OESTROGEN BINDING IN THE MOUSE UTERUS

ABSTRACT Tissue slices from immature mice were incubated at 37° C in a buffer with tritium-labelled oestrogens. The target tissues, uterus and vagina are found to take up much more 17β-oestradiol than several non-target tissues (the diaphragm, heart, thymus, spleen, stomach or kidney). In addition, when tissue slices, which have been pre-loaded with 17β-oestradiol, are washed, the uterus and vagina retain the oestrogen much more strongly than the non-target tissues. Uteri preloaded in vivo with 17β-oestradiol also retain the accumulated oestrogen strongly on washing in vitro. The synthetic oestrogen meso-hexoestrol is also selectively taken up and retained by the uterus but to a lower extent than 17β-oestradiol. The isomeric racemic hexoestrol is a much less potent oestrogen and is not selectively bound by the uterus. However, the retention of racemic hexoestrol both by the uterus and the diaphragm is high. The preferential uterine uptake of the potent oestrogens is inhibited by low incubation temperature. A low incubation temperature also inhibits the wash-out of oestrogens from the uterus. There was no evidence of extensive metabolic transformations of the oestrogens investigated. It is likely that the mode of oestrogen retention in the mouse uterus and vagina is due to non-covalent binding.