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How
much dihydrotestosterone is produced by each of type I and type
II 5 alpha reductase
The enzyme 5 alpha reductase converts testosterone into dihydrotestosterone
(DHT) and it is DHT that is most potent in promoting androgenetic
alopecia. The are at least two 5 alpha reductase isoenzymes, type
I and type II. They are active in different regions of the body,
but they both produce DHT that can circulate throughout the body
and exert effects in organs other than that where the DHT was produced.
Type II 5 alpha reductase is the most active enzyme form. It produces
60% to 70% of the total DHT in our bodies. Type produces the remaining
30% to 40% of DHT.
This means that 5 alpha reductase inhibitors, promoted as treatments
for androgenetic alopecia, should ideally block both types of isoenzyme
to have maximum effect. Finasteride is only a type II 5 alpha reductase
inhibitor and so can only reduce DHT levels by at most 70%. Some
experimental dual type I and type II 5 alpha reductase inhibitors
have been shown to reduce DHT levels by up to 95% after a single
oral dose.
How
much dihydrotestosterone is produced by each of type I and type
II 5 alpha reductase
- Gormley
GJ, Stoner E, Bruskewitz RC, Imperato-McGinley J, Walsh PC, McConnell
JD, Andriole GL, Geller J, Bracken BR, Tenover JS, et al. The
effect of finasteride in men with benign prostatic hyperplasia.
The Finasteride Study Group. N Engl J Med. 1992 Oct 22;327(17):1185-91.
- Peters
DH, Sorkin EM. Finasteride. A review of its potential in the treatment
of benign prostatic hyperplasia. Drugs. 1993 Jul;46(1):177-208.
- Schwartz
JI, Van Hecken A, De Schepper PJ, De Lepeleire I, Lasseter KC,
Shamblen EC, Winchell GA, Constanzer ML, Chavez CM, Wang DZ, Ebel
DL, Justice SJ, Gertz BJ. Effect of MK-386, a novel inhibitor
of type 1 5 alpha-reductase, alone and in combination with finasteride,
on serum dihydrotestosterone concentrations in men. J Clin Endocrinol
Metab. 1996 Aug;81(8):2942-7.
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