The relationship between gastrointestinal motility and secretion.

Few studies have addressed specifically or systematically the question of whether motility and secretion within the gastrointestinal tract are linked and if so by what mechanisms. The evidence for such a relationship is discussed in this review and we conclude that increased motor activity of the stomach is frequently associated with increased acid and pepsin secretion. Similarly, an increase in small intestinal motility is accompanied by elevated fluid and electrolyte secretion. Two possible mechanisms linking motility to secretion are considered. These could coexist. The first consists of parallel but separate neural pathways to smooth muscle and epithelium that might be activated synchronously and, therefore, produce simultaneous activation of motility and secretion. The existence of such parallel pathways in the stomach and small intestine are described, but their physiological significance is unresolved. The second mechanism we discuss is a sequential process in which increased motility provides a sensory stimulus for reflexly activated secretion. In the stomach the evidence for such a mechanism is largely deductive. In the intestine, however, we provide experimental evidence for an intrinsic neural mechanism activated by motor activity, which then stimulates fluid and electrolyte secretion. We conclude that such a sequential relationship exists and probably operates under physiological conditions but that further study is required.