Ultrastructural localization of secretory type II phospholipase A2 in atherosclerotic and nonatherosclerotic regions of human arteries.

We recently reported on the immunolocalization of type II secretory nonpancreatic phospholipase A2 (snpPLA2) in human atherosclerotic lesions. In the present study, we present data on the distribution and ultrastructural localization of snpPLA2 in adjacent nonatherosclerotic and atherosclerotic regions of human arteries. Electron microscopy (EM) of immunogold labeling techniques with a monoclonal antibody was used to analyze arterial tissue. The human specimens analyzed were obtained from autopsy and surgery cases. The results with EM showed a stronger snpPLA2 immunoreactivity in regions of arteries with atherosclerotic lesions than in regions without lesions from the same individual. snpPLA2 immunoreactivity was stronger in the arterial intima of atherosclerotic than of nonatherosclerotic tissue. EM-immunogold examination revealed that the majority of snpPLA2 was localized along the extracellular matrix, associated with collagen fibers and other extracellular matrix structures. Intracellular snpPLA2 was observed in electron-dense vesicles in intimal cells. snpPLA2 was also found in contact with large, extracellular lipid droplets. These results support the hypothesis that extracellular snpPLA2 is localized at sites where it may hydrolyze phospholipids from lipoproteins and lipid aggregates retained in the extracellular matrix of the arterial wall. This may be a mechanism for in situ release of proinflammatory lipids, free fatty acids, and lysophosphatidylcholine in regions of apolipoprotein B accumulation, which are abundant in atherosclerotic lesions.

Apoptosis is abundant in human atherosclerotic lesions, especially in inflammatory cells (macrophages and T cells), and may contribute to the accumulation of gruel and plaque instability.

Death of intimal tissue may lead to plaque rupture with thrombosis, which is the basis of the most severe clinical consequences of atherosclerosis. Little is known about the mechanisms that promote intimal cell death or its nature. This work was undertaken to elucidate the extent to which, the cell types in which, and where programmed cell death, apoptosis, might occur in atherosclerotic lesions. The material was fibrous or fibro-fatty non-ulcerated lesions from the human thoracic aorta and coronary arteries. Apoptosis was indicated by the in situ labeling of internucleosomally degraded DNA with the TUNEL technique, which has a preference for apoptosis as compared with cell necrosis and was combined with the immunohistochemical typing of cells. Apoptosis was corroborated by morphological criteria on the light and electron microscope levels and by the presence of an apoptosis-specific protein. It was common in the lesions and virtually absent in non-atherosclerotic regions. It occurred in smooth muscle cells subendothelially, in places of the fibrous cap, and in the underlying media, which may destabilize the plaque and promote rupture. Inflammatory cells, ie, macrophages and T cells, appeared abundantly subendothelially, in the fibrous cap, and in the shoulder regions, and apoptosis was common, maybe reflecting a means for quenching of the inflammatory reaction. Many macrophages contained abundant apoptotic material indicative of phagocytosis of apoptotic cells, but the occurrence of apoptosis, even in some of these cells, and of apoptotic material extracellularly and the very high numbers of apoptotic cells that were encountered may indicate insufficient mechanisms for the removal of apoptotic cells in the atherosclerotic lesion. It is not possible to decide as yet whether this is due to overloading with cellular material by inflammation and cell multiplication, to an increased frequency of apoptosis, to a reduction of the removal/degradation of apoptotic material by macrophages, or a combination of these factors.

Contrary effects of lightly and strongly oxidized LDL with potent promotion of growth versus apoptosis on arterial smooth muscle cells, macrophages, and fibroblasts.

