Wild Blueberry-Rich Diets Affect the Contractile Machinery of the Vascular Smooth Muscle in the Sprague–Dawley Rat

Abstract

Weanling male Sprague–Dawley rats were randomly fed a control diet (AIN-93) (C) or a blueberry diet (B) for 13 weeks, or a reverse diet (R) (C diet for 13 weeks, switched to the B diet for 8 weeks). Aortas were excised, and two intact and two endothelium-denuded rings were immersed in tissue baths containing physiological salt solution at 37°C and aerated with 95% O₂ and 5% CO₂ (pH 7.4). Following equilibration and preconditioning under 1.5-g preload, cumulative dose–response curves were generated with six doses of the α1-adrenergic receptor-selective agonist L-phenylephrine (L-Phe, 10^–8–3 × 10^–6 M) and relaxed with one dose of acetylcholine (3 × 10^–6 M) to assess intact endothelium. The maximum force of contraction (Fmax) and vessel sensitivity (pD₂) were determined in intact and endothelium-denuded rings. A two-way analysis of variance test revealed that blueberry-fed animals (B and R diets) developed a significantly lower F _max (0.873 ± 0.0463 and 0.9266 ± 0.0463 g, respectively) when contracted with L-Phe, compared with the animals on the C diet (1.109 ± 0.0463 g) (P < .05). The pD₂ of the intact rings was not significantly different among diet groups. Additionally, diet did not significantly affect the mean F _max or pD₂ of endothelium-denuded rings. Our results indicate for the first time that wild blueberries incorporated into the diet affect the vascular smooth muscle contractile machinery by suppressing the α1-adrenergic receptor agonist-mediated contraction while having no effect on membrane sensitivity of the endothelial or vascular smooth muscle cell layer. Furthermore, their mechanism of action seems to be accomplished through an endothelium-dependent pathway.