Changing standard chow diet promotes vascular NOS dysfunction in Dahl S rats

Abstract

We hypothesized that vascular nitric oxide synthase (NOS) function and expression is differentially regulated in adult Dahl salt-sensitive rats maintained on Teklad or American Institutes of Nutrition (AIN)-76A standard chow diets from 3 to 16 wk old. At 16 wk old, acetylcholine (ACh)-mediated vasorelaxation and phenylephrine (PE)-mediated vasoconstriction in the presence and absence of NOS inhibitor, N(ω)-nitro-L-arginine methyl ester (L-NAME), was assessed in small-resistance mesenteric arteries and aortas. Rats maintained on either diet throughout the study had similar responses to ACh and PE in the presence or absence of L-NAME in both vascular preparations. We reasoned that changing from one diet to another as adults may induce vascular NOS dysfunction. In the absence of L-NAME, small arteries from Teklad-fed rats switched to AIN-76 diet and vice versa had similar responses to ACh and PE. Small-arterial NOS function was maintained in rats switched to AIN-76A from Teklad diet, whereas NOS function in response to ACh and PE was lost in the small arteries from rats changed to Teklad from AIN-76A diet. This loss of NOS function was echoed by reduced expression of NOS3, as well as phosphorylated NOS3. The change in NOS phenotype in the small arteries was observed without changes in blood pressure. Aortic responses to ACh or PE in the presence or absence of L-NAME were similar in all diet groups. These data indicate that changing standard chow diets leads to small arterial NOS dysfunction and reduced NOS signaling, predisposing Dahl salt-sensitive rats to vascular disease.

Fig. 1.

A: diagram of diet-switch protocol performed in Dahl salt-sensitive (S) rats. Rats were fed Teklad diet or American Institutes of Nutrition (AIN) diet at weaning (3 wk old). Rats either remained on respective diet until 16 wk old, or, at 12 wk old, diets were switched, with Teklad-fed rats changed to AIN diet (Teklad→AIN), or AIN-fed rats changed to Teklad diet (AIN→Teklad). B: weekly body weights for Dahl S rats for Teklad (N = 9), AIN (N = 9), Teklad→AIN (N = 10), and AIN→Teklad (N = 9). Data were analyzed by two-way ANOVA.

Fig. 2.

Twenty-four-hour mean arterial blood pressure (MAP) (A) and heart rate (B) tracings in Dahl S rats fed Teklad (N = 6) or AIN (N = 4) standard chow diets since weaning (3 wk old). Twelve-hour MAP (C) and heart rate (D) (at 15 wk, 5 and 6 days old, and at 16 wk old) are shown. At 12 wk old, weaning-diet groups were divided, with a subset of rats undergoing a diet switch, thereby generating two additional diet groups: Teklad→AIN (N = 6) and AIN→Teklad (N = 3). Values are means ± SE. Data were analyzed by two-way ANOVA. N, night; D, day; bpm, beats per minute.

Fig. 3.

Acetylcholine (ACh)-mediated relaxation in the presence or absence of N^ω-nitro-l-arginine methyl ester (l-NAME) in small mesenteric arteries from adult (16 wk old) Dahl S rats fed Teklad (N = 6; A) or AIN (N = 6; B) since weaning (3 wk old). At 12 wk old, weaning-diet groups were divided, and a subset of rats underwent a diet switch, generating two additional diet groups: Teklad→AIN (N = 10; C) and AIN→Teklad (N = 6; D). N^ω-nitro-l-arginine methyl ester (l-NAME) was used at 100 μM to nonselectively inhibit nitric oxide synthese(NOS). Values are means ± SE. *P < 0.05 for maximum sensitivity to the vasoactive agonists (logEC₅₀) of l-NAME-treated vs. untreated mesenteric artery segments. Data were analyzed by t-test. PE, phenylephrine.

Fig. 4.

Phenylephrine (PE)-induced concentration in the presence or absence of l-NAME in small mesenteric arteries from adult (16 wk old) Dahl S rats fed Teklad (N = 7; A) or AIN (N = 6; B) since weaning (3 wk old). At 12 wk old, weaning-diet groups were divided, with a subset of rats undergoing a diet switch, generating two additional diet groups: Teklad→AIN (N = 9; C) and AIN→Teklad (N = 5; D). l-NAME was used at 100 μM concentration to nonselectively inhibit NOS. Values are means ± SE. *P < 0.05 for logEC₅₀ in l-NAME-treated vs. untreated mesenteric artery segments. Data were analyzed by t-test.

Fig. 5.

Densitometric analysis and representative Western blots of nitric oxide synthase (NOS) 3/β-actin (A and B), NOS3-phosphoserine-1177 (p1177)/NOS3 (C and D) protein expression in homogenates of mesenteric arteries and plasma nitrite (E) and nitrate (F) levels from Teklad-fed (T; N = 5) and AIN-fed (A; N = 4) adult (16-wk-old) Dahl S rats. At 12 wk old, weaning-diet groups were divided, with a subset of rats undergoing a diet switch, thereby generating two additional diet groups: Teklad→AIN (T→A; N = 7) and AIN→Teklad (A→T; N = 6). Values are means ± SE. *P < 0.05 vs. T. †P < 0.05 vs. corresponding weaning group (T or A). Data were analyzed by two-way ANOVA. AU, arbitrary units.