HISTAMINE DEPENDENCE OF PENTAGASTRIN-STIMULATED GASTRIC-ACID SECRETION IN RATS

Does gastrin stimulate gastric acid secretion by direct action on oxyn tic cells, by releasing histamine, or by being potentiated by histamin e? Previous studies in the mouse pointed to gastrin-regulated histamin e release. Guinea pig and rat are well known to vary in their sensitiv ity to histamine. Therefore, the effects of histamine and pentagastrin were compared quantitatively on isolated, lumen-perfused, stomach pre parations from these species in the absence and presence of histamine H-2-receptor blockade. The loss of potency of histamine in the rat was mirrored by a loss of potency of pentagastrin consistent with the ide a that pentagastrin acts by releasing histamine. In the rat, a well-de fined pentagastrin curve was obtained in the presence of histamine H-2 -receptor block as though pentagastrin acts both directly on the oxynt ic cell and indirectly by releasing histamine. It was not necessary to invoke a potentiating interaction between histamine and pentagastrin at the oxyntic cell; the two effects appeared simply to add. Potentiat ion was observed, however, between other combinations of stimuli, for example, between vagal nerve and pentagastrin stimulation. The physiol ogical consequences of these results are discussed.