Is there any API service to retrieve abstract of a journal article?
For the MEDLINE database, with the E-utilities you can: 


Use the esearch function to retrieve the PubMed ID (PMID) of the article that includes the DOI as a term (presumably only one article):

http://eutils.ncbi.nlm.nih.gov/entrez/eutils/esearch.fcgi?db=pubmed&amp;WebEnv=1&amp;usehistory=y&amp;term=10.1021/bi902153g
Then, use efetch function to retrieve the abstract among other bibliographic attributes of the article (you need to pass the query_key and WebEnv returned earlier by esearch).

http://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&amp;retmode=XML&amp;rettype=abstract&amp;query_key=1&amp;WebEnv=something




If you have the PMID, it is one step with efetch:


http://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&amp;id=17284678&amp;retmode=XML&amp;rettype=abstract