Differential effect of calcium and Bay K 8644 on the inhibitory action of estrogens in the rat uterus

Mifepristone is a Vasodilator Due to the Inhibition of Smooth Muscle Cells L-Type Ca2+ Channels

Derived from the estrane progestins, mifepristone was the first synthetic steroid of this class employed as abortifacient in the first months of pregnancy. Mifepristone reduces high potassium-induced contraction and prevents calcium-induced contraction. At the vascular level, mifepristone induces direct relaxation in rat and human arteries, and this effect seems to be endothelium- and NO independent, suggesting that the vascular smooth muscle is its target. Moreover, mifepristone's effect could involve the modulation of different calcium channels. The aim of the present study is to analyze the involvement of calcium channels in the relaxation induced by mifepristone on vascular smooth muscle cells (VSMCs). Planar cell surface area (PCSA) technique was used to analyze the effect of mifepristone on the VSMC contractility, and the whole cell configuration of patch-clamp technique to measure the activity of L-type Ca(2+) channels (LTCC) in A7r5 cells. Regarding the PCSA technique, mifepristone induced relaxation of the VSMC previously contracted by different agents. Also, a rapid inhibitory effect on basal and BAY K8644-stimulated calcium current was observed, which indicates that this drug has the ability to block LTCC. These results suggest that mifepristone induces relaxation on the VSMCs due to the inhibition of the calcium channels.

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.

Involvement of cAMP and beta-adrenoceptors in the relaxing effect elicited by flavonoids on rat uterine smooth muscle

1. The effect of the flavonoids genistein (3-100 microM), kaempferol (3-60 microM) and quercetin (1-100 microM) on KCl (60 mM)-induced tonic contraction in rat smooth muscle was assayed. In the same way, the modification of these effects in the presence of an inhibitor of protein kinase (PKA) (Rp-cAMPS), an inhibitor of phosphodiesterase (papaverine) and beta-adrenoreceptor blocking agents (propranolol and atenolol) was studied. 2. The flavonoids totally relaxed the KCl-induced tonic contraction (IC50: genistein 20.2 +/- 2.0 microM, n = 11; kaempferol 10.1 +/- 1.6 microM, n = 8; quercetin 13.2 +/- 1.2 microM, n = 8). 3. The incubation with Rp-cAMPS (10 and 100 microM) 30 min prior to KCl shifted the dose-response curve of the flavonoids to the right, increasing their IC50 up to 27.8 +/- 3.8 and 31.9 +/- 7.3 microM, respectively, for genistein; 24.7 +/- 0.2 and 19.6 +/- 4.9 microM, respectively, for kaempferol; 18.8 +/- 2.2 and 18.4 +/- 1.5 microM, respectively, for quercetin. 4. Papaverine (3-100 microM) also relaxed the contraction induced by KCl and this effect was significantly displaced to the right with Rp-cAMPS (10 microM) (IC50 12.1 +/- 2.2 vs. 16.5 +/- 3.1 microM). Papaverine (3 microM) added to the organ bath 15 min before the contractile agent increased the relaxing effect of the flavonoids and significantly decreased their IC50 (genistein 20.2 +/- 2.0 vs. 9.8 +/- 1.4 microM; kaempferol 10.1 +/- 1.6 vs. 6.6 +/- 0.7 microM; quercetin 13.2 +/- 1.2 vs. 7.8 +/- 1.4 microM). 5. The incubation with atenolol (10 microM) did not alter the relaxing effect of the flavonoids. In the same experimental conditions, propranolol (10 microM) did not modify the effect of genistein and kaempferol, but shifted the response curve of quercetin significantly to the right (13.2 +/- 1.2 vs. 17.7 +/- 3.4 microM). 6. The results suggest that genistein, kaempferol and quercetin produced the relaxation of uterine smooth muscle by increasing intracellular cAMP. Beta-adrenoceptors could also be involved in the effect of quercetin.

