Electron Microscope Study of the Normal Rat Aorta

Abstract

The fine structure of the normal rat aorta is described. The presence of a subendothelial layer, the oblique orientation of the smooth muscle cells with respect to the aortic axis, and the occurrence of desmosomes between these cells and adjacent elastic laminae, are emphasized. Lead-stained collagen presented a characteristic signetMng appearance on cross-section. The rats examined were the pair-fed controls for the lathyritic series described in a separate communication.Electron microscope studies on the normal aorta and large arteries of mammals are scant. Buck (1) described the endothelium of the aorta, femoral and splenic arteries of rats and rabbits, and Parker (2) reported the normal architecture of rabbit coronary arteries. The only papers that could be found on the whole aortic wall were by Berrian (3) on the rat, and a short abstract on the kitten aorta by Pease (4). Although the present study is in general agreement with these, it differs with Berrian on several points.I t was considered of interest, therefore, to investigate the fine structure of the normal rat aorta using the newer embedding and staining techniques. In addition, this investigation serves as a basis for the lathyritic and enzyme studies reported in separate communications. Materials and MethodsFive albino rats of Sprague-Dawley strain were weaned at 21 days and then fed Purina fox chow. Each was pair-fed with a litter mate given a sweet pea diet, and thus constituted the controls for the lathyritic animals reported in a separate paper (5). The intake averaged 9 to 11 gin. daily and all animals remained apparently healthy though hungry. They were sacrificed when 37, 38, 41, 54, and 60 days old. After anaesthetizing the animal with ether, the thoracic cage was opened and both ascending and descending aortae were removed as quickly as possible. (The actual arch was carefully avoided owing to the multidirectional elastic laminae at the origin of the great vessels (6)). Unwanted fat and connective tissue were removed and 2 mm. lengths of the ascending aorta were placed in ice-cold 2 per cent O~O4 buffered to pH 7.3 with veronal-acetate and containing sucrose as described by Caulfield (7). Short lengths of the descending thoracic aorta were put in 10 per cent formalin for light microscopy. After fixation for 1 to la/} hours at 0-5°C. and dehydration at room temperature, duplicate specimens for electron microscope examination were embedded in butyl methacrylate and araldite. The best results with methacrylate were obtained by polymerizing at 60°C. for 2 days. Difficulty was experienced in obtaining undistorted sections of tissue embedded in araldite, and this was partly due to the nature of the aortic wall which consists of alternating layers of elastin and muscle cells, each layer presenting a different cutting property. The commonest artifacts were washboarding and macroscopic disintegration of the specimen in the microtome collecting trough. Since methaerylate did not appear to produce such an accurate anatomical picture as arald...

The dimensional characteristics of smooth muscle in rat blood vessels. A computer-assisted analysis.

“…For example, it cannot be adequately assessed on the basis of the CTOss-sectional vs. longitudinal appearance of cells in arteries (Keech, 1960;Rhodin, 1962Rhodin, , 1967Osborne-Pellegrin, 1978). Other methods which have been used are scanning electron micrographs (Cope and Roach, 1975) and microdissection techniques (Strong, 1938;Bohr et al, 1962).…”

Mechanical properties of arteries

“…The muscle is usually attached directly to the main body of the elastic lamina, although occasionally the muscle may be attached to a stray tail, presumably of elastin, projecting from the lamina (Keech, 1960).…”

The three-dimensional micro- and nanostructure of the aortic medial lamellar unit measured using 3D confocal and electron microscopy imaging☆

“…SMC orientation is described as circumferential (Arner and Uvelius, 1982;Clark and Glagov, 1985;Dingemans et al, 2000;Gaballa et al, 1998;Hansen et al, 1980;Wolinsky and Glagov, 1967), oblique (Bierring and Kobayasi, 1963;Cliff, 1967;Fujiwara and Uehara, 1992;Keech, 1960;Wolinsky and Glagov, 1967), and helical (Gabella, 1983;Osborne-Pellegrin, 1978;Wolinsky and Glagov, 1967). SMC orientation relative to the vessel surface has been described as parallel (Clark and Glagov, 1985) and not parallel (Cliff, 1970;Fujiwara and Uehara, 1992;Keech, 1960;Pease and Paule, 1960).…”