Duodenal sensory and reflex mechanisms were examined during acute
experiments with isolated loops of duodenum in anaesthetised rabbits
and sheep.Mechanical stimulation of the rabbit duodenum caused reflex motor
responses in adjacent segments of the gut. The thresholds of these
reflexes were the same as the thresholds of mechanoreceptors whose
afferent activity was recorded in duodenal nerves during electro¬
physiological investigations. These mechanoreceptors were situated
in the muscularis externa, the serosa and the mesentery. Mechano¬
receptors in the muscularis externa were excited when the duodenum
was perfused with chemical solutions containing glucose.In the sheep duodenum the impulse activity of afferent units
from slowly adapting mechanoreceptors in the muscularis externa
coincided with local electromyographic (emg) and tension changes.
Units were excited by passive distension, compression, active increases
in muscle tension and alterations of temperature. The application
of chemical solutions or light mechanical stimulation of the mucosa
evoked intrinsic reflexes which modified impulse activity.
Receptors were excited by injections of peptide hormone analogues
and other drugs. With the exception of insulin, the responses
evoked by drugs coincided with increases in muscle tension and emg
activity.Slowly adapting mechanoreceptors in the sheep duodenal mucosa
were either silent in the absence of a mechanical stimulus or were
spontaneously active. Mucosal receptor units were selectively
sensitive to chemicals. One class of unit was excited by solutions
of potassium chloride and another was excited by volatile fatty acids.
No evidence was found for mucosal receptors sensitive to osmolality
or temperature changes.It was concluded that : (a) the mechanoreceptors in the muscularis
externa of the sheep duodenum are tension receptors which occupy a
position "in series" with longitudinal muscle; (b) post-prandially
released alimentary hormones may increase impulse activity in duodenal
tension receptors and thus, by a reflex mechanism, modify ingestive
behaviour and gastric emptying; (c) spontaneously active mucosal
receptors are associated with contractile elements in the muscularis
mucosa; (d) the responses of mucosal receptors to chemicals in
duodenal chyme makes them poor candidates for providing tonic afferent
inputs to the central nervous system; (e) these mucosal mechanoreceptors do not initiate reflexes requiring large mechanical stimuli;
and (f) the sensory receptors studied do not play a part in duodenal
reflex mechanisms initiated by osmotic changes
