Heart rate and blood pressure were recorded in conscious, freely behaving rats through a
catheter in the tail artery during administration of nitroprusside or phenylephrine through a
catheter in the jugular vein. The sympathetic and parasympathetic components were
distinguished by treating the rats with atenolol or methyl-atropine. Reflex bradycardia
induced by all doses of phenylephrine was almost totally blocked blocked following methyl-
atropine treatment. Reflex tachycardia induced by small to moderate doses of nitroprusside …