Effect of H2 histamine receptor blockade and stimulation on urinary acidification

Acid secretion by the stomach is enhanced by H2 histamine stimulation and is depressed by its inhibition. The present investigation was undertaken to assess the possible effect of H2 histamine activity on acid excretion by the kidney, the other major acid secreting organ. The study was stimulated by an earlier observation indicating a fall in urinary acid excretion in human associated with short-term administration of an H2 histamine antagonist (cimetidine). Female Sprague-Dawley rats were randomly assigned to the cimetidine-treated, histolog-treated and placebo-treated (control) groups. Urinary titratable acidity, NH4+, HCO3- and net acid excretion rates were determined following administration of either cimetidine, histolog or placebo. Excepting the above pharmacologic manipulations all other experimental conditions were similar. Urinary titratable and net acid excretion rates were significantly reduced with cimetidine and increased with histalog as compared with the control group. The observed urinary changes are not due to the effects of these agents on gastric acid secretion since if that was the case the opposite results would have been expected. The data suggest that urinary acidification is somehow influenced by acute changes of H2 histamine activity in rats. The precise mechanism, site of action in the kidney and pathophysiologic significance of this phenomenon remains to be elucidated.