Long-term daily melatonin infusion induces a large increase in N-acetyltransferase activity, hydroxyindole-O-methyltransferase activity, and melatonin content in the Harderian gland and eye of pinealectomized male Siberian hamsters (Phodopus sungorus).
The effects of long-term daily melatonin infusions on the melatonin synthetic pathway in the Harderian glands and eyes of male Siberian hamsters were studied. Hamsters were pinealectomized (PX) and infused daily for 8 hr with either melatonin (6 microg/hr) or vehicle for 7 days in short photoperiod (SP, 10L:14D), followed by 14 wk in either SP (SP group) or in constant darkness (DD group). After the infusion period (15 wk), the infusion was stopped and animals were transferred into SP for 3 wk. The hamsters were then killed at midday or midnight. Exogenous melatonin infusion caused an increase in the Harderian gland weight, which was still evident 3 wk after the end of the treatment. In addition, exogenous melatonin increased endogenous melatonin concentrations (4-fold) and hydroxyindole-O-methyltransferase (HIOMT) activity (2-fold). N-acetyltransferase (NAT) activity, however, was not increased, and no day/night difference in melatonin content and HIOMT activity was observed in the Harderian glands. In the eye, melatonin infusions significantly increased day and night-time melatonin levels (up to 3-fold) and both NAT and HIOMT activities (up to 3.5-fold). This effect of melatonin treatment was observed in both SP and DD groups. These observations demonstrate that exogenously-infused melatonin at relatively high doses activates the synthesis of endogenous melatonin in the Harderian gland and eye of the Siberian hamster. Circulating levels of melatonin were also markedly increased, indicating that in these conditions melatonin may be released from extra-pineal sites.
Djeridane
Y
Y
CNRS-UMR 7518, Neurobiologie des Fonctions Rythmiques et Saisonnières, Université Louis Pasteur, Strasbourg, France.
Pitrosky
B
B
Vivien-Roels
B
B
Simonneaux
V
V
Kirsch
R
R
Pévet
P
P
D000121:Acetylserotonin O-Methyltransferase / Q000378:metabolism*; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000378:metabolism*; D002940:Circadian Rhythm; D006224:Cricetinae; D004334:Drug Administration Schedule; D005123:Eye / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D006243:Harderian Gland / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D006984:Hypertrophy / Q000139:chemically induced; D007263:Infusions, Parenteral; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects; D017111:Phodopus; D010870:Pineal Gland / Q000601:surgery
D000121:Acetylserotonin O-Methyltransferase; D001191:Arylamine N-Acetyltransferase; D008550:Melatonin