We studied ultrastructurally cerebral perforating arteries in 60 stroke-prone spontaneously hypertensive rats (SHRSP), which were sequentially killed at 4-52 weeks of age before showing symptoms of stroke. Another 24 SHRSP were killed soon after they showed symptoms of cerebral infarction. The initial vascular lesions observed in the asymptomatic group included focal cytoplasmic necrosis in the outer layers of the media. This change progressed to widespread medial necrosis with time. In the infarction group, numerous monocytes were seen adhering to the endothelium of the arteries having advanced medial damage. Following the adherence of monocytes to the endothelium, large amounts of plasma components were visible in the arterial wall. The accumulation of the plasma components (especially fibrin) thickened the wall, narrowed the lumen, and resulted in occlusion. These results suggest that monocytes may affect the endothelium, perhaps disturbing the so- T here are many studies on hypertensive vascular lesions in humans and experimental animals.'" 7 Only a few investigators, however, have focused on the long-term effects of hypertension on the perforating arteries in the brain.8 " 12 In the present study we sequentially analyzed the ultrastructure of the perforating arteries in stroke-prone spontaneously hypertensive rats (SHRSP) as developed by Okamoto et al in 1974. 13 We discovered numerous monocytes that adhered to the endothelium. We have therefore tried to clarify the characteristic changes that develop into occlusions and have attempted to explain the role of monocytes in arterial lesions, especially those resulting in occlusion. Materials and MethodsOkamoto et al 13 and Yamori et al 14 developed SHRSP in which stroke (cerebral hemorrhage and/or infarction) develops spontaneously in > 8 0 % of the rats. The cerebral lesions resemble those found in humans. Since the development of this rat strain, we have continued to inbreed them selectively. At present we have > 1,500 SHRSP in our laboratory. A group of 24 SHRSP 28-50 weeks of age with symptoms of stroke composed a cerebral infarction group, and 60 asymptomatic SHRSP 4-52 weeks of age served as controls. Almost half the rats in the infarction group were in an Received October 29, 1986; accepted March 24, 1987. irritable state denoted as "Stage 2," while the other half were lethargic, labelled "Stage 3." 15 Rats in the infarction group were anesthetized with pentobarbital, and the cerebral arteries were perfused with a 1 % formaldehyde-1 .25% glutaraldehyde fixative in 0.1 M cacodylate buffer at pH 7.6 at room temperature 16 via the descending aorta at 180 mm Hg pressure for 4-5 minutes. After perfusion, the brains were carefully removed and fixed with a 2% formaldehyde-2.5% glutaraldehyde mixture in 0.1 M cacodylate buffer for 1 hour at 4° C. The infarcted cortices were then taken out and placed in the same fixative for 3 hours at 4° C and then washed overnight at 4° C in 0.1 M cacodylate buffer. Afterwards, the infarcted cortices were sectioned into sma...

Abstract• The scanning electron microscope (SEM) has been employed to study the effects of ischemia on the luminal surface of the common carotid artery. Fifteen adult rabbits were lightly anesthetized and the common carotid arteries surgically exposed. The right carotid artery was occluded with a single Heifetz clip for five minutes (five animals), 15 minutes (five animals), and 30 minutes (five animals). Following removal of the clip, the animals were immediately perfused with glutaraldehyde and the arteries excised and prepared for critical point drying. Four additional rabbits were perfused following the same method with no surgical procedures performed in the neck. Normal aortas were also examined. The nature and frequency of endothelial cell alterations were determined by analysis often randomly selected SEM fields. Examination of the endothelial surface of arterial segments distal to the occluding clip revealed the presence of numerous "crater-like" defects as well as outpouchings or "balloons." The numbers of craters and balloons were significantly increased in the ischemic (distal) arterial segment as compared to either proximal or sham-operated control segments (P < 0.001). These endothelial cell alterations were never observed in random micrographs of arterial segments taken from unoperated control animals, but were seen at the ostia of some intercostal arteries of the aorta. It is suggested that these craters and balloons could cause interference with blood flow and the formation of platelet thrombi by their protrusion into the lumen, as well as alteration of the permeability of the arterial intima.

