Ontogeny of epinephrine-induced anorexia in rats

Intraperitoneal or intraportal epinephrine elicits a strong inhibition of food intake in adult rats and dogs but has no effect when injected intramuscularly or intrajugularly, in spite of production of larger hyperglycemia and cardiovascular changes. These facts suggest that the effect of epinephrine on feeding is elicited via the liver. Ontogeny of this adrenergic control of food intake was studied in newborn and weanling rats. Anorexic effect of intraperitoneal epinephrine was clearly observed in dam-deprived 3-day-old neonatal rats (youngest in which it was tested), both when they were offered enriched milk through an anterior oral cannula while they were isolated from their dam and when they were allowed to suckle from her. However, anorectic effect was less in neonatal rats (day 3-13) than in adults. Weanling rats, 21-26 days old, were as sensitive to intraperitoneal epinephrine as adults. In 3- to 4-day-old rats it also reduced water intake, but this effect disappeared by day 12 and was not observed in mildly water-deprived adults. Peripheral adrenergic control of intake appears very early in ontogeny of rats. First, it affects food and water intake equally, but by day 12 it affects only food intake. Increase in sensitivity to epinephrine after weaning is probably due to an increase in number of hepatocytic adrenergic receptors and/or increase in enzymes necessary for hepatic effects of epinephrine.