Cardiovascular interactions between losartan and fructose in mice

Abstract

Aim: To determine whether pharmacological blockade of angiotensin (Ang) AT1 receptors alters the cardiovascular, metabolic, and angiotensin-converting enzyme (ACE and ACE2) responses to a fructose diet in mice.

Methods: C57BL male mice were fed with a 60% fructose diet for 8 weeks in combination with losartan treatment on week 9 (30 mg/kg per day). Blood pressure (BP), heart rate (HR), and autonomic balance were monitored using radiotelemetry with spectral analysis. Renal ACE and ACE2 activity and protein levels as well as Ang II and Ang 1-7 were measured.

Results: Fructose impaired glucose tolerance and increased plasma cholesterol and insulin. These effects were not corrected by losartan treatment. Fructose increased BP and HR but only during the dark period. Short-term losartan treatment decreased BP by 16% in the fructose group but had no effect in controls. This was accompanied by a decrease in BP variance and its low-frequency component. Fructose increased Ang II (plasma and kidney) and ACE 2 (renal activity and protein expression). Losartan alone increased plasma Ang II in plasma and ACE2 in kidney. There were no changes in renal Ang 1-7 levels.

Conclusions: Losartan reversed the pressor effect of a high fructose diet, demonstrating that there are prominent interactions between a dietary regimen that produces glucose intolerance and an antihypertensive drug that antagonizes Ang signaling. The mechanism of change may be via renal Ang II rather than the ACE2/Ang 1-7 pathway because the fructose losartan combination resulted in lowered renal Ang II without changes in Ang 1-7.

Figure 1

A, Blood glucose levels during a glucose tolerance test in control and fructose-fed mice, untreated and treated with losartan. Glucose levels were measured after an intraperitoneal (IP) glucose load (1.5 g/kg). There were significant effects of diet (F_1.90 = 32.5, P < .0001), treatment (F_1.90 = 12.5, P < .001), and time (F_4.90 = 38.8, P < .0001). B, Glucose tolerance test (GTT) estimated by area under the time curve (AUC) in control and fructose-fed mice, untreated and treated with losartan. There was a significant effect of diet (F_1.18 = 9.9, P < .005). †P < .05 control versus fructose, n = 8 per group.

Figure 2

Plasma angiotensin II (Ang II) (A), kidney Ang II (B), and kidney Ang 1-7 (C) in control and fructose-fed mice, untreated and treated with losartan. For plasma Ang II, analysis of variance (ANOVA) showed main effect of diet (F_1.16 = 6.3, P < .03) and treatment (F_1.16 = 10.6, P < .05). For kidney Ang II, there was a significant effect of interaction between diet and treatment (F_1.19 = 17.5, P < .0005). There were no changes in kidney Ang 1-7 levels. †P < .05 control versus fructose. #P < .05 untreated versus losartan, n = 6.

Figure 3

Renal angiotensin-converting enzyme (ACE) (A) and ACE 2 (B) activity and renal ACE (C) and ACE 2 (D) protein levels (Western blot, normalized by β-actin) in control and fructose mice, treated and untreated with losartan. A, There were no changes in ACE activity. B, ACE 2 activity was increased in fructose mice. There was a significant effect of diet (F_1.19 = 12.3, P < .003). C, Angiotensin-converting enzyme protein levels were decreased in fructose mice treated with losartan There was a significant effect of treatment (F_1.19 = 3.4, P < .005). D, Angiotensin-converting enzyme 2 protein levels were increased in fructose mice and control mice treated with losartan. There were significant effects of diet (F_1.19 = 4.4, P < .003) and treatment (F_1.19 = 5.7, P < .003). †P < .05 control versus fructose. #P < .05 untreated versus losartan, n = 6.