Lindane-induced inhibition of spontaneous contractions of pregnant rat uterus

Hexachlorocyclohexanes (HCHs) are prevalent insecticides. Lindane (gamma-HCH) inhibits uterine gap junctions but beta-HCH does not. Because gap junctions promote coordination of oscillatory uterine contractions, we hypothesized that lindane, but not beta-HCH, would inhibit uterine contractions. Uterine strips from midgestation rats were suspended in standard muscle baths and exposed to HCHs in a cumulative manner. Lindane induced concentration-dependent decreases in contraction force (ED50 of 9.2 microM) and complete uterine quiescence at 30 microM. In contrast, beta-HCH had no effect on contraction force, but 20 to 200 microM beta-HCH increased contraction frequency in a concentration-dependent manner. Isomer-specific differences in uterine responses were observed at similar HCH isomer tissue concentrations. Additionally, the phospholipase A2 inhibitor and antioxidant quinacrine increased the ED50 for contraction force inhibition to 84.5 microM lindane. Lindane also increased cAMP concentrations. Lindane and beta-HCH have distinctly different actions in the uterus. Lindane's inhibitory action may involve cAMP, arachidonic acid, or oxidative stress.

Positive inotropism induced by androgens in isolated left atrium of rat: evidence for a cAMP-dependent transcriptional mechanism

Steroid hormones exert their biological actions via intracellular receptors modulation of transcription. In addition, a number of molecular interactions, and the existence of membrane receptors in several tissues, support the hypothesis of nongenomic action of steroids. The androgens, 5alpha- and 5beta-dihydrotestosterone (0.1 to 100 microM), induce a rapid positive inotropism in the isolated left atrium of male Wistar rats whose time course of response might suggest that it is a non-genomic effect. However, the fact that the facilitation of contractility was inhibited by actinomycin D (5 microg/ml) and cycloheximide (10 microg/ml) indicates that a transcriptional component might play a role. The existence of a rapid functional genomic role would be somewhat surprising. However, rapid transcriptional mechanisms were also observed in certain cAMP-dependent responses. In the left atrium of rat, Rp-cAMPS (10 microM), a cAMP-dependent protein kinase inhibitor, antagonized 5alpha- but not 5beta-dihydrotestosterone-induced positive inotropism. The inhibition by Rp-cAMPS of isoproterenol- and forskolin-induced positive inotropism, and the fact that these cAMP-dependent effects were also inhibited by actinomycin D and cycloheximide, suggest that a cAMP-dependent transcriptional component may be partly involved in the positive inotropism induced by 5alpha-dihydrotestosterone. In addition, 5alpha-dihydrotestosterone might increase the basal adenylyl cyclase activity by acting on unoccupied beta-adrenoceptor-G-protein-adenylyl cyclase complexes, since the elicited inotropism was inhibited by a beta-blocker, atenolol (1 microM), a G-protein inhibitor, pertussis toxin (2 microg/ml, 3 h), and an adenylyl cyclase inhibitor, dideoxy-adenosine (10 microM).

Acute inhibition of spontaneous uterine contractions by an estrogenic polychlorinated biphenyl is associated with disruption of gap junctional communication

An estrogenic polychlorinated biphenyl, 4-hydroxy-2',4', 6'-trichlorobiphenyl (4-OH-TCB), inhibits oscillatory uterine contractions immediately. Because increased gap junction formation is associated with the development of synchronized uterine contractions at term, we examined whether the inhibitory effect of 4-OH-TCB on spontaneous oscillatory contractions was due to the disruption of gap junctional communication. The effect of 4-OH-TCB on gap junctional communication was determined by intercellular Lucifer yellow dye transfer in primary cultures of myometrial myocytes isolated from midgestation rats. Intercellular dye transfer was inhibited by 4-OH-TCB or 17beta-estradiol in a concentration-dependent manner. The inhibitory effect of 4-OH-TCB on intercellular dye transfer was reversed by tetraethylammonium (TEA). To examine effects on uterine contraction, longitudinal uterine strips were excised from midgestation rats and placed in muscle baths for isometric force measurement. Spontaneous uterine oscillation was suppressed by 4-OH-TCB or 17beta-estradiol. The inhibitory effects of 4-OH-TCB and 17beta-estradiol on spontaneous oscillations were counteracted by TEA but were not affected by a calcium ionophore (A23187) or a calcium-dependent potassium channel blocker (apamin). These results suggest that the acute inhibition of spontaneous oscillatory contractions by an estrogenic polychlorinated biphenyl may result from the disruption of intercellular communication.

