Impaired acetylcholine release from the myenteric plexus of Trichinella-infected rats

We examined the release of acetylcholine (ACh) from jejunal longitudinal muscle-myenteric plexus preparations in noninfected control rats and in rats infected 6, 23, or 40 days previously with Trichinella spiralis. ACh release was assessed by preincubating the tissue with [3H]choline and measuring the evoked release of tritium. The uptake of 3H was significantly less in tissue from T. spiralis-infected rats compared with control. In tissues from either infected or control animals, electrical field stimulation (30 V, 0.5 ms, 10 Hz for 1 min), or veratridine (6-30 microM) induced 3H release that was tetrodotoxin sensitive. Depolarization by KCl (25-75 mM) also caused 3H release, but this was only partially reduced by tetrodotoxin. Radiochromatographic analysis indicated evoked release of 3H to be almost entirely [3H]ACh. In rats infected 6 days previously with T. spiralis, [3H]ACh release induced by KCl, veratridine, and field stimulation were decreased at least 80%. The suppression of [3H]ACh release induced by veratridine or KCl was fully reversible after 40 days postinfection, but field-stimulated responses remained approximately 50% of control values. These results indicate that T. spiralis infection in the rat is accompanied by a reversible suppression of ACh release from the longitudinal muscle-myenteric plexus of the jejunum.