A fine structural study of the removal of the effectiveness of benzo-pyrone treatment of lymphoedema by the destruction of the macrophages by silica.

Macroscopical, light microscopical and electronmicroscopical observations were made of the diaphragm, skin and brain of rats, some of which were treated with intraperitoneal silica for 8 days (after being given it i.v. for 2 days). The diaphragms showed a most remarkable increase in fibroblast activity and fibrosis beneath the peritoneal mesothelium (which was disintegrating). Deep to this there were many disintegrating macrophages, and much oedema and increased protein concentration. Ligation of the cervical lymphatics produced the usual changes of lymphoedema in the skin and brain. This was greatly reduced in the animals treated with a mixture of benzo-pyrones. However, in those animals also treated with silica, the benzo-pyrones had no effect on the amount of oedema or of protein. In all the animals except those treated with silica, lymphoedema was accompanied by considerable numbers of macrophages entering the affected tissues; in those treated with silica, these numbers were greatly reduced.