Minoxidil, a trichogenic compound that stimulates the hair follicle, is a pro-drug converted to its active form, minoxidil sulfate, by sulfotransferase enzymes in the outer root sheath of hair. Minoxidil sulfate is required for both the promotion of hair regrowth and the vasodilatory effects of minoxidil. Minoxidil sulfate is an activator of the ATP-sensitive K+ (KATP) channel. The opening of K+ channels is thought to be an important mechanism in the regulation of hair follicles.