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: These results suggest the involvement of both adenosine receptors in the action of cocaine although agonists of A1 receptors seem to have stronger influence on it .
### Output Text:
These results suggest the involvement of both <span class="chemical">adenosine</span> receptors in the action of <span class="chemical">cocaine</span> although agonists of A1 receptors seem to have stronger influence on it . 