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: Possible mechanisms that involve a verapamil - related increase in platelet and / or vascular alpha 2 - adrenoreceptor affinity for catecholamines are discussed .
### Output Text:
Possible mechanisms that involve a <span class="chemical">verapamil</span> - related increase in platelet and / or vascular alpha 2 - adrenoreceptor affinity for <span class="chemical">catecholamines</span> are discussed . 