Vasoactive intestinal polypeptide as possible mediator of relaxation in the rat gastric fundus.
Relaxations were induced in longitudinal muscle strips of the rat gastric fundus by stimulation of non-adrenergic non-cholinergic (NANC) neurons and by administration of vasoactive intestinal polypeptide (VIP) or isoprenaline. The effect of antiserum against vasoactive intestinal polypeptide (VIP antiserum) and of control serum on these relaxations was investigated. Incubation with VIP antiserum (dilution 1/50) for 1 h almost completely prevented the relaxation by VIP. It partially prevented the relaxation evoked by electrical stimulation while the relaxation induced by isoprenaline was not influenced. Control serum decreased the VIP- and stimulation-induced relaxations much less than did VIP antiserum. In addition, the effect of the putative VIP antagonist (4Cl-D-Phe6, Leu17) VIP was studied on the relaxations induced by NANC neuron stimulation and by VIP. The VIP antagonist (3 x 10(-5) M, incubation time 10 min) had a relaxatory effect itself but had no influence on either VIP- or stimulation-induced relaxations. The results with VIP antiserum confirm the involvement of VIP in the inhibitory NANC neurotransmission of the rat gastric fundus.