CHRONIC FOOD RESTRICTION AND ACUTE FOOD-DEPRIVATION DECREASE MESSENGER-RNA LEVELS OF OPIOID-PEPTIDES IN ARCUATE NUCLEUS

Although opioid administration induces food intake, the relationship b etween endogenous opioid synthesis and food consumption is unclear. Tw o studies examined the effects of food restriction and deprivation on opioid mRNA levels in the arcuate nucleus (ARC) of the rat. Body weigh t significantly decreased following food restriction and deprivation ( P < 0.0001). In experiment 1, food restriction of 10, 20, 30, and 40% (g) of ad libitum intake for 14 days decreased proDynorphin (proDyn), proEnkephalin (proEnk), and proO-piomelanocortin (POMC) mRNA levels in a linear fashion relative to changes in body weight (r = 0.398, P = 0 .011, r = 0.455, P = 0.0028; r = 0.292, P = 0.0642, respectively). In experiment 2, 48 h deprivation significantly decreased mRNA levels of proDyn and POMC by 23.7% (P < 0.05) and 45.6% (P < 0.01), respectively , whereas 24 h food deprivation decreased POMC mRNA by 43.0% (P < 0.01 ). proEnk mRNA was not affected by 24- or 48-h food deprivation. Restr icting food intake suppressed mRNA levels of proDyn, proEnk, and POMC by 29.7, 22.3, and 44.4%, respectively, in 20% restricted rats and by 35.5, 26.8, and 45.6%, respectively, in 40% restricted rats (P < 0.01) . It appears that ARC mRNA levels of proDyn, proEnk, and POMC are dire ctly related to the amount of food consumed and/or changes in body wei ght in food-restricted and food-deprived rats.