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: PPA , 75 mg alone , increased blood pressure ( 31 + / - 14 mm Hg systolic , 20 + / - 5 mm Hg diastolic ) , and propranolol pretreatment antagonized this increase ( 12 + / - 10 mm Hg systolic , 10 + / - 7 mm Hg diastolic ) .
### Output Text:
<span class="chemical">PPA</span> , 75 mg alone , increased blood pressure ( 31 + / - 14 mm Hg systolic , 20 + / - 5 mm Hg diastolic ) , and <span class="chemical">propranolol</span> pretreatment antagonized this increase ( 12 + / - 10 mm Hg systolic , 10 + / - 7 mm Hg diastolic ) . 