SUMMARY Experiments were designed to study endothelium-dependent responses in salt-sensitive (DS) and salt-resistant Dahl rats (DR). The rats were fed a low sodium (0.1% NaCl) or high sodium (8% NaCl) diet for 8 weeks. Blood pressure in DS fed a high sodium diet was higher than that in the remaining animals. Aortic rings with and without endothelium were suspended for isometric tension recording. Acetylcholine, adenosine 5'-diphosphate, and thrombin induced endothelium-dependent relaxations that were significantly depressed in the aorta of DS fed a high sodium diet. The relaxations in response to sodium nitroprusside were only slightly, but significantly, depressed in DS fed a high sodium diet. Removal of the endothelium greatly enhanced the response to serotonin and norepinephrine. In rings with, but not without, endothelium taken from rats fed a high sodium diet, the tension developed in response to serotonin and norepinephrine was significantly greater than that in animals fed a low sodium diet. These experiments indicate that (1) endothelium-dependent relaxations to acetylcholine, adenosine 5'-diphosphate, and thrombin are depressed in hypertensive Dahl rats; (2) this effect probably reflects a decreased release of endothelium-derived relaxing factor(s), although structural changes might contribute; and (3) 4 Endothelium-dependent relaxations to acetylcholine are depressed in spontaneous hypertension, in aortic coarctation, and in mineralocorticoid hypertension of the rat.
"7 No information is available on endothelium-dependent responses of blood vessels in salt-induced hypertension. Received April 28, 1986; accepted August 20, 1986. Dahl developed two strains of rats with different propensities toward hypertension if fed a high sodium diet: a salt-sensitive strain, which becomes hypertensive when fed a high sodium diet, and a salt-resistant strain, which does not.8 This model may have similarities with a subgroup of human hypertension in which sodium contributes to the development of high blood pressure. 9 The present study was designed to investigate whether endothelium-dependent vascular responses are altered in salt-induced hypertension of the rat.
Materials and MethodsMale 6-week-old Dahl salt-sensitive (DS) and saltresistant rats (DR) weighing 257 ± 7 g were purchased from Brookhaven National Laboratories (Brookhaven, NY, USA). All rats were housed two to a cage and had free access to water. For 8 weeks both DS and DR were fed standard rat chow (Ralston-Purina, St. Louis, MO, USA) that contained either 8% NaCl or 0.1% NaCl. Four groups of rats were used in the study: DS fed 8% NaCl, DS fed 0.1% NaCl, DR fed 8% NaCl, and DR fed 0.1% NaCl. Systolic blood 157 Downloaded from http://ahajournals.org by on April 28, 2019