The inhibition of experimental atherosclerosis by antioxidants and the presence of oxidized LDL (oxLDL) in atherosclerotic lesions indicate that oxLDL may play what is perhaps a primary role in atherogenesis. LDL promotes the growth of arterial smooth muscle cells (SMCs), and oxLDL has cytotoxic effects. Since excessive intimal growth alternating with necrosis is typical of atherosclerotic lesions, we wondered whether these extreme changes in the lesions could be related to the extreme effects of LDL and oxLDL on cells. We therefore examined the effects of increasing LDL oxidation on its capacity to induce cell growth or cell death and whether the latter could be due to apoptosis. Cells of the types present in the atherosclerotic artery used, ie, SMCs (human arterial), macrophages (human macrophage-like cell line THP-1), and human fibroblasts. Growth was evaluated by measuring the synthesis of DNA and culture size (MTT method) and apoptosis by using the in situ labeling of internucleosomally degraded DNA and, in the case of SMCs, the appearance of chromatin condensation. The oxidation of LDL was by UV or Fe ions. Shortly oxidized LDL had a markedly increased growth-promoting effect on all cell types. With prolonged exposure to UV, but not to Fe, LDL became increasingly cytotoxic, and this toxicity was paralleled by the appearance of apoptosis in all cell types. After prolonged UV treatment, low-molecular-weight material from the partially degraded LDL was responsible for the induction of apoptosis. The dual effect of oxLDL, ie, its strong growth-promoting effect or the induction of cell death by apoptosis, depending on the degree of change by oxidation, is compatible with the notion that oxLDL plays a role not only in atherogenesis but also more extensively in the development of the structure typical of the atherosclerotic lesion, with focal excessive growth alternating with necrosis.

Growth-stimulating effect of lipoproteins on human arterial smooth-muscle cells and lung fibroblasts is due to apo B-containing lipoproteins, type LDL and VLDL, and requires LDL receptors.

Excessive growth of the arterial smooth muscle is essential for the development of atherosclerosis and leads to arterial insufficiency in several other conditions. It is therefore important to elucidate the mechanisms that regulate the growth of the human arterial smooth-muscle cell, SMC. Like other untransformed cells, SMC require plasma for sustained growth in vitro. As found in an earlier study most of the material in plasma which stimulates SMC growth is related to the lipoproteins (LP), and is widespread among LP of different density classes. In the present study we investigated whether the growth-stimulating activity might be more specifically related to certain lipoproteins defined by criteria other than density or particle size. Activity was assayed using human SMC and human lung fibroblasts as both a change of culture size and DNA synthesis. The growth-stimulating activity was confined to apo B-containing LP, as defined by their strong affinity to heparin-Sepharose, electrophoretic beta-mobility, the presence of apo B and the absolute requirement of low density lipoprotein (LDL) receptors for the growth-stimulating effect to appear. It was strongly potentiated by PDGF-BB. A much higher level of LDL was required to initiate synthesis of DNA in SMC than in fibroblasts but at optimal LDL concentration the degree of activation was similar for both cell types. Apo B-containing LP are very powerfully related to atherosclerosis. As intimal thickening is a primary change in atherogenesis, the growth-stimulating effect of them may be of direct pathogenetic importance.

Structural organization of reconstituted human arterial smooth muscle tissue.

We used human arterial smooth muscle cells (SMCs) that had been reorganized three-dimensionally into aggregates, so-called spheroids, as a model system that might more closely correspond to arterial smooth muscle in vivo than do conventional monolayer cultures. After reaggregation the presence of serum in the culture medium strongly promoted the maintenance of spheroidal SMCs. With access to fresh serum, the spheroids developed into highly organized structures with an outer laminated shell of spindle-shaped SMCs and a more porous core of rounded or polygonal SMCs. After several weeks in culture, extracellular matrix components appeared and the tissue assumed features characteristic of maturing intimal repair tissue. Many cells had features of programmed cell death (apoptosis). This feature may be important because it may indicate that regression of arterial smooth muscle tissue may be a much more strongly controlled process than hitherto realized. Without access to fresh serum, the spheroidal tissue showed degenerative features, much like those in atherosclerotic lesions, ie, the presence of foam cells, cellular debris, and some cell death. It is possible that this situation in vitro resembles that of atherosclerotic tissue in vivo, in which retention of plasma constituents is a conspicuous feature. In some respects, therefore, the small sample of human arterial tissue represented by the spheroid may represent an in vitro analogue of the arterial wall, which may undergo maturation or degenerative atherosclerosis-like changes depending on exogenous factors. The spheroidal SMC system may therefore also be a suitable model for in vitro studies of atherogenesis.

