Knud Kjeldsen

Enhancing influence of carbon monoxide on the development of atheromatosis in cholesterol-fed rabbits

Summary Twenty-four rabbits were fed Altromin-K® plus 2 % cholesterol. Twelve animals were exposed to small concentrations of carbon monoxide and 12 animals to room air. The following observations were made: (1) The degree of visible aortic atheromatosis and the content of total cholesterol in the aortic tissue was significantly higher in the rabbits exposed to carbon monoxide than in the controls. (2) In about 3/4 of the carbon monoxide exposed rabbits the hearts displayed macroscopic focal degenerative changes and scattered haemorrhages. Only one animal in the control group showed similar changes. (3) Microscopic examinations supported the macroscopic findings, as the vascular changes and their sequelae were significantly more pronounced in the carbon monoxide exposed group. (4) The underlying biochemical and physiological mechanisms are discussed and it is suggested that the differences observed in the two groups of animals may be explained by tissue hypoxia due to a carbon monoxide-induced displacement of the oxygen dissociation curve to the left, in combination with a decreased activity of certain enzymes inhibited by carbon monoxide. (5) The relation between the experimental findings and the demonstration of often very high concentrations of carboxyhaemoglobin in smokers with cardiovascular diseases in comparison to healthy smokers is briefly discussed.

EFFECT OF MODERATE CARBON-MONOXIDE EXPOSURE ON FETAL DEVELOPMENT

Abstract The effect of moderate carbon-monoxide exposure (180 p.p.m. and 90 p.p.m. carbon monoxide in atmospheric air) on fetal development was studied in rabbits. Exposure to 180 p.p.m. carbon monoxide (16-18% carboxyhaemoglobin) during pregnancy resulted in a 20% decrease of birth-weight, and a neonatal mortality of 35% as against 1% in the control group. Exposure to 90 p.p.m. carbon monoxide (8-9% carboxyhaemoglobin) had a less pronounced effect. In women there was a negative correlation between birth-weight and carboxyhaemoglobin concentration (p

Enhancing influence of arterial hypoxia on the development of atheromatosis in cholesterol-fed rabbits

Summary Twenty-four rabbits were fed standard rabbit pellets plus 2 % cholesterol. Twelve animals were exposed to about 10 % oxygen (atmospheric air + nitrogen) and 12 animals to 21 % oxygen (atmospheric air). The following observations were made: (1) The degree of visible aortic atheromatosis and the aortic content of total cholesterol and triglycerides were significantly higher in the hypoxic rabbits, while no changes were seen in aortic phospholipids. (2) In most of the hypoxic rabbits the hearts displayed macroscopic infarct-like areas and petechiae. None of the controls showed similar changes. (3) Microscopic examinations supported the macroscopic findings, as the vascular changes and their sequellae were far more pronounced in the hypoxic group. (4) The underlying biochemical and physiological mechanisms are discussed, and it is suggested that the increased arterial accumulation of lipids is caused by an increased endothelial permeability.

Reduced atherogenesis in cholesterol-fed diabetic rabbits. Giant lipoproteins do not enter the arterial wall.

In cholesterol-fed rabbits, alloxan-dlabetes has an antt-atherogenlc effect, which is associated with severe elevation of plasma triglyceride concentrations. To study this effect, we measured llpoprotein sizes and aortic permeability coefficients for chotesteryl ester and for albumin In hypertriglycerldemlc diabetic cholesterol-fed rabbits and In normotriglyceridemlc cholesterol-fed rabbits. With the same high cholesterol concentration in plasma, hypertrlglyceridemlc diabetic rabbits had 70% of plasma cholesterol In very large llpoprotelns (diameter >75 nm), whereas normotrlglycerldemlc rabbits had only about 10% of plasma cholesterol in these giant llpoprotelns. The aortic permeability coefficients for cholesteryl ester In hypertriglycerldemlc diabetic cholesterol-fed rabbits was only 10% to 50% of that In normotriglyceridemlc cholesterol-fed rabbits. Aortic permeability coefficients for albumin did not differ significantly between the hypertrlglyceridemlc and normotriglyceridemlc rabbits. The results suggest that the large size of a major fraction of plasma llpoprotelns in the hypertrlglyceridemlc diabetic cholesterol-fed rabbits Is responsible for the relatively low aortic permeability coefficient for cholesteryl ester from plasma and hence for reduced atherogenesis In these animals.

Effect of testosterone on atherogenesis in cholesterol-fed rabbits with similar plasma cholesterol levels

The aim was to examine the effect of testosterone on atherogenesis in cholesterol-fed, castrated male rabbits not mediated via different plasma cholesterol levels. The rabbits in the testosterone group (n = 19) and in the placebo group (n = 17) were injected intramuscularly twice weekly for 17 weeks with 25 mg testosterone enantate and placebo, respectively, reaching plasma testosterone levels of 50-150 nmol/l in the testosterone group. No effect of testosterone on liver function or body weight was detected, but at week 15 mean blood pressure was 75 +/- 2 mmHg (mean +/- S.E.) in the testosterone group compared with 69 +/- 2 mmHg in the placebo group (P < 0.05). To reduce variation in plasma cholesterol between the two groups, the amount of cholesterol fed to each rabbit was adjusted on the basis of weekly determinations of plasma cholesterol; the mean plasma cholesterol levels during the 17 weeks were 20.9 +/- 1.0 and 20.4 +/- 0.9 mmol/l for the placebo and testosterone groups. In the intima-inner medias of the aortic arch, the thoracic and the abdominal aorta there were no consistent significant differences in aortic cholesterol content, expressed either as nmol/cm2 or nmol/mg protein, between the two groups. However, the aortic cholesterol content tended to be lower in the testosterone group than in the placebo group. These findings suggest that in cholesterol-fed, castrated male rabbits, testosterone does not promote atherogenesis by an effect directly on the arterial wall.

