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: Endothelial - dependent relaxation and eNOS mRNA expression were greater in the Dex + Ato group than in the Dex only group ( P < 0 . 05 and P < 0 . 0001 , respectively ) .
### Output Text:
Endothelial - dependent relaxation and eNOS mRNA expression were greater in the <span class="chemical">Dex</span> + <span class="chemical">Ato</span> group than in the <span class="chemical">Dex</span> only group ( P < 0 . 05 and P < 0 . 0001 , respectively ) . 