But I reserve the right to change my mind about this. . These are blood vessel dialating hair regrowth stimulators. OTOH, most dialating agents don't stimulate hair regrowth. So, vessel dilatation is not directly related to hair regrowth. For a paper summarizing the evidence that minoxidil is an artificial form of nitric oxide, go here .
Nitric oxide is a very important messenger molecule.
NO is a ubiquitous transmitter which has identical effects to minoxidil on blood vessels. Similarly, as you might expect if nitric oxide is an important stimulator of hair regrowth, inhibitors of NO production reduce hair growth. Also, a peptone-derived copper binding peptide was recently patented by Loren Pickart, who did the work with prazotide. A form of Prazotide copper, Graftcyte, recently received FDA approval for preventing hair loss in hair transplant surgery. In the late 70's, we found that SODase prevents stress-induced hair loss in experimental animals.