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: We conclude that in streptozotocin - diabetic rats with an increased urinary albumin excretion , a reduced heparan sulphate charge barrier / density is found at the lamina rara externa of the glomerular basement membrane .
### Output Text:
We conclude that in <span class="chemical">streptozotocin</span> - diabetic rats with an increased urinary albumin excretion , a reduced <span class="chemical">heparan sulphate</span> charge barrier / density is found at the lamina rara externa of the glomerular basement membrane . 