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: These findings suggest that lowered serum prolactin levels in the early phase of bromocriptine treatment may result from an impaired secretion of prolactin due to decreasing numbers of cytoplasmic microtubules .
### Output Text:
These findings suggest that lowered serum prolactin levels in the early phase of <span class="chemical">bromocriptine</span> treatment may result from an impaired secretion of prolactin due to decreasing numbers of cytoplasmic microtubules . 