Ultrastructural Changes in Human Platelets During Arachidonic Acid-induced Aggregation

This study was undertaken to visualize the sequence of ultrastructural changes occurring in human platelets during aggregation induced by arachidonic acid. Aggregometer recordings were obtained up to the time of adding glutaraldehyde to begin fixation of platelets for electron microscopy. A correlation was shown between the degree of aggregation and changes in the fine structure of human platelets which had been allowed to aggregate for 15, 30, 90, or 180 sec. The pattern of ultrastructural changes found in the platelets aggregating in response to arachidonic acid was similar to that reported previously for other aggregating agents such as collagen or ADP. Amorphous material was observed within the dilated canalicular system of platelets, supporting the thesis that its channels serve as a pathway for the products released during aggregation. The dilatation of the canalicular system of platelets induced by arachidonic acid could be mediated by an intermediate in prostaglandin synthesis.