In vitro studies on cholecystokinin-induced inhibition of acid formation in gastric glands

Abstract: The design of methods useful for the preparation of viable glands and cells from the gastric mucosa allowed detailed studies on the mechanisms that regulate gastric acid secretion. The preparation of rabbit gastric glands was the first suitable method to be used and a number of important scientific contributions have been accomplished with this method. Using this method we studied the effect of CCK-like peptides on [14C]aminopyrine accumulation stimulated by histamine, in order to fmd out whether such peptides can inhibit the production of acid in the parietal cell. We also developed a method for the study of viable rat gastric glands that allowed comparative studies in the rat species.In rabbit gastric glands CCK-like pep tides inhibited histamine stimulated acid formation whereas gastrin peptides were ineffective. The most potent and efficacious peptides were CCK 8 and the cholecystokinetic amphibian decapeptide cemlein reducing the maximal histamine stimulation of aminopyrine accumulation by 35-38%. The concentration of peptide necessary for eliciting inhibition was in the range of that reported to stimulate amylase secretion in similar in vitro experiments on isolated pancreatic acini, representing a well established physiological function of CCK. Analyses of somatostatin content in the incubation medium revealed that biologically active concentrations of endogenous somatostatin were released into the incubation medium. The rate of somatostatin release increased after CCK 8 or cemlein was added, whereas with G 17, the concentration of somatostatin remained unchanged. In further experiments performed with rabbit mucosal cells prepared from the gastric glands, it was demonstrated that the inhibitory property of CCK 8 only was apparent if a sufficient amount of endocrine cells were present during incubation. In highly purified fractions of parietal cells, however, a small stimulatory effect appeared, a finding that is consistent with similar capacity of gastrin and CCK stimulating the CCK2 receptors present on the parietal cell.A method useful for the study of rat gastric glands was developed. The viability of the rat gastric glands appeared excellent as judged by morphological characterisation and functional assessment by means of [14C]aminopyrine accumulation. Upon stimulation with a high dose of histamine the production of acid increased 5-fold over basal. Pentagastrin and CCK 8 were ineffective stimulators per se, but in combination with histamine a marked potentiation occurred. Somatostatin effectively inhibited histamine-stimulated acid formation both in rabbit and rat gastric glands.In conclusion, CCK-like peptides inhibit histamine stimulated acid formation in gastric glands prepared from rabbit. The inhibition is mediated in a paracrine-like mode via the release of endogenous somatostatin. A method useful for the study of viable rat gastric glands was developed. In contrast to rabbit gastric glands, CCK 8 potentiated histamine stimulation in rat glands.