Physiological characteristics of ovine pyloric sphincter.

A special probe was validated to record in situ pyloric sphincter activity by changes in fiber-optic light transmission and sleeve pressure associated with the propagation of antroduodenal contractions, the onset of the phase of regular spiking activity (RSA) of the migrating myoelectric complex, the RSA-like events elicited by duodenal acidification, and the pharmacological stimulation of the gastroduodenal junction. Rapid changes in light transmission associated with antroduodenal contractions were super-imposed on slow variations, suggesting the existence of both phasic and tonic components in pyloric sphincter activity. The phasic activity coincided with isolated closures of the pyloric orifice, closures associated with antral or duodenal bulb contractions, and with long-lasting rhythmic closures during the development of the RSA phase. The resting tone increased during antral and/or duodenal stimulation and by feeding "appetizers" but decreased during antroduodenal quiescence and at the onset of general anesthesia. It is concluded that the ovine pylorus predominantly exists in a state of low resting tone but can act as a true sphincter with both inherent tonic and phasic activity.