EFFECT OF COMBINED FENTHION AND CIMETIDINE USE IN RATS ON LETHALITY, BLOOD CHOLINESTERASE ACTIVITIES, AND SERUM-CHOLINESTERASE ISOENZYMES

H-2-receptor antagonists inhibit cholinesterase (ChE) activity. We exa mined perturbations in ChE isoenzyme patterns and ChE activities of ra ts from the combined effects of fenthion (FEN) and cimetidine (CIM). S ixty-four female Sprague-Dawley rats were divided into 8 groups. Four rat groups were given FEN or gum arabic solution and each group divide d into 2 small groups according to the CIM or gum arabic administratio n. FEN was administered po at 12.3 mg/kg (1/20 LD50) or 24.5 mg/kg (1/ 10 LD50) for 14 days or 49 mg/kg (1/5 LD50) every 4 days. CIM was give n po at 1,500 mg/kg from days 7 to 13. Samples were collected 3 h afte r CIM administration on days 8 and 13. CIM did not influence ChE isoen zyme patterns or ChE activity. FEN inhibited both the ChE isoenzyme pa tterns and ChE activities without producing clinical signs. Although 1 rat in the 12.5 mg FEN/kg + CIM group died on day 10, all rats in oth er FEN (24.5 mg/kg or 49 mg/kg) + CIM groups died on days 8-10. Differ ences in suppression of ChE isoenzyme patterns were detectable between the FEN-dosed and FEN + CIM-dosed groups. There were no differences i n ChE activities between the FEN-dosed and FEN + CIM-dosed groups. The ip administration of 500 mg CIM/kg (LD50) did not suppress ChE activi ties.