Partial contribution of polyamines to the relaxant effect of 17 alpha-estradiol in rat uterine smooth muscle

1. The effects of 17 alpha-estradiol on KCl (60 mM), CaCl2 (30 microM to 10 mM) and vanadate (0.3 mM)-induced contractions in rat uterus have been assayed. Furthermore, the effect of 17 alpha-estradiol on calmodulin-stimulated cAMP-phosphodiesterase activity was also studied. 2. 17 alpha-estradiol relaxed the tonic contraction induced by KCl (60 mM) in a concentration-dependent way (IC50, 8.3 +/- 0.7 microM), and CaCl2 (0.1 to 10 mM) counteracted it. 3. CaCl2 (30 microM to 10 mM) produced concentration-dependent contraction of rat uterus in a calcium-free medium supplemented with 60 mM of KCl (EC50: 0.2 +/- 0.01 mM). 17 alpha-estradiol (8 microM) antagonized the contraction induced by CaCl2, increasing the EC50 value up to 0.7 +/- 0.1 mM (P < 0.01). 4. 17 alpha-estradiol (0.1 to 1 mM) relaxed in a concentration-dependent way the tonic contraction induced by vanadate in rat uterus incubated in a calcium-free medium and EDTA supplemented. The maximal relaxation achieved with 1 mM of 17 alpha-estradiol was 52.2 +/- 2.8%. 5. 17 alpha-estradiol (1 to 100 microM) did not modify the basal activity of cAMP-phosphodiesterase but inhibited the calcium plus calmodulin stimulated activity. The maximal inhibition achieved was 43 +/- 5.4%. 6. The relaxing effect of 17 alpha-estradiol on KCl (60 mM)-induced tonic contraction was unmodified with the antioestrogen tamoxifen (0.1 and 1 microM), the inhibitor of tirosine kinase (genistein, 10 microM) and the cAMP-dependent protein kinase inhibitor (Rp-adenosine 3',5'-monophosphothioate, triethylamine salt, 100 microM). However, the effect was antagonized with the inhibitor of transcription (actinomycin D, 5 micrograms/ml,), the inhibitor of protein synthesis (cycloheximide, 10 and 100 micrograms/ml), and the inhibitor of ornithine decarboxilase (alpha-difluoromethyl-ornithine, 10 mM). 7. Our results suggest that polyamines contribute to the relaxant effect of 17 alpha-estradiol in rat uterine smooth muscle behaving, presumably, as mediators of the transcriptional component involved in the effect of 17 alpha-estradiol.

Depolarization-dependent effect of flavonoids in rat uterine smooth muscle contraction elicited by CaCl2

