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: In contrast , cromakalim and pinacidil at all doses and nitroglycerin at doses higher than 0 . 3 micrograms / kg simultaneously and dose - dependently increased CxAD , coronary blood flow and heart rate and decreased coronary vascular resistance and aortic pressure .
### Output Text:
In contrast , <span class="chemical">cromakalim</span> and <span class="chemical">pinacidil</span> at all doses and <span class="chemical">nitroglycerin</span> at doses higher than 0 . 3 micrograms / kg simultaneously and dose - dependently increased CxAD , coronary blood flow and heart rate and decreased coronary vascular resistance and aortic pressure . 