AJP - Endocrinology and Metabolism, Vol 266, Issue 4 E606-E611, Copyright © 1994 by American Physiological Society
Prefeeding increase in paraventricular NE release is regulated by a feeding-associated rhythm in rats
M. Mitome, S. Honma, T. Yoshihara and K. Honma
Department of Physiology, Hokkaido University School of Medicine, Sapporo, Japan.
Extracellular norepinephrine (NE) in the vicinity of the paraventricular
nucleus was continuously measured over 24 h by means of in vivo
microdialysis in rats under restricted daily feeding and ad libitum
feeding. A 24-h rhythm in plasma corticosterone was monitored in separate
rats under identical conditions. Under ad libitum feeding, the
paraventricular NE showed a 24-h rhythm with lower levels in the light
period and higher levels in the dark period. The temporal pattern was not
affected by food deprivation for 3 days. The circadian peak of
paraventricular NE lagged slightly behind that of plasma corticosterone
under ad libitum feeding. On the other hand, when rats were fed for 2 h at
a fixed time of day for 3 wk, the NE rhythm was changed and showed a major
peak just before daily meals. To examine the nature of the prefeeding NE
peak, a 24-hour variation of paraventricular NE was measured in rats under
food deprivation that had been subjected to restricted daily feeding for 3
wk and subsequently to ad libitum feeding for 7 days. The paraventricular
NE was high around the time when meal had been supplied under restricted
daily feeding and low in the dark period. Similar changes were observed in
plasma corticosterone. The findings indicate that the prefeeding increase
in the paraventricular NE release is regulated by a feeding-associated
circadian rhythm manifest in rats under restricted daily feeding.
