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: Measurement of resting norepinephrine spillover rate to plasma and norepinephrine uptake indicated that overall resting sympathetic nervous system activity was not increased .
### Output Text:
Measurement of resting <span class="chemical">norepinephrine</span> spillover rate to plasma and <span class="chemical">norepinephrine</span> uptake indicated that overall resting sympathetic nervous system activity was not increased . 