The effects of phenylpropanolamine on Zucker rats selected for fat food preference.

Treatments of human and rodent obesity frequently involve administration of amphetamine derivatives, much like phenylpropanolamine, which suppress food intake. The Zucker rat is a commonly employed model of youth-onset obesity in which the homozygous genotype manifests hyperphagia as well as other characteristics that parallel human obesity. Using a macronutrient selection procedure, we examined phenylpropanolamine's differential actions in controlling dietary intake, spontaneous open-field activity, and regional hypothalamic neurotransmitter levels in obese female Zucker rats of varying fat food preference. We hypothesized that phenylpropanolamine would alter hypothalamic monoamine levels differently in low-fat preferring and high-fat preferring Zucker rats, and hence affect feeding behavior and activity differently in these two groups. It was found that in high-fat preferring animals, phenylpropanolamine significantly decreased spontaneous open-field activity, decreased only carbohydrate caloric intake, and increased serotonin and 5-HIAA levels in the paraventricular nucleus (PVN). In low-fat preferring animals, phenylpropanolamine decreased carbohydrate, protein, and total caloric intake, had no significant effect of spontaneous activity, and increased serotonin and 5-hydroxyindole acetic acid levels in the PVN. Inherent and induced physiological differences of low-fat and high-fat preferring animals are discussed as well as phenylpropanolamine's potential in combination drug therapy for the treatment of human hyperphagic obesity.