α-Linolenic acid and exercise training independently, and additively, decrease blood pressure and prevent diastolic dysfunction in obese Zucker rats

Abstract

Key points: α-linolenic acid (ALA) and exercise training both attenuate hyperlipidaemia-related cardiovascular derangements, however, there is a paucity of information pertaining to their mechanisms of action when combined. We investigated both the independent and combined effects of exercise training and ALA consumption in obese Zucker rats, aiming to determine the potential for additive improvements in cardiovascular function. ALA and exercise training independently improved cardiac output, end-diastolic volume, left ventricular fibrosis and mean blood pressure following a 4 week intervention. Combining ALA and endurance exercise yielded greater improvements in these parameters, independent of changes in markers of oxidative stress or endogenous anti-oxidants. We postulate that divergent mechanisms of action may explain these changes: ALA increases peripheral vasodilation, and exercise training stimulates angiogenesis.

Abstract: Although α-linolenic acid (ALA) and endurance exercise training independently attenuate hyperlipidaemia-related cardiovascular derangements, there is a paucity of information pertaining to their mechanisms of action and efficacy when combined as a preventative therapeutic approach. Therefore, we used obese Zucker rats to investigate the independent and combined effects of these interventions on cardiovascular disease. Specifically, animals were randomly assigned to one of the following groups: control diet-sedentary, ALA supplemented-sedentary, control diet-exercise trained or ALA supplemented-exercise trained. Following a 4 week intervention, although the independent and combined effects of ALA and exercise reduced (P < 0.05) the serum free/esterified cholesterol ratio, only the ALA supplemented-exercise trained animals displayed a reduction in the content of both serum free and esterified cholesterol. Moreover, although ALA and endurance training individually increased cardiac output, stroke volume and end-diastolic volume, as well as reduced left ventricle fibrosis, mean blood pressure and total peripheral resistance, these responses were all greater following the combined intervention (ALA supplemented-exercise trained). These effects occurred independent of changes in oxidative phosphorylation proteins, markers of oxidative stress or endogenous anti-oxidant capacity. We propose that the beneficial effects of a combined intervention occur as a result of divergent mechanisms of action elicited by ALA and endurance exercise because only exercise training increased the capillary content in the left ventricle and skeletal muscle, and tended to decrease protein carbonylation in the left ventricle (P = 0.06). Taken together, our data indicate that combining ALA and endurance exercise provides additional improvements in cardiovascular disease risk reduction compared to singular interventions in the obese Zucker rat.

Keywords: PUFA; angiogenesis; diabetic cardiomyopathy; exercise physiology; heart.

Figure 1. Serum free and esterified cholesterol contents

Serum TAG (A), free cholesterol (B), esterified cholesterol (C) and free/esterified cholesterol (D) (n = 7–8 for all groups). Data are expressed as the mean ± SE (P < 0.05). ^*Significant difference from C‐Sed animals. †Significant difference from ALA‐Sed animals. ‡Significant difference from C‐Ex animals. ξSignificant difference from the other three experimental groups.

Figure 2. Indices of cardiac function and morphology as assessed by echocardiography

Representative M‐mode images measured from the parasternal long axis of C‐Sed (top), ALA‐Sed (top middle), C‐Ex (bottom middle) and ALA‐Ex (bottom) animals (A), as well as Q (B), SV (C), EDV (D) and ESV (E) (n = 5–8 for all groups). Data are expressed as the mean ± SE (P < 0.05). ^*Significant difference from C‐Sed animals. ‡Significant difference from C‐Ex animals. ξSignificant difference from all other experimental groups.

Figure 3. Analysis of LV fibrosis

Composite wide‐field microscopy images of the LV from C‐Sed (top left), ALA‐Sed (top right), C‐Ex (bottom left) and ALA‐Ex (bottom right) animals using picrosirius staining (A) and quantification (% area) of fibrosis (B) (n = 7–8 for all groups). Data are expressed as the mean ± SE (P < 0.05). ^*Significant difference from C‐Sed animals. †Significant difference from ALA‐Sed animals. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 4. Western blot analysis of oxidative phosphorylation (OXPHOS) proteins in the LV

Complex I (NDUFBB), complex II (core 2), complex III (30 kDa), complex IV (cytochrome c oxidase 1 and 4), and complex V (ATP synthase α) subunits (A), and representative blots (B); n = 7–8 for all groups. αtubulin was used as a loading control. Data are expressed as means ± standard error; p < 0.05.

Figure 5. Markers of oxidative stress, and endogenous antioxidant contents in the LV

Representative blots showing 4‐HNE (A), protein carbonylation (B), catalase (C) and SOD2 (D) (n = 7–8 for all groups). αtubulin was used as a loading control. Data are expressed as the mean ± SE (P < 0.05).

Figure 6. Histochemical analysis of the LV

Composite wide‐field microscopy images of LV. Left to right: C‐Sed, ALA‐Sed, C‐Ex and ALA‐Ex animals (A), capillary to fibre ratio (B), cross‐sectional area (C), capillary density (D), VEGF (E), HIF1α (F) and eNOS (G) (n = 7–8 for all groups). α‐tubulin was used as a loading control. Data are expressed as the mean ± SE (P < 0.05). ^*Significant difference from C‐Sed animals. †Significant difference from ALA‐Sed animals. ξSignificant difference from all other experimental groups. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 7. Haemodynamic assessment of MBP and total peripheral resistance

MBP (A) assessed by haemodynamics and TPR (B) (n = 5–8 for all groups). Data are expressed as the mean ± SE (P < 0.05). ^*Significant difference from C‐Sed animals. ξSignificant difference from all other experimental groups.

Figure 8. Histochemical analysis of the red gastrocnemius muscle

Composite wide‐field microscopy images of the red gastrocnemius muscle. Left to right: C‐Sed, ALA‐Sed, C‐Ex and ALA‐Ex animals (A), capillary to fibre ratio (B), cross‐sectional area (C), capillary density (D), VEGF (E), HIF1α (F) and eNOS (G) (n = 7–8 for all groups). α‐tubulin was used as a loading control. Data are expressed as the mean ± SE (P < 0.05). ^*Significant difference from C‐Sed animals. †Significant difference from ALA‐Sed animals. [Color figure can be viewed at wileyonlinelibrary.com]