Binding characteristics and regional distribution of [125I]iodomelatonin binding sites in the brain of the human fetus.

The binding and pharmacological characteristics of [125I]iodomelatonin binding sites in human fetal brain membrane preparations were determined. Membrane preparations of the whole brain revealed a equilibrium binding constant (Kd) of 17.5 pmol/l with a total number of binding sites (Bmax) at 0.8 fmol/mg protein. Among the various brain regions studied, [125I]iodomelatonin binding was highest in the hypothalamus, and lowest in the mid-brain, pons-medulla, and cerebral cortex. The Kd of the hypothalamus was calculated to be 26.1 pmol/l and the Bmax 5.4 fmol/mg protein. Only 6-chloromelatonin, melatonin and N-acetylserotonin had significant inhibition in the binding. Our results suggest that melatonin receptors are present in the human brain and that melatonin may exert a central action.