A comparison of the effects of phenylpropanolamine, d-amphetamine and d-norpseudoephedrine on open-field locomotion and food intake in the rat.

d,l-Norephedrine (PPA) is available as an over-the-counter appetite suppressant and nasal decongestant in the U.S.A. The pseudoisomer d-norpseudoephedrine, is available as an appetite suppressant in Europe, and has been isolated as one of the stimulatory components (cathine) of the Khat plant. Some authors have misidentified cathine as PPA and this confusion in the literature has resulted. PPA and d-norpseudoephedrine possess significantly different pharmacological properties despite having identical structural formulae. Anorectic activity was determined in a food-deprived rat model. PPA and d-norpseudoephedrine were approximately one-tenth as potent as d-amphetamine with all compounds producing a dose-dependent decrease in food intake. Locomotor activity in an open-field apparatus was determined as an index of CNS stimulation. Male Sprague-Dawley rats treated with d-norpseudoephedrine, in doses between 10 and 50 mg/kg, exhibited significantly increased locomotor scores compared to saline (control) treated animals, an increase similar to that caused by 2 mg/kg d-amphetamine. PPA (5-50 mg/kg) failed to increase locomotion significantly. These results indicate that although each compound tested decreased food intake in a dose-dependent fashion, significant differences in open-field locomotion do exist between PPA, d-norpseudoephedrine, and d-amphetamine. Stereoisomeric compounds, although structurally similar, frequently have different pharmacological effects. Thus extreme care must be taken to properly identify these compounds in the literature.