tokens: Isoproterenol sensitivity was determined as the intravenous dose that increased heart rate by 25 bpm ( CD25 ) and this was increased from 1 . 8 + / - 0 . 3 micrograms after placebo to 38 . 9 + / - 8 . 3 micrograms after propranolol and 8 . 3 + / - 1 . 7 micrograms after atenolol .