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Although genetic polymorphisms in the endothelial nitric oxide synthase ( eNOS ) gene may impair endogenous NO formation , there is little information about how eNOS polymorphisms and haplotypes affect the responses to sildenafil .
 Chemical: nitric oxide; Chemical: NO; Chemical: sildenafil
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: nitric oxide; Chemical: NO; Chemical: sildenafil