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: Conversely , administration of rauwolscine ( 3 mg kg - 1 i . v . ) in chronic prazosin treated SHR decreased the basal MAP by 12 - 31 % ( n = 4 ) , and subsequent tilts induced further drops of MAP by 19 - 23 % in these rats .
### Output Text:
Conversely , administration of <span class="chemical">rauwolscine</span> ( 3 mg kg - 1 i . v . ) in chronic <span class="chemical">prazosin</span> treated SHR decreased the basal MAP by 12 - 31 % ( n = 4 ) , and subsequent tilts induced further drops of MAP by 19 - 23 % in these rats . 