The relaxant effect of sex steroids in rat myometrium is independent of the gamma-amino butyric acid system

Changes in the conflicting nongenomic effects of progesterone in rat myometrium during pregnancy

AIMS

Although the functions of progesterone in the myometrium are well-established, the nongenomic effects of progesterone in pregnant myometrial contractions are still unclear. Therefore, this study aimed to investigate changes in the nongenomic effects of progesterone during pregnancy.

MAIN METHODS

Myometrial strips were obtained from non-pregnant, pregnant, and postpartum rats, and the nongenomic effects of progesterone in the myometrium during pregnancy were examined. Additionally, the influence of actinomycin D and cycloheximide and the effects of Org OD-02-0 (a specific membrane progesterone receptor (mPR) agonist) in the myometrium were investigated. Moreover, DNA microarray and quantitative real-time polymerase chain reaction (qRT-PCR) were performed to identify genes involved in progesterone-induced effects in the myometrium.

KEY FINDINGS

Progesterone did not cause rhythmic contractions in non-pregnant myometrium but induced rhythmic contractions in pregnant myometrium, with the effects peaking at 20 d + 8 h of pregnancy. However, myometrial contractions decreased after delivery and were restored to non-pregnant levels at 7 d postpartum. Additionally, progesterone stably inhibited high KCl-induced myometrial contractions during pregnancy. Moreover, the nongenomic effects of progesterone were unaffected by actinomycin D or cycloheximide, and Org OD-02-0 effectively mimicked these effects. DNA microarray analysis and qRT-PCR revealed a significant increase in mPRβ gene expression during pregnancy. However, mPRα, mPRγ, mPRδ, and mPRε expression levels remained unchanged.

SIGNIFICANCE

The stimulatory nongenomic effect of progesterone, which was inducible and mPRβ-dependent during pregnancy, may be involved in parturition. The inhibitory effect, which was constitutive and depended on other mPRs, may be involved in pregnancy maintenance.

Conflicting Nongenomic Effects of Progesterone in the Myometrium of Pregnant Rats

Recently, it has been suggested that progesterone affects the contractile activity of pregnant myometrium via nongenomic pathways; therefore, we aimed to clarify whether progesterone causes and/or inhibits pregnant myometrial contractions via nongenomic pathways. Our in vitro experiments using myometrial strips obtained from rats at 20 days of gestation revealed that progesterone caused myometrial contractions in a concentration- and time-dependent manner at concentrations up to 5 × 10-7 M; however, this effect decreased at concentrations higher than 5 × 10-5 M. Similarly, progesterone enhanced oxytocin-induced contractions up to 5 × 10-7 M and inhibited contractions at concentrations higher than 5 × 10-5 M. Conversely, progesterone did not enhance high-KCl-induced contractions but inhibited contractions in a concentration- and time-dependent manner at concentrations higher than 5 × 10-7 M. We also found that RU486 did not affect progesterone-induced contractions or the progesterone-induced inhibition of high-KCl-induced contractions; however, progesterone-induced contractions were blocked by calcium-free phosphate saline solution, verapamil, and nifedipine. In addition, FPL64176, an activator of L-type voltage-dependent calcium channels, enhanced high-KCl-induced contractions and rescued the decrease in high-KCl-induced contractions caused by progesterone. Together, these results suggest that progesterone exerts conflicting nongenomic effects on the contractions of pregnant myometrium via putative L-type voltage-dependent calcium channels.

