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 normal conscious rats investigated by continuous cystometry , intravesically instilled prostaglandin ( PG ) E2 facilitated micturition and increased basal intravesical pressure .
### Output Text:
In normal conscious rats investigated by continuous cystometry , intravesically instilled <span class="chemical">prostaglandin ( PG ) E2</span> facilitated micturition and increased basal intravesical pressure . 