In this study the levels of mRNA for the pituitary gonadotropin hormone subunits luteinizing hormone β (LHβ), follicle stimulating hormone β (FSHβ) and the common α‐subunit were assessed during the acute feedback stages of estradiol benzoate (EB) action in ovariectomized (OVX) ewes with and without hypothalamo‐pituitary disconnection (HPD). In OVX/HPD ewes maintained on hourly pulses of 250 μg of gonadotropin‐releasing hormone (GnRH) a single i.m. injection of EB in oil caused a biphasic (decrease and then increase) change in plasma LH levels and a monophasic decrease in FSH levels. There was a decrease in pituitary α‐subunit and FSHβ mRNA levels during the acute negative (8 h post EB) and through the positive feedback (20 h post EB) stages of the response. No significant change was seen in LHβ mRNA levels following treatment with EB. In hypothalamic‐pituitary intact OVX ewes the same EB treatment as above caused a biphasic change in LH secretion with the positive feedback component being much greater than in GnRH‐pulsed OVX‐HPD ewes. The levels of mRNA for all three gonadotropin subunits were reduced by 8 h after EB injection and remained low throughout the positive feedback period. These data suggest that the LH surge in this experimental model does not require an increase in LHB mRNA levels. Furthermore, the fall in LHβ subunit mRNA seen after estrogen injection to OVX ewes is most likely due to an effect of estrogen to decrease GnRH secretion, since pulsatile GnRH replacement prevents this effect. These data also show that estrogen feedback can effect rapid alterations in pituitary gonadotropin subunit mRNA levels. Short‐term changes in FSHβ mRNA are reflected in changes in FSH secretion; the same is not true for LH.
|Number of pages||6|
|Journal||Journal of Neuroendocrinology|
|Publication status||Published - 1 Jan 1993|
- follicle stimulating hormone
- luteinizing hormone