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: Studies were performed to evaluate whether chronic prazosin treatment alters the alpha 2 - adrenoceptor function for orthostatic control of arterial blood pressure in conscious spontaneously hypertensive rats ( SHR ) .
### Output Text:
Studies were performed to evaluate whether chronic <span class="chemical">prazosin</span> treatment alters the alpha 2 - adrenoceptor function for orthostatic control of arterial blood pressure in conscious spontaneously hypertensive rats ( SHR ) . 