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: The results indicate that centrally applied AVP and ANP exert differential effects on blood pressure and baroreflex control of heart rate in WKY and SHR and suggest interaction of these two peptides in blood pressure regulation at the level of central nervous system .
### Output Text:
The results indicate that centrally applied <span class="chemical">AVP</span> and ANP exert differential effects on blood pressure and baroreflex control of heart rate in WKY and SHR and suggest interaction of these two peptides in blood pressure regulation at the level of central nervous system . 