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What
are the differences in mechanisms of androgenetic alopecia for men
and women
The steroidal interconversion system in our bodies is very complex.
There are a wide range of androgen subtypes interconverted by enzymes
in a cascade of events. Some androgen subtypes can be converted
other androgen subtypes and back again. The same can be said of
the estrogens. On top of this androgens can be metabolized to estrogens
by the Cytochrome P-450-aromatase enzyme. Under certain circumstances
aromatase can apparently convert estrogens back to androgens although
this is a much less frequent occurrence than conversion of androgens
to estrogens. These interconversions of hormones with different
levels of potency and influence on hair follicles are important
in defining the nature of androgenetic alopecia for men and women.
From the complex interactions of androgens and estrogens the basic
message for hair biologists is that in men testosterone is the major
precursor of dihydrotestosterone that is converted by the alpha
5 reductase type I and II enzymes. In women dehydroepiandrosterone
(DHEA) from the adrenal glands is a key precursor of dihydrotestosterone
and requires conversion by both alpha 5 reductase enzymes and hydroxysteroid
hydrogenase isomerase enzyme.
In male androgenetic alopecia hair loss is dependant on an interplay
between androgen receptors in the hair follicles, 5 alpha reductase
type I and II converting enzyme concentration and local concentrations
of dihyrotestosterone around hair follicles. In women the presumption
is that additional factors come into play such as the concentration
of Cytochrome P-450-aromatase near hair follicles that will metabolize
androgens to estrogens, and the ratio of androgens to estrogens
as estrogens will antagonize the effects of androgens.
Drs Price and Sawaya have conducted several analyses to compare
the nature of female androgenetic alopecia to male alopecia. They
have identified differing concentrations of androgen metabolizing
enzymes and androgen receptors in hair follicles from women compared
to men and they hypothesize these differences are what makes the
pattern of female hair loss different from that of male pattern
baldness. They found that Cytochrome P-450-aromatase content was
up to six times more concentrated in women's frontal hair follicles
compared to men's frontal hair follicles. They particularly note
that the aromatase enzyme is present in greater concentrations at
the back of the scalp and less so at the front in women whereas
men have only small amounts of aromatase present in any region of
their scalp. Women had around 3 times less alpha-5-reductase type
I or type II enzyme in their frontal hair follicles compared to
men. Conversely, androgen receptor content in frontal hair follicles
from men are 40% higher than for hair follicles from women. These
differences between men and women most likely account for the overt
clinical differences in patterns of hair loss.
Androgenetic alopecia in women can be promoted by hormone fluctuations.
The steroidal interconversion system can act on available hormones
particularly those involved in pregnancy or from using pregnancy
equivalent drugs such as contraceptives. Sudden hormonal changes
when starting or stopping contraceptives or at the beginning or
end of pregnancy and at the start of menopause, may promote androgenetic
alopecia onset.
What
are the differences in mechanisms of androgenetic alopecia for men
and women references
- Kaufman
KD. Androgen metabolism as it affects hair growth in androgenetic
alopecia. Dermatol Clin. 1996 Oct;14(4):697-711.
- Voigt W, Sawaya ME, Hsia SL, Amthor C:
Cutaneous production of potent androgens from dehydroepiandrosterone
in adult women. IRSC Med Sci 1982;10:529-530.
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