Effect of sex hormones on the excretion of free histamine by male and female rats.

The excretion of free histamine by male rats was increased 10-fold by treatment with oestrogen or castration. That of female rats was reduced to 1/10 by treatment with testosterone. Ovariectomy further increased the histamine excretion by female rats, which was slightly reduced by treatment with oestrogen, and at oestrus. The low level of free histamine excretion by male rats was not increased by compound SKF 525-A, and inhibition of diamine oxidase by aminoguanidine caused the same proportionate increase in both sexes. It is concluded that the conjugation of histamine by male rats requires the presence of androgens, and some preliminary indication is given regarding the possible mechanisms involved.