Estrogen dependent induction of low affinity binding sites in the nuclear fraction of rat uterus

In vitro effects of cytosolic inhibitor and opiates on the binding of [3H]oestradiol to nuclear type II binding sites of rat uterus and hypothalamus

The effect of cytosolic ultrafiltrates prepared from intact rat uteri, brain hemispheres and hypothalami and of some opiate analogues on oestradiol binding to nuclear type II sites in rat uterus and hypothalamus was studied. Opiate binding in nuclear fraction of rat uteri was also evaluated. Both uterine and hypothalamic low affinity nuclear oestradiol binding was inhibited by filtrate from uteri, while only hypothalamic nuclear binding was decreased in presence of hypothalamic filtrate. Filtrate from brain was ineffective on nuclear oestradiol binding of the studied tissues. Concentration dependent inhibition of uterine nuclear oestradiol binding could be demonstrated by some opiate analogues in vitro. Specific low affinity nuclear binding of opiate antagonist naloxone and agonist dihydromorphine was observed in rat uteri which could be inhibited by uterine filtrate and oestradiol but not by hypothalamic filtrate or other steroids. Present findings support the probable intracellular interplay of opiates and oestradiol action and suggest that cytosolic inhibitor factor might be involved.

Doisynolic-type acids--uterotropically potent estrogens which compete poorly with estradiol for cytosolic estradiol receptors

Doisynolic acids, a class of seco-steroid acids some of which exhibit greater uterotropic estrogenicity than estradiol-17 beta, are D-ring cleavage products of steroidal estrogens formed by fusion with KOH above 200 degrees C. We have found that electron-transfer reactions between estrone or estradiol and CCl4 or CBrCl3 in KOH-t-BuOH at 25 degrees C rapidly provide 16,16-dichloro- or -dibromodoisynolic acid, respectively, the former approaching estradiol in uterotropic potency. Simple esters from these highly hindered tertiary carboxylic acids, easily prepared via phase-transfer-catalyzed alkylations, also rival estradiol in uterotropic activity. Unlike natural steroidal estrogens or their commonly used artificial equivalents (DES, hexoestrol, ethynylestradiol, etc.) whose uterotropic activity is accompanied by substantial binding affinity for cytosolic estradiol receptors, these highly uterotropic doisynolic-type acids and esters exhibit binding affinities for this receptor of only about 1% that of estradiol-17 beta as determined by the usual competitive binding-inhibition studies with [3H]estradiol. Other highly uterotropic carboxylic acids may exhibit similar characteristics. These unusual results leave open the possibilities that uterotropic seco-steroid and related carboxylic acids undergo some unknown metabolic activation, are exceptionally persistent estrogens, bind to a cytosolic receptor site other than the conventional (type I) estradiol site, or bind directly to type I or type II nuclear receptor sites. At dosages of 1000 times those required for a uterotropic effect, the doisynolic-type acids (24 doses over an 8-week period) were neither toxic nor carcinogenic.