Microvillar bleb formation in primate hepatocytes irradiated with 32-meV protons.

Eight rhesus monkeys (Macaca mulatta) were whole-body irradiated with 6000 rads of 32-MeV protons. Animals were killed at several time intervals after exposure. Tissue blocks were fixed in glutaraldehyde, post-osmicated, and then embedded in Maraglas-D.E.R. 732 resin. Observation of ultrathin sections by electron microscopy revealed balloon-like enlargements of distal portions of hepatocytic microvilli (blebs) which were less dense than the proximal portion of microvilli. The blebs ranged widely in size; some were contained within the space of Disse, whereas many protruded into the sinusoidal lumen. In a few micrographs the sinusoidal lumen as filled with bleb-like structures. Such bleb formation suggests a possible mechanistic explanation for hepatic congestion following high levels of irradiation.