Lipoproteins are major and primary mitogens and growth promoters for human arterial smooth muscle cells and lung fibroblasts in vitro.

Smooth muscle proliferation leading to excessive intimal thickening is of prime importance in atherosclerosis. Human arterial smooth muscle cells (SMCs) and human lung fibroblasts are rather insensitive to mitogens under plasma-free conditions in vitro. This prompted us to study the distribution and nature of the growth-promoting material in human plasma. SMCs were obtained from explants of human aortic media. More than 80% of the growth-promoting activity of plasma was present in the lipoprotein (LP) fraction. The growth-promoting capacity of the different LPs was determined on fractions isolated with density gradient ultracentrifugation. Cytotoxic effects appeared if low-density lipoprotein (LDL) was not protected from oxidation and were aggravated with platelet-derived growth factor (PDGF)-BB. Very-low-density lipoprotein, LDL, and high-density lipoprotein (HDL) stimulated DNA replication and cell growth by themselves. The stimulation was considerable and equaled that obtained with PDGF-BB only. It was strongly increased in the presence of PDGF-BB. The effect on SMCs was not uniform for subfractions of HDL. A light portion inhibited growth in the absence but strongly stimulated it in the presence of PDGF-BB. For fibroblasts, HDL subfractions had a uniform effect, suggesting a cell type-dependent difference. Addition of cholesterol or essential fatty acids did not induce a growth response similar to that of LPs. This speaks strongly against mere nutritional supplementation as responsible for the mitogenic and growth-promoting effect of LPs and suggests that the effect may be more specific. Disordered LP metabolism is strongly related to atherosclerosis, and certain LPs have a potential role for the deposition of lipids. In addition to this, the distinct mitogenic and growth-stimulating effect of LPs by themselves, as demonstrated in the present report, suggests a mechanism by which intimal thickening, which is a prerequisite for atherosclerosis, may be induced. The pronounced amplification of this effect with PDGF-BB, a substance that also has been implicated in atherogenesis, might promote growth leading to the excessive intimal thickening in the atherosclerotic plaque.

Can we predict the long-term function of the subclavian flap angioplasty?

Neonatal operations have improved the prognosis for newborn children with aortic coarctation. The 30-day mortality of 123 neonates with isolated coarctation of the aorta collected from nine series was found to be 0.8%. The subclavian flap angioplasty was the most frequently used surgical procedure in this collected series. This technique is relatively new, however, and many questions have yet to be answered. In this study we have done subclavian flap repair in newborn pigs and followed them up to adult ages. The pigs were killed 28 or 44 weeks postoperatively, and the aortas were reexamined. All flaps had grown symmetrically in width and length and parallel to the growth of the descending thoracic aorta. The flaps were macroscopically intact. Signs of degenerative processes were not found. The wall thickness of the subclavian flap increased by growth of the individual fibroelastic lamellar units in the tunica media. This adaptation to the increased wall stress occurred early in life. The wall strength of the flap also increased by thickening of the intimal layer. We conclude that the subclavian flap is well suited to function as a part of the aorta in adult life.

Watanabe hyperlipidemic rabbit as a model of aortic degeneration of the medial lamellar elastin unit.

