Document Detail

Differential effects of inhibin on gonadotropin stores and gonadotropin-releasing hormone binding to pituitary cells from cycling female rats.
MedLine Citation:
PMID:  9075718     Owner:  NLM     Status:  MEDLINE    
Numerous studies of rat pituitaries have reported that inhibin suppresses the synthesis and release of FSH and decreases the release of LH. The latter effect seems to be related to the down-regulation of receptors for GnRH. The studies reported here identified cellular changes behind the inhibitory effects of inhibin on gonadotropes to learn whether its effects are mediated by changes in subtypes of gonadotropes. Cell populations from diestrous day 2 and proestrous (morning) rats were collected, dispersed to single cell populations, and plated in medium containing either recombinant 32-kDa inhibin or porcine follicular fluid for 24 h. GnRH binding was detected by exposing the cells to a biotinylated analog (Bio-GnRH) for 10 min before fixation, followed by avidin-peroxidase labeling protocols to detect the biotin on the analog. In parallel fields, the cells were further identified by immunolabeling for LH or FSH beta-subunits or for GH with a different colored reaction product. The most striking changes were seen in cells from proestrous rats. Inhibin reduced the percentages of Bio-GnRH target cells in the population by 60% and the area and density of Bio-GnRH label on the remaining cells. Inhibin reduced the percentages of FSH cells by 30% and caused nearly a 60% reduction in the binding of Bio-GnRH by this cell type (from 83% of FSH cells to 32% of FSH cells). Inhibin also reduced the area of FSH cells and the density of FSH stores. Inhibin's effects on LH cells were limited to a reduction in the area of the cells and the density of LH stores, but not the number of LH cells. In addition, it reduced the percentages of LH cells with Bio-GnRH receptors from 84% to 40%. When cells with GH were analyzed, inhibin had no effect on their percentages, areas, or GH stores. In populations from proestrous rats, inhibin reduced the percentages of GH cells with Bio-GnRH binding from 38% to 21%. These data suggest that inhibin's target cell is the abundant multihormonal gonadotrope that contains LH, FSH, and GH and predominates during proestrus. Inhibin's effects are most severe on FSH cells, which suggests that it may either selectively affect FSH synthesis and stores in bihormonal gonadotropes and/or affect monohormonal FSH cells. Thus, mechanisms behind its inhibitory effects include 1) a reduction in the percentage of Bio-GnRH target cells, 2) a reduction in the area of Bio-GnRH-binding sites on individual cells, and 3) a reduction in the stores of FSH and the percentages of FSH cells. These last effects are consistent with known reductions in FSH synthesis. The effects of inhibin on LH secretion may be secondary to the effects on Bio-GnRH receptors in bihormonal gonadotropes.
G V Childs; B T Miller; W L Miller
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Endocrinology     Volume:  138     ISSN:  0013-7227     ISO Abbreviation:  Endocrinology     Publication Date:  1997 Apr 
Date Detail:
Created Date:  1997-04-17     Completed Date:  1997-04-17     Revised Date:  2014-09-17    
Medline Journal Info:
Nlm Unique ID:  0375040     Medline TA:  Endocrinology     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1577-84     Citation Subset:  AIM; IM    
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MeSH Terms
Follicle Stimulating Hormone / metabolism*
Gonadotropin-Releasing Hormone / analogs & derivatives*,  metabolism
Inhibins / pharmacology*
Luteinizing Hormone / metabolism*
Pituitary Gland, Anterior / cytology*,  drug effects,  metabolism
Rats, Sprague-Dawley
Grant Support
Reg. No./Substance:
33515-09-2/Gonadotropin-Releasing Hormone; 52671-12-2/LHRH, Lys(6)-; 57285-09-3/Inhibins; 9002-67-9/Luteinizing Hormone; 9002-68-0/Follicle Stimulating Hormone

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