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: This study was designed to discern whether the reduction in urinary NOx in lead - induced hypertension is , in part , due to depressed NO synthase ( NOS ) expression .
### Output Text:
This study was designed to discern whether the reduction in urinary NOx in <span class="chemical">lead</span> - induced hypertension is , in part , due to depressed <span class="chemical">NO</span> synthase ( NOS ) expression . 