Influence of nitric oxide donors and of the α2-agonist UK-14,304 on acetylcholine release in the pig gastric fundus

This study in circular muscle strips of the pig gastric fundus aimed to measure the release of acetylcholine directly and to investigate whether NO and α2-adrenoceptor agonists can modulate acetylcholine release from cholinergic neurones. After incubation of the tissues with [3H]–choline, basal and electrically induced release of tritium and [3H]–acetylcholine were analyzed in a medium containing physostigmine (10−5 M) as well as atropine (10−6 M). The NO synthase inhibitor l-NG-nitroarginine methyl ester (3×10−4 M), and the NO donors sodium nitroprusside (10−5 M) and 3-morpholino-sydnonimine (10−5 M) did not influence the basal release nor the electrically evoked release, indicating that NO does not modify [3H]–acetylcholine release. The α2-adrenoceptor agonist UK-14,304 (10−5 M) significantly inhibited the electrically evoked release of [3H]–acetylcholine, and this effect was prevented by the α2-adrenoceptor antagonist rauwolscine (2×10−6 M), suggesting that presynaptic α2-adrenoceptors are present on cholinergic neurones of the pig gastric fundus.