1 an attempt was made to determine whether the extracellular adenosine receptor that mediates relaxation in the guinea-pig trachea is of the a ( 1 ) /r ( i ) or a ( 2 ) /r ( a ) subtype.2 dose-response curves to adenosine and a number of 5'- and n ( 6 ) -substituted analogues were constructed for the isolated guinea-pig trachea , contracted with carbachol.3 the 5'-substituted analogues of adenosine were the most potent compounds tested , the order of potency being 5'-n-cyclopropylcarboxamide adenosine ( ncpca ) > 5'-n-ethylcarboxamide adenosine ( neca ) > 2-chloroadenosine > l-n ( 6 ) -phenylisopropyladenosine ( l-pia ) > adenosine > d-n ( 6 ) -phenylisopropyladenosine ( d-pia ) .4 the difference in potency between the stereoisomers d- and l-pia on the isolated trachea was at the most five fold.5 responses to low doses of adenosine and its analogues were attenuated after treatment with either theophylline or 8-phenyltheophylline .
C0000275
2-chloroadenosine
C0001443
adenosine