Alterations of metallothionein isomers in Hg(0)-exposed rat brain

Previously we found that exposure to mercury vapor effectively induced brain metallothionein (MT) in rats. Here, using FPLC-gel chromatography, we examined time-dependent alterations in the MT isomers, MT-I/II and MT-III, following 3 weeks of exposure. Rats were exposed to mercury vapor at 8.3 mg/m3 for 15 h in total over 5 consecutive days. Total MT levels in rat cerebrum and cerebellum increased by 65% and 155%, respectively, 24 h after the final exposure. The increased levels in both tissues remained unchanged for at least 2 weeks after termination of exposure. Interestingly, most MT in control rat cerebrum and cerebellum was accounted for by MT-III, with MT-I/II being less than 10%. Through mercury vapor exposure, MT-I/II was quickly induced to a significant extent in both tissues, reaching a level comparable to that of MT-III. The induction rate of MT-I/II in the cerebellum was somewhat higher than in the cerebrum. Chromatograms showed that the MT-I/II thus induced began to decline at an early stage in both tissues. In the cerebrum, the amount of MT-I/II on day 22 was about 30% of the maximum level on day 1. On the other hand, the induction of MT-III was not that dramatic, but it did become evident, at least in the latter stage, when MT-I/II had begun to decrease. Thus, though the induction rate of MT-III was not as high as MT-I/II, it was sustained throughout the experimental period.