Activation of Adrenal Steroidogenesis and an Improvement of Mood Balance in Postmenopausal Females after Spa Treatment Based on Physical Activity

Spa treatment can effectively reestablish mood balance in patients with psychiatric disorders. In light of the adrenal gland’s role as a crossroad of psychosomatic medicine, this study evaluated changes in 88 circulating steroids and their relationships with a consolidation of somatic, psychosomatic and psychiatric components from a modified N-5 neurotic questionnaire in 46 postmenopausal 50+ women with anxiety-depressive complaints. The patients underwent a standardized one-month intervention therapy with physical activity and an optimized daily regimen in a spa in the Czech Republic. All participants were on medication with selective serotonin reuptake inhibitors. An increase of adrenal steroidogenesis after intervention indicated a reinstatement of the hypothalamic-pituitary-adrenal axis. The increases of many of these steroids were likely beneficial to patients, including immunoprotective adrenal androgens and their metabolites, neuroactive steroids that stimulate mental activity but protect from excitotoxicity, steroids that suppress pain perception and fear, steroids that consolidate insulin secretion, and steroids that improve xenobiotic clearance. The positive associations between the initial values of neurotic symptoms and their declines after the intervention, as well as between initial adrenal activity and the decline of neurotic symptoms, indicate that neurotic impairment may be alleviated by such therapy provided that the initial adrenal activity is not seriously disrupted.

Profiling of GABAA and GABAB receptor expression in the myometrium of the human uterus

AIMS

γ-aminobutyric acid (GABA) mediates its physiological effects through the GABA_A and GABA_B receptors. In this study the putative expression of GABA_AR and GABA_BR subunits in human myometrium tissue was investigated.

MAIN METHODS

The expression levels of the 19 GABA_AR subunits (α₁-α₆, β₁-β₃, γ₁-γ₃, δ, ε, π, θ, ρ₁-ρ₃) and the three GABA_BR subunits (GABA_B1a, GABA_B1b, GABA_B2) were characterized by RT-qPCR analysis on two commercial samples and six samples derived from surgically removed myometrial tissues from different women. We probed for functional GABA_AR expression in primary human myometrial smooth muscle cells (HMSMCs) by whole-cell patch-clamp electrophysiology.

KEY FINDINGS

The absolute mRNA levels of the 22 GABA_AR and GABA_BR genes varied considerably across the eight samples, but a pronounced overlap existed between the specific subunits detected in the samples, with α₂, β₂, β₃, ε, π, θ, GABA_B1a and GABA_B1b mRNAs being detected in most samples. The expression profile of GABA_AR and GABA_BR subunit mRNAs in HMSMCs correlated with that observed in the eight tissue samples, albeit the subunit transcripts were detected at lower relative levels. Neither muscimol nor GABA evoked significant currents in these cells in the patch-clamp recordings.

SIGNIFICANCE

While the expression of the GABA_B1 subunits on their own is unlikely to give rise to functional GABA_BR expression, the GABA_AR subunits identified at mRNA level would be able to form functional receptors in the human myometrial tissue. Although GABA_AR-mediated currents could not be recorded from HMSMCs in this study, this suggests a role for GABAergic transmission in the human myometrium.

The steroid hormone dydrogesterone inhibits myometrial contraction independently of the progesterone/progesterone receptor pathway

AIMS

In this study, we aimed to investigate the direct effects of steroid hormones on pregnant myometrial contraction.

MAIN METHODS

The effect of steroids on oxytocin-induced contraction was examined in vitro using pregnant rat or human myometrium. Subsequently, we evaluated whether RU486, a potent progesterone antagonist, influenced the effects of progestin on myometrial contraction. Additionally, we evaluated the effects of progestin on high-concentration KCl-induced contraction caused by voltage-dependent calcium channels in order to investigate the mechanisms involved in this process.

KEY FINDINGS

Of the natural steroids examined, 17β-estradiol, progesterone, testosterone, cortisol, and aldosterone did not influence oxytocin-induced contraction at concentrations <10^-6 M. Of the tested progestins, medroxyprogesterone acetate, norethisterone, chlormadinone acetate, levonorgesterol, 17α-hydroxyprogesterone capronate, and dienogest had no effect on contraction at <10^-6 M. However, dydrogesterone showed rapid and direct inhibition of contraction at 10^-6 M, and this inhibitory effect was dependent on dose and time. RU486 did not block the inhibitory effects of dydrogesterone on contraction. High-concentration KCl-induced contraction was also inhibited by dydrogesterone, and the inhibitory effects of dydrogesterone were observed at concentrations as low as 10^-7 M. Additionally, oxytocin-induced contraction in pregnant human myometrium was inhibited by 10^-6 M dydrogesterone.

