Comparative anorectic effects of metaraminol and phenylephrine in rats.

Structure-anorectic activity relationship of two substituted amphetamines has been investigated in this study. Literature reports showed conflicting results in their anorectic activities in spite of the similarity in chemical structures of metaraminol and phenylephrine. Hence, the effects of alpha-carbon atom substitution and primary (metaraminol) and secondary amine (phenylephrine) moieties of these substituted amphetamines on the anorexia of rats were investigated in this study in nonfood- and food-deprived rats. Food intake at 1, 3, 14, and 24 h intervals, water intake at a 24-h interval, and body weight alteration for 10 days were monitored after daily drug administration for 3 consecutive days. Both metaraminol and phenylephrine were found to be potent anorectic. The relative anorectic potencies of phenylephrine were 0.54 and 0.81 of that of metaraminol at 1- and 3-h intervals, respectively. Body weight of rats treated with metaraminol (5.0 mg/kg) and phenylephrine (10 mg/kg) decreased significantly from Days 1 to 9.