Smooth Muscle Cell Metabolism Research Articles

Smooth muscle relaxing compounds from Dodonaea viscosa.

Bioassay-directed fractionation of the chloroform-methanol (1:1) extract of Dodonaea viscosa (L.) Jacq. (Sapindaceae) resulted in the isolation of four active spasmolytic principles: sakuranetin (1), 6-hydroxykaempferyl 3,7-dimethyl ether (2) hautrivaic acid (3), and ent-15, 16-epoxy-9 alpha H-labda-13(16)14-diene-3 beta, 8 alpha-diol (4). All the isolated compounds elicited a concentration-dependent inhibition of the spontaneous and electrically-induced contractions of guinea-pig ileum. Sakuranetin and the ent-labdane inhibited ileum contractions evoked by acetylcholine (Ach), histamine, and barium chloride. In addition, both substances were capable of relaxing contractions of rat uterus induced by Ca2+ in K(+)-depolarizing solution, displacing to the right the concentration-response curves to Ca2+. These results suggest that sakuranetin and ent-15,16-epoxy-9 alpha H-labda-13(16)14-diene-3 beta, 8 alpha-diol produce an interference with calcium metabolism in smooth muscle cells. The spasmolytic activity exhibited by the active principles from D. viscosa, provides the pharmacological basis for the traditional use of the plant as an antispasmodic agent.

Differential phospholipid metabolism in rat aortic smooth muscle cells of varying proliferative potential upon long term exposure to phorbol 12-myristate 13-acetate

Subchronic exposure of rats to allylamine (AAM) modulates aortic smooth muscle cells (SMCs) from a quiescent to a proliferative phenotype. This response is associated with alterations in phospholipid metabolism and protein kinase C (PKC) activity. The present studies were conducted to evaluate the effects of long-term exposure to phorbol 12-myristate 13-acetate (PMA) on phospholipid metabolism in SMCs derived from control and AAM-treated animals, cells of varying proliferative potential. Measurements of 32P/[ 3H]myristic acid incorporation into parent phospholipids and phosphatidic acid (PA) and the extent of PKC-mediated histone phosphorylation were conducted following exposure of pre- and postconfluent subcultures of SMCs to PMA for 3 h. Increased 32P incorporation into phosphatidylcholine (PC) was observed in both pre- and postconfluent cultures of control and AAM cells treated with PMA relative to vehicle. This response was attenuated in pre- and postconfluent AAM cells relative to control counterparts. PMA enhanced 32P incorporation into phosphatidylinositol (PI) in preconfluent cultures of control cells, but decreased 32P incorporation in cultures of AAM cells relative to vehicle. A similar relationship was observed in the PI profile of postconfluent cultures. The alterations in primary phospholipid profiles induced by PMA correlated with the loss of PKC-mediated histone phosphorylation in the cytosolic and particulate fractions of both cell types. The pattern of 32P incorporation into PA, a phospholipid metabolite, paralleled that of PC in cultures of both cell types. In the presence of ethanol, vehicle-treated control and AAM cells exhibited a modest increase in phosphatidylethanol (PEt) formation, as measured by [ 3H]myristic acid incorporation. PMA enhanced PEt formation in control and AAM cultures, but selectively decreased [ 3H]myristic acid incorporation into PA in AAM cells. These data demonstrate that long-term PMA treatment differentially modulates phospholipid metabolism in aortic SMCs of varying proliferative potential. These alterations are associated with modulation of PLD-mediated hydrolysis of membrane phospholipids.

Metabolism of nitroglycerin by smooth muscle cells: Involvement of glutathione and glutathione S-transferase

Metabolism of nitroglycerin (GTN) in the vascular smooth muscle is required for the drug to be effective in the treatment of angina pectoris and congestive heart failure. The usefulness of GTN is limited by the development of tolerance to the drug. The metabolism of GTN was studied in its target tissue, vascular smooth muscle. Inorganic nitrite was produced by cultured smooth muscle cells when GTN was added to the culture dish. Nitrite production increased with increasing GTN concentration and with incubation time. The enzymatic nature of GTN metabolism to nitrite was assessed by enzyme inhibition studies. Indocyanine green, a non-substrate inhibitor of glutathione S-transferase, inhibited GTN metabolism by smooth muscle cells. Cellular glutathione is also involved in GTN metabolism by the smooth muscle cell. Pretreatment with phorone, a glutathione S-transferase substrate, depleted cellular glutathione and decreased nitrite production from GTN. Pretreatment with buthionine sulfoximine, an inhibitor of γ-glutamylcysteine synthetase, decreased intracellular glutathione and caused decreased GTN metabolism in smooth muscle cells. Removal of cysteine from the smooth muscle cell incubation medium in combination with buthionine sulfoximine pretreatment decreased GTN metabolism to a lower level than buthionine sulfoximine pretreatment alone. This study shows that glutathione S-transferase and glutathione are involved in GTN metabolism by cultured smooth muscle cells.

