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: Aspirin treatment reduced PGE2 synthesis in all regions , but outer medullary PGE2 remained higher in jj ( 18 + / - 3 ) than jJ rats ( 9 + / - 2 ) ( p less than 0 . 05 ) .
### Output Text:
<span class="chemical">Aspirin</span> treatment reduced <span class="chemical">PGE2</span> synthesis in all regions , but outer medullary <span class="chemical">PGE2</span> remained higher in jj ( 18 + / - 3 ) than jJ rats ( 9 + / - 2 ) ( p less than 0 . 05 ) . 