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: Estradiol treatment also increased the arrhythmogenicity of bupivacaine in myocyte cultures , but was only one fourth as potent as progesterone .
### Output Text:
<span class="chemical">Estradiol</span> treatment also increased the arrhythmogenicity of <span class="chemical">bupivacaine</span> in myocyte cultures , but was only one fourth as potent as <span class="chemical">progesterone</span> . 