Premium
Differential Effects of Estrogen and Progesterone on Levels of POMC mRNA Levels in the Arcuate Nucleus: Relationship to the Timing of LH Surge Release
Author(s) -
Petersen S. L.,
Keller M. L.,
Carder S. A.,
McCrone S.
Publication year - 1993
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.1993.tb00534.x
Subject(s) - medicine , endocrinology , proopiomelanocortin , estrogen , ovariectomized rat , estrous cycle , in situ hybridization , messenger rna , arcuate nucleus , biology , hypothalamus , surge , luteinizing hormone , hormone , chemistry , gene , biochemistry , physics , meteorology
Beta‐endorphin is thought be an important inhibitor of LHRH neuronal activity and also to play a role in conveying information about changes in steroid levels to LHRH neurons. We have previously shown that the mRNA encoding the precursor of ß‐endorphin, proopiomelanocortin (POMC), fluctuates during the estrous cycle with the most dramatic changes occurring on proestrus. POMC mRNA levels decline before the onset of LH surge release but then dramatically rise and remain elevated during the surge. In the present studies we tested the hypothesis that the decline in POMC mRNA levels immediately before the proestrous LH surge is mediated by estrogen and the rise during the surge by progesterone. To test this hypothesis, we compared changes in POMC mRNA levels between ovariectomized (OVX) and OVX estrogen (E 2 )‐treated rats and between OVX E 2 ‐treated rats with and without progesterone. Animals were examined at hourly intervals after the administration of progesterone, then at every 4h during the LH surge. Using in situ hybridization histochemistry, we found that E 2 decreased POMC mRNA levels in OVX rats before the onset of the LH surge and further suppressed levels during the surge. Compared to animals treated with E 2 alone, progesterone advanced the time at which both the LH surge began and the time at which POMC mRNA levels declined. After a transient decline, POMC mRNA levels rose in these progesterone‐treated animals and remained elevated throughout the period of the LH surge. These results support the hypothesis that progesterone times the LH surge and limits its appearance to one day by exerting a biphasic effect on the activity of ß‐endorphinergic neurons of the arcuate nucleus.