1. The effects of the flavonoids genistein (3-60 microM), kaempferol (3-60 microM) and quercetin (1-100 microM) on KCl (60 mM)-induced tonic contraction in rat uterus and their modifications with the inhibitor of cAMP-dependent protein kinases (TPCK, 3 microM), the inhibitor of ornithine decarboxylase [alpha-difluoromethyl ornithine (DFMO), 10 mM] and the polyamine spermine (1 mM) have been assayed. The effects of the three flavonoids were also studied on the contraction elicited by CaCl2 (30 microM to 10 mM) on rat uterus incubated in medium lacking calcium and supplemented with 33, 60 or 90 mM of KCl. For comparison, the effects of the calcium channel blockers nifedipine and verapamil and the activator of adenylyl cyclase forskolin were assayed on contractions induced by KCl and CaCl2. 2. Genistein (IC50: 20.2 +/- 1.0 microM, n = 11), kaempferol (IC50: 10.1 +/- 0.8 microM, n = 8) and quercetin (IC50: 13.2 +/- 0.5 microM, n = 8) relaxed the tonic contraction induced by KCl (60 mM) in a concentration-dependent way. Verapamil (IC50: 70.1 +/- 5.8 nM, n = 7), nifedipine (IC50: 8.4 +/- 0.7 nM, n = 6) and forskolin (IC50: 0.62 +/- 0.08 microM, n = 14) also relaxed the KCl-induced contraction. TPCK (3 microM) significantly antagonized the effect of quercetin, kaempferol and forskolin (P < 0.01) but did not modify the effect of genistein. 3. Spermine (1 mM) increased the effects of genistein and verapamil and antagonized the effect of quercetin but did not modify those of kaempferol and forskolin. DFMO (10 mM) did not modify the effect of quercetin but increased that of genistein and antagonized those of kaempferol and forskolin. The addition of spermine (1 mM) plus DFMO (10 mM) antagonized the effect of quercetin. Spermine counteracted the effect of DFMO on forskolin but not on genistein. 4. KCl (33, 60 or 90 mM) did not produce contraction in calcium-free solution, but CaCl2 (30 microM to 10 mM) induced concentration-dependent contraction after depolarizing with KCl. The EC50 values for CaCl2 were: 0.74 +/- 0.08 (n = 12), 0.34 +/- 0.03 (n = 14) and 0.48 +/- 0.02 (n = 12) mM in a medium with 33, 60 or 90 mM of KCl, respectively. 5. Genistein (20 microM), kaempferol (10 microM), quercetin (15 microM), verapamil (70 nM), nifedipine (10 nM) and forskolin (0.5 microM) inhibited the concentration-response curve to CaCl2 in medium supplemented with 33, 60 or 90 mM of KCl. The effect of kaempferol was independent of the concentration of KCl in the incubation medium. However, the inhibitory effect of genistein on CaCl2-induced contraction was inversely related to the concentration of KCl in the medium. On the contrary, the effect of quercetin was directly related to the concentration of KCl in the medium. 6. The antagonism of verapamil, nifedipine and forskolin on CaCl2-induced contraction seems to be related to the degree of depolarization because increasing the KCl in the medium counteracted their effects. 7. Our results suggest that (1) cAMP contributes to the relaxant effects of quercetin and kaempferol on KCl (60 mM)-induced tonic contraction; (2) polyamines are involved in the relaxant effects of forskolin and kaempferol on KCl-induced tonic contraction but not on CaCl2-induced contraction in the depolarized uterus, and (3) the flavonoids assayed also possess a calcium antagonist action but show a different behavior toward the calcium channel blockers and the cAMP enhancer forskolin.

Transcriptional mechanisms involved in the relaxant effect of zeranol on isolated rat uterus

1. The effect of zeranol (3-100 microM) on rat uterus contractions induced by KCl (60 mM) and CaCl2 (30 microM-10 mM) has been assayed. 2. Zeranol relaxed the tonic contraction induced by KCl in a concentration-dependent manner (IC50 15.62 +/- 2.66 microM). CaCl2 (0.1-10 mM) did not counteract the relaxing effect of zeranol. 3. CaCl2 (30 microM -10 mM) produced a concentration-dependent contraction of rauuterus in medium lacking calcium plus KCl (60 mM) (EC50 0.34 +/- 0.03 mM). Zeranol (8 microM) displaced the CaCl2 concentration-response curve to the right and increased the EC50 to 1.27 +/- 0.57 mM (P < 0.05) without modifying the Emax. 4. The antiestrogen tamoxifen (1 microM) and the inhibitor of cAMP-dependent protein kinase TPCK (3 microM) did not modify the effect of zeranol. However, the inhibitors of transcription (actinomycin D, 4 microM), protein synthesis (cycloheximide, 100 microM), and ornithine-decarboxilase (alpha-difluoromethyl-ornithine, 10 mM)) antagonized the effect of zeranol, increasing the IC50 to 50.2 +/- 6.2 microM, 122 +/- 6.9 microM, and 23.51 +/- 1.14 microM, respectively. 5. Our results suggest that the relaxing effect of zeranol on rat uterus smooth muscle is produced by mechanisms unrelated to cAMP and estrogen receptors, but involves transcriptional effects and polyamine synthesis.

