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GONADOTROPHINS: DIAGNOSTIC AND THERAPEUTIC TOOLS
Arver, S.
Director, Andrology Center, Karolinska University Hospital, Stockholm,
Sweden
The overall regulation of testicular function is governed by coordinated
control of gonadotropin secretion from the hypothalamus.
Though the two hormones LH and FSH address different
functions in the testis, they are both synthesised
and secreted from the same pituitary cells, the gonadotrophs,
and through GnRH secretion from the hypothalamus.
The differential control of these hormones depends
on differences in sensitivity to feed-back regulatory
signals. Current methods enable analysis of some of
the feed-back signals i.e. testosterone, oestrogen
and inhibin. Due to local metabolism and local secretion
of feed-back signals in the pituitary and the hypothalamus,
serum levels may not always appropriately represent
the actual situation in the vicinity of the gonadotrophs
or the GnRH nerves. Inhibin and FSH levels reflect
Sertoli Cell function, and are correlated to spermatogenesis,
though important exceptions exist. Aging is associated
with changes in gonadotropin secretion in males but
the sensitivity to GnRH stimuli seems more preserved,
disclosing a sensitivity related to functionality
of the GnRH neurons per se. The pattern of GnRH secretion
changes with fewer high amplitude peaks but consistent
secretory frequency. Assessment of blood levels of
LH and FSH in the elderly is affected by changes in
clearance rate, and seems to increase despite the
hampered secretory capacity of GnRH. Gonadotropin
therapy has been used extensively to restore fertility
in men with secondary hypogonadism, and different
regimens have been used. In this situation pulsatile
treatment with GnRH is also an option. The requirement
of FSH to stimulate spermatogenesis in men who have
an adult onset of gonadotropin deficiency has been
a matter of controversy. It seems however evident
that FSH improves spermatogenesis more than can be
achieved with hCG (LH) therapy alone. Different approaches
can be discussed in the clinical management of these
patients. LH or hCG therapy can also be used as a
tool for androgen replacement therapy in hypogonadal
men.
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