Neurochemical and biotransformational enzyme responses to manganese exposure in rats.

Adult male rats were exposed to 0.5% manganese as MnCl2 in their drinking water for 1, 4, or 6 weeks. Manganese content was measured in brain, liver, kidney, and intestine. Peak manganese concentrations were found in all tissues after one week exposure. Hepatic aryl hydrocarbon hydroxylase, ethoxycoumarin O-deethylase, and epoxide hydrase activities increased after one week manganese exposure, while intestinal and renal activities decreased. The activities returned nearly to the control level at six weeks of exposure. The UDPglucuronosyltransferase activity increased in the liver, kidney, and intestinal mucosa after one week exposure, decreasing thereafter nearly to the control level. In the brain, most significant changes were found after six weeks exposure when the succinate dehydrogenase activity decreased. The results suggest an adaptation to manganese absorption during continuous exposure. The biotransformation enzymes respond first to manganese exposure followed by neurochemical changes in the central nervous system.