Drospirenone: pharmacology and pharmacokinetics of a unique progestogen.

The pharmacology and pharmacokinetics of drospirenone, a unique progestogen, are reviewed in this paper. Unlike other progestogens, drospirenone, an analogue of spironolactone, has biochemical and pharmacologic profiles similar to endogenous progesterone, especially regarding antimineralocorticoid and antiandrogenic activities. Drospirenone counteracts the estrogen-induced stimulation of the renin-angiotensin-aldosterone system and blocks testosterone from binding to androgen receptors. Because of these characteristics, it has the potential to reduce body weight, blood pressure, and low-density lipoprotein levels and to enhance high-density lipoprotein levels. As a combination oral contraceptive, drospirenone with ethinyl estradiol is effective and has positive effects on weight and lipid levels. Additionally, it relieves menstrually related symptoms (e.g., negative affect and water retention) that are commonly observed with other combination oral contraceptives. Based on the biochemical and pharmacodynamic data, drospirenone appears to be a viable alternative to the currently available progestogens.

Synthesis and biological activity of 11,19-bridged progestins.

A synthetic approach to 11,19-bridged progestins is described. The key step in the synthesis is a 6-endo-trig radical cyclisation. The new progestins were tested for their biological activities in vitro and in vivo and compared to those of known progestins.

The novel progestin drospirenone and its natural counterpart progesterone: biochemical profile and antiandrogenic potential.

Drospirenone is a novel progestin under clinical development that is similar to the natural hormone progesterone, combining potent progestogenic with antimineralocorticoid and antiandrogenic activities. This specific pharmacological profile of drospirenone is defined by its pattern of binding affinities to a variety of steroid hormone receptors. In the present study the affinity of drospirenone to the progesterone receptor (PR), the androgen receptor (AR), the glucocorticoid receptor (GR), the mineralocorticoid receptor (MR), and the estrogen receptor (ER) was re-evaluated by steroid binding assays and compared to those obtained for the natural hormone progesterone. Drospirenone displayed high affinity to PR and MR and low binding to AR, similar to progesterone. Unlike progesterone, which showed considerable binding to GR, drospirenone exhibited only low binding to this receptor. Neither drospirenone nor progesterone did bind to the ER. In addition to receptor binding studies, transactivation assays were carried out to investigate the effects of drospirenone and progesterone on AR-, GR-, and MR-mediated induction of transcription. Both progestins showed no androgenic but antiandrogenic activity by inhibiting AR-mediated transcription in a dose-dependent manner. This observation could be confirmed by in vivo experiments carried out with orchiectomized male rats, where the antiandrogenic potency of drospirenone was found to be about five- to ten-fold higher than that of progesterone. In contrast to progesterone, drospirenone was devoid of glucocorticoid activity. Both progestins did not show any antiglucocorticoid action. Furthermore, drospirenone and progesterone both showed considerable antimineralocorticoid activity and weak mineralocorticoid activity.

PIP: In various research laboratories in Germany, researchers conducted receptor binding studies and transactivation assays in vitro and studied antiandrogenic activity in juvenile castrated male rats of the new progestin drospirenone and of the natural hormone progesterone. Drospirenone exhibited high affinity to the progesterone receptor (PR) and the mineralocorticoid receptor (MR), while it exhibited low affinity to the androgen receptor (AR). Progesterone also had low affinity to AR. Neither the new progestin nor progesterone bound to the estrogen receptor (ER). Neither drospirenone nor progesterone displayed androgenic activity. On the other hand, they thwarted AR-mediated transcription in a dose-dependent manner, therefore displaying antiandrogenic activity. The in vivo studies confirmed the antiandrogenic activity of drospirenone and progesterone. In fact, these studies revealed that drospirenone had an antiandrogenic potency 5-10 times greater than progesterone. Unlike progesterone, drospirenone exhibited no glucocorticoid activity, but both drospirenone and progesterone exhibited antiglucocorticoid activity. They also displayed strong antimineralocorticoid activity and weak mineralocorticoid activity.

Drospirenone: a novel progestogen with antimineralocorticoid and antiandrogenic activity.