Effect of trifluoperazine on cholesterol metabolism of smooth muscle cells exposed to hypercholesterolemic medium in vitro

We recently demonstrated that the preventive effect of trifluoperazine (a potent inhibitor of calmodulin, protein kinase C, and phospholipase A2) on cholesterol-induced atherogenic activity of smooth muscle cells was mediated through its ability to inhibit smooth muscle cellular DNA synthesis coupled with stimulation of LDL receptor synthesis. The present study addressed the effect of trifluoperazine on cholesterol metabolism of aortic SMCs enriched with cholesterol through the nonreceptor pathway and revealed that (a) TFP caused inhibition of cholesterol synthesis compared with control cells bathed with hypercholesterolemic medium alone. (b) The drug also caused inhibition of free cholesterol and cholesteryl ester accumulation within smooth muscle cells compared to control cells. These results demonstrate that the preventive effect of TFP on atherogenic activity of smooth muscle cells may also be due to its ability to affect the altered/modified cholesterol metabolism of smooth muscle cells exposed to hypercholesterolemic medium in vitro.

Effects of oxidized low density lipoproteins on arachidonic acid metabolism in smooth muscle cells.

The role of oxidized plasma lipoproteins in modifying arachidonic acid (AA) metabolism was studied in smooth muscle cells (SMC). Very low density lipoproteins (VLDL), unoxidized low density lipoproteins (LDLBHT) isolated with butylated hydroxytoluene (BHT), and oxidized LDL (LDLOXID) were separated from human serum. Thiobarbituric acid reactant (TBAR) levels were adjusted by saline incubations. Prostanoids in guinea pig SMC cultures were measured either by radioimmunoassay (RIA) or the isolation by high performance liquid chromatography (HPLC) of labeled prostanoids from SMC prelabeled with [14C]AA. Cell morphology and viability were studied by staining with Giemsa, nile red, and propidium iodide. VLDL and LDLBHT had little effect on prostanoid synthesis. Low-TBAR-LDLOXID enhanced total prostanoid levels and diminished the release of labeled prostanoids. Similar effects were found with exogenous free AA (unlabeled). Low-TBAR-LDLOXID did not affect the release of endogenous phospholipid AA as free AA. Synergism occurred between LDLOXID and exogenous free AA in prostanoid synthesis. Low-TBAR-LDLOXID evidently enhanced prostanoid levels in SMC both by supplying AA and by stimulating cyclooxygenase. High-TBAR-LDLOXID blocked prostanoid synthesis and enhanced cell death but time and pulse-recovery experiments showed that these effects were unrelated. High-TBAR-LDLOXID stimulated prostanoid synthesis when BHT was added to the incubation media. High-TBAR-LDLOXID also caused massive free AA release and the formation of many nonprostanoid derivatives. High-TBAR-LDLOXID evidently diminished overall prostanoid levels in SMC by inhibiting cyclooxygenase and at the same time stimulating AA release and the formation of other AA derivatives.

Platelet-neutrophil-smooth muscle cell interactions: lipoxygenase-derived mono- and dihydroxy acids activate cholesteryl ester hydrolysis by the cyclic AMP dependent protein kinase cascade

