Inhibition of gastrointestinal transit due to surgical trauma or peritoneal irritation is reduced in capsaicin-treated rats.

Treatment of newborn rats with capsaicin (0.16 mmol/kg) is known to cause a permanent degeneration of mainly unmyelinated afferent neurons. In this study, postoperative ileus and ileus produced by peritoneal irritation with iodine were investigated in adult rats treated with capsaicin as neonates. It was found that in capsaicin-treated rats both forms of ileus, measured as inhibition of gastrointestinal transit, were significantly reduced as compared with vehicle-treated control animals. Adrenoceptor blockade in untreated rats reduced the ileus in response to peritoneal irritation to approximately the same degree as treatment with capsaicin. In capsaicin-treated rats, however, adrenoceptor blockade was without effect on the irritation-induced ileus. It is concluded that ileus in response to surgery or peritoneal irritation is due, at least in part, to activation of a neural reflex. The afferent limb of this reflex may be constituted by capsaicin-sensitive nerve fibers, whereas the efferent limb seems to involve sympathetic adrenergic neurons.