Drospirenone (ZK 30595; 6 beta, 7 beta, 15 beta, 16 beta-dimethylen-3-oxo-17 alpha-pregn-4-ene-21, 17-carbolactone) is a novel progestogen under clinical development. Drospirenone is characterized by an innovative pharmacodynamic profile which is very closely related to that of progesterone. Potential applications include oral contraception, hormone replacement therapy and treatment of hormonal disorders. The pharmacological properties of drospirenone were investigated in vitro by receptor binding and transactivation experiments and in vivo in appropriate animal models. In qualitative agreement with progesterone, the compound binds strongly to the progesterone and the mineralocorticoid receptor and with lower affinity to androgen and glucocorticoid receptors. There is no detectable binding to the estrogen receptor. Steroid hormone agonistic and antagonistic activities of progesterone and drospirenone were compared in transactivation experiments. Individual steroid hormone receptors were artificially expressed together with a reporter gene in appropriate cell lines. Both hormones were unable to induce any androgen receptor-mediated agonistic activity. Rather, both progesterone and drospirenone distinctly antagonized androgen-stimulated transcriptional activation. Likewise, both compounds only very weakly activated the mineralocorticoid receptor but showed potent aldosterone antagonistic activity. Drospirenone did not induce glucocorticoid receptor-driven transactivation. Progesterone was a weak agonist in this respect. Drospirenone exerts potent progestogenic and antigonadotropic activity which was studied in various animal species. It efficiently promotes the maintenance of pregnancy in ovariectomized rats, inhibits ovulation in rats and mice and stimulates endometrial transformation in the rabbit. Furthermore, drospirenone shows potent antigonadotropic, i.e., testosterone-lowering activity in male cynomolgus monkeys. The progestogenic potency of drospirenone was found to be in the range of that of norethisterone acetate. The majority of clinically used progestogens are androgenic. Drospirenone, like progesterone, has no androgenic but rather an antiandrogenic effect. This property was demonstrated in castrated, testosterone propionate substituted male rats by a dose-dependent inhibition of accessory sex organ growth (seminal vesicles, prostate). In this model, the potency of drospirenone was about a third that of cyproterone acetate. Drospirenone, like progesterone, shows antimineralocorticoid activity, which causes moderately increased sodium and water excretion. This is an outstanding characteristic which has not been described for any other synthetic progestogen before. Drospirenone is eight to ten times more effective in this respect than spironolactone. The natriuretic effect was demonstrable for at least three weeks upon daily treatment of rats with a dose of 10 mg/animal. Drospirenone is devoid of any estrogenic, glucocorticoid or antiglucocorticoid activity. In summary, drospirenone, like progesterone, combines potent progestogenic with antimineralocorticoid and antiandrogenic activity in a similar dose range.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative progestational activity of norgestimate, levonorgestrel-oxime and levonorgestrel in the rat and binding of these compounds to the progesterone receptor.

The progestational activity of norgestimate (NORG), levonorgestrel-oxime (LNG-oxime) and levonorgestrel (LNG) were compared in a pregnancy maintenance study in rats. The compounds were administered subcutaneously to pregnant rats at several doses, blood samples were collected repeatedly, and the concentration of LNG was measured in these samples. It could be demonstrated that following the administration of NORG and LNG-oxime, LNG was a major metabolite present in the serum. The pharmacological response in rats treated with NORG and LNG-oxime could be related to the systemic exposure of these animals to metabolically derived LNG. Thus, both NORG and LNG-oxime can be regarded as pro-drugs of LNG, the latter being almost exclusively responsible for the pharmacological activity of both pro-drugs. This notion was further supported by studies on the comparative binding affinity of these compounds to rabbit and human progesterone receptor (PR). LNG exhibited the highest binding affinity of the compounds studied. Relative binding affinity (RBA) values of LNG using progesterone as reference (100%) were found to be 125% for rabbit PR (rPR), 143% for human uterine PR (hPR) and 125% for recombinant hPR, respectively. In contrast to LNG, NORG exhibited only a low affinity to the PR, which is documented by RBA values of 1.2% for rPR, 3.2% for uterine hPR and 9% for recombinant hPR. The corresponding values of LNG-oxime were 30% (rPR), 20% (uterine hPR) and 18% (recombinant hPR), respectively. Thus, the combined experimental evidence of the present study does not support the view of NORG being a progestogen on its own as has been suggested by others.

Drospirenone: a novel progestogen with antimineralocorticoid and antiandrogenic activity. Pharmacological characterization in animal models.