Calcium and depolarization-dependent effect of pregnenolone derivatives on uterine smooth muscle

1. The effects of several gestagens (pregnenolone [1 to 30 microM], 20 alpha-hydroxy-pregnenolone [1 to 30 microM], and 20 beta-hydroxypregnenolone [1 to 30 micro M]) on rat uterine contraction induced by KCl (60 mM) and CaCl2 (30 microM to 6 mM) have been assayed. 2. The three drugs relaxed the tonic contraction induced by KCl in a concentration-dependent way. The respective EC50 values were: 27.6 +/- 1.58 microM (pregnenolone), 4.1 +/- 0.12 microM (20 alpha-hydroxy-pregnenolone), and 11.2 +/- 1.04 microM (20 beta-hydroxypregnenolone). CaCl2 (1 to 10 mM) totally counteracted the relaxing effect of pregnenolone but only partially compared to that of 20 alpha- or 20 beta-hydroxy-pregnenolone. 3. CaCl2 (30 microM to 6 mM) produced concentration-dependent contraction of rat uterus in medium lacking calcium plus 30, 60, or 90 mM of KCl. The EC50 values of CaCl2 were: 0.38 +/- 0.072, 0.183 +/- 0.015, and 0.183 +/- 0.015 mM in a medium with 30, 60, or 90 mM of KCl, respectively. 4. Pregnenolone (10 microM) did not significantly modify the EC50 of CaCl2 in a medium with 30, 60, or 90 mM of KCl. However, 20 beta-hydroxypregnenolone (10 microM) antagonized, in a noncompetitive manner, the concentration-response curve to CaCl2. 5. 20 alpha-Hydroxypregnenolone (4 microM) antagonized the concentration-response curve to CaCl2 in a competitive manner. This antagonism was directly related to the concentration of KCl in the medium. 6. Our results suggest a different calcium antagonist effect of the three gestagens assayed.

17beta-estradiol in vitro affects Na-dependent and depolarization-induced Ca2+ transport in rat brain synaptosomes

Effects of 17beta-estradiol (E2) in vitro on Na-dependent Ca2+ efflux from, and depolarization-induced Ca2+ uptake into, the nerve cell were studied with the use of synaptosomes isolated from the brain stem, mesencephalic reticular formation (MRF), caudate nucleus and the hippocampus of long-term ovariectomized adult female rats. It was found that E2 (1) at a concentration of 10 nM or lower, stimulates Na-dependent Ca2+ efflux in the caudate nucleus and hippocampus, and does not affect the efflux in MRF and brain stem; (2) at concentrations above 10 nM has no effect on the Ca2+ efflux in any of the four structures investigated; and (3) produces a biphasic effect on the depolarization-induced Ca2+ uptake, increasing it in all structures except MRF at 10 nM concentration, and decreasing it at concentrations higher than 10 nM, irrespective of the structure investigated. These results suggest that E2, acting at extranuclear sites, modulates synaptic transmission via alterations of Ca2+ transport mechanisms in nerve endings.

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

The mechanism of action on the uterine-relaxant effect of sex steroids has been suggested to involve an interaction with gamma-amino butyric acid (GABA) receptors. However, other lines of evidence do not seem to support this suggestion. In view of this controversy, this study was designed to investigate the potential relaxant effect of GABA, muscimol (a GABA(A) receptor agonist), testosterone, progesterone and their 5-reduced metabolites in rat uterus at different endocrine stages (pregnant, nonpregnant and estrogenized), with particular emphasis on verifying if the relaxant effect of steroids involves an interaction with GABA(A) receptors. Contractions from uterine rings were recorded by isometric method, the sequential addition of either GABA (at different concentrations) on the spontaneous and KCl-induced contraction or muscimol (also at different concentrations) on the contraction induced by KCl was devoid of any significant effect. In contrast, the sequential addition of progesterone relaxed the tonic KCl-induced contraction in a concentration-dependent manner. This effect of progesterone was mimicked by its 5-reduced metabolites. The 5(beta)-configured isomers were more potent than progesterone and the 5(alpha)-configured ones. Interestingly, the relaxation produced by the above steroids was not blocked by the GABA(A) receptor antagonists, picrotoxin or bicuculline, but was reversed by calcium. Taken together, the above findings suggest that the relaxant action of the sex steroids analyzed in this study is not mediated by an interaction with GABA(A) receptors, instead a blockade of calcium influx appears to be responsible.