SIGNIFICANCE

These results suggested that the rapid and direct effects of dydrogesterone on myometrial contraction were caused by a nongenomic pathway and that the progesterone receptor was not required for dydrogesterone action. Additionally, the mechanism of dydrogesterone action may involve voltage-dependent calcium channels.

Dehydroepiandrosterone, its metabolites and ion channels

This review is focused on the physiological and pathophysiological relevance of steroids influencing the activities of the central and peripheral nervous systems with regard to their concentrations in body fluids and tissues in various stages of human life like the fetal development or pregnancy. The data summarized in this review shows that DHEA and its unconjugated and sulfated metabolites are physiologically and pathophysiologically relevant in modulating numerous ion channels and participate in vital functions of the human organism. DHEA and its unconjugated and sulfated metabolites including 5α/β-reduced androstane steroids participate in various physiological and pathophysiological processes like the management of GnRH cyclic release, regulation of glandular and neurotransmitter secretions, maintenance of glucose homeostasis on one hand and insulin insensitivity on the other hand, control of skeletal muscle and smooth muscle activities including vasoregulation, promotion of tolerance to ischemia and other neuroprotective effects. In respect of prevalence of steroid sulfates over unconjugated steroids in the periphery and the opposite situation in the CNS, the sulfated androgens and androgen metabolites reach relevance in peripheral organs. The unconjugated androgens and estrogens are relevant in periphery and so much the more in the CNS due to higher concentrations of most unconjugated steroids in the CNS tissues than in circulation and peripheral organs. This article is part of a Special Issue entitled "Essential role of DHEA".

5β-Reduced steroids and human Δ(4)-3-ketosteroid 5β-reductase (AKR1D1)

5β-Reduced steroids are non-planar steroids that have a 90° bend in their structure to create an A/B cis-ring junction. This novel property is required for bile-acids to act as emulsifiers, but in addition 5β-reduced steroids have remarkable physiology and may act as potent tocolytic agents, endogenous cardiac glycosides, neurosteroids, and can act as ligands for orphan and membrane bound receptors. In humans there is only a single 5β-reductase gene AKR1D1, which encodes Δ(4)-3-ketosteroid-5β-reductase (AKR1D1). This enzyme is a member of the aldo-keto reductase superfamily, but possesses an altered catalytic tetrad, in which Glu120 replaces the conserved His residue. This predominant liver enzyme generates all 5β-dihydrosteroids in the C19-C27 steroid series. Mutations exist in the AKR1D1 gene, which result in loss of protein stability and are causative in bile-acid deficiency.

Depletion of calcium stores contributes to progesterone-induced attenuation of calcium signaling of G protein-coupled receptors

Progesterone non-genomically attenuates the calcium signaling of the human oxytocin receptor and several other Galpha(q) protein-coupled receptors. High progesterone concentrations are found in the endometrium during pregnancy opposing the responsiveness of the underlying myometrium to labor-inducing hormones. Here, we demonstrate that within minutes, progesterone inhibits oxytocin- and bradykinin-induced contractions of rat uteri, calcium responses induced by platelet-activating factor in the human endometrial cell line MFE-280, and oxytocin-induced calcium signals in PHM1-31 immortalized pregnant human myometrial cells. Using human embryonic kidney (HEK293) cells as model system, we analyzed the molecular mechanisms underlying these effects. Our data indicate that progesterone rapidly depletes intracellular calcium stores. The resulting desensitization of the cells might contribute to the quiescence of the uterus during pregnancy.