No effect of nifedipine on atherogenesis in cholesterol-fed rabbits.

It was recently reported that the calcium antagonist nifedipine suppresses aortic cholesterol accumulation in cholesterol-fed rabbits without reducing hypercholesterolemia. We extended this study on plasma lipoprotein levels and aortic influx of cholesteryl ester. We gave 40 mg per day of nifedipine orally to 17 rabbits fed a 2% cholesterol diet for 8 weeks. For the same period of time 15 control rabbits received placebo capsules and the same diet. During the study, total cholesterol, HDL, LDL, and VLDL cholesterol concentrations in plasma were not significantly different in the experimental and control animals. At the end of the study we found no difference in the two groups in accumulation of cholesterol in the intima media of the proximal thoracic aorta, the distal thoracic aorta, and the corresponding media layers. Furthermore, aortic influx of free cholesterol, cholesteryl ester, and albumin from plasma measured by radioactive tracers was not significantly affected by nifedipine.

Aortic permeability to LDL as a predictor of aortic cholesterol accumulation in cholesterol-fed rabbits.

The aim of this study was to investigate the possibility that the permeability characteristics of the arterial wall are related to the development of atherosclerosis. The in vivo regional variation of aortic permeability to iodinated human low density lipoprotein (LDL) in normal rabbits was compared with the regional variation in aortic cholesterol accumulation in cholesterol-fed rabbits. Aortas were divided into the aortic arch, thoracic aorta, and abdominal aorta, and each of these three parts was further subdivided into four segments of similar size. The permeability to LDL was 40 +/- 7 nl.cm-2.hr-1 (mean +/- SEM, n = 11) in the most proximal segment of the aortic arch and decreased throughout the length of the aorta to 3 +/- 1 nl.cm-2.hr-1 in the most caudal segment of the abdominal aorta. In such normal rabbits the aortic cholesterol content was similar in all 12 arterial segments at 0.08 +/- 0.005 mumol/cm2 (mean +/- SEM, n = 3 x 12). Aortic cholesterol accumulation was determined in other rabbits with an average plasma cholesterol level of 32 +/- 1 mmol/l for 96 days; the cholesterol content in the most proximal segment of the aortic arch was 2.7 +/- 0.5 mumol/cm2 (mean +/- SEM, n = 11) and decreased with increasing distance from the heart to 0.17 +/- 0.03 mumol/cm2 in the most caudal segment of the abdominal aorta. Linear regression analysis showed a close positive association between the permeability to LDL of a given aortic segment and the cholesterol accumulation in that same aortic segment after cholesterol feeding (r2 = 0.96, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

ULTRASTRUCTURAL INTIMAL CHANGES IN THE RABBIT AORTA AFTER A MODERATE CARBON MONOXIDE EXPOSURE

Abstract 1. (1) Eight rabbits were fed a normal diet and placed in exposure chambers. Four were exposed to 0.018 vol. % carbon monoxide for 2 weeks, while the other 4 served as controls and were exposed to atmospheric air. At the end of the study tissue from arch and thoracic aorta was taken for transmission and scanning electron microscopy. 2. (2) The luminal aortic coats of the experimental animals showed pronounced changes, characterized first of all by a severe edematous reaction with extensive swelling, formation of subendothelial blisters, and plaque formation. Furthermore, the myointimal cells showed vacuolation and occasionally the endothelial cells showed severe degeneration with cytolysis and condensation. Apart from actual plaque formation, the surface structures were markedly swollen and irregular. Occasionally spotty or streaky lesions occurred, where the normal folding architecture had changed into a characteristic “cobblestone-like” picture formed by protruding, grossly edematous endothelial cells. 3. (3) The results support earlier findings of toxic effects of low concentrations of carboxyhaemoglobin on the arterial walls, thereby provoking increased endothelial permeability and formation of edema, leading to changes indistinguishable from early atherosclerosis.

REVERSAL OF RABBIT ATHEROMATOSIS BY HYPEROXIA

Summary Twenty-four rabbits were fed standard rabbit pellets plus 2 % cholesterol. Twelve animals were exposed for 10 weeks to 28 % oxygen (atmospheric air + oxygen) and 12 animals to 21 % oxygen (atmospheric air). The degree of visible aortic atheromatosis and the aortic content of total cholesterol, phospholipids and triglycerides were significantly lower in the hyperoxic rabbits. Microscopic examinations supported the macroscopic findings.

Effects of Carbon Monoxide on Myocardium Ultrastructural Changes in Rabbits After Moderate, Chronic Exposure

Sixteen rabbits were placed in exposure chambers: eight were continuously exposed to 180 ppm of carbon monoxide and eight were exposed to atmospheric air for 2 weeks. The myocardial ultrastructure of all the rabbits was examined. In rabbits exposed to carbon monoxide, local areas of partial or total necrosis of the myofibrils and degenerative changes of the mitochondria were found. Extra- and intracellular edema, increases in the number of ribosomes and lipofuscin granules, and reparative fibrotic changes also occurred. Varying degrees of injury were noted in the blood vessels. Capillary edema, but never total stenosis, was seen in some areas. Stasis and occasional small perivascular hemorrhages were typical on the venous side; on the arterial side the characteristic picture was one of endothelial swelling, formation of subendothelial edema, and degenerative changes of the myocytes. The present study supports the hypothesis that chronic exposure to low levels of carboxyhemoglobin can produce myocardial damage and account for the increased risk of myocardial infarction and sudden death seen in heavy cigarette smokers.