Actions of amrinone and milrinone on the guinea-pig ileum

The pharmacological activity of the cardiotonic agents amrinone and milrinone has been examined on the isolated guinea-pig ileum. Both compounds antagonised the presynaptic inhibitory action of adenosine on electrically evoked contractions, milrinone being the more potent. Higher concentrations of amrinone or milrinone produced contractions of the ileum which were prevented by atropine. Contractile responses to adenosine 5'-monophosphate were not inhibited by atropine. It is concluded that amrinone and milrinone can antagonise some effects of purines but this does not represent their only pharmacological action.