Selectivity in progesterone and androgen receptor binding of progestagens used in oral contraceptives.

The relative binding affinities (RBAs) of four progestational compounds (norethisterone, levonorgestrel, 3-keto-desogestrel and gestodene) for the human progesterone and androgen receptors were measured in MCF-7 cytosol and intact MCF-7 cells. For the binding to the progesterone receptor, both Org 2058 and Org 3236 (or 3-keto-desogestrel) were used as labelled ligands. The following ranking (low to high) for the RBA of the nuclear (intact cells) progesterone receptor irrespective of the ligand used is found: norethisterone much less than levonorgestrel less than 3-keto-destogestrel less than gestodene. The difference between the various progestagens is significant with the exception of that between 3-keto-desogestrel and gestodene, when Org 2058 is used as ligand. For the cytosolic progesterone receptor, the same order is found with the exception that similar RBAs are found for gestodene and 3-keto-desogestrel. The four progestagens clearly differ with respect to binding to the androgen receptor using dihydrotestosterone as labelled ligand in intact cells; the ranking (low to high) is: norethisterone less than 3 keto-desogestrel less than levonorgestrel and gestodene. The difference between 3-keto-desogestrel and levonorgestrel or gestodene is significant. The selectivity indices (ratio of the mean RBA for the progesterone receptor to that of androgen receptor) in intact cells are significantly higher for 3-keto-desogestrel and gestodene than for levonorgestrel and norethisterone. From these results we conclude that the introduction of the 18-methyl in norethisterone (levonorgestel) increases both the binding to the progesterone and androgen receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the receptor binding properties of nandrolone and testosterone under in vitro and in vivo conditions.

Previous in vitro binding studies with androgen receptors in rat seminal vesicles (Toth M. and Zakar T., J. steroid Biochem. 17 (1982) 653-660) have shown that the difference in the effects of nandrolone (N) and testosterone (T) is caused by the fact that 5 alpha-reduction increases the affinity of T and decreases the affinity of N. We confirmed this result using androgen receptors in rat prostate and intact human MCF-7 cells. We also analysed the receptor binding properties of N, T, dihydronandrolone (DHN) and dihydrotestosterone (DHT) in vivo following a combined 2-h infusion of a physiological dose of [3H]T and the same dose of [3H]N in castrated male rats, which permitted a direct comparison of the accumulation of [3H]N, [3H]T, [3H]DHN and [3H]DHT in different sub-cellular fractions of various tissues. There was a considerable accumulation of radioactivity in the liver, but no retention of active compounds. In the prostate there was a preferential retention of [3H]DHT over [3H] DHN in the receptor fractions whereas in thymus, spleen and muscular tissues [3H]N and [3H]T were retained in equal amounts. The kidney showed a preferential retention of [3H]N over [3H]T. The present results explain the relatively strong effect of nandrolone compared to that of testosterone on target tissues devoid of 5 alpha-reductase activity (e.g. muscular tissue) compared to its relatively weak effect on tissues with a relatively high 5 alpha-reductase content (e.g. prostate).

Metabolism and receptor binding of nandrolone and testosterone under in vitro and in vivo conditions.

The metabolism and receptor binding of nandrolone (N) and testosterone (T) were studied under in vitro and in vivo conditions. The results of both in vitro incubation studes with 3H-N and 3H-T in tissue homogenates from rats and in vivo infusion studies with 3H-N and 3H-T in conscious rats show the importance of the enzymes 5 alpha-reductase and 3 alpha/beta-hydroxysteroid-oxidoreductases in the prostate and the importance of the enzyme 17 beta-hydroxysteroid dehydrogenase in the kidney for the effects of N and T on these tissues. Following infusion of a combined dose of 3H-N and 3H-T there is a preferential retention at the receptor of 5 alpha-dihydrotestosterone (DHT) over 5 alpha-dihydronandrolone (DHN), N and T (DHT much greater than DHN greater than N greater than T) in the prostate because T is a better substrate than N for 5 alpha-reductase and because DHT binds more strongly to the androgen receptor than DHN, N and T. In the kidney 5 alpha-reductase is not important; there is a preferential retention of N in T (DHN and DHT were only present in small amounts) because N is less susceptible than T for metabolic inactivation by the enzyme 17 beta-hydroxysteroid dehydrogenase and N binds strongly to the androgen receptor. Both in vitro and in vivo studies show that N and T were relatively stable in spleen, thymus and muscular tissue (only shown in vivo) and, as a result, the same amount of N and T was bound to the receptor in these tissues in the in vivo infusion experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of progestagens to receptor proteins in MCF-7 cells.

With the aim of finding an explanation for the biological properties of progestagens currently used for contraceptive purposes, we have assessed their specificity for progesterone, androgen and oestrogen receptors in MCF-7 cells. The specificity of progestagens for the progesterone receptors in the cytosol fraction of MCF-7 cells was similar to that for progesterone receptors in human and rabbit myometrial cytosol but different from that for the progesterone receptor in rat myometrial cytosol. At 37 degrees C the relative affinity of 3-keto-desogestrel, the major metabolite of desogestrel, for the progesterone receptor in intact MCF-7 cells was twice that of levonorgestrel and Org 2058, three times that of medroxy-progesterone acetate (MPA), 4.5 times that of norethisterone and 5 times that of progesterone and cyproterone acetate whereas at 4 degrees C in the cytosol fraction of MCF-7 cells exposed to molybdate (nontransformed receptor complexes) 3-keto-desogestrel and Org 2058 displayed similar affinity. The stronger binding of 3-keto-desogestrel in intact cells was due to the higher stability of its complex with the progesterone receptor. At 37 degrees C the relative affinity of 3-keto-desogestrel for the androgen receptor in intact MCF-7 cells was half that of levonorgestrel, similar to that of norethisterone and medroxyprogesterone acetate (MPA) and at least three times higher than that of progestagens with anti-androgenic activity whereas at 4 degrees C in the cytosol fraction exposed to molybdate there was no clear difference between the relative affinities of progestagens with androgenic and anti-androgenic properties. Of the progestagens tested in this study, only norethinodrel displayed measurable but very low relative affinity for the oestrogen receptor in MCF-7 cells. We conclude that the present results of binding studies with intact MCF-7 cells correlate better with the known hormonal properties of progestagens than those obtained with the cytosol fraction exposed to molybdate at 4 degrees C.