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: We examined the potential role of prostaglandins in the development of analgesic nephropathy in the Gunn strain of rat .
### Output Text:
We examined the potential role of <span class="chemical">prostaglandins</span> in the development of analgesic nephropathy in the Gunn strain of rat . 