2.4. Rat-Isolated Aorta Model

To remove the thoracic aorta, the animals from both groups, NTR and SHR, were anesthetized intraperitoneally with ketamine (80 mg/kg) and xylazine (10 mg/kg). The descending thoracic aorta artery was removed and transferred to a recipient containing physiological saline solution (PSS; composition in mM: NaCl 110.8, KCl 5.9, NaHCO₃ 25, MgSO₄ 1.07, CaCl₂ 2.49, KH₂PO₄ 2.33, and glucose 11.51) heated to 37°C to remove connective tissue. Then, the vessel was sectioned into rings measuring approximately five mm in length. The obtained aortic rings were attached to two metallic rods conditioned in organ baths (with the capacity of 2 mL) containing the PSS and constantly aerated with 95% O₂ and 5% CO₂, kept at a temperature of 37°C, and submitted to a basal tension of 1 g. The isometric contraction was recorded through a signal amplifier and connected to a computer containing specific integration software (WinDaq Software, DATAQ Instruments, Akron, Ohio, USA). After 60 min of tissue stabilization, with PSS changes at 15 min, the preparations were contracted with a potassium chloride solution (60 mM, KCl) to identify tissue responsiveness. After a new interval of 30 min for stabilization of the preparations, a contraction was induced by the addition of phenylephrine (Phe, 1 μM), followed by the administration of acetylcholine (Ach, 1 μM) in the tonic phase of the contraction. Vessels with functional endothelium were considered for those preparations that obtained a relaxation equal to or greater than 80%.