2-[125I]Iodomelatonin Binding Sites in Hamster Brain Membranes: Pharmacological Characteristics and Regional Distribution*
- 1 May 1988
- journal article
- research article
- Published by The Endocrine Society in Endocrinology
- Vol. 122 (5), 1825-1833
- https://doi.org/10.1210/endo-122-5-1825
Abstract
Studies in a variety of seasonally breeding mammals have shown that melatonin mediates photoperiodic effects on reproduction. Relatively little is known, however, about the site(s) or mechanisms of action of this hormone for inducing reproductive effects. Although binding sites for [3H] melatonin have been reported previously in bovine, rat, and hamster brain, the pharmacological selectivity of these sites was never demonstrated. In the present study, we have characterized binding sites for a new radioligand, 2-[125I]iodomelatonin, in brains from a photoperiodic species, the Syrian hamster. 2-[125I]Iodomelatonin labels a high affinity binding site in hamster brain membranes. Specific binding of 2-[125I]iodomelatonin is rapid, stable, saturable, and reversible. Saturation studies demonstrated that 2-[125I]iodomelatonin binds to a single class of sites with an affinity constant (KJ of 3.3 ± 0.5 nM and a total binding capacity (Bmax) of 110.2 ± 13.4 fmol/mg protein (n = 4). The Kj value determined from kinetic analysis (3.1 ± 0.9 nM; n = 5) was very similar to that obtained from saturation experiments. Competition experiments showed that the relative order of potency of a variety of indoles for inhibition of 2-[125I]iodomelatonin binding site to hamster brain membranes was as follows: 6-chloromelatonin > 2-iodomelatonin > N-acetylserotonin > 6-methoxymelatonin > melatonin > 6-hydroxymelatonin > 6,7-dichloro-2-methylmelatonin > 5-methoxytryptophol > 5-methoxytryptamine > 5- methoxy-iV,iV-dimethyltryptamine > AT-acetyltryptamine > serotonin > 5-methoxyindole (inactive). Compounds known to act at serotonergic, adrenergic, or dopaminergic receptors were either inactive or relatively ineffective as compared to melatonin. These results suggest that 2-[125I]iodomelatonin is a selective, high affinity probe for identifying melatonin receptor binding sites in rodent brain. (Endocrinology122: 1825–1833, 1988)Keywords
This publication has 24 references indexed in Scilit:
- Melatonin: Identification of Sites of Antigonadal Action in Mouse BrainScience, 1981
- Effect of 5-methoxytryptophan and 5-methoxytryptamine on the reproductive system of the male golden hamsterJournal of Neural Transmission, 1981
- Hypothalamic cuts suggest a brain site for the antigonadotrophic action of melatonin in the syrian hamsterNeuroscience Letters, 1981
- LIGAND: A versatile computerized approach for characterization of ligand-binding systemsAnalytical Biochemistry, 1980
- Inhibition of Luteinizing Hormone Release and Ovulation by 6-Chloro- and 6-FluoromelatoninNeuroendocrinology, 1980
- Effects of 6-Hydroxy-, 6-Fluoro-, and 4,6-Difluoromelatonin on the in Vitro Pituitary Response to Luteinizing Hormone-Releasing Hormone*Endocrinology, 1980
- Specific Binding of Melatonin in Bovine Brain*Endocrinology, 1979
- Inhibition of thein VitroPituitary Response to Luteinizing Hormone-Releasing Hormone by Melatonin, Serotonin, and 5-Methoxytryptamine1Endocrinology, 1977
- A Rapid and Sensitive Method for the Quantitation of Microgram Quantities of Protein Utilizing the Principle of Protein-Dye BindingAnalytical Biochemistry, 1976
- REGIONAL STUDIES OF CATECHOLAMINES IN THE RAT BRAIN‐IJournal of Neurochemistry, 1966