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: It has been shown that bromocriptine - induced tachycardia , which persisted after adrenalectomy , is ( i ) mediated by central dopamine D2 receptor activation and ( ii ) reduced by 5 - day isoproterenol pretreatment , supporting therefore the hypothesis that this effect is dependent on sympathetic outflow to the heart .
### Output Text:
It has been shown that <span class="chemical">bromocriptine</span> - induced tachycardia , which persisted after adrenalectomy , is ( i ) mediated by central <span class="chemical">dopamine</span> D2 receptor activation and ( ii ) reduced by 5 - day <span class="chemical">isoproterenol</span> pretreatment , supporting therefore the hypothesis that this effect is dependent on sympathetic outflow to the heart . 