Non-cholinergic, non-adrenergic tonic component of the electrically-evoked contractions of guinea pig ileum.

Contractile responses of the longitudinal muscle layer of guinea pig ileum to 40-sec electrical field stimulation (0.8 msec, 20 V) applied at frequencies of 5 Hz or 30 Hz consisted in a fast phasic contraction followed by a low-amplitude tonic component. Atropin (3 microM) and prazosine (1 microM) decreased significantly the amplitude of the phasic contraction and had less influence on the tonic component. SC 19220 (50 microM) additionally lowered both the fast and the tonic contractions, the inhibitory effect being more pronounced on the tonic component. It is suggested that prostaglandins released during electrical stimulation could be involved in the non-cholinergic, non-adrenergic tonic component of the contractile responses.