Iron loading in the liver of parasitic adult lampreys, Petromyzon marinus L.

Electron microscopic and histochemical procedures were used to describe iron loading in the normal liver of parasitic adult sea lampreys. Petromyzon marinus L. Ferric iron is present in large quantities as ferritin in the cytoplasmic matrix, in hemosiderin granules, and in large vacuoles of hepatocytes. Ferritin is also found in the lateral intercellular space, in the perivascular space, and in the sinusoidal lumen. Large crystals in the cytoplasmic and nuclear matrices of some hepatocytes likely represent excessive aggregations of ferritin molecules. Ferrous iron is localized at the lateral cell membrane and vacuolar membranes of hepatocytes. Iron accumulation is less significant in Kupffer cells which are present in small numbers. The relationship of iron loading in the adult lamprey liver to the sanguivorous diet, the rate of erythrophagocytosis, the absence of bile ducts and canaliculi, and the nature of the iron-binding proteins in the plasma are considered. Emphasis is placed on the similarity of the above morphological findings to those resulting from experimentally induced and pathological states of iron loading in other vertebrates, and on the potential use of the lamprey as a model for studying iron loading in the vertebrate liver.