Type 1 is more prevalent in scalp/skin (thanks to the rich amounts of type 1 5a-reductase in sebaceous glands), but it's still the type 2 enzyme which is most responsible for hairloss. The evidence for that is that specific type 2 inhibitors (finasteride) obviously work against hairloss, but specific type 1 inhibitors (MK386 is an example) don't. Furthermore, the pseudohermaphrodites have normal levels of type 1, but lack the type 2 enzyme.
Here's a study which tested MK386 in stumptailed macaques: "Effects of 1 Year Treatment With Oral MK386, an Inhibitor of Type 1 5alpha-Reductase, in the Stumptail Macaque (Macaca Arctoides)". Linda Rhodes, et al. The abstract for this study was published in The Journal of Investigative Dermatology, 1995; 104:658. Hair and blood samples were collected from these animals for a total of 19 months; 7 months baseline, and 12 months on treatment. MK386, a specific 5AR type 1 inhibitor, caused a 30% to 50% decrease in serum DHT, but hair weights were similar in both treatment and placebo groups after a full year of treatment. This contrasts with a previous study using macaques and finasteride which showed hair weight increases after only six months of treatment.
And here's something John Ertel posted several years ago about HUMAN testing with MK386:
MK-386 under study for hair loss confirmed
By John Ertel
August 19, 1997
In an article shortly to be posted to alt.baldspot, it is confirmed that
Merck's research drug, MK-386, is currently being tested for hair loss. In
fact, the article is not new, but from 1995, so MK-386 has been in testing
for hair loss for over 2 years.
According to the article's conclusion, "MK-386... has been identified as a
potent type 1 selective inhibitor demonstrating time dependent kinetics.
Good bioavailability and a lack of significant safety liabilities have enabled
human clinical studies for acne and androgenic alopecia, which are
in progress" (Italics and bolding added).
Regrowth! has obtained information which will be posted shortly
regarding MK-386. It is not clear whether MK-386 has been continued in
hair loss trials. One statement obtained by Regrowth! from a 1995
convention for the Society of Investigative Dermatology states that at the
end of a one year trial, patients of MK-386 had no increase in hair weight.
This may support the theory that inhibition or removal of type 1 5-alpha
reductase alone is not enough to halt hair loss or regrow hair. Individuals
who have type 1 5-alpha reductase (the enzyme located in the skin and
hair follicles) but not type 2 5-alpha reductase (located primarily in the
prostate and liver) never go bald. When administered DHT, these
individuals do go bald. This indicates that for hair loss, either type 2
5-alpha reductase specifically plays a role in hair loss, or the total amount
of circulating DHT plays the initiating role in hair loss. Since type 2
creates about 2/3-3/4 of the circulating DHT in the body and type 1
creates only about 1/4-1/3, this may explain why Proscar, which inhibits
primarily type 2 5-alpha reductase is fairly effective at preventing hair loss
and regrowing hair and why MK-386, which inhibits type-1 alone, may not
be. MK-386 may still be an effective treatment for acne and skin sebum
production, which is more closely related to the DHT produced in the skin
itself.
Regrowth! is attempted to contact Merck through a physician to discover
the status of MK-386 in regards to hair loss. Perhaps the rumors that
they are in talks to purchase RU58841 from Roussel Uclaf are true and
caused by the fact that type-1 specific inhibitors which they have
developed are not panning out as hair loss treatments and RU58841 is
needed as their 'next generation' of hair loss treatments.
