Different structural vascular changes in angiotensin II-treated and cold-stressed rats

The role of the renin-angiotensin and sympathetic nervous system in the pathogenesis of structural vascular changes in experimental hypertension was investigated by comparing the effect of angiotensin II (ANG II) administration and of sympathetic stimulation by cold stress on the structure and composition of mesenteric arteries of rats. Adult male Sprague-Dawley rats were administered subcutaneously 100 ng/kg per min ANG II or exposed to 5°C cold overnight for 12 weeks. Sham-operated rats were controls. At the end of treatment, the mesenteric circulation of rats was perfusion-fixed for morphometric measurements by light microscopy and volume density measurements by point counting on electron micrographs. Tail systolic blood pressure of ANG II-treated rats increased by 37 mm Hg at week 2 and remained elevated for the rest of the experiment. The systolic BP of cold-stressed rats measured at room temperature did not change. These findings were confirmed by direct measurement of mean arterial pressure in free-moving rats. Compared to control rats, medial thickening of large and small arteries in ANG II-treated and cold-stressed rats was the main finding of this study. Thickening of the media in the two treated groups of rats appeared to be due to hypertrophy of vascular muscle, as indicated by the increased width of smooth muscle cells. Loose matrix (interstitial fluid compartment) was increased in media of large arteries of ANG II-treated rats, and collagen was increased in the outer media of arteries of cold-stressed rats. Measurements of compositional changes in addition to morphometric changes are needed to detect differences in the pathogenesis of structural vascular changes in the various forms of hypertension.