In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: 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 .
### Output Text:
<span class="chemical">Isoproterenol</span> 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 <span class="chemical">propranolol</span> and 8 . 3 + / - 1 . 7 micrograms after <span class="chemical">atenolol</span> . 