2.1. Materials

A standard chow diet (AIN93G) and a modified vitamin D-deficient diet (SF03-009) were purchased from Specialty Feeds Pty Ltd. (Glen Forrest, Western Australia). The standard diet contains 1000 IU/kg of vitamin D₃. Both diets also contained 0.47% calcium and 0.35% phosphorus. Acetylcholine hydrochloride, calcium ionophore, sodium nitroprusside, phenylephrine hydrochloride, and streptozotocin (STZ) were purchased from Sigma Chemical Co. (St. Louis, MO, USA). Salbutamol hemisulfate was purchased from Tocris Bioscience (Bristol, UK). _L-NAME hydrochloride was obtained from Cayman Chemicals (Ann Arbor, MI, USA). Calcitriol (Rocaltrol) was purchased from Roche (Switzerland). Primary antibody against eNOS (AB76198), mouse monoclonal antibody to β-actin (AB8226), and horseradish peroxidase- (HRP-) conjugated secondary antibody (AB6721) were purchased from Abcam (Cambridge, UK).