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 effect of a 6 - week treatment with the calcium channel blocker nitrendipine or the angiotensin converting enzyme inhibitor enalapril on blood pressure , albuminuria , renal hemodynamics , and morphology of the nonclipped kidney was studied in rats with two - kidney , one clip renovascular hypertension .
### Output Text:
The effect of a 6 - week treatment with the <span class="chemical">calcium</span> channel blocker <span class="chemical">nitrendipine</span> or the <span class="chemical">angiotensin</span> converting enzyme inhibitor <span class="chemical">enalapril</span> on blood pressure , albuminuria , renal hemodynamics , and morphology of the nonclipped kidney was studied in rats with two - kidney , one clip renovascular hypertension . 