title: Kinetic changes of melatonin release in rat pineal perifusions at different circadian stages. Effects of corticosteroids.
abstract: The kinetic characteristics of melatonin release were documented in perifused pineal glands removed from rats sacrificed at six circadian stages (light/dark = 12:12): three during the light phase, i.e. 3, 7 and 11 hours after light onset (HALO), and three during the dark phase, i.e. 15, 19 and 23 HALO. Whatever the circadian stage, the melatonin release decreased during the first 3-4 h and then remained fairly constant and roughly similar up to 8 h of perifusion. However, the kinetics of the release in the first 3 h differed in perifusions of pineal glands removed during the light (progressive decline during 3 h) as compared to perifusions of pineal glands removed during the dark (sharp decline during the first hour and then a progressive decline until reaching a constant level after 3 h). As the effects of steroid administration on melatonin secretion are a matter of controversy, we also studied the direct effects and their circadian stage dependence, if any, of corticosterone, deoxycorticosterone and dexamethasone on melatonin secretion by pineal glands removed 7 HALO (about the middle of the light phase) and 19 HALO (about the middle of the dark phase). High concentrations of corticosterone (0.8 x 10(-3) mol/l) and dexamethasone (0.4 x 10(-3) mol/l) resulted in a significant (p < 0.001) inhibitory effect on melatonin production (about a 50% and a 30% decrease, respectively) whatever the circadian stage, whereas lower concentrations (10(-4)-10(-5) mol/l) of both steroids did not affect melatonin production.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Biochemical Department, Faculté de Médecine Pitié-Salpêtrière, Paris, France.
authors.forename: Z Y
authors.initials: ZY
authors.lastname: Zhao
authors.forename: Y
authors.initials: Y
authors.lastname: Touitou
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D003345:Corticosterone / Q000494:pharmacology*; D003900:Desoxycorticosterone / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008297:Male; D008550:Melatonin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009994:Osmolar Concentration; D010477:Perfusion; D010870:Pineal Gland / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D003900:Desoxycorticosterone; D003907:Dexamethasone; D008550:Melatonin; D003345:Corticosterone