Journal
JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS
Volume 306, Issue 2, Pages 694-702Publisher
AMER SOC PHARMACOLOGY EXPERIMENTAL THERAPEUTICS
DOI: 10.1124/jpet.103.049916
Keywords
-
Categories
Funding
- NIA NIH HHS [T32AG00260] Funding Source: Medline
- NIMH NIH HHS [MH52685, R01 MH052685, R01 MH052685-08] Funding Source: Medline
Ask authors/readers for more resources
This study investigated the receptor mechanism(s) by which the hormone melatonin directly affects ovarian function. Expression of MT1 and MT2 melatonin receptor mRNA was detected in the rat ovaries both by reverse transcriptase-polymerase chain reaction and in situ hybridization with digoxigenin-labeled oligoprobes. Specific 2-[I-125] iodomelatonin binding was significantly higher in ovarian tissue from animals sacrificed during proestrus than in metestrus, suggesting regulation of melatonin receptors by estrogens. Additionally, basal and melatonin-mediated stimulation of guanosine 5'-O-(3-[S-35]thio) triphosphate ([S-35] GTPgammaS) binding to ovarian sections was higher in proestrus compared with metestrus. During proestrus, both luzindole (0.1 muM) and 4-phenyl-2-propionamidotetraline (4P-PDOT) (0.1 muM), acting as inverse agonists, inhibited basal [S-35] GTPgammaS binding to ovarian sections, suggesting the presence of MT1 constitutively active melatonin receptors. In primary cultures of ovarian granulosa cells, melatonin inhibited forskolin-stimulated cAMP accumulation through activation of G(i)-coupled melatonin receptors. This inhibition was blocked by both, luzindole, and 4P-PDOT, acting as competitive receptor antagonists. Exposure of granulosa cells in culture to 17beta-estradiol seems to alter the state of melatonin receptor coupling. Indeed, the efficacy of 4P-PDOT on forskolin-stimulated cAMP formation was reversed from an MT2 partial agonist in vehicle-treated cells to that of an MT1 inverse agonist in 17beta-estradiol (0.1 muM)-treated granulosa cells. We conclude that MT1 and MT2 melatonin receptors expressed in antral follicles and corpus luteum may affect steroidogenesis through cAMP-mediated signaling. These results underscore the implications of the levels of ovarian estrogen when melatonin receptor ligands are used as therapeutic agents.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available