Analog binding to melatonin receptors in chick brain: Effects of GTP and prazosin

2-[¹²⁵I]Iodomelatonin binding studies were carried out in chick brain membranes to compare the high-affinity melatonin receptor pharmacology of various 2-phenylmelatonin-based compounds, the naphthalenic agonist S-20098, and melatonin. Competition binding studies with 2-phenylmelatonin revealed a single class of binding sites with an inhibitory constant (K(i)) of 186 ± 8.31 pM that failed to show any change in the presence of GTP (K(i) = 200 ± 38.0 pM), suggesting that this compound is an antagonist at melatonin receptors in the chick brain.