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: In unanesthetized , spontaneously hypertensive rats the decrease in blood pressure and heart rate produced by intravenous clonidine , 5 to 20 micrograms / kg , was inhibited or reversed by nalozone , 0 . 2 to 2 mg / kg .
### Output Text:
In unanesthetized , spontaneously hypertensive rats the decrease in blood pressure and heart rate produced by intravenous <span class="chemical">clonidine</span> , 5 to 20 micrograms / kg , was inhibited or reversed by <span class="chemical">nalozone</span> , 0 . 2 to 2 mg / kg . 