An increase in the concentration of hepatic iron during the metamorphosis of the lamprey Geotria australis is accompanied by increased superoxide dismutase activity.

The concentration of total non-haem iron and its ferritin iron component, and the activity of the enzyme superoxide dismutase (SOD), were measured in the livers of ammocoetes, metamorphosing animals (stages 1-7) and recently metamorphosed downstream migrants of the lamprey Geotria australis. Total non-haem iron in the liver rose significantly from 0.15-0.55 μg.mg wet weight(-1) in ammocoetes and metamorphosing stages 1-3 to 2.2-2.9 μg.mg(-1) in stages 5-7 and to 8.8 μg.mg(-1) in downstream migrants. The comparable values for ferritin iron were 0.06-0.26, 1.4-2.0, and 5.3 μg.mg(-1). Superoxide dismutase activity fell sharply from 0.39 μg.mg(-1) in large ammocoetes to between 0.07 μg.mg(-1) in stage 1 and 0.15 μg.mg(-1) in stage 6, before rising significantly to 0.26 μg.mg(-1) in stage 7 and 0.35 μg.mg(-1) in downstream migrants. The sharp fall in SOD activity at the beginning of metamorphosis is assumed to be related to the marked decline in plasma iron which occurs at the onset of this non-trophic phase in the life cycle. It is proposed that the subsequent increase in SOD activity in the liver of G. australis with increasing iron represents a mechanism aimed at reducing the potentially toxic effects of iron accumulation. This view is consistent with the significant and positive correlation found between both total non-haem and ferritin iron and SOD activity in the liver of non-trophic animals.