Capsaicin-sensitive afferent neurones and gastrointestinal propulsion in the rat

Gastrointestinal propulsion (gastric emptying and gastrointestinal transit) of a test meal containing charcoal and 51Cr as well as defaecation in relation to food intake were studied in adult rats pretreated with capsaicin (0.40 mmol kg-1 S.C.) or its solvent one week before experimentation. In solvent-treated rats, gastrointestinal propulsion did not differ when the test meal was given to conscious animals or when the meal was administered under ether anaesthesia. In rats treated with capsaicin, gastrointestinal propulsion was unchanged as compared with solvent-treated rats when the test meal was administered to conscious animals. When, however, the meal was given under ether anaesthesia capsaicin-treated rats showed a delayed gastrointestinal propulsion as compared with solvent-treated rats. This delay in gastrointestinal propulsion was abolished by pretreatment of the animals with guanethidine (67 mumol kg-1 S.C.). Rats treated with capsaicin exhibited a prolonged sleeping time in response to ether as compared with solvent-treated rats. Defaecation in relation to food intake was not changed in rats treated with capsaicin as compared with solvent-treated animals. These results indicate that capsaicin-sensitive afferent neurones do not participate in the physiologic control of gastrointestinal propulsion. The delay in gastrointestinal propulsion observed in capsaicin-treated rats when fed under ether anaesthesia seems to involve the sympathetic nervous system. This finding suggests that secondary functional changes in the autonomic nervous system following capsaicin treatment can influence physiologic processes in which capsaicin-sensitive afferent neurones are not primarily implicated.