norethindrone ( 17beta-hydroxy-19-nor-17alpha-pregn-4-en-20-yn-3-one ) and norethindrone acetate ( 17beta-acetoxy-19-nor-17alpha-pregn-4-en-20-yn-3-one ) interfered to a varying degree , by competitive inhibition , with the binding of progesterone and oestradiol to respective cytoplasmic receptors in the human uterus .
C0028356
norethindrone
C0068980
norethindrone acetate