4.8. Vascular Reactivity of Aorta Rings

The effect of HDL on endothelial function was evaluated using aorta rings of New Zealand rabbits in an isolated organ bath as previously described [60]. Aorta rings were incubated with HDL to a final concentration of 50 mg/dL of cholesterol in Krebs solution (118.1 mM NaCl, 4.7 mM KCl, 1.2 mM MgSO₄, 1.20 mM KH₂PO₄, 2.5 mM CaCl₂, 25.0 mM NaHCO₃, and 11.1 mM glucose at pH 7.4), continuously bubbled with 95% O₂ and 5% CO₂, at 37 °C, 1 h prior to the test. After an equilibrium period, aorta rings were precontracted with 3 × 10⁻⁴ M phenylephrine. The endothelium-mediated relaxation (vasodilation) was evaluated using a dose–response curve to acetylcholine (5 × 10⁻⁹–8 × 10⁻⁷ M). Contractions were measured isometrically with an FT−03 Grass Force Displacement Transducer and recorded on a Grass Polygraph (Model 7D, Grass Medical Instruments, Quincy, MA, USA). All experiments were run in duplicate, and vasodilation of aorta rings was expressed as the percentage of pre-contraction with phenylephrine.