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: Both epinephrine and exercise produced myocardial ischemia as evidenced by ST segment depression and angina .
### Output Text:
Both <span class="chemical">epinephrine</span> and exercise produced myocardial ischemia as evidenced by ST segment depression and angina . 