At age 3 years, WHHL rabbits are near the end of their lifespan, frequently dying from the progression of their hyperlipidemic disease from events such as myocardial infarction. Out of a colony of 20 three-year-old WHHL rabbits raised as part of a NIH breeding project, 2 rabbits actually died of a ruptured thoracic aortic aneurysm. The need for a model to study abdominal aortic aneurysm formation led us to explore further the abdominal aortic pathology in aged WHHL rabbits. Six rabbit abdominal aortas from 3-year-old WHHL rabbits were preserved in formalin, sectioned, and stained for elastin. These were compared to the same sections of six normolipidemic age matched New Zealand white (NZW) rabbits. There was significant (P less than or equal to .001) destruction of the medial lamellar elastin unit in the aorta of the WHHL rabbits compared with the control NZW rabbits. Severe cholesterol deposits appeared to destroy the medial lamellae from the inside out. No definite aneurysm formation was seen in the abdominal aorta despite the significant changes in the medial lamellar elastin units. Thus, this model could be used to study the elastin degeneration of the media, but not necessarily abdominal aortic aneurysm formation.

Effects of transforming growth factor-beta 1 on human arterial smooth muscle cells in vitro.

Control of the thickness of the arterial wall is critical, as excessive overgrowth of constituent smooth muscle cells (SMCs) may interfere with blood flow. Effects on SMCs in vitro of several growth factors that are present in blood and/or that are produced endogenously in the arterial wall under certain conditions suggest that influences of endocrine, paracrine, and autocrine nature from stimulating and inhibiting factors may control the smooth muscle tissue mass in the artery. This possibility was explored further by investigating the degree of myodifferentiation in terms of the presence of differentiation-specific filamentous alpha-smooth muscle actin and growth, as measured by the synthesis of DNA and cell number, of SMCs as influenced by their exposure to the mitogens, platelet-derived growth factor and epidermal growth factor, and the bifunctional growth factor, transforming growth factor-beta 1 (TGF-beta 1). Exposure to TGF-beta 1 markedly enhanced differentiation-specific filamentous alpha-smooth muscle actin. This effect did not require arrest of growth, which speaks against a direct causal relation between loss of myodifferentiation (modulation) and multiplication. When quiescent cultures were exposed to TGF-beta 1, alpha-smooth muscle actin was further increased, indicating a more specific differentiation-promoting effect by TGF-beta 1 than mere inhibition of growth. Exposure to TGF-beta 1 also increased spreading, which occurred in parallel with increased filamentous alpha-smooth muscle actin and appearance of stress fibers. Exposure to platelet-derived growth factor under serum-free conditions and to epidermal growth factor in cultures exposed to serum markedly decreased the number of alpha-actin-positive SMCs, indicating a dedifferentiating effect by these mitogens. Exposure of SMCs to TGF-beta 1 under serum-free conditions had pronounced effects on growth, with a concentration-dependent inhibition of platelet-derived growth factor-induced DNA synthesis and cell multiplication. The basal synthesis of DNA in the absence of added growth factors was also greatly inhibited. With serum-free cultures, some loss of cells occurred even with very low concentrations of TGF-beta 1 (5 pg/ml), against which platelet-derived growth factor or a dense cultural state had a protective effect. Enhancement of cell multiplication was not detected for cultivated human SMCs exposed to TGF-beta 1, irrespective of culture density, in contrast to that reported for dense cultures of rat SMCs. TGF-beta 1 is present in and may be released from platelets in situations that promote platelet adherence such as endothelial injury; TGF-beta 1 may also be released from activated macrophages and T lymphocytes either during an immune reaction or inflammation or from the endothelium.(ABSTRACT TRUNCATED AT 400 WORDS)

Aortic compliance in hypercholesterolemic Watanabe rabbits compared to normal New Zealand controls.

