CLONIDINE IN-VIVO MIMICS THE ACUTE SUPPRESSIVE BUT NOT THE PHASE-SHIFTING EFFECTS OF LIGHT ON CIRCADIAN-RHYTHM OF SEROTONIN N-ACETYLTRANSFERASE ACTIVITY IN CHICK PINEAL-GLAND
Jb. Zawilska, CLONIDINE IN-VIVO MIMICS THE ACUTE SUPPRESSIVE BUT NOT THE PHASE-SHIFTING EFFECTS OF LIGHT ON CIRCADIAN-RHYTHM OF SEROTONIN N-ACETYLTRANSFERASE ACTIVITY IN CHICK PINEAL-GLAND, Journal of pineal research, 17(2), 1994, pp. 63-68
Comparative in vivo studies on effects of pulses of light and clonidin
e, a selective agonist of alpha(2)-adrenergic receptors, on the circad
ian rhythm of serotonin N-acetyltransferase (NAT) activity in chick pi
neal gland were performed. Six-hour pulses of white light caused an ac
ute suppression of the nocturnal NAT activity and phase-dependent phas
e shifts of the circadian rhythm of the enzyme activity relative to co
ntrols. Systemic administration of clonidine acutely, suppressed NAT a
ctivity of chick pineal gland, but did not affect the phase of subsequ
ent cycles in constant darkness. These results give further support to
the concept based on in vitro studies that ol,-adrenergic receptors a
re involved in regulation of melatonin biosynthesis in chick pineal gl
and by a mechanism distal to the pacemaker that generates the circadia
n melatonin rhythm.