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: Testosterone replacement almost restored the STL1 and STL2 in castrated rats , and significantly prolonged the STL1 and STL2 in STZ - treated rats .
### Output Text:
<span class="chemical">Testosterone</span> replacement almost restored the STL1 and STL2 in castrated rats , and significantly prolonged the STL1 and STL2 in <span class="chemical">STZ</span> - treated rats . 