Comparison of stress-induced modulation of smooth-muscle activity between ileum and colon in male rats.

Stress is a well-known cause of numerous digestive conditions, including gastrointestinal-function disorders. The autonomic nervous system regulates intestinal movements via cholinergic and adrenergic efferent fibers; however it is not clear how stress could affect these control mechanisms and in particular whether in a site-dependent manner. In this study we tested in vitro the effects of topical application of acetylcholine (Ach) and adrenalin (Adr) on smooth-muscle contractions of intestinal segments isolated from stress-conditioned rats. Stress was loaded by hypergravity stimulation (10min/day) for periods of 1, 6 or 30days. As a result, stress-conditioning affected intestinal sensitivity to Ach and Adr differently at sections of the ileum and colon. In the ileum no significant differences were found between control and stress-conditioned rats, whereas in the colon, samples from 6- and 30-day stress-conditioned rats showed larger amplitudes of Ach-induced contraction, as well as greater antagonization by Adr application. These results suggest that stress conditioning can modify autonomic control of intestinal movements by altering smooth-muscle sensitivity to Ach and Adr.