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 present study was designed to investigate the cardioprotective effects of betaine on acute myocardial ischemia induced experimentally in rats focusing on regulation of signal transducer and activator of transcription 3 ( STAT3 ) and apoptotic pathways as the potential mechanism underlying the drug effect .
### Output Text:
The present study was designed to investigate the cardioprotective effects of <span class="chemical">betaine</span> on acute myocardial ischemia induced experimentally in rats focusing on regulation of signal transducer and activator of transcription 3 ( STAT3 ) and apoptotic pathways as the potential mechanism underlying the drug effect . 