Inhibition of sympathetic neurotransmission in the rat anococcygeus muscle by diazepam

Abstract

In the rat anococcygeus muscle, diazepam (1.8 X 10(-6) - 2.8 X 10(-5) M), dipyridamole (2 X 10(-6) - 3.2 X 10(-5) M) and ATP (2 X 10(-4) - 6.4 X 10(-3) M) concentration-dependently inhibited the motor response to field stimulation. Glycine (up to 7.5 X 10(-3) M) and GABA (up to 10(-4) M) had no effect on field stimulation. Concentrations of diazepam and dipyridamole which reduced motor response to field stimulation did not relax the tonically contracted rat anococcygeus muscle. However, at these concentrations, diazepam and dipyridamole potentiated the inhibitory responses of the tonically contracted rat anococcygeus muscle to ATP and field stimulation. It is suggested that diazepam and dipyridamole reduced the motor response to field stimulation by potentiating the inhibitory transmitter released during nerve stimulation. Also, since the time-course of the effect of diazepam and dipyridamole on the inhibitory responses to ATP and field stimulation are closely similar, the results would tend to provide additional support for the concept of purinergic transmission in the rat anococcygeus muscle.