Congener-specific effects of PCBs on contractions of pregnant rat uteri

Both increased and decreased gestation lengths have been reported following exposures to polychlorinated biphenyl (PCB) mixtures and congeners. Because oscillatory uterine contractions are essential for parturition, we hypothesized that the disparate findings on gestation length may be the result of distinct PCB congener-specific actions on oscillatory uterine contractions. This study examined the acute effects of PCB congeners on isometric contractions of isolated pregnant uteri and the structure-activity relationship for individual congeners. After cumulative exposure to individual PCB congeners (0.5 microM to 150 microM), oscillatory contractions were: 1) not altered by 2,4,5,2',4',5'-hexachlorobiphenyl, 3,4,5,3',4'-pentachlorobiphenyl, or 3,4,3',4'-tetrachlorobiphenyl; 2) significantly inhibited by 4-hydroxy-2',4',6'-trichlorobiphenyl; and 3) markedly increased by 2,4,6-trichlorobiphenyl and 2,4,2',4'-tetrachlorobiphenyl, when compared to solvent controls. The uteri were more sensitive to PCB congeners with ortho-substituted light chlorination than those highly chlorinated, or those interacting with the Ah-receptor.

Mechanisms involved in the relaxant effect of estrogens on rat aorta strips

The effects of estrogens 17beta-estradiol (17beta-E2), 17alpha-estradiol (17alpha-E2) and diethylstilbestrol (DES) on CaCl2 (3mM)-induced contractions on rat aorta strips have been assayed. Both 17alpha-E2 and DES, but not the 17beta-E2 relaxed and inhibited the contraction induced by CaCl2. The antiestrogen tamoxifen (0.1, 1 and 3 microM) antagonizes, in a concentration-dependent way, the relaxant effect of 17alpha-E2 but the relaxation induced by DES is only significantly antagonized with 3 microM of tamoxifen. Cycloheximide (0.1 and 0.3 mM) does not modify the 17alpha-E2 or DES effects. However, the inhibitors of cAMP-dependent protein kinase TPCK (1 microM) and Rp-cAMPS (10 microM) inhibit the relaxation induced by 17alpha-E2 and DES. The elimination of endothelium by rubbing, significantly inhibits the effect of DES but does not modify the effect of 17alpha-E2. Our results suggest that estrogen-induced relaxation is a non-genomic effect possibly or presumably produced by activation of estrogenic receptors and mediated by cAMP. The DES-effect is partially endothelium-dependent but the effect of 17alpha-E2 is independent of endothelium.

Influence of hormonal status in relaxant effect of diethylstilbestrol and nifedipine on isolated rat uterus contraction

1. The effects of diethylstilbestrol (DES, 10(-7)-10(-5) M) and nifedipine (10(-10)-10(-7) M) on KCl (60 mM)-induced tonic contraction in the uterus of ovariectomized and 17 beta-estradiol (0.1 mg/kg/day, s.c.)-, 17 alpha-estradiol (0.1 mg/kg/day, s.c.)-, or progesterone (2 mg/kg/day, s.c.)-treated rats have been assayed. 2. The dose-dependent relaxation produced by nifedipine in ovariectomized rats (EC50 = 5.59 +/- 1.25 x 10(-9) M) is potentiated in uterus of rats treated with 17 beta-estradiol and progesterone (EC50 = 0.59 +/- 0.1 and 0.49 +/- 0.1 x 10(-9) M, respectively) but not in the 17 alpha-estradiol-treated rats (3.01 +/- 0.6 x 10(-9) M). 3. The relaxation produced by DES on ovariectomized rats (EC50 = 0.84 +/- 0.14 x 10(-6) M) is reduced when the rats are treated with 17 beta-estradiol (EC50 = 2.22 +/- 0.2 x 10(-6)M) or progesterone (EC50 = 1.24 +/- 0.08 x 10(-6) M), but unmodified by 17 alpha-estradiol (EC50 = 0.58 +/- 0.01 x 10(-6) M). 4. The nifedipine-induced relaxation is reversed with Bay K 8644 (10(-10)-10(-6) M) in all experimental conditions. However, Bay K 8644 counteracted the relaxation of DES at 45.7% on ovariectomized rats but this was lower than 30% in the other groups. 5. Our results suggest that in ovariectomized rats the effects of both nifedipine and DES are similar, but 17 beta-estradiol and progesterone produce a contrary effect on the relaxation induced by nifedipine and DES (by increasing the nifedipine and decreasing the DES effects).(ABSTRACT TRUNCATED AT 250 WORDS)

