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Biomedical subjects

M B Stemerman

Publications and source records attributed to M B Stemerman.

At least 73 records · Page 4Linked to original sources
PubMed1980

In vivo aortic muscle cell growth kinetics. Differences between thoracic and abdominal segments after intimal injury in the rabbit.

Focal proliferation of smooth muscle cell (SMC) is an integral part of atherosclerotic plaque formation: characterization of regional variation in SMC growth kinetics is therefore important to the understanding of atherogenesis. SMC growth kinetics of rabbit abdominal and thoracic segments were compared. Rabbit aortas were denuded of endothelium and the animals killed after 3H-thymidine and Evans blue injections at 0 to 48 days after denudation. Incorporation of 3H-thymidine into both aortic segments peaked at 48 hours; no detectable incorporation occurred in the first 24 hours. Abdominal segment DNA specific activity (SA, dpm/micrograms DNA) and total kinetic activity (TKA, dpm/0.1 mm internal elastic lamina) at 48 hours were significantly greater than values for the thoracic aorta. Abdominal SA and TKA curves decreased exponentially after the 48-hour peak and parallel thoracic levels after day 7. SA and TKA values for each segment reflected the subsequent SMC intimal growth rates as measured morphometrically. Therefore, both segments share similar growth kinetic characteristics; however, the abdominal response to initimal injury is greater than the thoracic and leads to greater myointimal proliferation. The difference in response to injury in the two segments suggests regional variation in SMC's which are phenotypically similar.

Animals↗
PubMed1979

Vascular smooth muscle cell kinetics: a new assay for studying patterns of cellular proliferation in vivo.

A new quantitative assay for studying the kinetics of vascular smooth muscle cells in vivo is reported. The assay was used to determine the specific activity of DNA from rabbit aortic smooth muscle cells stimulated to grow by removal of the endothelial layer. The specific activity of the DNA was correlated with the rate of tritiated thymidine incorporation as measured by autoradiography and with the rate of DNA synthesis as estimated by direct measurement of cellular proliferation. Smooth muscle cells exhibit a 24-hour latent period in vivo prior to DNA synthesis; the synthesis peaks at 48 hours and then rapidly declines. The decline in DNA synthesis is not related to endothelial regrowth, and may be of homeostatic significance in limiting luminal stenosis. The assay offers a rapid and reliable alternative to autoradiographic and morphometric techniques for evaluating growth kinetics and growth regulation in vivo.

Animals↗
PubMed1979

Role of endothelium and hypercholesterolemia in intimal thickening and lipid accumulation.

In experiments reported here we tested the hypothesis that persistent absence of endothelium favors intimal thickening, lipid accumulation, and atherosclerosis. Rabbit aortas were de-endothelialized with a balloon catheter at Day 0. Initially, all rabbits were fed a diet low in lipid. Some rabbits (Group I) were continued on a diet low in lipid for 8 to 20 weeks after de-endothelialization. Beginning 4 to 9 weeks after de-endothelialization, other rabbits were fed semisynthetic lipid-rich diets (Group II) or cholesterol-supplemented diets (Groups III) for 4 to 20 weeks. Lipid accumulation in all groups was significantly greater in the re-endothelialized intima than in adjacent intima lacking an endothelial lining. In aortas of Groups I, II, and III the degree of intimal thickening was significantly greater in re-endothelialized areas than in adjacent areas lacking endothelium. Intimal thickness was enhanced in re-endothelialized areas of hypercholesterolemic rabbits of Group III compared with normocholesterolemic rabbits of Group I but not in areas lacking endothelium. Thus, results of these experiments do not support the hypothesis that the absence of endothelium particularly favors intimal thickening and intimal lipid accumulation. Results indicate that intima covered by regenerated endothelium is significantly thicker and more likely to accumulate lipid.

Animals↗
PubMed1978

The roles of endothelium, platelets, and smooth muscle cells in intimal healing.

The continual remodeling of the artery wall significantly narrows the lumen. It contributes to the development of atherosclerotic plaque through the incorporation of lipid into the arterial intima. The steps in the repair of arterial intima include platelet accumulation followed by leukocyte attachment to denuded areas, smooth muscle migration from the media, deposition of extracellular connective tissue components, and endothelial progression seem related to re-endothelialization, platelets, the pituitary, and unidentified factors.

Aging↗
PubMed1978

The influence of the pituitary on arterial intimal proliferation in the rat.

The formation of arteriosclerotic fibromusculoelastic intimal thickening following arterial de-endothelialization is well documented. Recent findings, both in vitro and in vivo, suggest that platelets are a major participant in the pathogenesis of this lesion by releasing a mitogen to medial smooth muscle cells (SMC). This mitogen results in SMC migration to and proliferation within the intima. A similar mitogen has been described as originating in brain and pituitary tissue. We now report that, in hypophysectomized rats with normal platelet counts, intimal hyperplasia is markedly delayed; pair-fed intact controls normally develop lesions. It therefore appears that the pituitary gland plays a significant role in the experimental arteriosclerotic response.

