The morphology of the kidney in young adult anadromous sea lampreys, Petromyzon marinus L., adapted to seawater. II. Distal and collecting segments, the archinephric duct, and the intertubular tissue and blood vessels

Gradual acclimation of young adult anadromous sea lampreys, Petromyzon marinus L., to full-strength (100%) seawater results in changes in the morphology of the distal and collecting segments, the archinephric duct, and the intertubular tissue and blood vessels. The alterations first appear in animals in 60% seawater and mainly are represented by a luminal precipitate in the distal and collecting segments and increased numbers of cytoplasmic granules in the cells of these segments. Luminal debris of degradating cells, concentric rings of an amorphous material, or a crystalline material is characteristic of distal segments from animals adapted to 80% seawater and it is accompanied by flattening of the epithelium and a further granulation and a vacuolation of the cytoplasm. The above features are present to a lesser extent in the collecting segment. In 100% seawater, further flattening, vacuolation, granulation, and apparent degeneration of distal cells occurs and there are many more small-diameter renal tubules. Granulation of endothelial cells of efferent arterioles in animals at concentrations of 80 and 100% may indicate that these cells are recruited to absorb macromolecules. The tubular interstitium at these two highest salinities possesses many cells involved in the phagocytosis of red blood cells. The morphological transformation of the renal cells indicates that young adult anadromous P. marinus may have some difficulty in osmoregulating in hyperosmotic environments.