Effects of lead, cadmium and mercury on brain adenylate cyclase

The effects of lead, cadmium and mercury ions on adenylate cyclase activity of rat cerebrum, cerebellum and brain stem were studied in vitro and in vivo. Adenylate cyclase activity in homogenates of cerebellum as well as cerebrum and brain stem was found to be inhibited by micromolar concentrations of these heavy metal ions in vitro. Administration of lead acetate trihydrate (25 mg/kg body wt i.v.) produced an initial increase of adenylate cyclase activity in the cerebellum and brain stem 1 h after injection, followed by a significant decrease of enzyme activity in cerebrum and cerebellum 4 h after the injection. Chronic lead treatment achieved by feeding lead containing diets, which generated blood lead levels of 31.3 +/- 3.8, 68.8 +/- 1.5 and 121.5 +/- 8.6 microgram Pb/100 g blood resp., produced a significant increase of brain lead levels and a 10-30% reduction of adenylate cyclase activity in cerebrum, cerebellum and brain stem. Phosphodiesterase activity was reduced under these conditions in the range of 10-20% in cerebellum and brain stem, but not in cerebrum.