Effects of Guanethidine and Imidazole on Histamine Metabolism

Abstract

Chronic treatment with guanethidine increased histamine excretion, as shown in a previous paper (Can. J. Physiol. Pharmacol. 50, 539–544 (1972)). This increase was due to a partial inhibition of a degradation enzyme, imidazole N-methyltransferase, rather than to histamine liberation. Testosterone and noradrenaline diminished the high histaminuria caused by guanethidine. Imidazole, which was also shown to increase histamine excretion, was not affected by testosterone or noradrenaline. The mode of action of imidazole is still unknown, but its molecular configuration suggests competitive effects with histamine at many sites.