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: On the other hand clentiazem did not prevent epinephrine - induced down - regulation of alpha and beta adrenoceptors .
### Output Text:
On the other hand <span class="chemical">clentiazem</span> did not prevent <span class="chemical">epinephrine</span> - induced down - regulation of alpha and beta adrenoceptors . 