Localization, characterization and subtyping of melatonin receptors in rat uterine endometrium in estrous stage

Abstract

This study was undertaken to identify the rat uterine melatonin receptors. Autoradiography showed that 2-[125I]iodomelatonin binding were localized in the rat uterine endometrial stroma. The specific binding of 2-[125I]iodomelatonin was stable, saturable, reversible and of high affinity. Scatchard analysis of the 2-[125I]iodomelatonin binding in membrane preparations of rat uterine endometrium in estrous stage had an equilibrium dissociation constant (Kd) of 28.9 B 3.59 pmol/l (n = 8) and a maximum number of binding sites (Bmax) of 1.6 B 0.15 fmol/mg protein (n = 8). The Kd value determined from kinetic analysis was 16.5 B 3.02 (n = 3). Competition studies using various indoles and neurotransmitters demonstrated that 2-iodomelatonin, melatonin, 6-chloromelatonin, 6-hydroxymelatonin, N-acetylserotonin showed significant inhibition of the 2-[125I]iodomelatonin binding, while the other compounds had no significant inhibition. Nucleotide sequencing demonstrated that MEL1A but not MEL1B receptor mRNAs were expressed in uterine endometrium in estrous stage after reverse transcription-Polymerase chain reactions (RT-PCR) and nested PCR. Our results indicate the presence of MEL1A receptor subtype in the rat uterine endometrial stroma.