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: Such effects of THP were reversed by RAMH indicating the involvement of histamine H ( 3 ) - receptors .
### Output Text:
Such effects of <span class="chemical">THP</span> were reversed by <span class="chemical">RAMH</span> indicating the involvement of <span class="chemical">histamine</span> H ( 3 ) - receptors . 