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 SOD - induced increase in glomerular filtration rate was associated with a marked improvement in RBF , an increase in urinary cGMP excretion , and a decrease in renal renin and endothelin - 1 content .
### Output Text:
The SOD - induced increase in glomerular filtration rate was associated with a marked improvement in RBF , an increase in urinary <span class="chemical">cGMP</span> excretion , and a decrease in renal renin and endothelin - 1 content . 