BRIEF REPORT |
Correspondence to: Gwen V. Childs, Dept. of Anatomy, Univ. of Arkansas for Medical Sciences, 4301 West Markham Street, Slot 510, Little Rock, AR 72205-7199.
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Summary |
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This study focused on expression of estradiol receptors (ER) during the estrous cycle. Labeling for ER or ß antigens and luteinizing hormone (LH) or follicle-stimulating hormone (FSH) ß-subunits was done on freshly dispersed pituitary cells. The lowest expression of ER
and ß was seen in estrus (23% and 12%, respectively). Expression increased to 4254% of pituitary cells by diestrus. In males, cells with ER
or ß were 37% or 20% of the population, respectively. ER
or ß and gonadotropin antigens were in 69% of pituitary cells from male rats. Early in the cycle (estrus and metestrus), less than 5% of pituitary cells expressed ER
or ß with gonadotropins. These values doubled to reach a peak of 10% during proestrus (just before ovulation). These data show that a rise in expression of both ER
and ERß is a part of preovulatory differentiation of pituitary gonadotropes.
(J Histochem Cytochem 49:665666, 2001)
Key Words: estrous cycle, estrogen receptors, pituitary cells, differentiation
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Introduction |
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Estrogen receptors (ER) were first discovered in the 1960s ( and ERß are found in the pituitary of most species (
The stage of the cycle was determined by vaginal smears. The ACUC committee, University of Texas Medical Branch, approved the animal care and use protocol. Pituitaries were dispersed, cultured for 12 hr, fixed in 2% glutaraldehyde (30 min), and washed four times in phosphate buffer with 4% sucrose ( or ß with polyclonal rabbit anti-ER
(1:500) or goat anti-ERß (1:500) (Santa Cruz Biotechnology; Santa Cruz, CA) and streptavidin peroxidase detection kits (DAKO; Carpinteria, CA) that used either a biotinylated anti-rabbit antibody (1:100, 30 min for the anti-ER
) or anti-goat antibody (1:100, 30 min for the anti-ERß) as second antibody. Peroxidase was detected by nickel-intensified diaminobenzidine (
Estrous animals had only 12 ± 1% or 23 ± 1% cells with ERß or , respectively. A significant rise in expression to 4142% of the population was seen on the morning of metestrus. Diestrous rats showed a continued rise in ER
-bearing cells to 54 ± 2%, but no further increase in cells with ERß. Proestrous rats maintained relatively high percentages of ER
cells (48 ± 1%), whereas those with ERß declined (36 ± 2%). Populations from male rats expressed 37 ± 5% or 20 ± 2% cells with ER
or ß, respectively.
Pituitary cells with ER or ß and LH antigens increased from 4.7 ± 0.6% at estrus to 10 ± 1.6% at proestrus. Percentages of pituitary cells with ER
or ß and FSH were lower at estrus (2.7 ± 0.2% or 1.3 ± 0.1%, respectively). After remaining below 5% during diestrus, cells with FSH and ER
or ß increased to reach a peak of 9.5 ± 1% or 8 ± 0.3%, respectively, by proestrus. In male rats, percentages of pituitary cells with ER
or ß and gonadotropins were similar to peak levels in proestrus. Fig 1 illustrates dual labeling for ERß and FSH antigens in proestrous female rat pituitary cells. In most cells, the labeling is concentrated in the nucleus (see arrows in figure). However some cells exhibit either cytoplasmic or plasma membrane labeling (not shown).
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Estrogen positive feedback on pituitary gonadotropes during diestrus promotes differentiation by stimulating the production of gonadotropin-releasing hormone receptors ( and ß during proestrus may facilitate the positive feedback, and the negative feedback after the surge activity. Our counts agree with previous studies that looked at ER
only (
To summarize, although these studies have not detected a function for ERß, they have shown that this new receptor type increases early in the cycle and that peak expression parallels that seen for ER. This points to some cooperative potential for these receptors. The non-parallel expression seen in LH and FSH gonadotropes may reflect expression by monohormonal cells and/or unique functions for each of these receptors in different gonadotrope subtypes.
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Footnotes |
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Presented in part at the Joint Meeting of the Histochemical Society and the International Society for Analytical and Molecular Morphology, Santa Fe, NM, February 27, 2001.
Received for publication December 19, 2000; accepted February 16, 2001.
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