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: Estrogen replacement ( 17beta - estradiol subcutaneous pellet , 14 . 2 microg / day , 12 wk ) of Ovx rats restored the hemodynamic and locomotor effects of alpha - methyldopa to sham - operated levels .
### Output Text:
Estrogen replacement ( <span class="chemical">17beta - estradiol</span> subcutaneous pellet , 14 . 2 microg / day , 12 wk ) of Ovx rats restored the hemodynamic and locomotor effects of <span class="chemical">alpha - methyldopa</span> to sham - operated levels . 