Effect of Angiotensin(1-7) on Heart Function in an Experimental Rat Model of Obesity

Abstract

Aim: Obesity is a risk factor for the development of cardiovascular diseases. Recently it was shown that overexpression of the Mas-receptor antagonist angiotensin(1-7) could prevent from diet-induced obesity. However, it remained unclear whether diet-induced obesity and angiotensin(1-7) overexpression might also have effects on the cardiovascular system in these rats.

Methods: Twenty three male Sprague Dawley rats were fed with standard chow (SD+chow, n = 5) or a cafeteria diet (SD+CD, n = 6) for 5 months. To investigate the effect of angiotensin(1-7) transgenic rats, expressing an angiotensin(1-7)-producing fusion protein in testis were used. These transgenic rats also received a 5 month's feeding period with either chow (TGR+chow, n = 6) or cafeteria diet (TGR+CD, n = 6), respectively. Hemodynamic measurements (pressure-volume loops) were carried out to assess cardiac function and blood pressure. Subsequently, hearts were explanted and investigated according to the Langendorff technique. Furthermore, cardiac remodeling in these animals was investigated histologically.

Results: After 5 months cafeteria diet feeding rats showed a significantly increased body weight, which could be prevented in transgenic rats. However, there was no effect on cardiac performance after cafeteria diet in non-transgenic and transgenic rats. Moreover, overexpression of angiotensin(1-7) deteriorated cardiac contractility as indicated by impaired dp/dt. Furthermore, histological analysis revealed that cafeteria diet led to myocardial fibrosis in both, control and transgenic rats and this was not inhibited by an overproduction of angiotensin(1-7).

Conclusion: These results indicate that an overexpression of circulating angiotensin(1-7) prevents a cafeteria diet-induced increase in body weight, but does not affect cardiac performance in this experimental rat model of obesity. Furthermore, overexpression of angiotensin(1-7) alone resulted in an impairment of cardiac function.

Keywords: angiotensin(1-7); cafeteria diet; heart; obesity; transgenic rats.

Figure 1

Body parameters of male wild type Sprague Dawley rats (SD) and transgenic rats (TGR), overexpressing Ang(1-7) after a 5 month feeding period with either standard chow alone or simultaneously chow and cafeteria diet (CD). CD increased body weight (A), altered heart weight to femur length ratio (B) and elevated body weight to femur length ratio (C) in wild type SD rats. In transgenic rats an overexpression of Ang(1-7) prevented the CD-induced effects on body parameters. Data expressed as means ± SEM of n experiments. Significant changes vs. chow rats are indicated by a hash key (p < 0.05), significant changes between groups are indicated by an asterisk (p < 0.05). Body weight was analyzed by Kruskal-Wallis followed by pairwise comparison using the Dwass-Steele-Chritchlow-Fligner. Heart weight to femur length ratio and body weight to femur length ratio were analyzed by ANOVA followed by pairwise comparison using Tukey HSD.

Figure 2

Hemodynamic measurements of the left ventricle of male wild type Sprague Dawley rats (SD) and transgenic rats (TGR), overexpressing Ang(1-7) after a 5 month feeding period with either standard chow alone or simultaneously chow and cafeteria diet (CD). (A,B) Recordings of systolic and diastolic blood pressure were carried out under baseline conditions, using a Millar catheter, which was inserted into the left carotid artery. TGR+chow rats showed a significantly impaired systolic and diastolic blood pressure in comparison to SD+chow rats. TGR+CD rats exhibited a significant increase in systolic and diastolic blood pressure compared to TGR+chow rats. Significant changes vs. chow rats are indicated by a hash key (p < 0.05), significant changes between groups are indicated by an asterisk (p < 0.05). (C) Evaluation of dp/dt has been carried out under baseline conditions and under venous injection of dobutamine, using a Millar catheter, which was inserted into the left ventricle via the left carotid artery. CD had no effect on dp/dt(max) and dp/dt(min) in wild type SD rats. TGR+chow rats showed an impairment of dp/dt(max) and dp/dt(min) under baseline conditions and after dobutamine stimulation compared to SD+chow rats. CD in TGR rats resulted in an increase in dp/dt(max) under baseline and after dobutamine stimulation as well as baseline dp/dt(min) compared to TGR+chow rats, whereas dobutamine response regarding dp/dt(min) was unaltered. Significant changes vs. dobutamine stimulation are indicated by a hash key (p < 0.05), significant changes between groups are indicated by an asterisk (p < 0.05). Data are expressed as means ± SEM of n experiments. Hemodynamic parameters were analyzed by Kruskal-Wallis followed by pairwise comparison using the Dwass-Steele-Chritchlow-Fligner.

Figure 3

Epicardial mapping analysis of isolated-perfused hearts of male wild type Sprague Dawley rats (SD) and transgenic rats (TGR), overexpressing Ang(1-7) after a 5 month feeding period with either standard chow alone or simultaneously chow and cafeteria diet (CD). Isolated-perfused rat hearts were prepared according to Langendorff-technique. Epicardial mapping was performed as previously described by Dhein et al. (1993). (A) Coronary flow was related to heart weight and is given as coronary flow to heart weight ratio. TGR+CD rats showed significantly reduced coronary flow to heart weight ratio compared to SD+CD rats. (B) Furthermore, PQ duration of rat hearts was measured. CD in combination with an overexpression of Ang(1-7) led to a significant prolongation of PQ duration in comparison to SD+CD rats. Data expressed as means ± SEM of n experiments. Significant changes between groups are indicated by an asterisk (p < 0.05). Coronary flow to heart weight ratio and PQ duration were analyzed by Kruskal-Wallis followed by pairwise comparison using the Dwass-Steele-Chritchlow-Fligner.

Figure 4

Total collagen content in the myocardium of male wild type Sprague Dawley rats (SD) and transgenic rats (TGR), overexpressing Ang(1-7) after a 5 month feeding period with either standard chow alone or simultaneously chow and cafeteria diet (CD). (A) Original histological images of 2 μm sections of rat myocardium stained with Picrosirius Red. (B) Quantitative analysis of total collagen content. CD caused myocardial fibrosis in both WT and transgenic rats, without differences between these groups. Data are expressed as means ± SEM of n experiments. Significant changes vs. chow rats are indicated by a hash key (p < 0.05). Total collagen content was analyzed by ANOVA followed by pairwise comparison using Tukey HSD.

Figure 5

Capillary to muscle fiber ratio in the myocardium of male wild type Sprague Dawley rats (SD) and transgenic rats (TGR), overexpressing Ang(1-7) after a 5 month feeding period with either standard chow alone or simultaneously chow and cafeteria diet (CD). CD led to a decrease in capillary to muscle fiber ratio in WT rats, whereas CD in transgenic rats resulted in an increase in capillary to muscle fiber ratio. Data are expressed as means±SEM of n experiments. Significant changes vs. chow rats are indicated by a hash key (p < 0.05), significant changes between groups are indicated by an asterisk (p < 0.05). Capillary to muscle fiber ration was analyzed by ANOVA followed by pairwise comparison using Tukey HSD.