title: Cannabinoids attenuate norepinephrine-induced melatonin biosynthesis in the rat pineal gland by reducing arylalkylamine N-acetyltransferase activity without involvement of cannabinoid receptors.
abstract: Cannabinoids modulate neuronal and neuroendocrine circuits by binding to cannabinoid receptors acting upon cAMP/Ca(2+)-mediated intracellular signaling cascades. The rat pineal represents an established model to investigate intracellular signaling processes because a well defined input, the neurotransmitter norepinephrine, is transformed via cAMP/Ca(2+)-dependent mechanisms into an easily detectable output signal, the biosynthesis of melatonin. Here we investigated the impact of cannabinoids on norepinephrine-regulated melatonin biosynthesis in the rat pineal. We demonstrated that treatment of cultured rat pineals with 9-carboxy-11-nor-delta-9-tetrahydrocannabinol (THC), cannabidiol or cannabinol significantly reduced norepinephrine-induced arylalkylamine N-acetyltransferase (AANAT) activity and melatonin biosynthesis. These effects were not mimicked by the cannabinoid receptor agonist WIN55,212-2 and were not blocked by cannabinoid 1 and 2 receptor antagonists. The cannabinoids used did not affect norepinephrine-induced increases in cAMP/Ca(2+) levels. Notably, cannabinoids were found to directly inhibit AANAT activity in lysates of the pineal gland. This effect was specific in so far as cannabinoids did not influence the activity of hydroxyindole-O-methyltransferase (HIOMT), the last enzyme in melatonin biosynthesis. Taken together, our data strongly suggest that cannabinoids inhibit AANAT activity and attenuate melatonin biosynthesis through intracellular actions without involvement of classical cannabinoid receptor-dependent signaling cascades.
authors.affiliation: Dr Senckenbergische Anatomie, Anatomisches Institut II, Fachbereich Medizin der Johann Wolfgang Goethe-Universität, Frankfurt/Main, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Koch
authors.forename: Faramarz
authors.initials: F
authors.lastname: Dehghani
authors.forename: Iris
authors.initials: I
authors.lastname: Habazettl
authors.forename: Christof
authors.initials: C
authors.lastname: Schomerus
authors.forename: Horst-Werner
authors.initials: HW
authors.lastname: Korf
mesh_terms: D000818:Animals; D019540:Area Under Curve; D047068:Arylalkylamine N-Acetyltransferase / Q000378:metabolism*; D002186:Cannabinoids / Q000494:pharmacology*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D008550:Melatonin / Q000096:biosynthesis*; D009638:Norepinephrine / Q000494:pharmacology*; D009924:Organ Culture Techniques; D010870:Pineal Gland / Q000166:cytology / Q000187:drug effects*; D011874:Radiometry / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D043882:Receptors, Cannabinoid / Q000502:physiology*
chemical_list: D002186:Cannabinoids; D017362:Cyclic AMP Response Element-Binding Protein; D004791:Enzyme Inhibitors; D043882:Receptors, Cannabinoid; D000242:Cyclic AMP; D047068:Arylalkylamine N-Acetyltransferase; D008550:Melatonin; D009638:Norepinephrine