Ultrastructural distribution of peroxidase in thrombocytes of mammals and submammals.

The localization and distribution of peroxidase (PPO) activity were studied ultracytochemically in thrombocytes from lampreys, carps, frogs, snakes, tortoises, rabbits, sheep, dogs, and monkeys. PPO activity was not detectable in the thrombocytes of lampreys, carps, frogs, and snakes. However, this enzyme activity was demonstrated in the nuclear envelope and endoplasmic reticulum of tortoise thrombocytes. Dog and monkey thrombocytes (blood platelets) exhibited PPO activity in the dense tubular system, but this enzyme activity was not detectable in rabbit and sheep thrombocytes. Our observations are interpreted to suggest that thrombocytes from animals lower than amphibia are peroxidase negative. Furthermore, it can be said that thrombocytes from animals higher than reptiles are generally positive, although there are exceptions. PPO activity was localized in the endoplasmic-reticulum system, but not in the cytoplasmic granules of thrombocytes common to submammals and mammals. In this study, we also compared the distribution of peroxidase activity in thrombocytes, neutrophils, and eosinophils and conclude that these are significant differences in the distribution of PPO and myeloperoxidase.