domingo, 19 de febrero de 2012

andrógenos en mujeres inglés

Androgen metabolism in women
Androgens are secreted by the ovaries and adrenal
glands in response to their respective tropic hormones.
The principal circulating androgens are
dehydroepiandrosterone, dehydroepiandrosterone
sulfate (DHEAS), androstenedione, testosterone
and 5a-dihydrotestosterone. Like other steroid
hormones, these C19-steroids are derived from cholesterol
[3].Only testosterone and dihydrotestosterone
are ‘‘true’’ androgens with the ability to
interact with the androgen receptor. The total levels
of testosterone are about 1–3 nmol/L in women
and consequently only about 1/10 of the levels in
men [4].
The relative contribution of the ovary and adrenal
glands to circulation testosterone in the normal
premenopausal female is about 25% each. The rest
is produced by the peripheral conversion of androstenedione
in adipose tissue. After menopause, the
primary steroid products of the climacteric ovary
are androstenedione and testosterone [5], and almost
all estradiol is derived from the peripheral
aromatization of androstenedione. Thus, there is
a drastic change in the androgen-to-estrogen ratio
because of the sharp decrease in estradiol levels
and unchanged levels of testosterone [6,7]. The
frequent onset of a mild hirsutism after menopause
reflects this striking shift in the hormone ratio.
Effects of androgens in women
Cognition, mood, and behavior
Sex differences in human cognition have intrigued
investigators for many years. In humans, testosterone
or actually its aromatized metabolite estradiol,
binding to estrogen receptors, accounts for nearly
all known sex differences in neural structure and
behavior [8]. At early stages of development, the female
brain normally escapes this testosterone-triggered
masculinization of the nervous system.
Studies have suggested that differences in brain
structure established during development by the
presence or absence of androgens may account for
performance differences between the sexes
[9,10]. Evidence from studies of adults, indicate
that androgen levels correlate negatively with performance
on verbal tasks, but positivelywith performance
on spatial tasks [11]. Moreover, testosterone
supplement selectively improves spatial performance
in female-to-male transsexuals [12,13].
Self-reported measures of aggression, irritability
and hostility exhibit several significant positive correlations
with testosterone in both men and women
[14–18], and although androgens are not related to
depression in a simple linear fashion, women who
have free testosterone levels just beyond the range
of normal are generally more depressed than women
within the normal range [19].
Roughly 1 in 2000 girls is exposed to slightly elevated
levels of androgens prenatally. Congenital
adrenal hyperplasia causes the fetal adrenal glands
to produce androgens such as testosterone that
could potentially masculinize the fetal brain. These
girls are more likely than other girls to engage in
male-typical play [20]. As adult women these girls
are more likely to report a homosexual orientation
than are other women [21].
Body composition
In addition to increased aggression and irritability,
elevated androgens in women have a profound effect
on body composition. Testosterone is known
to change the proportion of lean body mass and fat
mass to the advantage of the former [22]. This is
abundantly clear in athletics using anabolic steroids
[23]. Beside from increased muscle mass, the composition
of muscle tissue is altered. Female rats given
testosterone change their muscle fiber
composition from type II oxidative fibers to the more
‘‘athletic’’, type II glycolytic fibers [24], indicating
an effect of androgens on muscle myosin synthesis.
Circulating testosterone levels seem to correlate
with total fat mass in women [25], although
the causality remains uncertain. However, a statistical
association between androgens and truncal
obesity is found in women with polycystic ovary
syndrome (PCOS) [26] as well as in pre- and postmenopausal
women [27]. Moreover, female-tomale
transsexuals who are given androgens tend
to store lipids inside the abdominal cavity rather
than subcutaneously on the thighs and hips [28].
This testosterone-triggered masculinization is most
likely mediated by the androgen receptor, which
occur in a high density in visceral fat.
Genetically male (XY) individuals with a dysfunctional
androgen receptor gene develop testes that
secrete testosterone, but the body exterior, without
a functional androgen receptor, develops a
feminine phenotype. People with complete androgen
insensitivity are usually undetected at birth because
they appear to be girls, and as adults
mistaken as women [29].
Carbohydrate and lipid metabolism
In female rats, administration of testosterone induces
insulin resistance [24]. The elevated testos-
2 Rosmond

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