Gastrointestinal myoelectric correlates of vomiting in the dog

Prior to vomiting, two gastrointestinal contractile events occur in succession: a giant contraction that propagates retrograde from mid-small intestine to the antrum (RGC) and a series of phasic contractions that occur at all levels of the gastrointestinal tract. We quantitatively examined the gastrointestinal myoelectric events associated with vomiting and correlated them with the previously defined contractile events. Twelve dogs of either sex were implanted with electrical or contractile recording devices implanted on the stomach and small intestine. After an overnight fast, gut activity was recorded before and after apomorphine administration (2.5-15 micrograms/kg, iv). We found that the RGC was correlated with two successive electrical events: disruption of electrical control activity (ECA) cycling and a potential change occurring at the upstroke of the RGC. However, the initial myoelectric event associated with vomiting was ECA frequency slowing of the antrum and lower half of the small intestine. The post-RGC phasic contractions were associated with ECA-dependent response activity and occurred during the period of ECA frequency slowing. Atropine (100 micrograms/kg iv) blocked the RGC and its associated electrical events but not the slowing of ECA frequency. Supradiaphragmatic vagotomy eliminated all gastrointestinal contractile and myoelectric events but antral ECA frequency slowing. Spontaneous occurrences of the myoelectric correlates of vomiting were not different from those activated by apomorphine. These results suggest that ECA disruption may be important for retrograde propagation of the RGC. The function of ECA frequency slowing, however, remains unknown.