Pineal melatonin in rats: suppression by the selective alpha2-adrenoceptor agonist medetomidine.
Eur J Pharmacol
; 326(2-3): 229-36, 1997 May 20.
Article
in En
| MEDLINE
| ID: mdl-9196276
ABSTRACT
This study was done to clarify the role of alpha2-adrenoceptors in the regulation of pineal melatonin synthesis. A selective alpha2-adrenoceptor agonist, medetomidine, and antagonist, atipamezole, were injected subcutaneously into rats and their pineal melatonin contents were measured by radioimmunoassay. Medetomidine (120 microg/kg) suppressed melatonin at night to a similar extent during the rising and descending phase of melatonin synthesis, but it did not affect the daytime level. A dose of 12 microg/kg was ineffective; doses of 30-180 microg/kg suppressed nocturnal melatonin levels close to the daytime levels. Significant suppression was reached within 15 min and the effect started to fade 3 h after the injection (120 microg/kg). At midday, medetomidine did not inhibit isoproterenol-stimulated synthesis of melatonin. Atipamezole (0.4 or 1.2 mg/kg) had no effect alone, but it counteracted the medetomidine-induced suppression. The effects of alpha2-adrenoceptor ligands on melatonin synthesis depend on the time of day and/or on the activity of the pineal sympathetic nerves.
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Collection:
01-internacional
Database:
MEDLINE
Main subject:
Pineal Gland
/
Adrenergic alpha-Agonists
/
Adrenergic alpha-Antagonists
/
Imidazoles
/
Melatonin
Limits:
Animals
Language:
En
Journal:
Eur J Pharmacol
Year:
1997
Document type:
Article
Affiliation country:
Finland