Different routes of progesterone administration and polycystic ovary syndrome: a review of the literature

Polycystic ovary syndrome (PCOS) is a common endocrine disorder in woman of reproductive age. Although extensive studies have been performed in past decades to investigate the pathobiological mechanisms underlying the unset of this disease, its etiology remains unknown. Progesterone is a hormone of paramount importance in ovulation, implantation and luteal phase support. Low levels of progesterone have been found in the early luteal phase in PCOS patients. Granulosa cells from polycystic ovaries show an altered progesterone production. Moreover, the lack of cyclical exposure to progesterone may have a role in the development of the gonadotropin and androgen abnormalities found in PCOS patients. Ovulation failure and progesterone deficiency may facilitate the hypothalamic-pituitary abnormalities causing the associated disordered luteinizing hormone secretion in PCOS. Progesterone may be administered to PCOS patients in the following cases: to induce withdrawal bleeding, to suppress secretion of luteinizing hormone, in ovulation induction in clomiphene citrate-resistant patients and in luteal phase support in assisted reproduction. We discuss the pharmacologic characteristics of the different routes of progesterone administration with reference to these diverse indications, the therapeutic objectives and patient compliance.

Androgens Induce Relaxation of Contractile Activity in Pregnant Human Myometrium at Term: A Nongenomic Action on L-Type Calcium Channels1

It has long been accepted that progesterone regulates uterine contractile activity. However, little is known about the role of androgens in female physiology, and their importance and biological function on myometrial contractility so far have received limited attention. In this work, we examined the direct effect of androgens on the contractile activity of the isolated human myometrium. Myometrial biopsies were obtained, with consent, from pregnant women undergoing elective cesarean section at term. Each androgen tested (dehydroepiandrosterone, testosterone, 5alpha- and 5beta-dihydrotestosterone, androsterone, or androstanediol) caused a concentration-dependent inhibition of spontaneous contractile activity; a relaxing effect of these androgens was also observed on the contractions induced by high potassium (KCl) solution. Interestingly, nonpregnant myometrium was also sensitive to androgen-induced relaxation. 5beta-Dihydrotestosterone (5beta-DHT) was dramatically more potent than the other androgens in inducing myometrial relaxation in all preparations. Relaxation response to androgens had very rapid time courses and was affected by neither the specific antiandrogen (flutamide) nor inhibitors of protein synthesis (cycloheximide) and transcription (actinomycin D), implying that androgens act through a nongenomic mechanism. Importantly, 5beta-DHT significantly reduced the increase in intracellular calcium concentration associated with exposure to KCl in human myometrial smooth-muscle cells loaded with Fura-2-AM. The blockade of l-type calcium channels seems to be involved in the nongenomic relaxing action of androgens. These observations demonstrate that androgens may play a crucial role in maintaining pregnancy.

The vasodepressor effect of androgens in pithed rats: potential role of calcium channels

Estrogens induce vasodilatation and/or hypotension in several experimental models, probably by a blockade of calcium currents. However, very little is known about the potential cardiovascular effects of androgens. We have previously shown that 5 beta-reduced androgens are more potent vasorelaxants than their precursors (delta 4-3 keto), 5-reduced progestins and 17beta-estradiol. The present study set out to investigate if this vasorelaxant effect of 5-reduced androgens is operative in vivo in the analysis of the potential vasodepressor effect of these compounds in vagosympathectomized, pithed rats. After increasing diastolic blood pressure (DBP) by a continuous infusion of norepinephrine (0.059 micromol x kg(-1)min(-1)), i.v. bolus injections of 3 alpha-hydroxy-5 beta-androstan-17-one (etiocholanolone), 5 beta-dihydrotestosterone (5 beta-DHT), and its isomer 5 alpha-dihydrotestosterone (5 alpha-DHT) (5-25 micromol x kg(-1) each) produced, separately, dose-dependent vasodepressor responses. These responses were biphasic: an immediate fall in DBP (reaching the nadir within 1.7 min) was followed by a further slow decrease that reached a maximum between 80 and 100 min after steroid administration. The order of potency of androgens in decreasing DBP was: 5 beta-DHT>5 alpha-DHT=etiocholanolone for the short-lasting response and 5 alpha-DHT>5 beta-DHT>or=etiocholanolone for the longer lasting response. Importantly, the same doses of these compounds produced no significant changes in heart rate. Moreover, 5 beta-DHT significantly antagonized the vasopressor responses to methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluromethylphenyl)-pyridine-5-carboxylate (Bay K 8644) with a blocking profile similar to that of nifedipine (NIF). This finding suggests that a blockade of voltage-operated calcium channels may be involved in androgen-induced hypotension.

