Effect of L-dopa administration to fine structures of brain, heart and kidney in rats, with special reference to appearance of microvascular thrombosis and its pathological significance.

L-dopa (100-200 mg/kg/day) was given orally to rats for one, two, or three months. The cerebrum, cerebellum, heart and kidney were then examined using the light and electron microscope. With the light microscope, there was observed the occurrence of small hemorrhagic foci and occlusion of the capillaries, venules and occasionally small veins by amorphorus eosinophilic material or agglutinating red blood cells in all the tissues examined. On the other hand, with the electron microscope, there was seen the presence of two distinct changes in the brain, heart and kidney, which were never found in the corresponding tissues from the control rats. One was concerned with intravascular abnormalities, i.e. formation of thrombi in the microvasculatures. Above all, microthrombi that were thought to be equivalent to amorphous eosinophilic material in light microscopy consisted of diffusely distributed, electron-dense, fine granular substances and randomly scattered, much electron-denser, large granular material. The other was concerned with mitochondrial alterations in the parachymal cells, i.e. nerve cells, cardiac muscle cells and renal parenchymal cells. In general all the changes that were detected by search at both light and electron microscopic levels tended to be developed increasingly with prolongation of the period to sacrifice from commencement of L-dopa administration so that effect of L-dopa on their formation was apparently time related.