Drospirenone (ZK 30595; 6 beta, 7 beta, 15 beta, 16 beta-dimethylen-3- oxo-17 alpha-pregn-4-ene-21, 17-carbo-lactone) is a novel progestogen under clinical development. Potential applications include oral contraception, hormone replacement therapy and treatment of hormonal disorders. Drospirenone is characterized by a pharmacodynamic profile very closely related to that of progesterone. The progestogenic activity of drospirenone has been analysed in a variety of animal models. The compound efficiently promotes the maintenance of pregnancy in rats, inhibits ovulation in rats and stimulates endometrial transformation in the rabbit. Furthermore, drospirenone shows potent antigonadotropic, i.e. testosterone-lowering, activity in male cynomolgus monkeys. The progestogenic potency of drospirenone was found to be in the range of that of norethisterone acetate or cyproterone acetate. Like progesterone, drospirenone has been shown to have an antimineralocorticoid effect in rats and humans. It has now been demonstrated that the compound has a long-lasting natriuretic activity in rats on administration of a daily dose of 10 mg s.c. for three weeks. Under identical conditions, spironolactone, a widely-used antimineralocorticoid, becomes ineffective after the initial treatment phase. Drospirenone exhibits antiandrogenic activity in castrated, testosterone-substituted male rats as shown by dose-dependent inhibition of accessory sex organ growth (prostate, seminal vesicles). In this model, the potency of drospirenone was found to be about one-third that of cyproterone acetate. The compound is devoid of androgenic, estrogenic, glucocorticoid and antiglucocorticoid activity. Possible drug interaction between drospirenone and ethinylestradiol (EE) was also investigated. EE did not interfere with either the progestogenic or the antimineralocorticoid activity of drospirenone. In conclusion, drospirenone represents a novel type of synthetic progestogen since it combines potent progestogenic characteristics with antimineralocorticoid and antiandrogenic activity. Thus, the pharmacological profile of drospirenone is more closely related to that of the natural hormone progesterone than is that of any other synthetic progestogen in use today. Therefore, drospirenone is anticipated to give rise to a number of additional health benefits both for users of oral contraceptives and hormone replacement therapy recipients.

Estrogen action on hepatic synthesis of angiotensinogen and IGF-I: direct and indirect estrogen effects.

In the present study effects of estrogens (natural estradiol and synthetic ethinyl estradiol) on liver derived proteins (angiotensinogen, IGF-I) were investigated in vivo in ovariectomized rats and in vitro in a rat hepatoma cell line (Fe33). The aim of this study was to establish both an animal and an in vitro model for quantification of the hepatic activity of given estrogenic compounds, and to study underlying mechanisms as regards the question of direct or indirect mode of estrogen action. In ovariectomized rats subcutaneous (s.c.)-treatment for 11 days with either estradiol (E2) or ethinyl estradiol (EE) (dose range 0.1-3 micrograms/animal/day) induced a comparable dose-dependent increase in uterine weight indicating a similar estrogenic potency of the two estrogens. Equipotency was also found as regards the effects on IGF-I plasma levels which dose-dependently decreased by about 50% at the highest dose tested (3 micrograms/animal/day). The decrease in IGF-I serum levels was accompanied by a significant 40% decrease in liver IGF-I mRNA. In contrast angiotensinogen plasma levels were affected only by EE (60% increase for the 3 micrograms/animal/day dose) but not by E2. When rats, in addition to ovariectomy, were also hypophysectomized (substituted with human growth hormone and dexamethasone) angiotensinogen again increased by 80% upon administration of 3 micrograms/animal/day EE, whereas IGF-I remained unaffected by EE. In a rat hepatoma cell line (Fe33) which is stably transfected with an estrogen receptor expression plasmid, 10 nmol/l EE for 24 h caused a 2.4-fold increase in angiotensinogen mRNA level. We conclude from our studies that estrogen effects on angiotensinogen serum levels in the rat are direct effects via the hepatic estrogen receptor, whereas estrogen effects on IGF-I serum levels are indirect effects, the primary target of estrogen action being probably the pituitary. The changes in angiotensinogen serum levels in the rat model are comparable to the situation in humans indicating the rat model and the Fe33 model to be useful tools to study the hepatic activity of estrogenic compounds.

Current-noise analysis of Na absorption in the embryonic coprodeum: stimulation by aldosterone and thyroxine.

