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: TCR protected against pathological changes induced by isoproterenol in rat heart .
### Output Text:
<span class="chemical">TCR</span> protected against pathological changes induced by <span class="chemical">isoproterenol</span> in rat heart . 