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: Oral pre - treatment with PK ( 80 mg kg ( - 1 ) day ( - 1 ) for 15 days ) significantly prevented the isoproterenol - induced myocardial infarction and maintained the rats at near normal status .
### Output Text:
Oral pre - treatment with PK ( 80 mg kg ( - 1 ) day ( - 1 ) for 15 days ) significantly prevented the <span class="chemical">isoproterenol</span> - induced myocardial infarction and maintained the rats at near normal status . 