The effects of chronic manganese feeding on the activity of monoamine oxidase in various organs of the developing rat.

1. Chronic manganese feeding of rat with doses as high as 10 mg/ml in drinking water had no effect on body weight increases during postnatal development. The organ weight increases in brain, liver, heart and kidney also remained unaffected, but spleen weight was consistently lower than in the age-matched controls after Mn-feeding, being more marked at the higher doses. An increase in the Mn concentration to 20 mg/ml led to drastic body weight losses not unlike that seen in malnutrition. 2. There were differential developmental changes in monoamine oxidase (MAO) with respect to tissue type and substrate used. Manganese feeding did not affect the developmental patterns of MAO in brain, heart and kidney. However, hepatic MAO activities towards 5-HT and BzNH2 were found to increase after 10--15 days of postnatal life. 3. In contrast, the activity in the spleen towards 5-HT was lower in the high Mn-treated group in the first few days post-partum.