Quantitative analyses of lesion areas of coronary atherosclerosis in cholesterol-fed rabbits

Chromium chloride administration causes a substantial reduction of coronary lipid deposits, aortic lipid deposits, and serum cholesterol concentration in rabbits

This experiment was carried out to test the null hypothesis that intramuscular trivalent chromium administration would not remove lipids from the heart and ascending aorta of the hyoercholesterolemic rabbits and would not lower their serum cholesterol levels. A novel computer-based method, previously described, was used to assess the sizes of the intracardiac and aortic lesions. Clinical chemistry and histopathology were performed through routine methods. The sizes of the lipid deposits in the coronary vasculature of the hypercholesterolemic rabbits were greatly reduced as a result of the intramuscular chromium chloride injections. Lipid deposits in the ascending aorta were similarly reduced, as well as the serum cholesterol concentrations. The terminal serum chromium concentrations in the chromium-treated group were in the range of 3,258-4,513 microg/L, whereas, in the untreated animals, the concentrations were 3.2 to 6.3 microg/L. The general condition of the chromium-treated animals was good and they were continuing to gain weight up to the time they were killed. However, it was found that their liver function tests had become abnormal even though there was no evidence of hepatic histopathological lesions specifically affecting the chromium-treated group. The kidney function tests and histopathology were normal. These findings suggest that a more aggressive approach than those tried hitherto might be useful in treating atherosclerotic human patients with chromium.

A novel computer-based method for the measurement of the lipid “load” in the coronary vessels of rabbits

INTRODUCTION

This study reports the development of a new, accurate and reproducible method which combines histological and computer techniques for the determination of fatty load in cholesterol-fed rabbits.

METHODS

New Zealand male rabbits were randomly divided into three groups. The animals in group 1 (control) received neither cholesterol nor drugs. Those in group 2 received a 2% cholesterol diet for 30 days, followed by a normal diet for 45 days. In addition during the latter period (day 31 to day 75) animals received 200 g of chopped carrots each morning. The rabbits in group 3 followed the same dietary regime as those in group 2 except that 8.36 mg of simvastatin and 1.76 g cholestyramine were mixed with their carrots. On the 76th day, the animals were sacrificed and their blood and hearts were collected. Histological sections (15 microm thick) of hearts were cut at 90 degrees to the long axis using a motorized freezing microtome. Every tenth section was mounted on a glass slide and stained with Oil Red O. A total of hundred slides prepared from each heart were scanned into a computer and the area stained by Oil Red O was measured, giving a measure of the total fatty "load" in each heart.

RESULTS

There was a highly significant increase in the coronary fatty deposits in the hearts of the animals fed with cholesterol rich diet (group 2) as compared to the control rabbits in group 1. Treatment of rabbits with simvastatin plus cholestyramine (group 3) significantly reduced the coronary lipids load.

DISCUSSION

The combination of histological and computer-based techniques used in this study provides an accurate and reproducible method for the quantitation of fatty deposits in rabbit coronary vessels. This report is based on the measurement of coronary lipid depositions rather than aortic lesions. It also overcomes the shortcoming of the majority of the earlier published methods which are generally limited to the measurement of fatty plaques in only few major coronary vessels, totally neglecting the many small distributive vessels which are often responsible for cardiac ischemic disease.

Macroscopic distribution of coronary atherosclerotic lesions in cholesterol-fed rabbits

In the present study we macroscopically examined a change in the distribution of coronary atherosclerosis in cholesterol-fed rabbits. Rabbits were fed a cholesterol-enriched diet for 15 weeks, then replaced by a normal diet, and were sacrificed at 15, 24, 32 and 42 weeks after the start of the experiment. The coronary atherosclerosis in the cholesterol-fed rabbits was distributed more densely in the proximal portion than in the middle and distal portions, and the lesions were severe at 24 and 32 weeks after the start of the experiment. comparison of lesions in the three portions at these time points showed that the percentages of lesion areas in the proximal portion, the middle portion and the distal portion were approximately 51%, 21 to 25% and 0.2 to 3.7%, respectively. Macroscopic observation of the coronary atherosclerotic lesions showed that the lesions formed over the vessel lumen in the proximal portion within the range of approximately 5 mm from the orifice of the left coronary artery. In the middle portion, the lesions formed predominantly around the orifices of branches as small patchy lesions from 1 to 3 mm in diameter. These findings support previous histopathological reports that suggested that the incidence of stenosis in the proximal portion was high, and the incidence of lesion occurrence in the middle and the distal portions varied. The method, macroscopical investigation of the coronary artery, is useful for analyzing coronary atherosclerosis in the rabbit.