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: In rats of the experimental group , the mean concentration of : PRL was more than twice higher , whereas T concentration was almost twice lower than that in the control group .
### Output Text:
In rats of the experimental group , the mean concentration of : <span class="chemical">PRL</span> was more than twice higher , whereas <span class="chemical">T</span> concentration was almost twice lower than that in the control group . 