IMPAIRED ACETYLCHOLINE-RELEASE IN THE INFLAMED RAT INTESTINE IS T-CELL INDEPENDENT

We investigated mechanisms underlying the suppression of [H-3]acetylcholine ([H-3]ACh) release from myenteric plexus-longitudinal muscle preparations of rats infected 6 days previously with Trichinella spiralis. There was a 73% suppression of KCl-evoked release of [H-3]ACh in the jejunum, and a 76% suppression was observed in the worm-free ileum, indicating that the local presence of the parasite in the lumen is not prerequisite for the suppression of ACh release from the myenteric plexus. Treatment of rats with betamethasone (3 mg.kg-1.day-1 ip) during the infection prevented the acute inflammatory response and attenuated the suppression of [H-3]Ach release (from 73 to 22%) in the jejunum of infected rats. This finding is consistent with the hypothesis that the suppression of ACh release occurs as a result of the inflammatory process. Marked suppression of [H-3]ACh release was also seen in T spiralis-infected nude athymic rats, which were shown to lack functioning T lymphocytes. Thus changes in ACh release are not dependent on T lymphocytes. Taken in conjunction with our previously published study showing that altered muscle function in this model is T cell dependent, the results of the present study indicate that different components of the inflammatory response mediate changes in smooth muscle and myenteric nerves in the T. spiralis infected rat.