Single pulses of 100 msec duration and 1-25 V amplitude were applied at different phases of the gastric control wave (slow wave) cycle to study the refractoriness properties of relaxation oscillators in gastric muscle of dogs. The initial phase (up to 20-70%) of the control wave cycle beginning at the occurrence of a normal control potential was absolutely refractory to the production of premature control potentials (PCP). The duration of the absolutely refractory state (ARS) in the antrum was less than that in the corpus in both the normal and the reserpinized dogs. When the duration of the ARS was less than 40% of the duration of the control wave cycle, physostigmine increased the duration of the ARS; otherwise it had no effect. Atropine (iv) reduced the duration investigates the ARS in the antrum. These drugs had no effect on the duration of the ARS in the corpus. PCPs could be produced in the rest of the cycle. The threshold stimulus required to produce PCPs reduced progressively with increasing time in the cycle. Atropine reduced the threshold levels in the antrum and physostigmine raised them. Similar results were obtained in reserpinized dogs. Refractoriness properties of gastric relaxation oscillators explain the reasons for the upper limit to which these oscillators can be driven by electronic pacemakers and the effect of parasympathetic activity on this limit.
ASJC Scopus subject areas
- Physiology (medical)