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: We first tested whether chronic hyperprolactinemia inhibited two neuroendocrine parameters necessary for female fertility : pulsatile LH secretion and the estrogen - induced LH surge .
### Output Text:
We first tested whether chronic hyperprolactinemia inhibited two neuroendocrine parameters necessary for female fertility : pulsatile LH secretion and the <span class="chemical">estrogen</span> - induced LH surge . 