Differential effects of progesterone and 17beta-estradiol on the Ca(2+) entry induced by thapsigargin and endothelin-1 in in situ endothelial cells

The effects of progesterone and 17beta-estradiol on Ca(2+) signaling in in situ endothelial cells were investigated using front-surface fluorometry of fura-2-loaded strips of porcine aortic valve. Progesterone inhibited the thapsigargin-induced sustained [Ca(2+)](i) elevation (IC(50)=33.9 microM, n=4), while 17beta-estradiol added a transient [Ca(2+)](i) elevation. Progesterone and 17beta-estradiol had no significant effect on the thapsigargin-induced [Ca(2+)](i) elevations in the absence of extracellular Ca(2+). A Mn(2+)-induced decline of fluorescent intensity at 360 nm excitation was accelerated by thapsigargin. This acceleration was completely reversed by progesterone, but not by 17beta-estradiol. Progesterone inhibited, and 17beta-estradiol enhanced the endothelin-1 (ET-1)-induced [Ca(2+)](i) elevation, while both had no effect on the ET-1-induced Ca(2+) release observed in the absence of extracellular Ca(2+) or in the pertussis toxin-treated strips. Progesterone and 17beta-estradiol thus had different effects on Ca(2+) signaling, especially on Ca(2+) influx, in endothelial cells.

Mechanism of mifepristone-induced spasmolytic effect on isolated rat uterus

Mifepristone, a synthetic 19-norsteroid, relaxed the KCl-induced tonic contraction in isolated rat uterus in a concentration-dependent way and CaCl2 (0.1 to 10 mM) counteracted it. This effect was similar to other steroids although the mechanisms involved are unclear. Before adding the contracturant, tissue was incubated with actinomycin D (10 microM), cycloheximide (300 microM), TPCK (3 and 10 microM), Rp-cAMPS (30 microM), DDA (100 microM) and H-7 (1 microM). None of these modified the relaxing effect of mifepristone. Incubation with drugs that interfere with cGMP such as a nucleotide analogue DDG (100 microM), a soluble guanylyl cyclase inhibitor ODQ (1 microM) and an inhibitor of protein kinase G 8pCPTcGMPS (1 microM) significantly modified the effect of mifepristone, increasing its IC50.

Possible role of Ca2+ channels in the vasodilating effect of 5beta-dihydrotestosterone in rat aorta