Sodium dodecyl sulfate (SDS), an anionic hydrophobic ligand, is known to alter the mechanical properties of elastic fibers. In order to analyze the mechanism of the alteration, two forms of fibrous elastins, "solid" and "powder" elastins, which consisted of fascicular elastic fibers and single or oligomeric elastic fibers, respectively, were prepared from bovine aorta, and the interactions of SDS with these elastins in the presence and absence of 0.15 M NaCl were studied. The solid elastin was able to retain 1.2- to 1.4-fold larger amounts of SDS than the powder elastin under both conditions, and both elastins retained 1.2-fold or larger amounts of SDS in the presence of NaCl than in its absence. Whereas both elastins released the retained SDS gradually on repeated washing with an SDS-free buffer, the release rates from the solid elastin, especially the rate in the presence of NaCl, were much smaller than those from the powder elastin, and the solid elastin retained approximately 40% of the bound SDS under conditions where the powder elastin lost most of its SDS. The SDS-binding capacities of both elastins were significantly lower than those of soluble kappa-elastin and serum albumin, which bound SDS homogeneously on the polypeptide chains. When the washed SDS-bound solid elastin was incubated with methylene blue and examined under a microscope, most of the methylene blue-SDS complex was located at the interfiber spaces of the elastic fibers. These results suggest that SDS alters the mechanical properties of elastic fibers by binding to the interfiber spaces and surfaces of the fibers rather than by binding to the internal polypeptide chains.

The effects of temporary vascular occlusion with surgical clips on the underlying endothelial lining were studied with scanning (SEM) and transmission (TEM) electron microscopy. Twenty-five rabbits were anesthetized and both common carotid arteries exposed. A Heifetz clip was used to occlude the right carotid artery for 5, 15, and 30 minutes, and 2 hours in five animals each. The clips were removed and the vessels immediately perfused with glutaraldehyde. In five remaining animals, the right carotid arteries were occluded for 30 minutes followed by removal of the clip and resumption of blood flow for 30 minutes prior to fixation. Combined SEM and TEM examination of the endothelium of compressed segments revealed "craters" and "balloons", blebs and vacuoles, swollen mitochondria, dilated granular endoplasmic reticulum, and subendothelial edema. There were also areas of endothelial cell flattening, discontinuity, and desquamation exposing the subendothelial tissues. Following restoration of flow, platelets and fibrin were found adherent to altered endothelial cells and to exposed subendothelial tissues. Endothelial craters and balloons were also found distal and, significantly less frequently, proximal to the site of occlusion. It is suggested that antiplatelet aggregating agents may prove beneficial for the prevention of thrombus formation at the site of the clip as well as craters and balloons distal to the clip following procedures requiring temporary vascular occlusion.

The introduction of the scanning electron microscope into biological research has revolutionized the possibilities of studying the surface structures of biological specimens. The method was used originally for the surface of hard tissue ; however, the improved fixation method, which preserves quite well the ultrastructure of soft tissues as shown by Barber and Boyde (1968) ,1) has now made it possible to observe the fine structure of the surface of soft tissues.The present investigation is a study of the surface of vascular endothelium in the rabbit and man. These endothelia have already been studied by transmission electron microscopy, so their structure is partially known. This is the preliminary report of the study. Materials and methods.The endothelial surface of aortas, coronary and renal arteries, inferior vena cavas, right and left ventricles and atria from 13 male rabbits and aortas, inferior vena cavas, right and left ventricles and atria of two men, 21 and 74 years old, who died of Crohn's disease and myeloma, respectively, were examined in the present study.The method of Barber and Boyde (1968)1) was modified and used. Namely, the isolated specimens were carefully washed by LockeRinger's solution, then 1 % osmium tetroxide (with veronal acetate to pH 7.4) was poured into the vessel lumen. The specimen was cut into small blocks 3 mm x 10 mm in size. The blocks were fixed for one hour under cold temperature in an ice-box and were dehydrated in graded Analar acetone solutions of 50%, 70%, 80%, 90%, 95%, and two changes of absolute acetone.After air drying, the specimens were mounted at an angle of 45° to an evaporation source and rotated during the deposition of a conducting coat of about 100300 A of gold in a vacuum.The specimens were studied with a scanning electron microscope (JSM-II) of Japan Electron Optics Laboratory Co. Ltd., using a beam accelerating voltage of 610 0 Ky. The micrograph recorded with a scanning electron beam on the film with an exposure time of 3060 seconds.