Diurnal rhythm of apolipoprotein A-IV in rat hypothalamus and its relation to food intake and corticosterone.
Apolipoprotein A-IV (apo A-IV) is a satiety protein synthesized in the small intestine and hypothalamus. To further understand the roles of central apo A-IV in the management of daily food intake, we have examined the diurnal patterns of hypothalamic apo A-IV gene and protein expression in freely feeding and food-restricted (food provided 4 h daily between 1000 h and 1400 h) rats. In freely feeding rats, the hypothalamic apo A-IV mRNA and protein levels fluctuated, with high levels during the light phase, peaking at 0900 h (3 h after lights on), and low levels during the dark phase, with a nadir at 2100 h (3 h after lights off). The daily patterns of the fluctuation, however, were altered in food-restricted rats, which had a marked decrease in hypothalamic apo A-IV mRNA and protein levels during the 4 h-feeding period of the light phase. Although corticosterone (CORT) secretion temporally coincided with the decreasing phase of apo A-IV in the hypothalamus, depletion of CORT by adrenalectomy significantly decreased, rather than increased, hypothalamic apo A-IV mRNA and protein levels. These results indicate that the diurnal expression of hypothalamic apo A-IV is regulated by factors other than the circulating CORT, for example, the reduced food intake and body weight in adrenalectomized animals. The fact that hypothalamic apo A-IV level and food intake were inversely related during the normal diurnal cycle as well as in the period of restricted feeding suggests that hypothalamic apo A-IV is involved in the regulation of daily food intake.
Liu
Min
M
Cincinnati Obesity Research Center, Department of Pathology and Laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0507, USA. lium@uc.edu.
Shen
Ling
L
Liu
Yin
Y
Tajima
Daisuke
D
Sakai
Randall
R
Woods
Stephen C
SC
Tso
Patrick
P
D000315:Adrenalectomy; D000818:Animals; D001054:Apolipoproteins A / Q000235:genetics / Q000378:metabolism*; D001835:Body Weight / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D003345:Corticosterone / Q000097:blood*; D004435:Eating / Q000502:physiology*; D007031:Hypothalamus / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley
D001054:Apolipoproteins A; D012333:RNA, Messenger; C022205:apolipoprotein A-IV; D003345:Corticosterone