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: These results suggest that hypertension after chronic intrarenal noradrenaline infusion is produced by relatively higher levels of circulating noradrenaline and by triggering of an additional intrarenal pressor mechanism .
### Output Text:
These results suggest that hypertension after chronic intrarenal <span class="chemical">noradrenaline</span> infusion is produced by relatively higher levels of circulating <span class="chemical">noradrenaline</span> and by triggering of an additional intrarenal pressor mechanism . 