This study was designed to test the hypothesis that severe atherosclerosis changes aortic compliance. Compliance of a vessel is defined as change in volume per unit change in pressure and is a measure of the stiffness or distensibility of the vascular wall. Part of the energy delivered by the left ventricle in systole is used to propel the blood forward into the aorta and part of it to distend the aorta and major vessels. During diastole, the arterial walls recoil and provide energy for propulsion of blood, thereby making blood flow continuous. It is known that Watanabe hereditary hyperlipidemic rabbits develop severe atherosclerosis beginning at 6 months of age. Compliance of the ascending thoracic aorta was studied angiographically in eight Watanabe hereditary hyperlipidemic rabbits of ages greater than 6 months and six normal lipidemic New Zealand white rabbits of ages greater than 6 months, used as controls. The normal New Zealand white rabbits had an average blood cholesterol of 27.4 mg/dL, SD = 13.8, and a regional compliance in the ascending aorta of 0.004 mL/mm Hg, SD = 0.002, compared to the Watanabe hereditary hyperlipidemic rabbits with a cholesterol of 583.1 mg/dL, SD = 162.7, and a compliance of 0.0022 mL/mm Hg, SD = 0.0015. These are significant differences (p less than .05). In addition, the histopathology of the aorta of the Watanabe hyperlipidemic rabbit compared to that of the controls showed a significant decrease in the number of medial lamellar elastin units, an indicator of the decreased elasticity of the blood vessel wall.

Biochemical characterization of elastin in neointimal hyperplasia of rabbit aorta.

Elastin synthesized in response to vascular injury was characterized in terms of its amino acid composition, the biosynthetic labeling of the desmosines and of the heat coacervable polypeptides present in the 2 M urea extract. Neointimal hyperplasia of the chronic variety was induced in rabbit aorta by superficial mechanical lesions. At 4 months following injury the reendothelialized neointimal thickening and the media were excised. Aliquot samples were incubated with [3H] lysine, extracted with 2 M urea, 0.1 M Tris, pH 7.4 and hydrolysed with collagenase. In the residue of the digests the [3H] desmosines were quantified after electrophoretic separation. Elastin was purified from the nonlabeled aliquots of the media and neointimal hyperplasia. It accounted for 60% and 25% of the dry weight of the media and the neointima respectively. Elastin isolated from the media and the neointima had essentially the same amino acid composition. The incorporation of [3H] lysine into desmosines and into coacervable polypeptides indicated that the synthesis of crosslinked elastin is still active in the hyperplasia at 4 months following injury.

Rupture of renal arterial aneurysm in pregnancy. Case report.

The case is described of a patient at term of her second pregnancy with spontaneous rupture of a renal arterial aneurysm, successfully delivered by caesarean section with primary repair of the renal artery. Sixteen cases have previously been reported, but only one was dealt with in a similar way. The literature is reviewed and the aetiology of pregnancy-related arterial aneurysm is discussed.

Impaired fibrinolysis-inducing capacity for postinjury phenotype of cultivated human arterial and human atherosclerotic intimal smooth muscle cells.

Impaired fibrinolysis is believed to promote atherosclerosis and contribute to myocardial infarction. The major triggering factor for fibrinolysis is vascular tissue plasminogen activator (t-PA), and the aim of this study was to evaluate the capacity of human arterial smooth muscle cells (SMC) for induction of fibrinolysis. SMC were plated on labeled fibrin gels, and lysis was measured as release of label. Fibrinolytic capacity was dependent on the phenotypic state of SMC. The "multilayered phenotype" to which SMC modulate after cellular injury had a much lower fibrinolysis-inducing capacity than the more ordinary "monolayered" SMC type. Fibrinolysis was mediated by activation of plasminogen. In long-term experiments under conditions imitating thrombolysis, platelet-derived growth factor promoted fibrinolysis indirectly by increase of SMC number, and a direct effect on cellular production of t-PA was not detected. SMC from atherosclerotic intima had a much lower capacity for induction of fibrinolysis than cells from adjacent nonatherosclerotic intima. SMC also displayed several structurally detectable interactions with the fibrin substratum, such as organization of the gel by means of extension of numerous filamentous processes and contraction and wrinkling of the gel. In conclusion, human arterial SMC in vitro induce fibrinolysis by activation of plasminogen. This capacity is dependent on phenotype and lowered for SMC from atherosclerotic intima, suggesting impairment after arterial injury and in atherosclerosis.

