SELECTIVE LABELING OF HISTAMINE IN RAT GASTRIC MUCOSA: APPLICATION TO MEASUREMENT OF TURNOVER RATE

¹ Laboratory of Chemical Pharmacology, National Heart Institute, National Institutes of Health, Bethesda, Maryland

Within 1 hr after the injection of small amounts of H³-histamine into rats, the labeled amine taken up by the stomach disappeared by an exponential decay with a half-life of about 1 hr. The histamine in gastric juice had the same specific activity as that in the stomach. Thus, the H³-histamine behaved as though it were evenly distributed in the endogenous pool of histamine in the stomach. The turnover rate of the endogenous amine was calculated from the product of the histamine level and the rate constant for the decline of histamine specific activity in stomach. The magnitude of this value, 15 to 20 µg/hr/g of rat stomach, indicated that histamine in the mucosa turned over at a rapid rate. A decrease in gastric secretion caused by atropine or exclusion of saliva from stomach was accompanied by a decrease in the turnover rate of histamine. On the other hand, an increase in gastric secretion produced by cholinergic stimulation was accompanied by an increase in the turnover rate of histamine. However, the changes in the turnoverrate were not accompanied by changes in histamine levels, indicating that the rate of histamine synthesis was increased or decreased parallel to changes in the rate of histamine loss. These results suggest that the turnover of gastric histamine is related to the secretory activity of the gastric mucosa and that a regulatory mechanism exists for rapid adjustment of histamine synthesis to maintain constant levels of histamine.