The mechanism and regulation of sodium transport in the embryonic coprodeum of chicken were investigated with isolated epithelia in vitro by electrophysiological techniques. Electrogenic sodium transport (INa) was measured in Ussing chambers by the short-circuit current (Isc) technique and identified by the diuretic amiloride or by removal of sodium from the apical medium. Apical sodium channels and the kinetics of amiloride binding were investigated by current-noise analysis. Isc and INa were measured under control conditions and under the influence of in vitro incubation with aldosterone and thyroxine. At 20 days the embryonic coprodeum has an Isc of 12.6 +/- 1.4 microA/cm2 and a transepithelial resistance of 519 +/- 40 omega.cm2. Amiloride blocks 9.0 +/- 1.3 microA/cm2 of the Isc, which represents electrogenic Na+ absorption and can be inhibited by serosal ouabain. Aldosterone does not stimulate Isc or INa, whereas thyroxine increases Isc and INa about threefold. Aldosterone in combination with thyroxine increases Isc and INa further to about five- to sixfold. In both cases the hormonal stimulation can be totally blocked by spironolactone. Current-noise analysis of the apical Na+ entry step reveals amiloride-sensitive Na+ channels with a single-channel current of approximately 2.3 pA and a channel density of 9-16 million/cm2 under stimulated conditions. Half-maximal amiloride block occurs at 0.8-1 microM. The hormones stimulate Na+ absorption by increasing the Na+ channel density and not the single-channel current.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrolyte transport through a cation-selective ion channel in large intestinal enterocytes of Xenopus laevis.

Electrogenic ion transport through the colon epithelium of the African clawed toad (Xenopus laevis) was investigated with electrophysiological methods in vitro. Interest was focused on a previously described phenomenon, that removal of Ca2+ from the mucosal Ringer's solution increases electrogenic sodium absorption. Our results clearly show that Ca2+ removal reveals an apical ion channel that is not a specific Na+ channel, but a non-selective cation channel with an 'apparent' ion selectivity of the order K+ greater than Na+ = Rb+ greater than Cs+ greater than Li+. This Ca2(+)-sensitive current increased linearly with the mucosal pH, and could be inhibited by other divalent cations (Mg2+, Ba2+) and the organic ion channel blockers quinidine and verapamil. The mucosal Ca2+ concentration that induced a half-maximal inhibition of the Ca2(+)-sensitive current was about 1 mumol l-1 and was independent of the mucosal pH. Owing to the high Ca2+ sensitivity, a regulation of the channel conductivity by extracellular Ca2+ is ruled out. It is concluded that this channel, which is almost identical to similar channels found in amphibian skin and bladder, acts as a pathway for cation absorbing or secreting processes. Possibly the binding of extracellular Ca2+ is related to selectivity changes of the Ca2(+)-sensitive ion channel.

Different modes of electrogenic Na+ absorption in the coprodeum of the chicken embryo: role of extracellular Ca2+.

Transepithelial electrogenic Na+ transport (INa) was investigated in the coprodeum of 20-days-old chicken embryos in Ussing chambers. Short circuit current (Isc) and transepithelial resistance (Rt) were 14.7 +/- 4.8 microA.cm-2 (n = 12) and 0.53 +/- 0.09 k omega.cm-2 (n = 12), respectively. INa was calculated from changes in Isc by substitution of mucosal Na+ by (N-methyl-D-glucamine) (NMDG). Isc inversed during Na+ removal, and INa was found to be 27.8 +/- 4.7 microA.cm-2 (n = 12). Amiloride (100 mumol.l-1) inhibited only about 60% of INa. Analysis of Isc fluctuations revealed a Lorentzian component in the power density spectrum with a corner frequency of about 57 Hz. This component was not correlated to INa, and its origin is still unclear. Removal of mucosal Ca2+ increased INa about 2.5-fold due to an increase of the amiloride-insensitive component of INa in additionally investigated adult tissues. The results clearly show that this is due to a non-selective cation channel with an "apparent" order of selectivity Cs+ greater than Na+ = K+ greater than Rb+ greater than Li+. The Ca2+ concentration required to block 50% of the Isc was about 18 mumol.l-1. The IscCa could also be suppressed by other divalent cations such as Mg2+ and Ba2+. Additionally, an INa-linked Lorentzian component occurred which dominated the control spectrum with a significantly higher corner frequency (about 88 Hz). The results indicate that Na+ absorption in the coprodeum of the chicken embryo is more complex than in adult hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Ca-sensitive sodium absorption in the colon of Xenopus laevis.

Transepithelial electrogenic Na transport (INa) was investigated in the colon of the frog Xenopus laevis with electrophysiological methods in vitro. The short circuit current (Isc) of the voltage-clamped tissue was 24.2 +/- 1.8 microA.cm-2 (n = 10). About 60% of this current was generated by electrogenic Na transport. Removal of Ca2+ from the mucosal Ringer solution stimulated INa by about 120%. INa was not blockable by amiloride (0.1 mmol.l-1), a specific Na-channel blocker in epithelia, but a fully and reversible inhibition was achieved by mucosal application of 1 mmol.l-1 lanthanum (La3+). No Na-self-inhibition was found, because INa increased linearly with the mucosal Na concentration. A stimulation of INa by antidiuretic hormones was not possible. The analysis of fluctuations in the short circuit current (noise analysis) indicated that Na ions pass the apical cell membrane via a Ca-sensitive ion channel. The results clearly demonstrate that in the colon of Xenopus laevis Na ions are absorbed through Ca-sensitive apical ion channels. They differ considerably in their properties and regulation from the amiloride-sensitive Na channel which is "typically" found in the colon of vertebrates.

