Evidence for central α2-adrenergic modulation of rat pineal melatonin synthesis |
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Authors: | S. M. Mustanoja, T. H t nen, A. Alila-Johansson,Laakso |
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Affiliation: | a Department of Physiology, Institute of Biomedicine, University of Helsinki, Helsinki, Finland;b Neural Networks Research Centre, Helsinki University of Technology, Espoo, Finland |
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Abstract: | This study was performed to distinguish central and peripheral α2-adrenoceptors in the inhibition of rat pineal melatonin synthesis. The rats received lipo- or hydrophilic α2-adrenoceptor ligand injections at middark; after 1 or 2 h the pineal melatonin contents were measured. The lipophilic agonist medetomidine (100 μg/kg s.c.) suppressed the melatonin contents significantly, while the hydrophilic agonists ST-91 and p-aminoclonidine (10 or 100 μg/kg i.v.) did not. The suppression by medetomidine was counteracted by the lipophilic antagonist yohimbine (0.3–3.0 mg/kg i.p.) but not by the hydrophilic antagonist L-659,066 (1–10 mg/kg i.v.). In conclusion, the suppression of nocturnal melatonin synthesis by α2-adrenoceptor agonists is mainly of central origin. |
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Keywords: | α 2-Adrenoceptor Pineal gland Melatonin Medetomidine |
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