Non-genomic effects of catecholestrogens in the in vitro rat uterine contraction

1. The effects of catecholestrogens 2-hydroxyestradiol (2-OH E2, 0.6-30 microM), 4-hydroxyestradiol (4-OH E2, 1-30 microM) and 2-methoxyestradiol (2-MeO E2, 0.6-30 microM) on rat uterine contraction induced by KCl (60 mM), have been assayed. 2. All drugs assayed relaxed the tonic-contraction induced by KCl in a concentration-dependent way. The EC50s were: 4.4 +/- 0.5, 4.2 +/- 0.3 and 8.5 +/- 0.7 microM for 2-MeO E2, 2-OH E2 and 4-OH E2, respectively. This relaxing effect was counteracted by CaCl2 (1-10 mM) but not by the calcium channel agonist Bay k 8644 (1 nM-1 microM). 3. The effect of 2-MeO E2 is not modified by propranolol (1 microM), cycloheximide (35 microM), actinomycin D (4 microM), alpha-difluoromethyl-ornithine (10 mM) or genistein (10 microM). Nor did cycloheximide (35 microM) or actinomycin D (4 microM) modify the relaxing effect of 2-OH E2 and 4-OH E2. Propranolol (1 microM) significantly increased the effect of 4-OH E2 but not the effect of 2-OH E2. 4. Our results suggest that the relaxing effect of catecholestrogens in the rat uterus is a non-genomic effect and could be related to inhibition of extracellular calcium entry.

Progesterone and pregnanolone derivatives relaxing effect on smooth muscle

1. The effect of gestagens, 5 alpha-hydroxyprogesterone (10(-6) x 10(-5) M), 5 beta-hydroxyprogesterone (10(-6)-3 x 10(-5) M), progesterone (6 x 10(-6)-10(-4) M), pregnanolone (10(-6)-10(-5) M), allopregnanolone (10(-6)-10(-4) M) and epipregnanolone (10(-6)-6 x 10(-5) M) on rat uterine contractions induced by KCl (60 mM), has been assayed. 2. All drugs assayed relaxed the tonic-contraction induced by KCl in a concentration-dependent way. The respectives IC50 were 31.3 +/- 4.1 x 10(-6) M (progesterone), 8.9 +/- 0.8 x 10(-6) M (5 alpha-hydroxyprogesterone), 3.8 +/- 0.3 x 10(-6) M (5 beta-hydroxyprogesterone), 3.1 +/- 0.1 x 10(-6) M (pregnanolone), 21.2 +/- 3.1 x 10(-6) M (allopregnanolone) and 6.3 +/- 1.3 x 10(-6) M (epipregnanolone). This relaxing effect was partially or totally counteracted by CaCl2 (1-10 mM) 3. Cycloheximide (10 micrograms/ml) significantly shifted to the right the effect of allopregnanolone but not the effect of the other drugs. Actinomycin D (5 micrograms/ml) did not modify the effect of allopregnanolone. 4. Our results suggest that the relaxing effect of gestagens in the rat uterus could be related to inhibition on calcium influx and mainly occur through non-genomic mechanisms.

Genomic and non-genomic effects of steroidal drugs on smooth muscle contraction in vitro

The effect of steroidal drugs on KCl (60 mM)-induced tonic contraction in in vitro rat uterus has been assayed. Ouabain had no effect and aldosterone only relaxed the KCl contraction up to 27 +/- 7.3%. However, estradiol, testosterone, progesterone, cortisol and alphaxalone relaxed the contraction in a dose-dependent way, and CaCl2 (0.1 to 6 mM) counteracted this effect. Cycloheximide (1 and 10 micrograms/ml) did not modify the effect of progesterone, testosterone or alphaxalone. Cycloheximide, but not actinomycin D (5 micrograms/ml), reduced the effect of cortisol. Both cycloheximide and actinomycin D shifted righward the relaxing effect of estradiol. This suggests that the steroidal relaxing effect in smooth muscle is preferably non-genomic and at plasma membrane level. However, cortisol and estradiol also act at intracellular levels and induce transcriptional (estradiol) or non-transcriptional (cortisol) effects.

