Effects of Guanethidine and Imidazole on Histamine Response

Abstract

Guanethidine was shown to increase sensitivity (as measured by blood pressure response) not only to noradrenaline but to acetylcholine and histamine (H) as well. This effect of guanethidine on H is not likely explained by lack of reflex sympathetic activity resulting from chronic treatment but possibly by a reduced uptake of H. Similarly, chronic treatment with guanethidine, by increasing H release, could have increased tolerance to H, thus explaining some of the results obtained. This is not the case since chronic treatment with H was shown to increase rather than decrease response to H in the rat. Imidazole, which was also shown to increase histaminuria (Can. J. Physiol. Pharmacol. 50, 539–544, 1972), did not potentiate H, noradrenaline, or acetylcholine response and possesses some slight antihistaminic effect. Finally noradrenaline blocks the effect of guanethidine on release of H but has no effect on the action of imidazole.