tokens: The pressor responses and bradycardia to the alpha 1 - agonist cirazoline ( 0 . 6 and 2 micrograms kg - 1 i . v . ) , the alpha 2 - agonist Abbott - 53693 ( 1 and 3 micrograms kg - 1 i . v . ) , and noradrenaline ( 0 . 1 and 1 . 0 micrograms kg - 1 i . v . ) were determined in conscious SHR with and without chronic prazosin pretreatment .