Estrogen and antiestrogen non-genomic effect in rat uterus contraction in calcium-free solution

1. The effects of estrogens estradiol (E2, 10(-6)-10(-4) M) and diethylstilbestrol (DES, 10(-6)-10(-4) M) and the antiestrogens nafoxidine (N, 10(-6)-10(-4) M), tamoxifen (T, 10(-6)-6 x 10(-4) M), tamoxifen ethyl bromide (TEB, 10(-4) M) and ICI 164,384 (ICI, 10(-5) M) on tonic contractions induced by oxytocin (2 x 10(-8) M) or vanadate (3 x 10(-4) M) in rat uterus incubated in calcium-free EDTA treated solution have been assayed. 2. E2 and DES relaxed the tonic contraction induced by oxytocin in a dose dependent way (EC50: 1.11 +/- 0.01 x 10(-4) M and 1.5 +/- 0.07 x 10(-5) M). The vanadate-induced contraction only was relaxed with DES (57.62 +/- 2.38% at 10(-3) M). 3. The effect of DES on oxytocin contraction was unmodified by the protein synthesis inhibitor cycloheximide (10 micrograms/ml) and by the cyclooxygenase inhibitor indomethacin (3 x 10(-6) M), but enhanced by the intracellular calcium release inhibitor TMB-8 (10(-5) M). The antiestrogen tamoxifen (3 x 10(-5) M) promotes the relaxing effect of DES. 4. The antiestrogens N, and T, but not ICI, relaxed the oxytocin-induced contraction (EC50: 4.51 +/- 0.43 x 10(-5) M and 2.27 +/- 0.05 x 10(-4) M). TEB (10(-4) M) produces a relaxation of 74.5 +/- 2.11%. The vanadate contraction is also relaxed by T (EC50: 6.03 +/- 0.04 x 10(-4) M). 5. The effect of T on oxytocin contraction was unmodified with cycloheximide or TMB-8 but decreased with indomethacin.

Effects of androgens on isolated rat uterus

The 5 alpha- and 5 beta-dihydrotestosterone (DHT) androgens relax KCl-induced tonic contraction in rat uterus, in a dose-dependent way. The 5 alpha and 5 beta-DHT relaxing effect is counteracted by CaCl2 (0.1-10 mM). The 5 alpha-DHT, but not the 5 beta-DHT, effect was reduced by cycloheximide (10 micrograms/ml) and by actinomycin D (5 micrograms/ml). Flutamide at 10(-6) M shifted the effect of 5 alpha-DHT to the right. However, other doses of flutamide or cyproterone acetate did not modify the effect of both androgens. We suggest a non-genomic effect of 5 alpha-DHT and 5 beta-DHT in rat uterus contraction but that intracellular and genomic actions play a part in the relaxing effect of 5 alpha-DHT.

Effects of antiandrogens and progesterone on isolated rat uterus

1. The effect of progesterone (P, 6 x 10(-6)-6 x 10(-5) M) and the antiandrogens cyproterone acetate (CPA, 10(-7)-10(-5) M), flutamide (F, 10(-6)-6 x 10(-5) M) and spironolactone (S, 10(-6)-6 x 10(-5) M) on the KCl-induced tonic contraction of the isolated rat uterus have been assayed. 2. The antiandrogens relaxed, in a dose-dependent way, the KCl-induced contraction (EC50, 2.804 +/- 0.506 x 10(-6); 1.671 +/- 0.308 x 10(-5); and 3.042 +/- 0.14 x 10(-5) M, respectively for CPA, S and F). P also relaxed the KCl-induced contraction (EC50, 2.436 +/- 0.524 x 10(-5) M). 3. CaCl2 (0.1-10 mM) counteracted the relaxing effect of CPA, S, F, and P, respectively, up to 100, 80.63, 60.66 and 90.57%. 4. The 17-OH-progesterone derivative CPA, but not S or F, reduces at small doses (6 x 10(-8) M), but not at higher concentrations (6 x 10(-7)-6 x 10(-6) M), the relaxing effect of progesterone.