Autoregulation of apical sodium entry in the colon of the frog (Rana esculenta).

1. Na transport (INa) in the K-depolarized colon of the frog was investigated by electro-physiological current-voltage analysis. 2. INa and the intracellular Na activity [(Na)c] increased with increasing mucosal Na concentration ([Na]m), whereas the apical Na-permeability (PNam) and the transepithelial resistance (RT) decreased. 3. The results are consistent with a Na self-inhibition mechanism; however, a feedback inhibition of INa by intracellular Na must also be considered.

Noise analysis of cAMP-stimulated Na current in frog colon.

The effects of oxytocin and cAMP on the electrogenic Na+-transport in the short-circuited epithelium of the frog colon (Rana esculenta, Rana temporaria) were investigated. Oxytocin (100 mU.ml-1) elevated the short-circuit current (Isc) transiently by 70% whereas cAMP (1 mmol.l-1) elicited a comparable sustained response. The mechanism of the natriferic action of cAMP was studied by analysing current fluctuations through apical Na+-channels induced by amiloride or CDPC (6-chloro-3,5-diaminopyrazine-2-carboxamid). The noise data were used to calculate Na+-channel density (M) and single apical Na+-current (iNa). iNa-Values obtained with amiloride and CDPC were 1.0 +/- 0.1 pA (n = 5) and 1.1 +/- 0.2 pA (n = 6) respectively and unaffected by cAMP. On the other hand, cAMP caused a significant increase in M from 0.23 +/- 0.08 micron-2 (n = 5) to 0.49 +/- 0.17 micron-2 (n = 5) in the amiloride experiments. In our studies with CDPC we obtained smaller values for M in control (0.12 +/- 0.04 micron-2; n = 6) as well as during cAMP treatment (0.19 +/- 0.06 micron-2; n = 6). However, the cAMP-induced increase in M was also significant. We conclude that cAMP stimulates Na+-transport across the frog colon by activating "silent" apical Na+-channels. Thus, the mechanism of regulation of colonic Na-transport in frogs differs considerably from that in other vertebrates as mammals and birds.

Circadian rhythm of apical Na-channels and Na-transport in rabbit distal colon.

In vivo and in vitro studies showed that electrogenic sodium transport in rabbit distal colon is modulated by aldosterone. It varies in a circadian rhythm; the external synchronizer is the light-dark cycle. The site of regulation was found to be in the apical membrane of colonic epithelial cells, in which the number of conducting sodium-channels is increased by aldosterone.

Electrophysiological analysis of sodium-transport in the colon of the frog (Rana esculenta). Modulation of apical membrane properties by antidiuretic hormone.

Sodium transport and apical bioelectrical membrane properties were investigated in frog colonic epithelium in the absence and presence of the antidiuretic hormone arginine-vasotocin (AVT). Apical Na-permeability and intracellular Na-activity were evaluated by analysis of current-voltage relationships in the serosally K-depolarized tissue. Tissue- and apical membrane capacitance were measured by voltages step analysis. The frog colon was found to be a tight epithelium with a transepithelial resistance of 2.63 +/- 0.25 k omega.muF (n = 17). 85-90% of short circuit current (11.2 +/- 1.1 microA.microF.l-1; n = 17) was related to electrogenic Na-transport from mucosa to serosa. Graded doses of amiloride (less than 50 mumol.l-1) induced Michaelis-Menten-type inhibition kinetics. Serosal addition of 10(-6) mol.l-1 AVT induced a significant increase in sodium current (25%), apical sodium permeability (19%) and tissue capacitance (4.3%) whereas intracellular Na-activity remained unchanged. There was a good correlation between increased Na-current and apical Na-permeability. No correlation was found between Na-current and membrane capacitance. Our results demonstrate that in contrast to other species the amphibian colon shows a natriferic reaction to AVT. We suggest that the regulation of Na-transport in frog colon is similar to that in the toad urinary bladder. It is caused by an activation of preexisting apical Na-channels and not by fusion of subapical cytoplasmic vesicles with the apical membrane.