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Title: GnRH binding sites in the human placenta
Author: McPhie, Christine A.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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Binding sites for GnRH in the human placenta differ from the well-characterised pituitary GnRH receptor. The pituitary superagonists Buserelin and Tryptorelin were found by the placenta, as were the salmon and chicken-II isoforms of GnRH, however placental binding of the GnRH agonist analogues was not enhanced compared to the two isoforms, which were not bound by the pituitary receptor. Specific activity of binding of GnRH, GnRH isoforms and GnRH agonist analogues to the human placental binding site varied with stage of gestation. The high levels observed in early trophoblast (6-8 weeks) fell to almost non-detectable levels at 12-18 weeks, before increasing to maximal levels by term. Rebinding data suggested that differential tracer degradation could not account for gestational age-related variations in binding, and decreased binding was not related to contamination of the membrane fraction by non-villous tissue. Although the specific activity of binding to placental binding sites varied with gestation, specificity was unchanged: Tryptorelin, Buserelin, chicken GnRH-II, salmon GnRH > mammalian GnRH π lamprey GnRH, chicken GnRH-I. Buserelin, Tryptorelin and chicken GnRH-II were displaced from the membrane binding site by cytosolic extracts of placenta of all stages of gestation. Cytosol fractions from 12-18 weeks displaced iodinated GnRH tracers from the binding sites of membrane preparations from the same stage of gestation to a greater extent than an excess of non-iodinated Buserelin, but did not displace tracer from term membrane binding sites to the same degree. Membrane binding and the displacement effect of cytosol were reduced in the presence of protease inhibitors, however this was due to the presence of ethanol (as a solvent) in the inhibitor cocktail. The exact nature of this ethanol effect is unknown.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available