Identification and characterization of luteotrophic activity in the rabbit placenta
Marcinkiewicz, Jennifer Lynn
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Permalink
https://hdl.handle.net/2142/18937
Description
Title
Identification and characterization of luteotrophic activity in the rabbit placenta
Author(s)
Marcinkiewicz, Jennifer Lynn
Issue Date
1991
Doctoral Committee Chair(s)
Bahr, Janice M.
Department of Study
Animal Sciences
Discipline
Animal Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Agriculture, Animal Culture and Nutrition
Language
eng
Abstract
The corpus luteum of the rabbit requires estrogen and the conceptus to maintain progesterone production throughout pregnancy. The factor produced by the fetal placenta which is responsible for maintaining progesterone production has not been conclusively identified. Therefore, the focus of this thesis was to identify and characterize the luteotrophic activity in the rabbit placenta.
The first objective was to determine whether gonadotropin-releasing hormone (GnRH), previously identified in the rabbit placenta, was necessary to maintain pregnancy. Immunoneutralization of GnRH bioactivity had no adverse effects on progesterone concentrations or on pregnancy, indicating that placental GnRH is probably of little importance in maintaining pregnancy in the rabbit.
The second objective was to directly identify luteotrophic activity in the rabbit placenta. To meet this goal, a bioassay system utilizing corpora lutea explants incubated with placental extracts and other treatments was developed and validated. Placental extracts, in combination with estradiol, stimulated progesterone production; whereas, neither estradiol nor placental extracts alone affected progesterone production. These results mesh well with the physiological requirement of both follicular estradiol and the fetal placenta for maintained progesterone production during pregnancy.
The third objective was to characterize the ionic charge, approximate molecular weight and heat and trypsin stability of the active placental factor. Four placental fractions obtained from carboxymethyl-cellulose ion exchange chromatography were examined for their activity in the luteotrophin bioassay system. Fraction 1, the most acidic fraction obtained, significantly stimulated progesterone production in a dose-dependent manner when combined with estradiol. The ability of fraction 1 to increase progesterone production was lost following heat and trypsin treatment, indicating that the active component is a protein. Size fractionation by dialysis indicated that the active factor is greater than 12,000-14,000 molecular weight.
In conclusion, the results of these experiments indicate that the rabbit placenta contains a luteotrophic factor with the characteristics of an acidic, heat-sensitive protein greater than 12,000-14,000 molecular weight which acts with estradiol to stimulate progesterone production by the corpora lutea.
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