Abstract
In our previous retrospective studies on diabetic patients, we found that hyerinsulinism plays an important role in the development of diabetic macroangiopathy.
In the present experiment, we examined the metabolic effects of insulin upon the arterial wall of experimental animals.
Forty young adult male Wistar rats weighing 200 g were divided into two groups. One group was subjected to daily subcutaneous injection of insulin zinc suspension (group I, N=25), whereas the other was treated with saline (group S, N=15). After one year, all animals were sacrificed and the lipid contents in the intima-media of their arota were biochemically measured. For morphological studies, further parts of the ascending aorta were dissected out and examined by light and electron microscopy.
1) The biochemical data obtained showed significant increases in triglyceride (TG) content in the aorta tissues of group I as compared with those in the tissues of control group S (p<0.05).
The TG/phospholipid (p<0.05) and TG/total cholesterol (p<0.01) ratios were also significantly increased in the experimental group.
2) The light microscopic examination revealed that the intima of the aorta in group I rats was apparently thickened and the subendothelial tissue consisted of eosinophilic fiber bundles, amorphous ground substances and irregularly arranged cells containig a long oval nucleus. Electron micoscopically, the majority of fibers in the intima of the aorta of group I rats were found to show collagenous and elastic fiber-like structures, and the cells contained microfilaments, dense bodies and sub-plasmamembranous vesicles in the cytoplasm. From these electron microscopic features, the cells were identified as being of smooth muscle cell origin.
In conclusion, arteriosclerosis-like lesions can be induced by long-term insulin injection in the aorta of rats. The present results suggest that hyperinsulinism plays an important role in both the occurrence and development of diabetic macroangiopathy.
