Summary of Effects of Endothelium Removal, or Incubation (40 min) with l-NAME (100 μM), Prazosin (1 μM), Rauwolscine (100 nM), l-arginine (1 mM), BEC (10 μM), l-NOHA (10 μM), Urea (100 μM), and Ornithine (100 μM), Alone or in Combination, on Contractions to Increasing Concentrations (10 nM to 10 μM) of Dexmedetomidine