RELEASE OF VASOACTIVE INTESTINAL POLYPEPTIDE FROM THE RAT GASTRIC FUNDUS

1 Auxotonic responses and release of vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) induced by electrical field stimulation (EFS) were studied in longitudinal muscle strips from the gastric fundus of reserpinized rats suspended between parallel platinum electrodes in Krebs solution containing atropine (1-mu-M), 5-hydroxytryptamine (3-mu-M) and bovine serum albumin (50 mgl-1). 2 EFS (supramaximal voltage, 1 ms, 0.25-32.0 Hz, trains of 2 min) induced frequency-dependent relaxations. 3 EFS at frequencies greater-than-or-equal-to 8 Hz also produced significant increases in VIP-LI release. 4 VIP-LI release induced by EFS at 16 Hz no longer occurred in the presence of tetrodotoxin (1-mu-M) or a Ca2+ -free medium. 5 Detection of VIP-LI upon activation of inhibitory non-adrenergic, non-cholinergic neurones indicates that VIP meets the 'detectable release' criterion for an inhibitory neurotransmitter in the rat gastric fundus.