Serial Changes in MATO (FGP) Cells During Structural Changes in Cerebral Arterioles in SHR-SP Rats

SHR-SP rats established by Okamoto and Yamori spontaneously develop severe hypertension. Recently, it was reported that SHR-SP rats were insulin resistant and deficient in Cd 36. Tagami et al. demonstrated wide spread necrosis of smooth muscle cells in the cerebral vascular wall in these hypertensive rats and assumed that the degeneration of smooth muscle cells was caused by malnutrition of the cerebral microvessels.However, the cerebral microvessels are enwrapped by novel perivascular cells, MATO FGP cells (M cells), and these M cells scavenge waste products and oxidized LDL to maintain favorable milieu for cerebral microvessels.In this paper, the authors employed control Wistar and SHR-SP rats aged 4, 6, 10, 20, 24 and 28 weeks old, and were performed functional and morphological studies of M cells during changes in vascular architecture of the cerebral arterioles in SHR-SP rats.Experimental animals were studied by histochemical and morphological techniques. Further, the uptake capacity of M cells for administered intravenously HRP (horseradish peroxidase) was examined at each developmental stage.As a result of the present study, the following evidence was obtained;1) PAS stainability of lysosomal inclusions in M cells decreased with growth-especially at 20 weeks after birthin SHR-SP rats, while in control rats, the stainability increased. Neutral fat droplets appeared and increased in M cells of SHR-SP rats 10 to 20 weeks, but not in those of the control rats.2) In general, the differentiation of M cells was retarded, but some M cells were also degenerated in SHR-SP rats. Immature M cells increased in the perivascular space at 20 weeks, and surrounded the hypertrophied vascular walls, which were composed of atrophic and degenerated smooth muscle cells at 24 to 28 weeks. The immature type of M cells (fibroblastoid cells) produce collagen fibers.3) The uptake capacity of M cells for HRP was inclined to decrease especially in the cerebral cortices as the animals advanced in age.From these findings, the authors conclude that differing from those in control Wistar rats, some M cells in SHR-SP rats degenerate during the early stage of growth, while other M cells transform to fibroblastoid cells and surround the disintegrating vascular wall. The fibroblastoid may participate in the process of cerebral arteriolosclerosis and microaneurysm formation.