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: RESULTS : In Nx dogs , OCT significantly decreased serum PTH levels soon after the induction of renal insufficiency .
### Output Text:
RESULTS : In Nx dogs , <span class="chemical">OCT</span> significantly decreased serum PTH levels soon after the induction of renal insufficiency . 