Peter R. L. Mosse

Balloon catheter injury to rabbit carotid artery. I. Changes in smooth muscle phenotype.

Stereology was used to Investigate the changes In ultrastructure of smooth muscle cells during the formation of an experimental Intimal thickening Induced by Injury with an Inflated balloon catheter. The volume density of myofllaments in the cell cytoplasm was measured In smooth muscle cell-lined areas (which are freely permeable to Evans blue dye and, hence, stain blue) and In re-endothellalized areas (which remain white after Injection of Evans blue) of the rabbit carotid artery. Two weeks after Injury, the volume densities of myofllaments In the Intimal smooth muscle cells In both white and blue areas were significantly less than that for control medial smooth muscle (67.9%±3.6%; mean±SE), being 38.8%±1.0%and 35.9±3.3%, respectively. By 6 weeks after injury, the volume density had Increased significantly In both white (55.1%±3.4%) and blue areas (53.5%±3.0%), and these values did not change significantly by 18 weeks. The volume density of myofllaments in the luminal (lining) smooth muscle cells In the blue areas was significantly less than that of control medial cells and remained low (26.7%±2.1%) up to 18 weeks after Injury. The Initial balloon-Induced Injury caused considerable damage to the smooth muscle cells In the media, and the remaining medial cells underwent similar changes In ultrastructure to the cells in the neointlma. At 2 weeks, the cells had a low volume density of myofllaments (44.9%±2.4%), which returned to a level not significantly different from the control artery by 6 weeks after Injury. There were no differences in the estimates of the volume density of myofllaments between the Inner and outer media of the Injurled arteries. These findings suggest that, after Injury produced by a balloon catheter, the smooth muscle cells In both the media and the resultant Intimal thickening undergo a reversible change In ultrastructure.

Smooth muscle phenotypic expression in human carotid arteries. II. Atherosclerosis-free diffuse intimal thickenings compared with the media.

The volume fraction of synthetic organelles in smooth muscle cells from areas of atherosclerosis-free, diffuse intimal thickenings (DIT) and media of human carotid artery has been determined morphometrically. Tissue was obtained at autopsy from men and women aged 35 to 80 years, at 6 to 12 hours after death. With both sexes, the volume fraction of synthetic organelles in smooth muscle cells from the DIT was not significantly different from the volume fraction of synthetic organelles in cells of the subjacent media (0.25 and 0.21, respectively). This is in marked contrast to our earlier study in which the volume fraction of synthetic organelles in smooth muscle cells of DIT from a similar region of artery, but adjacent to atheromatous plaques, was highly significantly different from cells of the subjacent media (0.48 and 0.23, respectively). Only in regions near atherosclerotic plaques do the majority of smooth muscle cells of DIT express a different phenotype from cells of the media.

The distribution of capillaries in the somatic musculature of two vertebrate types with particular reference to teleost fish.

SummaryThe distribution of capillaries in teleost and rat striated muscles was investigated using a number of different methods. A new method for directly viewing capillaries was developed.Teleost white muscle has a capillary: fibre (C∶F) ratio of between 0.2 and 0.3; and 0.6 to 1.0 peripheral capillaries per muscle fibre. 26–49% of fibres had no peripheral capillaries. Values for the rat gastrocnemius were 1.2, 2.6 and 4.8% respectively which compares well with literature values.Flathead red muscle had a C∶F ratio of between 1.9 and 2.5; and between 5.3 and 6.6 peripheral capillaries per muscle fibre depending on the method used. Values for rat soleus were 1.8 and 4.1 respectively.Teleost pink fibres had an intermediate number of capillaries.Rat striated muscle, particularly the gastrocnemius, was found to be heterogeneous with respect to the distribution of capillaries. Flathead red muscle was homogeneous whilst teleost white muscle was only slightly variable.Flathead red muscle fibres are well supplied with subsarcolemmal mitochondria. These show a clumped distribution corresponding to the position of capillaries. In contrast teleost white fibres are almost totally devoid of these and all other mitochondria.No differences were observed in the vascularisation of either muscle type along the length of the fish.The results are discussed in relation to the division of labour between fibre types during swimming.

Capillary distribution and metabolic histochemistry of the lateral propulsive musculature of pelagic teleost fish

SummaryMetabolic and vascular adaptation of teleost lateral propulsive musculature to an active mode of life was investigated in four pelagic teleosts (mackerel, yellowtail scad, pilchard and Australian salmon). Histochemical profiles and capillarisation data of the red and white muscle were compared to those of less active demersal species.Pelagic white muscle stained positively for the aerobic enzymes succinate dehydrogenase and NADH diaphorase, and had both subsarcolemmal and intermyofibrillar mitochondria which corresponded to the loci of the histochemical stain. Subsarcolemmal mitochondria tended to be localised close to capillaries. In contrast, white muscle from demersal species was unstained for the same enzymes and was devoid of mitochondria. Red muscle of all species had abundant mitochondria and stained intensely for aerobic enzymes.Capillarisation was quantified by determining the percentage of fibres surrounded by a given number of peripheral capillaries, mean fibre diameter, mean number of peripheral capillaries, capillary: fibre ratio and sharing factor where appropriate.Red muscle of mackerel, Australian salmon, pilchard and scad are better vascularised than red muscle of the flathead having 153, 200, 242, 291 and 309 μm2 of cross-sectional fibre area per peripheral capillary, respectively.White muscle of mackerel, pilchard and scad are better vascularised than white muscle of the Australian salmon and flathead having 2040, 3367, 4992, 9893 and 10,469 μm2 of cross-sectional fibre area per peripheral capillary respectively.Red muscle of Australian salmon had distinct regional variation. Deep red muscle was found to be more highly vascularised (4.2 peripheral capillaries per muscle fibre) than lateral red muscle (1.9 peripheral capillaries per muscle fibre). Red muscle of the other species was less heterogeneous. White muscle capillarisation was slightly variable in all species.It is concluded that the white muscle of the pelagic species studied is functionally and structurally adapted for sustained aerobic activity with relatively abundant mitochondria being preferentially situated close to the source of gas and metabolite exchange.

