2-[125I]Iodomelatonin binding sites in hamster and chick exhibit differential sensitivity to prazosin

Binding of 2-[125I]iodomelatonin to putative receptors for melatonin has been well documented in chicken and hamster tissues. Differences in the potency of N-acetyl-5-hydroxytryptamine in these tissues suggested distinct central and peripheral binding sites. Prazosin was found to be much more potent (Ki = 6.5 nM) in hamster hypothalamus than in chick retina (Ki = 740 nM). N-acetyl-5-HT also was more potent in hamster hypothalamus (Ki = 14 nM) than in chick retina (Ki = 1050 nM). A comparison of hamster hypothalamus to chick forebrain revealed a similar difference in potency for prazosin. In light of these findings, the dissimilarity between the potencies of N-acetyl-5-HT and prazosin in hamster and chick would appear to be due to a species difference as the central and peripheral sites seem alike within either species.