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: MAP and HR were monitored before and after i . v . injections of either vehicle or 1 , 10 and 50 ng of AVP and 25 , 125 and 500 ng of ANP .
### Output Text:
MAP and HR were monitored before and after i . v . injections of either vehicle or 1 , 10 and 50 ng of <span class="chemical">AVP</span> and 25 , 125 and 500 ng of ANP . 