Development of a Large Fibromuscular Intimal Thickening Does Not Impair Endothelium-Dependent Relaxation in the Rabbit Carotid Artery

The release of endothelium-derived relaxing factor (EDRF) was examined in the rabbit carotid artery 6 weeks after denudation with an inflated balloon catheter in vivo. A concentric, fibromuscular intimal thickening of variable width developed in all areas lined with either regenerated endothelium or modified luminal smooth muscle cells. In vitro studies showed that in vessels precontracted with serotonin, only the re-endothelialized areas could relax to the endothelium-dependent dilators methacholine, substance P and the Ca2+ ionophore A23187. Re-endothelialized areas with large concentric, fibromuscular intimal thickening (between 10 and 20 cells thick) relaxed with a similar sensitivity and maximum to methacholine compared with control areas. It is concluded that newly generated endothelial cells release EDRF whilst the specialized lining smooth muscle cells present 6 weeks after injury do not, and that the presence of a large fibromuscular intima does not prevent EDRF from reaching the media to cause relaxation.

A Comparison of the Avascular Capsule Surrounding Free Floating Intraperitoneal Blood Clots in Mice and Rabbits

&NA; The development of the avascular fibrous capsule which surrounds free floating intraperitoneal blood clots in mice and rabbits is described. In mice, the capsule at 2 wk consisted of an outer layer of partially flattened macrophage‐like cells overlying a thick layer of myofibroblasts embedded in a collagenous stroma. In contrast, in rabbits the capsule at 2 wk consisted of 3 distinct layers: an outer layer of mesothelial cells; an underlying relatively acellular layer containing a few macrophages; and, immediately adjacent to the clot, an innermost layer of variable thickness consisting mostly of myofibroblasts. The myofibroblasts of the rabbit capsule were fewer in number than those of the mouse. Detailed examination of the formation of these capsules suggests that myofibroblasts may develop from cells within the peritoneal cavity that show morphological features characteristic of monocytes/macrophages.

Vascular anatomy of the lateral musculature of the flathead,Platycephalus bassensis (Teleostei: Perciformes)

SummaryThe vascular anatomy of the lateral musculature of the flatheadPlatycephalus bassensis, was studied by scanning electron microscopy of corrosion casts. Arteries and veins showed an alternating pattern in neighbouring vertebral segments. The red muscle was supplied by five major branches of the intermuscular artery, and the white muscle by infrequent branches of the intermuscular artery, dorsal segmental artery and ventral segmental artery. Venous drainage of the red and white muscles broadly mimicked the arterial supply. The functional unit of the trunk vasculature can be considered as an artery, a vein and connecting fine blood vessels. There appear to be 2 over-lapping types leading to alternating clockwise and counter-clockwise flows of blood. Small satellite vessels were observed running parallel to most of the larger blood vessels. No anatomical A-V shunt vessels, or series vascular connections between the red and white muscle, were observed. The irregular, alternating adult system is postulated to have developed from an earlier system showing strict bilateral symmetry and equal arterial and venous development in each vertebral segment.

Spontaneous arterial lesions: Their possible role in arteriosclerosis

Spontaneous lesions of the arterial wall involving the internal elastic lamellae and variable amounts of the intima are described in the spontaneously hypertensive rat caudal, renal, and mesenteric arteries. A simple model for producing similar circumferential lesions in rat and rabbit carotid arteries has been developed and the subsequent repair of these lesions is described. Two types of circumferential lesion can be produced by the application of 50-160 g of longitudinally applied tension. Small lesions can be up to 400 micron in length and are characterized by the loss of a small area of endothelium and rupture of the internal elastic lamellae. No demonstrable damage to the media is detected in these lesions. Larger lesions can be up to 1 mm in length and are characterized by the loss of endothelium and rupture of the internal as well as a variable number of medial elastic lamellae. Little, if any, damage to the medial smooth muscle cells is observed although the extracellular matrix is often disrupted. Small lesions are completely reendothelialized within 24 hr and larger lesions within 7-10 days. Both large and small lesions repair without the formation of an intimal thickening of smooth muscle cells, despite quite marked damage to the media of the larger lesions.

The morphology and cell culture of the striated musculature of the rat azygos vein

SummaryThe azygos vein of the rat can be divided into three regions: 1) The proximal cardiac region, where the wall is composed of two and sometimes three layers of cardiac muscle and a thin discontinuous layer of smooth muscle cells. Vascular casts of this region demonstrate layers of capillaries closely following the orientation of the cardiac fibres. 2) A transitional zone, where both cardiac and smooth muscle cells interdigitate. In this zone, close associations between smooth muscle and cardiac muscle cells can be observed, however, gap junctions do not appear to be present. 3) Beyond this transitional zone the vessel resembles a typical thin-walled vein.The cells of the media of the entire length of azygous vein have been isolated and grown in culture and two separate viable populations identified corresponding to smooth and cardiac muscle.