Hypercholesterolemia and Changes of Vascular Contractile Responses in Experimentally Uremic Rats

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Abstract
Arterial contractile responses were studied in experimentally uremic rats. The ligation of 75% of the terminal branches of the left renal artery, followed by contralateral nephrectomy induced a chronic renal failure, as evidenced by significantly higher BUN concentrations and an elevation in blood pressure. Uremic rats exhibited elevations in total and HDL cholesterol, increased triglyceride levels, and significantly lowered HDL/total cholesterol ratios compared to control groups: 1) untreated control, 2) experimental control receiving renal infarction without contralateral nephrectomy, and 3) two kidney, one clip (2K1C) model of hypertension. Plasma total cholesterol levels in uremic rats increased by 50% in the first week following final surgery and plateaued at approximately 100% above control levels during postoperative weeks 3 through 10. Plasma transaminase levels were similar among all of the groups of rats studied indicating no effects of surgery on hepatic function. The contractile responses of aortic rings from uremic rats to submaximal concentrations of serotonin and clonidine were significantly increased and decreased, respectively, whereas the contractile response to norepinephrine was not altered. The enhanced sensitivity to serotonin of aortic rings from uremic rats was abolished following disruption of the endothelium. Neither the alteration of aortic contractile properties nor changes in plasma BUN and cholesterol concentrations were observed in hypertensive 2K1C rats. However, there was a tendency for decreased acetylcholine-induced relaxation in aortic rings of uremic and 2KlC rats. No significant histological evidence of atherosclerosis was found in aortic tissues of uremic rats during the interval of study. These results indicate that hypercholesterolemia, hypertriglyceridemia, and altered vascular sensitivity to serotonin and clonidine are likely to be primary changes in the uremic rat and are not secondary to the development of blood pressure elevation or overt evidence of structural change in the vessels of this model.