VIP inhibits histamine-induced ultrastructural changes related to acid secretion by parietal cells

We have studied the in vitro effect of VIP and histamine on ultrastructure of the parietal cells in isolated guinea pig fundic glands. The morphological changes induced by histamine in the parietal cells can be compared to those observed after histamine stimulation in vivo or in vitro on gastric mucosa preparations. In contrast, VIP incubation did not produce the ultrastructural changes related to gastric acid secretion, in resting parietal cells. Pretreatment of the glands by VIP resulted in a remarkable suppression of the histamine effect, since the parietal cells assumed an almost resting state. The data (1) indicate that the parietal cells in isolated gastric glands of the guinea pig retain in vitro the capacity to undergo the ultrastructural changes that are related to acid secretion in vivo after histamine or cAMP and (2) suggest that VIP is an inhibitor of histamine-induced gastric acid secretion in the guinea pig. It is proposed that VIP could act directly on the parietal cell via cAMP-phosphodiesterase activation, or indirectly via gastric somatostatin and/or prostaglandin secretions, inhibiting the H 2 receptor-cAMP system of the parietal cell.