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: Intracellular PRL content ranged from 1 . 9 to 9 . 4 times control levels , and PRL release in vitro was significantly and consistently higher than controls , after at least 8 days of DES exposure .
### Output Text:
Intracellular PRL content ranged from 1 . 9 to 9 . 4 times control levels , and PRL release in vitro was significantly and consistently higher than controls , after at least 8 days of <span class="chemical">DES</span> exposure . 