Urinary Excretion of Histamine and Methylhistamine in Male and Female Rats

Abstract

The urinary excretion of histamine and of methylhistamine was measured in male and female rats and in gonadectomized male and female rats during eighteen consecutive days. The animals received daily subcutaneous injections of aminoguanidine. On the seventh day the animals were injected intramuscularly with 5.0 mg testosterone propionate.

Rat urine purified on a Dowex 50 column prior to bioassay yielded higher values for histamine than when assayed directly. The values for urinary excretion of histamine obtained by use of a chemical method based on reaction with dinitrofluorobenzene (DNFB) and by use of bioassay after previous purification of the urine on a Dowex 50 column agreed fairly well when the urine contained more than approximately 40 μg histamine base per 24 hours. It is concluded that the current method of direct bioassay of diluted urine for histamine determination may give falsely low values, particularly in urine containing small amounts of histamine.

Male rats excreted more methylhistamine than intact female or gonadectomized rats. Testosterone increased the urinary excretion of methylhistamine in gonadectomized rats whereas in male and female rats it was less effective. It seems established that the sex difference in the urinary excretion of histamine in the rat is due to a larger capacity of the male to methylate histamine, dependent on the effect of testicular hormones like testosterone. Oestrogen and testosterone may be antagonists.

Key-words:

• Aminoguanidine
• bioassay
• gonadectomy
• histamine
• methylhistamine
• rat
• sex difference
• testosterone