Agglomeration to nodules modulates human arterial smooth muscle cells to distinct postinjury phenotype via foam cell transition.

Cultures of arterial smooth muscle cells (SMCs) tend to form loci with multilayered growth as "hills" or "nodules," which is unusual for normal but common for transformed cells. Earlier it was shown that such nodules were composed of SMCs with the distinctive properties of small cell size, low adhesivity, and scarce or no fibronectin and filamentous actin, features which may also characterize tumor cells. Similar properties could be induced by cultivation of SMCs in aggregates, indicating modulation of SMCs to a distinct "multilayered" phenotype, rather than selection of variant SMCs with preference for multilayered growth. Transfer of SMCs to a three-dimensional arrangement by agglomeration to nodules, "spheroids," by seeding of SMCs on low-adhesive substratum, like agarose, was followed by signs of SMC injury with focal autodigestion and with loss of material from the cells, which to some extent was deposited extracellularly, transition to foam cells with cholesterol accumulation mainly as cholesteryl esters, and eventually decrease in cell size. Identically treated fibroblasts showed similar, but much less pronounced, changes and were largely protected by whole blood serum, in contrast to SMCs. The results indicate that the "multilayered" SMC type can be conceived of as a postinjury phenotypic state which is preceded by overt cellular injury and transition to foam cells in conjunction with sudden transfer to three-dimensional arrangement in spheroids. It is suggested that similar modulation may be important in atherosclerosis, in which foam cell transition and deposition of debris are prominent changes.

Subclavian flap angioplasty with absorbable suture polydioxanone (PDS). An experimental study in growing piglets.

The fate of the subclavian flap in aortoplasty was studied and a new synthetic monofilament, absorbable vascular suture (polydioxanone, PDS) was evaluated. In 11 piglets submitted to the aortic repair, the diameter of the aortic arch and descending aorta and the length and width of the subclavian flap were measured. The aortoplasty was performed with a continuous running suture of 6/0 PDS. All the animals survived and grew normally. They were sacrificed 6-26 weeks postoperatively, when the mentioned variables were reestimated. No aortic narrowing was found and no suture material was detectable in the lumen. The subclavian flap had grown uniformly in length and width. Histologic examination showed evening of the inner surface by intimal proliferation and healing of the anastomoses. There was no sign of flap destruction and tissue reaction to PDS suture was minimal, indicating normal growth and viability in all parts of the flap. The suture material was absorbed 26 weeks postoperatively. Continuous suture with absorbable PDS seems to be a good alternative for repair of aortic coarctation in early infancy.

Esterification of exogenously derived free cholesterol by cultured fibroblasts.

The incorporation and esterification by cultured human fibroblasts of vesicle- or low density lipoprotein-derived free [3H]cholesterol was examined. The rate of the cellular uptake of free [3H]cholesterol from lipid vesicles was similar in both LDL-receptor positive lung fibroblasts and in LDL-receptor negative fibroblasts. When human LDL was used as the carrier of free [3H]cholesterol, however, the LDL-receptor positive lung fibroblasts incorporated significantly more [3H]cholesterol than did the LDL-receptor negative cells. The exchangeable free [3H]cholesterol was available for intracellular esterification. The formation of [3H]cholesteryl esters was markedly inhibited by lysosomotropic drugs, either indicating a partly lysosomal esterification reaction, or implying that free [3H]cholesterol moves through the lysosomal compartment on its way to intracellular esterification sites. Either way, the lysosomes appear to have a metabolic role in the metabolism of exchangeable free [3H]cholesterol.

Arterial remodeling following mechanical injury. The role and nature of smooth muscle cells.

