Minoxidil sulphation in human liver and platelets. A study of interindividual variability

Minoxidil requires to be sulphated to exert its hypotensive effect. We report on interindividual variability in the rate of minoxidil sulphation in 118 specimens of human liver and in platelets obtained from 100 healthy subjects and 100 newborns. The frequency distribution histogram of the hepatic activity of minoxidil sulphotransferase was positively skewed; the mean was 631 pmol.min-1 x mg-1. After logarithmic transformation of the enzyme activity, the frequency distribution histogram became symmetrical and did not significantly deviate from normality. The rate of minoxidil sulphation was not different in platelets from adults (0.74 pmol.min-1 x mg-1) and newborns (1.16 pmol.min-1 x mg-1). The frequency distribution histograms were positively skewed and the results of normal equivalent deviation analysis was compatible with the presence of at least two subgroups of sulphotransferase in liver and platelets. Thus, two phenotypes of sulphotransferase exist in human liver and platelets, and the "extensive sulphator" phenotype contributes to skewing the frequency distribution. In platelets, the percentage of subjects that fall in the two subgroups is different at birth and in adulthood. This can explain the different shape of the frequency distribution in newborn and adult platelets and suggests that platelet minoxidil sulphotransferase undergoes modification after birth.