Comparison of results from in situ and in vitro perfusions of rabbit uterus with labeled estrone and estradiol.

The interconversion of labeled estrone (E1) and estradiol (E2) in rabbit uterus was studied in vivo and in vitro, in order to evaluate the influence of incubation conditions upon the preferred direction of the reversible conversion of E2 to E1. In a typical experiment, one uterine horn was perfused intraluminally in situ with a mixture of [3H]E2 and [14C]E1, while the other horn was dissected and used for in vitro perfusions with the same tracers, both intraluminally and on tissue slices. The ratios of rate constants corresponding to the oxidative and reductive reactions were found to be similar under the three perfusion conditions, as calculated from the isotopic data. The rate constant of conversion of E1 to E2 was 10-20 times larger than the rate constant of the opposite reaction. Equal E2 nuclear saturation levels were obtained by perfusion of the uterine tissue with excess [3H]E2 in situ and in vitro after slicing.