perfusion of a beta-adrenergic blocker ( propranolol ) or an alpha-adrenergic blocker ( phentolamine ) through the third and fourth cerebroventricles had no effect on the increase in renin during sinus hypotension , whereas centrally administered clonidine , and alpha-agonist , blocked the response .
C0033497
propranolol
C0020649
hypotension