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: In summary , our results showed that betaine pretreatment attenuated isoproterenol - induced acute myocardial ischemia via the regulation of STAT3 and apoptotic pathways .
### Output Text:
In summary , our results showed that <span class="chemical">betaine</span> pretreatment attenuated <span class="chemical">isoproterenol</span> - induced acute myocardial ischemia via the regulation of STAT3 and apoptotic pathways . 