The effects of exercise on low-density-lipoprotein-receptor mediated clearance and atherosclerotic lesions in dietary induced hyperlipidemic NZW rabbits
[Thesis]
T. J. Pujol
R. C. Westerfield
The University of Alabama
1991
89
Ed.D.
The University of Alabama
1991
The purpose of this study was to investigate the effect of regular exercise on LDL-receptor mediated clearance of plasma LDL. In addition, the study was designed to determine the effect of exercise on thoracic aorta stainable tissue lipids. The correlation between LDL-receptor mediated clearance and the extent of atherosclerotic lesions was also determined. Twenty New Zealand White rabbits were randomly assigned to exercise and sedentary groups. Identical environmental conditions existed for all subjects. After 12 weeks of daily physical exercise on a small animal treadmill, determination of LDL-receptor mediated clearance was performed. Fractional catabolic rate (FCR) was determined by injection of native I-LDL and methylated I-LDL. Native LDL is cleared by both receptor and non-receptor pathways, whereas methylated LDL is not recognized by the receptor. The difference between the disappearance rate of the two labeled species is the FCR. Subjects were anesthetized and a 50 millimeter segment of the thoracic aorta was removed for determination of atherosclerotic lesions. The atherosclerotic lesions were detected by staining the intima of the artery with Sudan IV. The total area stained was determined from enlarged photographs of the area and expressed as a percentage of the total aortic area inspected (% area involved). T-tests indicated no significant difference between exercise and sedentary groups for FCR at any of the first twelve hour samples. From 12 to 24 hours, the sedentary group FCR was significantly higher (p < 0.05) than the exercise group. T-tests showed exercise subjects had significantly lower (p < 0.05) atherosclerotic development in the aortic intima. No correlation was found to exist between FCR and % area involved. The results of this study indicate that exercise did not increase LDL-receptor mediated clearance. However, exercise did attenuate the development of atherosclerotic lesions. These findings indicate that exercise has an effect on atherosclerotic development beyond the control of plasma lipoprotein levels.