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Abstract

The mechanism of action of along-acting steroid contraceptive, norethisterone oenanthate, was studied by comparative analysis of its binding characteristics
with both eytosol and nuclear progesterone receptors. Immature female rabbits
were primed with estradiol for five days to enchance the uterine level of progesterone receptors. Using 3H-progesterone exchange method, we have measured the receptor contents in this tissue and its dissociation constants by Scatchard plot.The Kd for cytosol receptor is 4.20±1.59×10~(-9)mol/L and 1.54±0.52×10~(-9)mol/L for nuclear receptor. The RBA (relative binding affinity) of norethisterone eenanthate to progesterone receptor was evaluated by competitive combination analysis using ~(3)H-progesterone. Norethisterone oenanthate was found to be weaker in RBA than that of progesterone. The duration of nuclear retention of progesterone-receptor complex was also
investigated in E_(2) primed rabbits. The results demonstrated that the norethisterone oenanthate was shown to have a significant longer retention in nuclei (above 24 hours) than that of progesterone (above 6 hours).This correlates well with its biological activity and it is, therefore, suggested that a close relationship exists between the long-acting property and the duration of nuclear retention of the receptor complex.

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Citing This Article：

. . Acta Physiol Sin 1987; 39 (2): (in Chinese with English abstract).