Fluid-phase interactions between hematologic cells and those of the vessel wall were studied in order to define a role for lipoxygenase products as cell signals in the control of vascular cholesterol metabolism. A functional parameter for hydroxy acids in this system has not been previously demonstrated. We report herein for the first time a biochemical effect of lipoxygenase-derived eicosanoids in the modulation of cholesterol metabolism in smooth muscle cells. Products of platelet-neutrophil interactions served as cell signals in vitro to modulate cholesterol metabolism. We demonstrate that 12-HETE, 12,20-DiHETE, and 12-HETE-1,20-dioic acid activate both lysosomal and cytoplasmic cholesteryl ester (CE) hydrolytic activities, although no effect was observed on CE synthetic (ACAT) activity. The platelet lipoxygenase product, 12-HETE, was the most effective stimulator of CE hydrolysis in the smooth muscle cell, and its conversion to 12,20-DiHETE and the dioic acid derivative by the neutrophils was not necessary for the activation of CE hydrolase. A 2-fold enhancement on CE hydrolysis occurred and was independent of any "cross-activation" by hydroxy acids on production of cyclooxygenase or other lipoxygenase products. The activation of cytoplasmic CE hydrolysis had a lesser cofactor dependence on bile salts in the presence of 12-HETE. This suggested a reduced requirement for surface-active agents in an enzyme-substrate interaction where enzymes are hydrolyzing insoluble lipid substrates. Moreover, 12-HETE induced an additive effect with several lipolytic hormones in the activation of CE catabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions of arterial cells. Studies on the mechanisms of endothelial cell modulation of cholesterol metabolism in co-cultured smooth muscle cells.

Fluid phase interactions between arterial endothelial cells (EC) and smooth muscle cells (SMC) have been studied in vitro to assess the regulation of lipid metabolism in SMC (Hajjar, D. P., Falcone, D. J., Amberson, J. B., and Hefton, J. M. (1985) J. Lipid Res. 26, 1212-1223; Davies, P. F., Truskey, G. A., Warren, H. B., O'Connor, S. E., and Eisenhaure, B. H. (1985) J. Cell Biol. 101, 871-879). To identify EC-derived agonists which may modulate cholesterol metabolism in co-cultured SMC, we assessed the role of EC-derived eicosanoids and platelet-derived growth factor (PDGF) in the regulation of cholesteryl ester (CE) hydrolysis in SMC. The major eicosanoids synthesized by EC include PGI2 and 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) and, to a lesser extent, prostaglandin E2. Exogenously added PGI2 and 12-HETE stimulated CE hydrolytic activity in SMC by 49 and 35%, respectively, when co-cultured with aspirin-treated EC. Aspirin-treated EC when co-cultured with SMC did not stimulate CE hydrolytic activity in SMC, as was the case with non-aspirin-treated EC, suggesting a role of eicosanoids in the regulation of cholesterol metabolism. Other humoral agents derived from EC such as PDGFc stimulated CE hydrolytic activity almost 2-fold in SMC cultured alone or co-cultured with EC. Aspirin-treated EC, incubated with 10 ng/ml PDGF, did not stimulate CE hydrolytic activity in co-cultured SMC. These results suggest that growth factor-promoting activity may enhance CE hydrolysis via the PGI2-cyclic AMP-CE hydrolysis cascade. This hypothesis supports our observations that PDGF stimulates PGI2 production in SMC. Elevated PGI2, in turn, can stimulate CE hydrolysis in these cells. Our findings suggest that the regulation of cholesterol metabolism in SMC can involve, at least in part, growth factors and EC-derived eicosanoids. These may play a central role in the regulation of hemostasis and the inflammatory response.

Heparin induces specific protein release from human intestinal smooth muscle cells

Human intestinal smooth muscle cells have recently been identified as the major cell type responsible for stricture formation in Crohn's disease. Heparin, a sulfated glycosaminoglycan, has been shown to be a key modulator of vascular smooth muscle cell growth both in vivo and in vitro . and to affect the release of proteins from these cells. Heparin has also been shown to affect the growth of human intestinal smooth muscle cells. In this report we demonstrate that heparin, in addition to its effects on proliferation, also has very specific effects on proteins released by these cells in vitro . Examination of the culture medium proteins of heparin-treated human intestinal cells revealed an increase in three proteins of molecular weight between 150–250 kd, an increase in a 37 kd protein and a decrease in synthesis of lower molecular weight (<20 kd) proteins. In substrate-attached material a transient effect on a 48 kd protein was observed. No effects on intracellular labeled proteins could be demonstrated. The 35S-methionine labeled protein profile of human intestinal smooth muscle cells exposed to heparin is similar to that observed in rat vascular smooth muscle cells yet distinct differences do exist. Extracellular processing does not account for the released proteins nor is de novo protein synthesis required suggesting that altered intracellular protein processing is the mechanism for the heparin-induced protein pattern. The release of specific proteins following exposure to heparin may reflect a significant influence of this glycosaminoglycan on the metabolism of smooth muscle cells in general and particularly in the human intestine.

