Analysis of the innervation of the gastroduodenal region

Under isometric conditions simultaneous recordings are made of the contractile activity of smooth-muscle strips isolated along the circular axis from the pyloric sphincter (PS) and at 1 cm proximally an distally from it -- from the antrum (A) and duodenum (D). The effect of transmural electrical stimulation is studied after the method of Burn and Rand (1960) (duration of the impulses 0.5 ms, frequency from 2 to 20 Hz and supramaximal current values for 20 s). The responses of the smooth-muscle strips isolated from A and D to transmural electrical stimulation are similar. Switching on of the stimulation causes contraction (on-response) throughout the entire stimulation period, while its switching off leads to additional last contraction (off-response). A dependence is observed between the amplitudes of the on- and off-responses and the frequency of the impulses, the maximum being reached in the high-frequency range (16-20 Hz). After Atropinum sulfuricum (5 x 10(-6)M) the on-response is considerably reached, no off-response being observed. In PS triggering of the stimulation results in inhibition of the phasic activity, accompanied by marked relaxation (on-response). The amplitude and the duration of the relaxation depend on the frequency of the impulses applied, the amplitude being maximal at 4-6 Hz, while its duration reaches the maximum between 16 and 18 Hz. Atropinum sulfuricum (5 x 10(-6)M) does not change essentially the amplitude of the relaxation. After Atropinum sulfuricum, Phentolamine and Propranolol (10(-5)M) the amplitude of the relaxation increases significantly in the low-frequency region (4-8 Hz), while its duration decreases considerably.