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: The enhanced alpha - methyldopa hypotension in Ovx rats was paralleled with further reduction in SDRR and a reduced locomotor activity .
### Output Text:
The enhanced <span class="chemical">alpha - methyldopa</span> hypotension in Ovx rats was paralleled with further reduction in SDRR and a reduced locomotor activity . 