Interaction of arterial cells. I. Endothelial cells alter cholesterol metabolism in co-cultured smooth muscle cells.

Results of previous in vivo experiments indicated that the presence of arterial endothelium modifies cholesteryl ester (CE) metabolism and the retention of low density lipoproteins (LDL) in injured arteries. We describe herein the effects of bovine arterial endothelial cells (ENDO) on the CE cycle, fluid phase endocytosis, and cell proliferation in co-cultured bovine arterial smooth muscle cells (SMC). Following several days of cultivation on confluent SMC, ENDO were removed from SMC by treatment of the co-cultures with 1.0% collagenase (type II). Removal of only ENDO from the co-culture dishes was confirmed by immunofluorescent staining for Factor VIII antigen, hemotoxylin-eosin staining, and biochemical analyses. We observed that ENDO grown to 75% confluency on confluent SMC induced: 1) a reduction of CE hydrolysis as a result of decreased lysosomal CE hydrolytic activity in SMC as compared to SMC cultured alone; and 2) an increase in the rate of incorporation of labeled oleate into CE as a result of increased acyl CoA:cholesterol O-acyltransferase activity in SMC as compared to SMC cultured alone. Neither endothelial cell-derived culture media (ECDM) nor fibroblasts modulated CE metabolism in co-cultured SMC. Additional experiments showed that the presence of endothelial cells or ECDM decreased the proliferation of co-cultured SMC by 50%, but enhanced the endocytotic rate of labeled sucrose into SMC threefold. Results of experiments described herein demonstrate that, in addition to providing a thrombo-resistant surface and regulating permeability, endothelial cells may also serve to modulate cholesteryl ester metabolism in smooth muscle cells derived from the arterial wall.

Metabolic cooperation between vascular endothelial cells and smooth muscle cells in co-culture: changes in low density lipoprotein metabolism.

A microcarrier co-culture system for aortic endothelial cells and smooth muscle cells (SMCs) was developed as a model for metabolic interactions between cells of the vessel wall. Low density lipoprotein (LDL) metabolism in SMCs was significantly influenced by co-culture with endothelium. The numbers of high affinity receptors for LDL was increased more than twofold (range, 2.1-5.6), with concomitant increases in LDL receptor-mediated endocytosis and degradation. These effects reached a plateau at an endothelial cell/SMC ratio of 1. Kinetic analysis of the endocytic pathway for LDL in SMCs indicated that, in co-culture with endothelium, there was no alteration in the binding affinity of LDL to its receptors but that the internalization rate constant declined and the rate constant for degradation increased. This analysis suggested that the formation and migration of endocytic vesicles was the rate-limiting step of enhanced LDL metabolism under co-culture conditions. Two mechanisms by which endothelial cells influenced smooth muscle LDL metabolism were identified. First, mitogen(s) derived from endothelial cells stimulated entry of SMCs into the growth cycle, and the changes in LDL metabolism occurred as a consequence of G1-S transition. Second, SMC lipoprotein metabolism was stimulated in the absence of mitogens by a low molecular weight (less than 3,500) factor or factors. Co-culture was a required condition for the latter effect, suggesting that the mediator(s) may be unstable or that cell-cell communication was necessary for expression. These results (a) demonstrate that vascular cell interactions can modify LDL metabolism in SMCs, (b) provide some insights into the mechanisms responsible, and (c) identify co-culture as an experimental approach appropriate to certain aspects of vascular cell biology.

Effect of heparin on vascular smooth muscle cells. I. Cell metabolism.

