Lysosomes in healing process of arterial fibrinoid degeneration in hypertensive rats.

Twelve 3-week-old, Wistar inbred rats were made hypertensive by bilateral constriction of renal arteries with silver clip. At 3-8 weeks after induction of hypertension, nodular lesions of mesenteric arteries were biopsied, and constricting clips were removed. At 5-28 days after removal of the clips, the animals were killed. Systolic blood pressure of the rats was 200mm Hg and over before removal of the clips, and decreased at the time when they were sacrificed. Ultrastructurally, modified smooth muscle cells were seen among the fibrinoid substance during healing process of fibrinoid degeneration in the intima. Fine cytoplasmic processes of these cells contained numerous lysosomes. The fibrinoid substance became reticular and reduced its density. The cytoplasmic processes with lysosomes were seen neither in the biopsied specimens nor in the tissues which showed cellulofibrous intimal thickening. Lysosomal enzymes were considered to increase in the modified smooth muscle cell during healing process of the fibrinoid degeneration. The enzymes were believed to be discharged extracellularly and to digest the fibrinoid substance partially. The partially dissolved substance might be phagocytized by the modified smooth muscle cells to form vacuoles of a medium electron density.