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: Suppression of irCRF secretion in response to nitroprusside - induced hypotension is observed and occurs at a plasma corticosterone level between 8 - 12 micrograms / dl .
### Output Text:
Suppression of irCRF secretion in response to <span class="chemical">nitroprusside</span> - induced hypotension is observed and occurs at a plasma <span class="chemical">corticosterone</span> level between 8 - 12 micrograms / dl . 