Diurnal variation of phenylpropanolamine anorexia in rats.

An examination of the effects of the diurnal cycle on phenylpropanolamine (PPA) anorexia was conducted using two groups of rats, differentiated on the basis of time (Night or Day) of drug injection (0, 10, 20, or 30 mg/kg PPA). The results demonstrate that PPA, over a range of doses, has greater anorectic potency during the dark phase of the diurnal cycle. Moreover, the effect of PPA on water intake was not influenced by the diurnal cycle, suggesting that the diurnal effect was limited to the inhibitory action of PPA on feeding. Other studies are cited which, combined with the present results, suggest that the diurnal cycle may modulate feeding control processes, and that the impact of an anorectic agent such as PPA on feeding behavior may be, in part, a function of the diurnal cycle.