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: Thus , indomethacin by inhibition of prostaglandin synthesis may diminish the blood pressure maintaining effect of the stimulated renin - angiotensin system in sodium and volume depletion .
### Output Text:
Thus , <span class="chemical">indomethacin</span> by inhibition of <span class="chemical">prostaglandin</span> synthesis may diminish the blood pressure maintaining effect of the stimulated renin - <span class="chemical">angiotensin</span> system in <span class="chemical">sodium</span> and volume depletion . 