Noradrenergic inhibition and alpha 2-adrenergic stimulation of melatonin secretion in the pigeon.
Adrenergic regulatory mechanisms of melatonin synthesis and secretion were studied in the pigeon in vivo. Late-afternoon intraperitoneal injection of noradrenaline (NA; 1 mg/kg) resulted in a significant decrease in plasma melatonin levels in 3 h. The same effect was seen after phenylephrine treatment (1 mg/kg i.p.), indicating that an alpha 1-adrenergic mechanism may mediate the inhibition. Propranolol treatment had no effect on plasma melatonin levels, supporting this concept. Detomidine (1 mg/kg i.p.), an alpha 2-adrenergic agonist, increased melatonin levels. This stimulatory effect was blocked by yohimbine, an alpha 2-adrenergic antagonist. However, yohimbine alone had no effect on the plasma melatonin levels, suggesting that alpha 2-adrenergic transmission is not primarily responsible for the nocturnal stimulation of melatonin synthesis and secretion in the pigeon.
Vakkuri
O
O
Department of Physiology, University of Oulu, Finland.
Rintamäki
H
H
Leppäluoto
J
J
D000818:Animals; D002940:Circadian Rhythm; D010856:Columbidae; D007093:Imidazoles / Q000494:pharmacology; D008550:Melatonin / Q000037:antagonists & inhibitors* / Q000097:blood / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013566:Sympathomimetics / Q000494:pharmacology; D013997:Time Factors
D007093:Imidazoles; D011942:Receptors, Adrenergic, alpha; D013566:Sympathomimetics; C041255:detomidine; D008550:Melatonin; D009638:Norepinephrine