Previous work from our laboratory has shown that heparin inhibits the proliferation of vascular smooth muscle cells in vivo and in vitro. The mechanism of action of this glycosaminoglycan is unknown. In this communication, we have examined the antiproliferative effect of heparin on smooth muscle and other cell types, and have investigated several aspects of heparin on smooth muscle cell metabolism. Smooth muscle and closely related cell types from several species, including human, were much more sensitive to heparin than any other cell type tested, including primary and established cell lines, normal and transformed cell pairs, fibroblasts, epithelial, and endothelial cells. Flow microfluorimetric analysis of cell cycle distribution indicated that heparin blocked either the G0----S transition or a very early S-phase event in smooth muscle cells. Heparin rapidly inhibited DNA and RNA synthesis, but did not affect the rate of protein synthesis. The decrease in nucleic acid synthesis could be accounted for by an inhibition of thymidine and uridine uptake. Interestingly, heparin did not block amino acid or glucose transport. Although no change in the overall rate of protein synthesis was observed in the presence of heparin, we noted at least two changes in the synthesis of specific proteins by smooth muscle cells: two 35,000-dalton proteins which appeared in the culture medium of heparin-treated cells, and the transient disappearance of a 48,000-dalton protein in the substrate attached material of smooth muscle cells exposed to heparin. The role of the observed changes in smooth muscle cell metabolism is yet to be determined, but they may provide valuable clues to the molecular mechanisms controlling the antiproliferative activity of heparin.

A single-step gel-filtration method for the isolation of procollagens from cell culture conditioned medium

Procollagens are the major proteins secreted into the conditioned medium of cultured arterial smooth muscle cells. Methods for the isolation and quantification of these macromolecules have traditionally required preliminary salt precipitation of procollagens from the conditioned medium followed by cellulose ion-exchange chromatography. The method described here exploits the elongated conformation of soluble procollagens and allows the direct recovery of procollagens from culture medium by a single gel-filtration chromatographic step under nondissociating conditions. Procollagens are isolated in high yield and show minimal processing by procollagen N- or C-terminal peptidase activity. This method results in rapid recovery of highly purified procollagens, free of most proteoglycans of other products of smooth muscle cell metabolism.

A secretory product of human monocyte-derived macrophages stimulates low density lipoprotein receptor activity in arterial smooth muscle cells and skin fibroblasts.

The ability of macrophages to influence the metabolism of native low density lipoprotein by arterial smooth muscle cells was evaluated using cultured human monocyte-derived macrophages. Macrophage-conditioned medium stimulated the binding and degradation of low density lipoprotein by cultured arterial smooth muscle cells and skin fibroblasts. Sterol synthesis also was stimulated by macrophage-conditioned medium as was cholesterol esterification in the presence of high concentrations of low density lipoprotein. These findings suggest that macrophages secrete a factor that enhances the activity of the low density lipoprotein receptor. Low density lipoprotein degradation by arterial smooth muscle cells also was enhanced by macrophage-conditioned medium in the presence of high concentrations of low density lipoproteins in the medium. The macrophage factor that stimulates low density lipoprotein metabolism is stable to freezing, is inactivated by acid hydrolysis, tryptic digestion, and boiling, and is of large molecular weight (greater than 12,000 to 14,000 daltons). Modulation of arterial smooth muscle cell metabolism of low density lipoprotein by a macrophage secretory product may be of importance in the pathogenesis of atherosclerosis.

Diabetes and atherosclerosis: an overview.

Atherosclerosis is the most common complication of diabetes. Epidemiologic and pathophysiologic evidence suggest a number of possible reasons for this. They include alterations in lipoproteins, platelets, soluble clotting factors, the balance of prostacyclin-thromboxane, blood pressure regulation, and arterial smooth muscle cell metabolism and proliferation. Many of these alterations may accompany hyperinsulinemia and may account for the recent evidence that hyperinsulinemia is a risk factor for atherosclerosis. Advances in this area will require the recognition that neither diabetes nor atherosclerosis are single disorders. Furthermore, new approaches are needed to study these disorders in which there may be many years of very subtle changes before any end point is apparent.

Aerobic and anaerobic metabolism in smooth muscle cells of taenia coli in relation to active ion transport.

