Megakaryocyte and platelet ultrastructure in the Wistar Furth rat.

Wistar Furth (WF) rats were studied and compared with Sprague-Dawley (SD) rats to determine if ultrastructural abnormalities in platelets or megakaryocytes could explain their macrothrombocytopenia. WF rats had one third of the platelet count of healthy rats and two times the platelet volume. Megakaryocyte number was decreased and the size of mature stage three megakaryocytes also was decreased. WF platelets had large membranous inclusions, and otherwise showed normal ultrastructural morphology. The WF megakaryocytes showed abnormal aggregates of the demarcation membrane system. Ruthenium red staining was more intense on WF megakaryocytes and platelets, indicating a possible increase in surface mucopolysaccharides. It is possible that abnormal megakaryocyte membrane structure may lead to WF macrothrombocytopenia.