Sybille Dr. Beier

Gestodene: A novel synthetic progestin — characterization of binding to receptor and serum proteins

Gestodene, 17 alpha-ethinyl-13-ethyl-17 beta-hydroxy-4,15-gonadien-3-one, is a new orally active progestational agent, which is available for clinical use in oral contraceptives. The aim of the present study is to make a broad characterization of gestodene at the receptor level and to discuss the results in comparison to those of established progestogens. Kinetic studies of 3H-gestodene uptake show a rapid increase in the amount of specific binding during the first three hours. After saturation, the amount of specifically bound 3H-gestodene remained almost constant up to 24 hours at 4 degrees C. The dissociation of 3H-gestodene from the cytoplasmic myometrial progestone receptor, measured by displacement of labeled steroid with dextran-coated charcoal treatment at 4 degrees C at various times, showed a biphasic or two-component first order dissociation curve. As anticipated, sucrose gradient centrifugation analysis of the 3H-gestodene-labeled cytosol of human myometrial tissue showed that the gestodene binding components sedimented in the 4S and 8S region. A 200-fold molar excess of nonradioactive gestodene reduced only the 8S binding of 3H-gestodene. 4S binding of 3H-gestodene was not reduced, which indicate the existence of a second high capacity binding component. In biological test systems, such as the Clauberg test or Kaufmann test, gestodene has proved to be a very effective progestogen. Among nortestosterone derivatives it is one of the most potent and resembles progesterone biologically in its progestogenic effects. This biologically identical gestagenic activity of gestodene and progesterone is reflected by a very similar behavior in vitro in terms of binding to progesterone receptors of human uterus cytosol. Furthermore, competitive studies indicated that gestodene like other synthetic progestagens also displays some affinity for androgen and glucocorticoid receptors but no measurable affinity for the estrogen receptor. Remarkable is the high binding affinity of gestodene to the binding sites of the mineralocorticoid receptor of rat kidney with a RBA value of 350% compared to aldosterone.

Suitability of the beagle dog as a test model for the tumorigenic potential of contraceptive steroids “short review”

Abstract The purpose of this short review is to assess the present state of knowledge on the suitability of the beagle dog as a test model for the tumorigenic potential of contraceptive steroids. The beagle dog differs markedly from other species, including man, as regards its reproductive physiology and endocrinology. Studies on the influence of contraceptive steroids on canine mammary gland, pituitary gland and uterus have led to the conclusion that the stimulation of development of mammary tumours in dogs by certain progestagens or progestagen-oestrogen combinations must be considered as being a species-specific effect, related to the high hormonal potency (progestational activity) of these compounds in the dog and their stimulatory effect on canine growth hormone. Based on the present state of our knowledge and because of the marked interspecies differences of action of contraceptive steroids in dog and man, the steroid-related canine mammary tumours, especially with regard to the doses necessary for contraception, are unlikely to be indicative of a potential hazard to the human female.

The progestational activity of different gestagens used for human contraception in the beagle bitch

Abstract In long-term studies chlormadinone acetate (CMA) and cyproterone acetate (CPA) have much more pronounced mammotropic effects in dogs than norethisterone acetate (NA) or levonorgestrel (LN). To evaluate gestagenic potency of these compounds in dogs as a potential determinant of these substance differences, a quantitative canine gestagen bioassay was developed. Ovariectomized adult beagles were sequentially treated with 30 μg estradiol (E 2 )/d s.c. for 15 days and gestagen (s.c., p.o.) + 3 μ g E 2 / d s.c. days 16–29. This regimen was found optimal for endometrial gestagen effects. According to their s.c. transformatory potency in day 29 endometrial biopsies, the compounds could be ranked as follows; progesterone (P) Related to p, LN and NA have a much lower gestagenic potency in dogs than in humans. The opposite is true for CMA and CPA. The low oral activity of NA and LN in dogs points to an important first liver passage metabolism of both compounds in this species. Serum determinations substantiate the very low or high oral. bioavailability in case of LN, NA and CPA. Clinically, by the oral route of administration, there is no doubt of the fact that CMA is markedly less potent than NA which itself is less potent than LN whereas in the dogs, CMA is unequivocally the most potent of the progestagens under consideration. This implies that the dogs are overdosed with several human multiples when CMA is administered and probably underdosed with NA, at least on a comparative basis. Our data are consistent with the view that the ability or inability of gestagens to induce mammary tumours in chronic toxicity studies might reflect a dog-specific high or low gestagenicity.

3H-ZK 98,734, a new 11β-aryl substituted antigestagen: Binding characteristics to receptor and serum proteins

Recently, in the laboratories of Schering in Germany a competitive progesterone antagonist, ZK 98,734, was synthetized, which is characterized by a similar antigestagenic activity as RU 38,486, synthezised by Roussel-Uclaf in France, as assessed by inhibition of nidation tests in rats and guinea pigs. However, this compound has a substantially lower antiglucocorticoid activity measured in cell culture systems than RU 38,486. The purpose of this study was to present a comparison of biochemical and physical properties of the complexes formed by the human uterine progesterone receptor with 3H-ZK 98,734 on one hand and with other well-established progestins on the other hand. ZK 98,734 competed in the same order of magnitude as progesterone or RU 38,486 for the 3H-R5020 binding site of progestin receptor, whereas R5020, Org 2058 or progesterone were unable to compete against 3H-ZK 98,734. This apparent contradiction could be explained by means of FPLC-chromatography and sucrose density centrifugation technique. FPLC-chromatography with an anion exchange column (Mono Q, Pharmacia, Uppsala, Sweden) showed that 3H-ZK 98,734 forms at least two stable complexes with uterine cytosol, on one hand with serum albumin, which presents almost 90% of bound radioactivity, and on the other hand with the two native progestin receptor forms, corresponding to 4S and 8S receptor forms in sucrose density gradient analysis. Competition experiments in liver cytosol of adrenalectomized rats with increasing concentrations of unlabeled ligands other than dexamethasone showed that ZK 98,734, RU 38,486 and cortisol displaced 3H-dexamethasone efficiently from the binding sites in the cytosol. Furthermore, results concerning the specificity of 3H-cortisol binding to serum proteins in diluted pregnant serum demonstrated that ZK 98,734 did not compete with 3H-cortisol for serum binding.