Previous studies have shown that acute, oral administration of malathion modulated the humoral immune response to T-cell-dependent antigen, mitogenic responses, macrophage function, and mast cell degranulation. While administration of malathion for 14 days did not affect the generation of an immune response to antigen, it was possible that macrophage and mast cell functions were affected. In this report, the effect of malathion administration for 14 days upon these parameters were assessed. This treatment regimen increased the respiratory burst capacity to a maximal level at a dose of 1 mg/kg/day or greater. The effect of oral administration of malathion for 14 days on the degranulation of mast cells in various organs (heart, skin, and small intestine) and peritoneal lavage fluid was also assessed. At doses of 1 mg/kg/day and above, the number of mast cells that was undegranulated decreased and the number that was severely degranulated increased. There was no change in mast cell integrity in biopsies from heart and skin, and in peritoneal fluid after 14-day administration of 0.1 mg/kg/day. However, the number of mast cells associated with the small intestine that had undergone degranulation was increased at this dose of malathion. These data indicate that repeated administration of malathion increased macrophage function at doses as low as 1 mg/kg/day and led to mast cell degranulation at doses as low as 0.1 mg/kg/day.
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