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: Plasma concentration and urine excretion of the renin - angiotensin system proteins are altered in rats with nephrotic syndrome ( NS ) .
### Output Text:
Plasma concentration and urine excretion of the renin - <span class="chemical">angiotensin</span> system proteins are altered in rats with nephrotic syndrome ( NS ) . 