Melatonin receptors were studied in quail livers using the melatonin agonist 2-[125I]iodomelatonin ([125I]MEL) as the radioligand. The specific binding of [125I]MEL to membrane preparations of liver was rapid, stable, saturable, reversible and of high affinity. Scatchard analysis of the specific binding data indicated an equilibrium dissociation constant (Kd) of 19.4 ± 1.01 pmol/l (n = 7) and a maximum number of binding sites (Bmax) of 1.16 ±0.19 fmol/mg protein (n = 7) in the quail liver collected at mid-light. The Hill coefficient approached 1.0, suggesting a single class of [125I]MEL binding sites in the quail liver. The diurnal variation study showed that the value of Kd was 64.4% higher (p < 0.05) at mid-dark compared to mid-light, with no significant change in Bmax. The kinetic analysis showed that the Kd value was 25.0 ± 3.94 pmol/l at mid-light, which was comparable with values determined from saturation studies. Aside from 2-iodomelatonin, melatonin and 6-chloromelatonin, all indole analogs and neurotransmitters tested in inhibition studies had slight or no displacement of [125I]MEL binding. These studies demonstrated that [125I]MEL binding sites were highly specific for melatonin. The presence of 10 and 50 µmoI/l guanosine 5´-O-(3-thiotriphosphate) significantly increased (p < 0.05) the Kd values and depressed the Bmax values, proposing that [125I]MEL binding sites in quail livers were coupled to a G-protein. Our results indicate that melatonin may exert a direct action on liver functions.

Keywords:
Melatonin receptor, Pineal gland, G-Protein, GTP, Diurnal rhythm
This content is only available via PDF.
© 1995 S. Karger AG, Basel
1995
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.