It has previously been shown that the androgen, 5beta-dihydrotestosterone (17beta-hydroxy-5beta-androstan-3-one, 5beta-DHT), is able to produce an endothelium-independent vasodilating effect in rat aorta. The present study analyzed the mechanisms underlying the above vasodilator effect of 5beta-dihydrotestosterone, with particular emphasis on verifying a possible interaction with GABA(A) receptors, beta-adrenoceptors and Ca2+ channels. Rat aortic rings without endothelium were isometrically recorded. 5Beta-dihydrotestosterone produced a concentration-dependent relaxation on the contractions induced by noradrenaline (NA; 0.3 microM) or K+ (KCl; 60 mM), with the latter being more sensitive to 5beta-dihydrotestosterone-induced relaxation than the former; the concentration-response curves showed that 5beta-dihydrotestosterone is significantly more potent than 17beta-estradiol(1,3,5(10)-estratrien-3,17beta-diol) to induce vasodilatation. The vasodilating effect of 5beta-dihydrotestosterone on noradrenaline-induced contraction was resistant to blockade by the GABA(A) receptor antagonists, picrotoxin or bicuculline, and the beta-adrenoceptor antagonist, propranolol, a finding that excludes an interaction of the steroid with GABA(A) receptors and beta-adrenoceptors. Interestingly, the contractions evoked by calcium in depolarized tissues were substantially inhibited by 5beta-dihydrotestosterone, implying that this steroid could be an endogenous calcium channel blocker; consistent with this finding, 5beta-dihydrotestosterone was able to relax tissues precontracted with the calcium channel opener, Bay K 8644. Moreover, although the rings precontracted with noradrenaline and potassium were almost equipotently relaxed by 5beta-dihydrotestosterone. Nifedipine was more potent than 5beta-dihydrotestosterone to block the potassium-induced contraction, but the steroid was more effective than nifedipine to prevent noradrenaline-induced contraction. The above results suggest that 5beta-dihydrotestosterone causes relaxation of rat aorta by acting directly on the membrane of smooth muscle cells; this non-genomic action may be explained in terms of a blockade of voltage- and receptor-dependent calcium channels, a mechanism that restricts the availability of extracellular calcium in the contractile machinery.

Oral versus intramuscular progesterone for in vitro fertilization: a prospective randomized study

OBJECTIVE

To evaluate the efficacy of oral micronized progesterone compared with IM progesterone in oil for luteal support in patients undergoing IVF who are treated with a GnRH agonist.

DESIGN

Randomized prospective clinical trial.

SETTING

University-based IVF center.

PATIENT(S)

Women <40 years of age who were undergoing IVF with luteal GnRH pituitary down-regulation.

INTERVENTION(S)

Patients were randomized to receive either oral micronized progesterone (200 mg three times daily) or IM progesterone (50 mg daily).

MAIN OUTCOME MEASURE(S)

Progesterone levels at standardized days 21 and 28, and pregnancy and embryo implantation rates.

RESULT(S)

Day 21 progesterone levels were 77.6+/-13.2 ng/mL in the IM group and 81.5+/-16.2 ng/mL in the oral group. Day 28 progesterone levels were 76.3+/-15.0 ng/mL in the IM group and 53.6+/-10.1 ng/mL in the oral group. The clinical pregnancy rates were 57.9% and 45.8% for the IM and oral groups, respectively. The implantation rate per embryo was significantly higher in the IM group (40.9%) than in the oral group (18.1%).

CONCLUSION(S)

When used according to our protocols, oral progesterone and IM progesterone result in comparable levels of circulating progesterone. However, oral progesterone results in a reduced implantation rate per embryo.

Inhibitory effect of sex steroids on guinea-pig airway smooth muscle contractions

We assessed the possible inhibition of airway smooth muscle contraction by progesterone and pregnanolones (5 alpha and 5 beta-reduced). Progesterone and 5 beta-pregnanolone prevented histamine- or carbachol-induced contraction in isolated guinea-pig trachea and potency was related to their respective chemical structure; progesterone was the most potent inhibitor in a concentration-dependent manner. The steroids also exhibited calcium antagonist activities in this tissue as assessed by their action on calcium entry in depolarized preparations; this event involved the immediate blockade of the extracellular calcium influx in the muscle cell membrane, indicating a nongenomic action. Classical GABAA antagonists did not block the progesterone response, implying no involvement of the GABAA-receptor complex. Our results suggest a bronchodilating effect induced by sex steroids, and probably by other related compounds, before the genomic mechanisms take place. This nongenomic action of steroids could have potential therapeutic usefulness in the treatment of asthma.