ISSN:
1600-079X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
It has been difficult, so far, to obtain melatonin analogs possessing high selectivity for the respective melatonin receptors, mt1 and MT2. In the present work, we report the synthesis and pharmacological characterization of a new compound N-{2-[5-(2-hydroxyethoxy)-1H-indol-3-yl)] ethyl} acetamide or 5-hydroxyethoxy-N-acetyltryptamine (5-HEAT). To assess the activity of the compound, the following tests were performed: affinity determination for the high- and low-affinity receptor states (2-[ 〈displayedItem type="mathematics" xml:id="di-fml-1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:07423098:JPI290406:JPI_290406_m1"/〉I]iodomelatonin binding), potency and intrinsic activity in inducing G protein activation ([〈displayedItem type="mathematics" xml:id="di-fml-2" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:07423098:JPI290406:JPI_290406_m2"/〉 S]GTPγS binding assay). 5-HEAT showed little selectivity for the mt1 receptor, with pKi values of 7.77 for mt1 and 7.12 for the MT2 receptors, respectively. 5-HEAT was able to differentiate between the high- and the low-affinity receptor states in the mt1 but not in the MT2 receptor. 5-HEAT induced a high level of G protein activation when acting through the mt1 receptor, with a relative intrinsic activity of 0.92. On the contrary, it elicited only minimal MT2 receptor-mediated G protein activation, with a relative intrinsic activity of 0.16, and was also able to inhibit the melatonin-induced MT2 receptor-mediated G protein activation, with a pKB value of 7.4. In conclusion, it appears that 5-HEAT possesses very different efficacies at the two melatonin receptors, behaving as a full melatonin receptor agonist at the mt1 and as an antagonist/weak partial agonist at the MT2 receptor. Therefore, it is a promising ligand for use in functional studies aimed at distinguishing between the effects mediated by the different melatonin receptors in the human.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1034/j.1600-0633.2002.290406.x