Animals↗
PubMed1977

The effect of thrombocytopenia on experimental arteriosclerotic lesion formation in rabbits. Smooth muscle cell proliferation and re-endothelialization.

This study was designed to investigate the mechanisms involved in fibromusculoelastic lesion formation produced by selective de-endothelialization by the intra-arterial balloon catheter technique in thrombocytopenic rabbits. Thrombocytopenia was induced and maintained for up to 30 days by daily injections fo highly specific sheep anti-rabbit platelet sera (APS). Evidence for re-endothelialization was obtained by i.v. Evans blue dye 30 min before sacrifice. Rabbits received daily injections of APS, which reduced the mean platelet count to 5,600/cm3; control animals received identically treated normal sheep sera on the same schedule, and had mean daily platelet counts of 363,000/cm3. Evaluation of intimal thickness was assessed by counting cell layers in semithin sections. Intimal thickening in aortae from rabbits treated with APS was strikingly suppressed, in contrast to those from normal sheep sera-treated animals which showed a mean intimal thickness of 18 cell layers within 28 days often after de-endothelialization. Re-endothelialization was not affected by APS treatment. These results indicate that the proliferation of smooth muscle cells is dramatically inhibited by reduction of platelets.

Animals↗
PubMed1977

Intimal healing. The pattern of reendothelialization and intimal thickening.

Studies were undertaken to investigate further the basis of intimal proliferation and the identity of the surface lining cell in rabbit aortas subjected to extensive deendothelialization. Endothelial cells were selectively removed by passage of an inflated balloon catheter through the arterial lumen. The healing response was evaluated at intervals up to 36 weeks by several techniques: 1) permeability to Evans blue, 2) reappearance of endothelial cells as indicated by the specific marker, adsorbed goat anti-rabbit tissue factor-horseradish peroxidase, 3) planimetric measurements of intimal thickness, and 4) electron microscopy. The results indicate that endothelial cell recovery progressed slowly and that it extended only from areas spared denudation. The regions not covered by endothelial cells were lined by cells of smooth muscle cell origin. Such areas were permeable to Evans blue-protein complex, and their luminal smooth muscle cells were associated with connective tissue-like material at their luminal surface; this material apparently acted as a base for platelet accumulation. The present findings indicate that the lumen of the extensively denuded vessel is lined by either endothelial or smooth muscle cells and that intimal healing is related to restoration of endothelial cell cover. In addition, intimal thickening reached a maximum well before reendothelialization was complete.

Animals↗
PubMed1977

Estrogen suppression of surgically induced vascular intimal hyperplasia in rabbits.

Since estrogen has been shown to reduce aortic medial hypertrophy in hypertensive rats, a naturally occurring estrogen compound, estradiol, was studied for its ability to suppress the intimal hyperplasia which follows vessel transection and anastomosis. Suture lines and adjacent abdominal aortas were examined by light and electron microscopy 1 month after surgery, in 23 rabbits. Test animals were given 200 microgram of Depoestradiol I.M. weekly, starting 3 days preoperatively. Control animals were similarly manipulated but received no estrogen. Control animals showed striking intimal thickening over the sutures, in contrast to the estrogen-treated group in which there was significantly less growth of corresponding tissue (p less than 0.01).

Animals↗
PubMed1977

Tissue-factor coagulant activity of cultured human endothelial and smooth muscle cells and fibroblasts.

The tissue-factor (thromboplastic) activity of cultured human endothelial cells and fibroblasts is low at time of transfer into fresh medium but increases 3-10 fold. Endothelial cells reach peak activity (400 U/10(5) cells) 5-8 hr after subculture. Activity in fibroblast cultures peaks (3000-12,000 U/10(5) cells) 7-12 hr after subculture. After attaining maximum activity, endothelial and fibroblast tissue-factor content decreases in a time course similar to other cells studied in this laboratory, approaching basal levels by 24-50 hr after subculture. If medium over fibroblasts is changed every 12 hr, activity can be sustained at the peak level for an additional day but cannot be maintained at a high level indefinitely. The kinetics of expression of smooth muscle cell tissue factor are markedly different from other cell types. There is always a pronounced lag (30 hr or more) before the activity increases, and then, in most cases, there is no subsequent decline in activity even though the cells are not refed or restimulated. The activity of each of these cell types is cryptic but becomes available after freeze-thaw disruption of cells.

Blood Group Antigens↗
PubMed1976

Platelet interaction with human umbilical cord vascular basement membrane.

