Pathologic evidence of microvascular rarefaction in the brain of renal hypertensive rats

Hypertension results in microvascular rarefaction in various organs. In this study, we investigated the pathogenesis of microvascular rarefaction in hypertensive rat brain. Light microscopy of the arterioles showed hyalinosis and fibrinoid changes. X-ray images of rat brain injected with barium exhibited a decrease of microvessels. Scanning electron microscopy using casting method showed a decrease of microvessels and the presence of blind end structures. Scanning electron microscopy without casting method showed leukocyte and platelet adhesion to the endothelial cells of arterioles. Transmission electron microscopy of the hypertensive rat arterioles revealed fibrinoid deposits in the intima with luminal narrowing and thrombotic occlusion. The muscle cells in the arteriolar media had disappeared, and cell debris and a lamellarly increased basement membrane were observed. The capillaries of the hypertensive rats sporadically showed collapse and thrombotic occlusion. The basement membrane of the capillaries was mildly thickened and occasionally duplicated. The pericytes of hypertensive rats showed irregular profile, islet-like fragmentation of their cytoplasmic processes and large defect of them around the capillaries. The basement membrane of the pericytes was thickened, and rarely found cell debris in it. We conclude that microvascular rarefaction in hypertensive rat brain results from both an elevated arteriolar and capillary pressure, which induces secondary arteriolar, capillary, and pericyte lesion via overperfusion.