The main feature of an atherosclerotic plaque is the formation of a new tissue in the arteries. In this respect atherosclerosis is similar to other conditions where non-neoplastic tissue formation occurs like in embryogenesis, in healing or in repair processes. A progressive intimal thickening occurs in the early phase of human atherosclerotic lesions and also in certain experimental models. Long-standing aortic intimal thickening could be induced by mechanical injury to the inner surface of the aorta with a microsurgical instrument, which causes controlled endothelial denudation. The injury is followed by an arterial remodeling. The latter process is caused by the development of an intimal plaque which consists of two main components: the smooth muscle cell (SMC) and the intercellular matrix. The matrix components are mostly synthetized by the SMC. Two distinct SMC populations could be distinguished by morphological means in the intimal proliferation: the synthetizing type and the proliferating type. Their role will be discussed and their morphological appearance will be compared with SMC present in other lesions.

Cultivated human arterial smooth muscle displays heterogeneous pattern of growth and phenotypic variation.

Human arterial smooth muscle grows in primary, as well as passaged, cultures with a heterogeneous pattern of monolayered regions alternating with multilayered with formation of tissue-like mounds or nodules. Cells in the monolayered region are large and well spread, whereas the multilayers are composed of smaller cells with poor spreading on tissue culture plastic. The two cell types were separated from passaged cultures of human arterial media. They were investigated with regard to capacity for attachment to tissue culture plastic, native collagen, and substrata coated with plasma fibronectin, the presence and distribution of cellular fibronectin and actin, as evaluated with specific staining, and the presence of cell-substratum contacts with interference reflection microscopy. The cells from monolayered regions were high adhesive and had abundant filamentous actin, often organized like stress fibers, numerous punctate and streak-like focal contacts with the substratum, and abundant fibronectin of which some was organized as streaks. In contrast, cells from multilayered regions were low adhesive, had very little filamentous actin, and had few or no stress fibers, fibronectin content was low and variable, and focal contacts with the substratum were poorly developed. The results demonstrate phenotypic heterogeneity in arterial smooth muscle cultures with expression toward a cell type with monolayered growth pattern or toward cells with a tendency for multilayered growth.

Natural history of renal artery aneurysm elucidated by repeated angiography and pathoanatomical studies.

The findings from repeated angiographies in 16 female and 5 male patients with altogether 34 renal artery aneurysms were studied. The mean interval between the first and last angiography was 35 months. Seven patients had multiple aneurysms. Two to four angiographies were performed in each patient. They showed no change in 28 aneurysms and slight or minimal enlargement, thrombosis or calcification in the other 6. The clinical course was uneventful except for severe hypertension in 3 patients. No rupture occurred. Eight patients, of whom 5 had solitary, saccular aneurysms, were operated upon. Pathoanatomically, fibromuscular dysplasia or secondarily changed fibromuscular dysplasia was found in 7 of them. Four died of unrelated disease having been followed up for 55-204 months (mean 102 months). Nine were alive and symptomless at the end of follow-up 11-195 months (mean 97 months) after the first angiography. The study supports the view that the risk of rupture of a renal artery aneurysm is very small, and indicates that fibromuscular dysplasia is common even when the angiography shows solitary, saccular aneurysm only.

Uptake and esterification of exogenous cholesterol by low-density-lipoprotein-receptor-negative human fibroblasts in culture.

The incorporation and metabolism of both vesicle- and LDL (low-density lipoprotein)- derived [3H]cholesterol by LDL-receptor-negative fibroblasts were studied. Independent of the cholesterol source, free [3H]cholesterol was readily incorporated into the cells and was available for esterification. 7-Oxocholesterol stimulated both [3H]cholesterol incorporation, by increasing the exchange rate, and the subsequent esterification of it irrespective of the source of exogenous [3H]cholesterol. The 7-oxocholesterol-stimulated esterification of exogenously derived LDL free [3H]cholesterol was progesterone-sensitive and energy-requiring.