Stimulation of splanchnic afferents reflexly relaxes tracheal smooth muscle in dogs

Although chemical stimulation of abdominal visceral afferents has been shown to reflexly increase cardiovascular and ventilatory function, the effect of stimulating these afferents on airway smooth muscle is unknown. Therefore, we recorded transverse smooth muscle tension from an innervated segment of trachea in chloralose-anesthetized dogs while we topically applied capsaicin (200 μg/ml) and bradykinin (0.01-10 μg/ml) to the serosal surfaces of the stomach, small intestine, and gallbladder. Application of these irritant substances to the stomach and small intestine decreased tracheal tension and increased mean arterial pressure. However, application of capsaicin and bradykinin to the gallbladder had only small effects on both of these variables. Cutting the splanchnic nerves abolished or greatly attenuated the decreases in tension and increases in mean arterial pressure, whereas cutting the vagi had no effect on them. We conclude that stimulation of splanchnic afferent endings in the stomach and small intestine reflexly relaxes tracheal smooth muscle in dogs. This effect may be one component of the constellation of automatic responses reflexly evoked by abdominal visceral pain and inflammation.