Theophylline does not affect morphine inhibition of the isolated vas deferens.

1 Adenosine and morphine both produced an inhibition of the electrically-evoked twitch of the isolated superfused vas deferens of the mouse. 2 Theophylline, 10 or 100 muM, reduced the inhibitory action of adenosine but did not change inhibition by morphine. 3 It is suggested that adenosine release is not a necessary prerequisite for morphine inhibition of transmitter release. It is also suggested that the involvement of adenosine may follow activation only by opiate mu-receptors.