Studies on the stereoselectivity of the P2-purinoceptor on the guinea-pig vas deferens.

ATP, 2-chloro-ATP, 2-methylthio-ATP and their unnatural L-enantiomers, Rp and Sp diastereoisomers of the ATP phosphorothioate analogues, ATP alpha S and ATP beta S, were tested on the guinea-pig vas deferens. The 2-substituted analogues of ATP were no more effective than ATP in causing contraction of the vas deferens. However, stereoselectivity was observed with each pair of enantiomers of ATP, 2-chloro-ATP and 2-methylthio-ATP. No stereoselectivity was observed for the phosphorothioate analogues. Rp- and Sp-ATP beta S were more effective than ATP at eliciting contractions of the vas deferens. These results show that unlike the P2-purinoceptor mediating excitatory responses in the guinea-pig bladder, the P2-purinoceptor mediating contraction in the guinea-pig vas deferens displays stereoselectivity.