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 endothelial ultrastructure was unaffected by D - pen , and no differences in aortic 131I - HSA radioactivity or aorta / serum - ratio were recorded between experimental and control groups 10 minutes after tracer injection , indicating that the permeability of the endothelial barrier to albumin remained unaffected by D - pen treatment .
### Output Text:
The endothelial ultrastructure was unaffected by <span class="chemical">D - pen</span> , and no differences in aortic 131I - HSA radioactivity or aorta / serum - ratio were recorded between experimental and control groups 10 minutes after tracer injection , indicating that the permeability of the endothelial barrier to albumin remained unaffected by <span class="chemical">D - pen</span> treatment . 