Effect of the exogenous glutamate and the NMDA on electric field-stimulated contractions of isolated rat ileum

While neurotransmitter role of glutamate in gastrointestinal intrinsic nervous system was shown, its effects in various segments of gastrointestinal tract were not yet understood completely. In our study, we have investigated effects of exogenous glutamate on electric field-stimulated contractions of isolated rat ileum. The ilea from forty Wistar rats of both sexes were isolated in an organ bath, according to the Magnus mounting method, and exposed to field stimulation with square wave pulses (20 V over the electrodes, 400 mA, 1 ms duration, frequency 16 Hz, pulse trains for 30 s with 30 s pause). The stimulation produced tonic contractions and relaxations recorded with an isometric system. Atropine (2.3×10 −6 M/l) completely abolished contractions of isolated rat ileum produced by the field stimulation, while relaxations remained unaffected. Glutamate (from 7.8×10 −6 to 3.5×10 −3 M/l) and N-Methyl- d-aspartic acid (NMDA) (from 9.1×10 −9 to 1.3×10 −5 M/l) caused concentration-dependent inhibition of the field-stimulated contractions of isolated rat ileum (EC 50 was 90.17±1.81×10 −5 and 53.51±3.68×10 −9 M/l, respectively) while not affecting the field-stimulated relaxations. On the other hand, (RS)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) (from 6.0×10 −9 to 9.3×10 −6 M/l), kainic acid (from 5.8×10 −9 to 8.3×10 −6 M/l) and (±)-1-aminocyclopentane- trans-1,3-dicarboxylic acid ((±)-trans-ACPD) (from 7.0×10 −9 to 1.1×10 −5 M/l) did not influence both the field-stimulated contractions and the field-stimulated relaxations of isolated rat ileum. The results of our study suggest inhibitory effect of glutamate on acetylcholine release from intrinsic neurons of rat ileum, mediated through NMDA receptors.