Response of Megakaryocytes of the ‘August’ Rat to X-irradiation

Summary

Methods of evaluating the numbers of megakaryocytes of the ‘August’ rat are described. As a result of these studies, it is concluded that irradiation causes a block in cell-divisions in the stem-cell preceding the megakaryoblast, and results in a fall in numbers of megakaryocytes, and consequently of platelets. A similar conclusion was reached by Zajicek and Zeuthen (1956). Megakaryocyte numbers are readily reduced by x-rays, a dose of 80 r effecting a reduction of 50 per cent within 7 days of irradiation. Studies on partially shielded animals demonstrated a pronounced megakaryocyte hyperplasia in the shielded sites. Recovery in the irradiated areas was found to commence earlier than after whole-body radiation. These results throw some light on the mechanisms by which platelet levels are maintained after partial-body irradiation.