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: To clarify the mechanisms of FK 506 - induced hypertension , we studied the chronic effects of FK 506 on the synthesis of endothelin - 1 ( ET - 1 ) , the expression of mRNA of ET - 1 and endothelin - converting enzyme - 1 ( ECE - 1 ) , the endothelial nitric oxide synthase ( eNOS ) activity , and the expression of mRNA of eNOS and C - type natriuretic peptide ( CNP ) in rat blood vessels .
### Output Text:
To clarify the mechanisms of <span class="chemical">FK 506</span> - induced hypertension , we studied the chronic effects of <span class="chemical">FK 506</span> on the synthesis of endothelin - 1 ( ET - 1 ) , the expression of mRNA of ET - 1 and endothelin - converting enzyme - 1 ( ECE - 1 ) , the endothelial <span class="chemical">nitric oxide</span> synthase ( eNOS ) activity , and the expression of mRNA of eNOS and C - type natriuretic peptide ( CNP ) in rat blood vessels . 