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: These results show that 15 - day isoproterenol pretreatment not only abolished but reversed bromocriptine - induced tachycardia to bradycardia , an effect that is mainly related to further cardiac beta - adrenoceptor desensitization rather than to impairment of autonomic regulation of the heart .
### Output Text:
These results show that 15 - day <span class="chemical">isoproterenol</span> pretreatment not only abolished but reversed <span class="chemical">bromocriptine</span> - induced tachycardia to bradycardia , an effect that is mainly related to further cardiac beta - adrenoceptor desensitization rather than to impairment of autonomic regulation of the heart . 