AJP - Endocrinology and Metabolism, Vol 250, Issue 4 341-E345, Copyright © 1986 by American Physiological Society
Estrogen inhibition of LH and FSH secretion: effects of a GnRH antagonist
M. C. Charlesworth and N. B. Schwartz
Follicle-stimulating hormone (FSH) levels are not suppressed as rapidly or
to the same degree as luteinizing hormone (LH) levels in ovariectomized
rats treated with either gonadotropin-releasing hormone (GnRH) antagonist
or estrogen. The acute inhibitory effects of various doses of estrogen on
FSH and LH secretion were examined in cannulated, 2-wk ovariectomized rats.
No dose of 17 beta-estradiol, up to 2,500 ng injected intravenously,
suppressed FSH, although LH secretion was inhibited 50% within 1 h by 100
ng. In another experiment, estradiol benzoate (EB; 10 or 250 micrograms; sc
injection in oil) was only marginally effective in suppressing FSH,
compared with LH, levels in serum. Treatment with EB 24 h before or after a
500 micrograms dose of a GnRH antagonist did not reduce LH or FSH to levels
lower than those achieved with antagonist alone. These results indicate
that the GnRH-dependent component of FSH release and the GnRH-independent
component that is unmasked in the presence of GnRH antagonist are sensitive
to negative feedback by estrogen, indicating that this steroid is not the
primary inhibitory ovarian factor regulating FSH in the rat.
