  
Pars Tuberalis ◽  
Suprachiasmatic Nuclei ◽  
Daily Rhythms

The development of melatonin-binding sites in the ovine fetus

1994 ◽  
Vol 142 (3) ◽  
pp. 475-484 ◽  
Author(s):  
R J A Helliwell ◽  
L M Williams
Keyword(s):  
G Protein ◽  
Binding Sites ◽  
Early Stage ◽  
Specific Binding ◽  
Melatonin Receptors ◽  
Pars Tuberalis ◽  
Dependent Manner ◽  
Pars Distalis ◽  
Specific Expression ◽  
Fetal Sheep

Abstract The pineal hormone, melatonin, is important in the timing of seasonal reproduction in the sheep. Melatonin of maternal origin readily crosses the placenta; its function in the fetal sheep is, however, unclear. To gain an insight into the role of melatonin in ovine development we have identified specific melatonin receptors throughout gestation using 2-[125I]iodomelatonin and quantitative in vitro autoradiography. Specific binding was found at the earliest time studied at 30 days of gestation, over the developing thyroid (term=145 days). At 31 days of gestation specific labelling was found over the thyroid and pituitary glands, the spinal nerves, nasal cavity and developing bronchi. This binding was diminished by over 50% in the presence of 10−4 m GTPγS (an analogue of guanosine triphosphate) indicating that the 2-[125I]iodomelatonin binding at this early stage of gestation represents a receptor coupled to a regulatory G-protein. By 40 days of gestation specific binding was found over the nasal epithelium, cochlear epithelium, regions of the brain, especially the hind brain and the vestibulocochlear and glossopharyngeal nerves, and both the pars distalis and pars tuberalis of the pituitary. As gestation proceeded, labelling over the pars distalis appeared to become more scattered in nature while that on the pars tuberalis remained consistent. Saturation studies of both the neuronal and pituitary binding sites at 121 days of gestation and in the newborn lamb revealed a single class of high-affinity binding sites with Kd values in the picomolar range. Also at 121 days of gestation, binding over the fetal pars tuberalis was diminished in a dose-dependent manner by GTPγS, again confirming that specific binding is indicative of a receptor coupled to a regulatory G-protein. These data demonstrate a potential for sensitivity to melatonin from early in gestation, as well as the developmentally specific expression of the melatonin receptor in certain tissues, and suggest a wider role for melatonin in ovine fetal development than previously considered. Journal of Endocrinology (1994) 142, 475–484

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