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 effects of microinjection of clonidine ( 1 - 10 micrograms in 1 microliter ) into a region adjacent to the ventrolateral surface of the medulla oblongata on cardiovascular function were assessed in urethane - anesthetized rats .
### Output Text:
The effects of microinjection of <span class="chemical">clonidine</span> ( 1 - 10 micrograms in 1 microliter ) into a region adjacent to the ventrolateral surface of the medulla oblongata on cardiovascular function were assessed in <span class="chemical">urethane</span> - anesthetized rats . 