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 hemodynamic effects of captopril and other angiotensin - converting enzyme inhibitors may be mediated by the endogenous opioid system .
### Output Text:
The hemodynamic effects of <span class="chemical">captopril</span> and other <span class="chemical">angiotensin - converting enzyme inhibitors</span> may be mediated by the endogenous opioid system . 