[The liver sinusoids in rats following fractionated local telecobalt-irradiation. A transmission and scanning electron microscopic study (author's transl)].

Changes in liver sinusoids following fractionated irradiation were studied by use of TEM and SEM. Rats received telecobalt-irradiation of their liver regions in daily doses of 500 r for 9 days, a total dose of 4500 r. One day after the end of the irradiation series the fine structure of hepatocytes was almost intact. In SEM the liver sinusoids contained numerous corpuscles, which in TEM were recognized as cellular blebs separated from endothelial cells. 8 days after irradiation small foci of necrotic hepatocytes could be visualized. Instead of complexes of small fenestrations (sieve plates) the endothelial cells contained striking round or oval holes in their tenuous processes. After 120 days small groups of hepatocytes with alterated fine structure of their organelles and some necrotic parenchyma cells were still present. Away from these focal necroses the endothelial cells now resembled sinusoidal endothelium in control animals. Fat-storing cells appeared to have multiplied and were enlarged. There was distinct fibrosis only in perisinusoidal spaces. The formation and discharge of electron lucent blebs is discussed as a mechanism compensating for an enhanced uptake of fluid into irradiation injured endothelial cells. In order to form holes in the tenuos processes of endothelial cells a disordered synthetic pattern and the shearing forces of the circulating blood are thought to be necessary. Repair of these intracellular holes may be possible. In rats irradiation induced lesions of the small intrahepatic vessels can be excluded as a cause of the late changes in liver parenchyma cells.