Relative roles of inhibin B and sex steroids in the negative feedback regulation of follicle-stimulating hormone in men across the full spectrum of seminiferous epithelium function.
OBJECTIVE
Our aim was to explore the relative roles of gonadal sex steroids and inhibin B in the regulation of FSH across a spectrum of seminiferous epithelium function.


METHODS
The study included three groups: group I, healthy men (n = 31); group II, men with idiopathic hypogonadotropic hypogonadism receiving pulsatile GnRH (n = 12) selected to represent a spectrum of seminiferous tubular development, testicular size, and baseline inhibin B levels; and group III, men with functional anorchia (n = 3) receiving testosterone replacement.


METHODS
Subjects were studied before and after 3 d of acute sex steroid withdrawal.


METHODS
The study was conducted at the Mallinckrodt General Clinical Research Center of Massachusetts General Hospital.


METHODS
Acute biochemical castration was achieved using high-dose ketoconazole (groups I and II) or withdrawal of androgen therapy (group III).


METHODS
The relationship between FSH and inhibin B in both normal and castrate sex steroid milieu was measured.


RESULTS
In both normal and castrate sex steroid milieus, there was a negative relationship between inhibin B and FSH, best described by a logarithmic model. Acute biochemical castration resulted in the most dramatic increases in FSH in men with the lowest baseline inhibin B levels.


CONCLUSIONS
We came to the following conclusions: 1) in the human male, inhibin B is the principal gonadal feedback regulator of FSH secretion unless seminiferous tubular function is severely compromised, and a logarithmic model best describes this relationship; and 2) sex steroid inhibition of FSH secretion is most apparent when serum inhibin B levels fall well below the normal range.
Boepple
Paul A
PA
Reproductive Endocrine Unit, Department of Medicine, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA.
Hayes
Frances J
FJ
Dwyer
Andrew A
AA
Raivio
Taneli
T
Lee
Hang
H
Crowley
William F
WF
Pitteloud
Nelly
N
D000328:Adult; D025461:Feedback, Physiological; D005640:Follicle Stimulating Hormone / Q000097:blood*; D012739:Gonadal Steroid Hormones / Q000502:physiology*; D006801:Humans; D007265:Inhibins / Q000097:blood / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D012670:Seminiferous Epithelium / Q000502:physiology*
D012739:Gonadal Steroid Hormones; C422364:inhibin B; D007265:Inhibins; D005640:Follicle Stimulating Hormone