INTERINDIVIDUAL VARIABILITY OF HISTAMINE N-METHYLTRANSFERASE IN THE HUMAN LIVER AND KIDNEY

1. The aim was to investigate the possibility of interindividual varia bility of histamine N-methyltransferase (HNMT) in the human liver and renal cortex. The activity of HNMT was measured in 99 specimens of the human liver and in 75 specimens of the renal cortex. 2. In the liver the activity of HNMT was positively skewed. It ranged 2.9-fold with a median of 1.72 pmol/min/mg. In the renal cortex the activity of HNMT w as normally distributed and ranged 2.6-fold with a mean and coefficien t of variation of 1.35 pmol/min/mg and 21%, respectively. 3. The activ ities of catechol methyltransferase and thiopurine methyltransferase w ere measured in the renal cortex and any correlations with HNMT activi ty were assessed. There was a weak but significant correlation (r = 0. 294, p = 0.010) between HNMT and catechol methyltransferase activities whereas HNMT activity was not correlated with thiopurine methyltransf erase activity. 4. These results are consistent with the view that HNM T is well expressed in the human liver and renal cortex and that it va ries among subjects.