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: Intracerebroventricular ( i . c . v . ) injection of U - II causes hypertension and bradycardia and stimulates prolactin and thyrotropin secretion .
### Output Text:
Intracerebroventricular ( i . c . v . ) injection of <span class="chemical">U - II</span> causes hypertension and bradycardia and stimulates prolactin and thyrotropin secretion . 