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: Sulpiride did not affect the magnitude of a steroid - induced LH surge or the percentage of GnRH neurons activated during the surge .
### Output Text:
<span class="chemical">Sulpiride</span> did not affect the magnitude of a <span class="chemical">steroid</span> - induced LH surge or the percentage of GnRH neurons activated during the surge . 