The difference in the metabolism of injected [14C]histamine in male and female rats.

[(14)C]Histamine was injected subcutaneously in rats. The urine was collected for 24 hr. and analysed for [(14)C]histamine and its various metabolites. It was found that male rats excreted less unchanged [(14)C]histamine than female ones, the difference between the sexes existing also when the animals were treated with aminoguanidine. The cause of the sexual difference appeared to be that the male rats had a larger capacity to methylate histamine.