Bioactive 5-reduced 16 alpha,17 alpha-cyclohexanoprogesterone derivatives weakly interact with proteins of the soluble uterine fraction.

We studied competitive activities of 16 alpha,17 alpha-cyclohexano-5 alpha- and 5 beta-dihydroprogesterone in replacing(3)H-progesterone and(3)H-16 alpha,17 alpha-cyclohexano-6 alpha-methylprogesterone from protein complexes. Direct binding of(3)H-5-reduced derivatives with proteins of soluble fractions from rat and rabbit uteri was also assayed. C(d) values for 5-reduced derivatives were in the micro- or submicromolar range. The data suggest that biological effects of these analogues are not mediated via soluble uterine receptors.