1. The O2 consumption and lactic acid production of the guinea-pig's taenia coli have been studied in relation to the active Na-K transport, in order to estimate the ratio: active Na extrusion/active K uptake/ATP hydrolysis. 2. By applying different procedures of partial metabolic ingibition, it was found that a reactivation of the active Na-K transport in K-depleted tissues could occur in an anaerobic medium, provided glucose was present and in an aerobic medium free of added metabolizable substrate. The active Na-K transport was rapidly blocked in an anaerobic-substrate free medium. 3. Readmission of K to K-depleted tissues under aerobic conditions stimulates both O2 consumption and lactic acid production. While the O2 consumption creeps up slowly and requires 50 min to reach control values, the aerobic lactic acid production increases to a maximum within 10 min and decreases again during the next 50 min to its steady-state value. 4. A reactivation of the Na-pump in K-depleted cells in a N2-glucose medium causes an immediate increase of the lactic acid production, which decreases to its control value after 60 min. The maximal increase in anaerobic lactic acid production during reactivation of the Na-K pump is a function of [K]O. The system can be cescribed with first order kinetics having a Vmax = 0-72 mumole.g-1 f. wt. min-1 and a Km = 1-1 mM. 5. By varying the glucose concentration of [K]O during reactivation of the Na-K pump, different Na-K pumping rates can be obtained. The ratios net Na extrusion/ATP or net K accumulation/ATP amount to -1-32 +/- 0-19 (36) and 1-02 +/- 0-11 (36), in the experiments with different glucose concentrations. Taking into account the interference by net passive fluxes, one can estimate a ratio:active Na transport/active K transport/ATP, of 1-7/0-8/1. This ratio is not very different from the values observed in other tissues.

Atherosclerosis in rabbits: Architectural and subcellular alterations of smooth muscle cells of aortas in response to hyperlipemia

Rabbits have been extensively used in the past for experimental production of arterial lesions by simple short-term cholesterol feeding. However, most lesions thus produced have been composed principally of foam cells and have seldom developed necrosis and complications such as calcification, ulceration, and thrombosis, in sharp contrast to human atherosclerotic lesions. Some recent experiments have indicated that by introducing certain types of dietary regimen non-necrotic proliferative arterial lesions and also necrotic intimal lesions strikingly similar to human atheroma can be produced in rabbits. However, the necrotic lesions were presumably transformed from foam cell lesions and the sequence of events does not appear to have been precisely the same as in man. The current study was carried out in an attempt to (1) produce by dietary means atherosclerotic lesions in rabbits with a pathogenetic sequence of events more closely approximating those in man, and (2) study by electron microscopy changes that might occur in architectural arrangement and subcellular components of smooth muscle cells of the inner media and of the intimal masses in the early stages of atherosclerosis. By feeding rabbits high fat-cholesterol diets, non-necrotic, and necrotic atherosclerotic lesions closely resembling human atheroclerosis have been produced within 12 weeks. The most prominent feature of non-necrotic lesions produced was the smooth muscle cells in either the mature or immature form or in any stage of maturity between the two extremes. Smooth muscle cells containing a large amount of lipid and macrophages containing variable amounts of fat were far more common in rabbit lesions than in most human lesions. In man non-necrotic atherosclerotic lesions consisting largely of smooth muscle cells appear to progress to necrotic atherosclerotic lesions. In the current study this occurred in only one rabbit, probably because of the short duration of experiments. In the atherosclerotic lesions of these rabbits cells that appear to be extremely active exist side by side with cells appearing much less active, which may even contain degenerative elements. The direct effect of the diet may be to depress and damage smooth muscle cells of the vessel wall with the “active cells” appearing as a secondary phenomenon in response to products released by injured cells. Another possibility is that the direct effect of the diet is to stimulate the metabolism of smooth muscle cells of the intima with damage of some occurring as a result of excessive stimulation. Other explanations are also possible but all must take into account the metabolism of smooth muscle cells of inner media and intima. In both man and rabbits changes in the internal elastica and the inner media appear concomitantly with intimal changes. The changes in the internal elastica include widening of the fenestrae making the intima and inner media essentially one unit in many areas. Changes in the smooth muscle cell of the inner media parallel those of the smooth muscle cell in the intima and include distention with lipid and appearance of fibroblast-like smooth muscle cells. Many smooth muscle cells actually lie within the fenestrae of the internal elastica leading to a speculation that smooth muscle cells migrate between the inner media and intima, perhaps in both directions. The essence of the pathogenesis of atherosclerosis in both man and rabbits would appear to be the direct or indirect response of smooth muscle cells in the intima and inner media to excess lipids. Difference in response between rabbits and man seem to be largely a matter of degree. Qualitative differences in response of the arterial wall due to species specificity may be present but there is little or no evidence to support this idea. With the information available the rabbit would appear to be as suitable for the study of certain fundamental aspects of atherosclerosis as any other mammal in spite of the fact that he is primarily a herbivore.