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Binding Characteristics, Regional Distribution and Diurnal Variation of [ 125 I]‐Iodomelatonin Binding Sites in the Chicken Brain
Author(s) -
Yuan He,
Tang Fai,
Pang Shiu Fun
Publication year - 1990
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1990.tb00707.x
Subject(s) - binding site , diurnal temperature variation , distribution (mathematics) , melatonin , circadian rhythm , biology , medicine , endocrinology , chemistry , zoology , biochemistry , physics , mathematical analysis , mathematics , atmospheric sciences
The [ 125 I]‐iodomelatonin binding sites in chicken brain membrane preparations were studied. The binding of [ 125 I]‐iodomelatonin to the membrane preparations of chicken brain was rapid, stable, saturable, and reversible. The order of pharmacological affinities of [ 125 I]‐iodomelatonin binding sites in the chicken brain membrane preparations was: melatonin > 6‐chloromelatonin > N‐acetylserotonin > 5‐hydroxytryptamine > tryptamine > 5‐methoxytryptophol, >> 1‐acetylindole‐3‐carboxaldehyde, 5‐hydroxyindole‐3‐acetic acid, L‐tryptophan, 5‐hydroxytryptophan, 3‐acetylindole. Compounds known to act on the receptor of norepinephrine or acetylcholine were inactive as compared to melatonin. Among the various brain regions studied, melatonin binding had maximal level in the hypothalamus, intermediate levels in the mid‐brain, ponsmedulla, and telencephalon, and minimum level in the cerebellum. Subcellular fraction studies indicated that 40% of the binding was located in the mitochondrial fraction, 27% in the nuclear, 26% in the microsomal, and 6% in the cytosol fraction. Scatchard analysis of the membrane preparations revealed a dissociation constant (Kd) of 199.6 ± 17 pM and a total number of binding sites (Bmax) of 16.6 ± 0.75 fmol/mg protein at midlight. Thus, our results showed the presence of specific melatonin binding sites in the chicken brain membrane preparations. Saturation studies demonstrated that [ 125 I]‐iodomelatonin binding capacity in chicken brain membrane preparations were 40% greater at midlight (16.6 ± 0.75 fmol/mg protein) than at middark (10.6 ± 0.56 fmol/mg protein), with no significant variation in their binding affinities.