Effect of age, hypertension and atherosclerosis on blood vessels

Several studies have shown that the water content of human, rat and dog arteries is increased in hypertension, and this increased water content may be associated with an increased wall thickness [64, 65]. Due to the limitations in studying samples from human subjects, animal models (mainly rats) have been employed. Mallov [66] found that the aorta from hypertensive rats had more smooth muscle than normal aorta. Greenwald and Berry [67] reported increased elastin and decreased collagen content in the aorta from spontaneous hypertensive rats when compared with the normal aorta. Wolinsky [25] observed an increase in the absolute amounts of both medial elastin and collagen contents in hypertensive rats. However, the relative percentage of these elements remained essentially constant. Experimental studies [67-69] showed an increase in vessel stiffness with the development of hypertension. This increase in vessel stiffness results in a smaller vessel diameter for a given distending pressure, i.e. a decrease in the distensibility [70]. 

It is generally accepted that substantial changes in the arterial wall occur with atherosclerosis in man. In human atherosclerotic arteries, it appears that there may be an absolute increase in collagen and a decrease in muscle fibers when compared with normal arteries [28]. In canine iliac 

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