The basement membrane of the human umbilical vein was studied by electron microscopy with respect to its ultrastructure, susceptibility to digestion by collagenase or trypsin, and reactivity with human platelets. Electron microscopic examination of this vessel showed a continuous reticulated basement membrane which morphologically resembled those of mammalian capillaries and rabbit heart valves. The vascular endothelium was removed by freezing and thawing, thus uncovering the underlying connective tissue. The vessels were sliced into rings which were incubated with collagenase or trypsin. The basement lamella appeared to be susceptible to digestion by either enzyme. Platelet interaction with exposed vascular basement mambrane was studied by rotating frozen-thawed everted and noneverted rings in anticoagulated whole human blood. In heparinized or citrated blood, large aggregates of degranulated platelets adhered to collagenous controls; in contrast, the test rings with exposed basement membrane were partially covered with a monolayer of platelets which appeared to retain discoid or spherical shape and granules. In EDTA-anticoagulated blood, the collagen control rings accumulated a platelet monolayer, whereas little or no adhesion occurred on the basement membrane surface. In this system the basement membrane of the human umbilical vein appears to be a poor platelet reactive surface as compared to collagen.

Basement Membrane↗
PubMed1976

Electron microscopic immunohistochemical identification of endothelial cells in the rabbit.

Antibody to tissue factor apoprotein was adsorbed against gamma-globulin and coupled to horseradish peroxidase; this complex was applied to various rabbit tissues. The distribution of the peroxidase marker then was observed by electron microscopy. We examined fixed or frozen sections, as well as breis of aorta, vena cava, brain, heart, lung, liver, spleen, kidney, bone marrow, mesothelial gut lining, erythrocytes, and platelets. All endothelial cells that had been exposed to the antibody complex were positive and in all cases only the endothelial cells showed localization of the electron-dense reaction product. Tissues that had been incubated with complexes prepared with gamma-globulin from animals not immunized with tissue factor apoprotein showed no staining. Prior treatment of the tissue with uncoupled anti-tissue factor gamma-globulin blocked binding by the coupled antibody. In blood vessel preparations that had been specifically designed to expose the media to the anti-tissue factor complex, medial smooth muscle cells and connective tissue showed no reaction product. Parenchymal cells of the other other organs mentioned likewise were devoid of reaction product. Similarly, the leukocytes and platelets occasionally observed in vessel lumens showed no evidence of binding. Platelets adhering to arterial subendothelial structure after injury also were unreactive. These findings suggest that in normal rabbits anti-tissue factor-horseradish peroxidase complex combines selectively with endothelial cells.

Adsorption↗
PubMed1975

Intimal injury and regrowth in the rabbit aorta; medial smooth muscle cells as a source of neointima.

The present study was undertaken to determine the mechanism of neointima formation in rabbit arteries subjected to extensive endothelial desquamation. Endothelial cells were selectively removed from the abdominal aorta by passing an inflated balloon catheter through the vessel. The healing response was then studied serially for up to a week, when neointima formation had provided a virtually complete cover. In en face preparations, the early neointimal cells appeared in random locations; they did not develop in apposition to residual, healthy endothelium. The possibility of blood cell colonization was explored by inserting killed aortic homografts. Since these homografts showed neointima formation only close to the site of junction with the normal aorta and as a direct extension of healthy endothelium, the likelihood of significant blood cell colonization was deemed small. Histologic and electron microscopic sections provided evidence that the early neointimal cells in the healing aorta were derived from medial smooth muscle cells. Healing of the injured arterial intima was accompanied by thickening instead of prompt restoration to normal, and the thickened intima resembled an arteriosclerotic plaque. The present study thus supports the concept that arteriosclerosis is a disease involving proliferation of medial smooth muscle cells.

Animals↗
PubMed1975

The aortic intima. II. Repair of the aortic lining after mechanical denudation.

This article reports the ultrastructure of the aortic lining during the repair of mechanically denuded aortic intima in the rat. Three main features were observed: a) Although platelets form a pavement on the exposed components of the aortic intima, platelet thrombi do not form on the denuded surface. b) During the first weeks after injury, a temporary false endothelial lining is formed by modified intimal smooth muscle cells. While the modified smooth muscle cells do not constitute a continuous cell layer, they are like true endothelial cells in that platelets do not adhere to the cell membrane of either cell type. c) A continuous layer of true endothelial cells is formed within 2 months after the original injury. Even after reestablishment of a continuous endothelium, however, abnormalities persist in the form of incompletely formed intercellular junctions. This abnormal endothelium is associated with areas of intimal smooth muscle cell proliferation. These observations are compatible with two alternative interpretations of the role of endothelial injury in the intimal proliferation seen following injury to the vessel wall: a) persistent defects in the endothelium may result in proliferation of underlying arterial smooth muscle cells or b) the proliferation, in converse, may in some manner delay the healing process of the overlying endothelium.

Animals↗