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

Non-dioxin-like polychlorinated biphenyl 19 has distinct effects on human Kv1.3 and Kv1.5 channels

Polychlorinated biphenyls (PCBs) are persistent and serious organic pollutants and can theoretically form 209 congeners. PCBs can be divided into two categories: dioxin-like (DL) and non-DL (NDL). NDL-PCBs, which lack aryl hydrocarbon receptor affinity, have been shown to perturb the functions of Jurkat T cells, cerebellar granule cells, and uterine cells. Kv1.3 and Kv1.5 channels are important in immune and heart functions, respectively. We investigated the acute effects of 2,2',6-trichlorinated biphenyl (PCB19), an NDL-PCB, on the currents of human Kv1.3 and Kv1.5 channels. PCB19 acutely blocked the Kv1.3 peak currents concentration-dependently with an IC₅₀ of ~2 μM, without changing the steady-state current. The PCB19-induced inhibition of the Kv1.3 peak current occurred rapidly and voltage-independently, and the effect was irreversible, excluding the possibility of genomic regulation. PCB19 increased the time constants of both activation and inactivation of Kv1.3 channels, resulting in the slowing down of both ultra-rapid activation and intrinsic inactivation. However, PCB19 failed to alter the steady-state curves of activation and inactivation. Regarding the Kv1.5 channel, PCB19 affected neither the peak current nor the steady-state current at the same concentrations tested in the Kv1.3 experiments, showing selective inhibition of PCB19 on the Kv1.3 than the Kv1.5. The presented data indicate that PCB19 could acutely affect the human Kv1.3 channel through a non-genomic mechanism, possibly causing toxic effects on various human physiological functions related to the Kv1.3 channel, such as immune and neural systems.

The effect of polychlorinated biphenyls (PCBs) on bovine oviductal contractions and LIF synthesis during estrous cycle, in vitro studies

Polychlorinated biphenyls (PCBs) are a group of synthetic xenobiotics that have been used in many industrial applications. Currently, PCBs are among the most prominent environmental contaminants. Previously we showed that PCBs impair secretion of prostaglandins (PGs) at the oviduct. PGs are involved in the regulation of oviductal contractions and the synthesis of leukemia inhibitory factors LIF. Since oviductal contractions are crucial for gamete and embryo transport, and LIF is essential for embryo implantation, the direct effect of PCBs on oviductal motor activity and LIF mRNA expression were investigated. Oviductal strips and cells were taken from cows during the estrous cycle and were treated with PCBs at concentrations close to their environmental ranges. All the studied PCBs decreased the force of the contractions of the longitudinal and circular muscles of the isthmus. Additionally, these PCBs decreased the amplitude of the longitudinal muscle of the oviduct. Moreover, PCB-30-OH and PCB-153 increased the mRNA expression of LIF. Since PCBs inhibit the motor function of the oviduct and stimulate the synthesis of LIF, it is possible that PCBs can slow gamete or embryo transport and increase the potential for pathological embryo implantation in the oviduct.

Inhibitory effect of Bisphenol A on in vitro feline uterine contractions

Bisphenol A (BPA) is an environmental pollutant used as a plasticizer in the manufacture of many plastic products, such as packaging, containers, and water and beverage bottles. There are deleterious effects of BPA on metabolic, endocrine, nervous, and reproductive systems. This is the first study in which there was investigation of the in vitro effect of BPA on the spontaneous contractions of the cat uterus. The tubal uterine segments (1 cm) collected from queens in estrus were suspended in an isolated organ bath. Following tissue stabilization, spontaneous contractions were recorded for 10 min to constitute the control group. The effects of the solvent (alcohol) and BPA at different concentrations (1, 10, and 100 μM) on uterine contractions were subsequently evaluated at 10 min intervals in terms of frequency and mean amplitude variables. The ethanol vehicle did not alter the uterine contractions compared to the control group. All concentrations of BPA used in the study resulted in a reduction (P < 0.05) in amplitude of uterine contractions in a dose-dependent manner, while only the largest dose of BPA decreased the frequency of contractions (P < 0.05). In reproductive physiology, regular uterine contractions facilitate successful fertilization, migration, implantation, and maintenance of pregnancy, as well as fetus expulsion. The results of this study indicate BPA has an inhibitory effect on spontaneous contractions of the cat uterus. It is proposed that this suppressive effect of BPA on uterine contractions might lead to queen infertility.

The inhibition of myometrial contractions by chlorinated herbicides (atrazine and linuron), and their disruptive effect on the secretory functions of uterine and ovarian cells in cow, in vitro

The effect of atrazine and linuron, the popular and widely used chlorinated herbicides, on both myometrial contractions and secretory functions of bovine uterus and ovaries in vitro, was investigated. The pesticides inhibited (P<0.05) the basal and oxytocin (OT)-stimulated myometrial strips contractions, as well as the effect of OT on secretion of prostaglandins (PGs: PGF2α and PGE2) from endometrium. But only linuron inhibits the effect of OT on myometrial contractions. Neither of herbicides affected PGs secretion from myometrium and PGF2α from endometrium. Only the lowest dose of both tested compounds decreased PGE2 secretion from endometrium. The pesticides increased (P<0.05) the OT secretion from granulosa. However, only linuron stimulated (P<0.05) the OT secretion from the luteal cells, and it increased (P<0.05) the expression of mRNA for the OT precursor. Both compounds stimulated (P<0.05) the secretion of testosterone and atrazine increased (P<0.05) also the secretion of estradiol from the granulosa cells. While atrazine and linuron reduced (P<0.05) the progesterone secretion from the luteal cells. The data show that atrazine and linuron altered the secretory functions of ovarian cells and inhibited the myometrial contractions in vitro.

Secretory function of ovarian cells and myometrial contractions in cow are affected by chlorinated insecticides (chlordane, heptachlor, mirex) in vitro

The aim of the study was to investigate the effect of chlordane, heptachlor and mirex, on hormonal regulation of the force of myometrial contractions. Myometrial, endometrial, granulosa and luteal cells as well as strips of myometrium from non-pregnant cows were incubated with three insecticides at environmentally relevant doses (0.1, 1 or 10ng/ml). None of the insecticides affected the viability of studied cells. Chlordane stimulated, while heptachlor and mirex inhibited, secretion of testosterone and estradiol from granulosa cells as well as secretion of progesterone from luteal cells, respectively. Secretion of oxytocin (OT) from granulosa cells was increased after incubation with all studied insecticides. Only mirex stimulated OT secretion from luteal cells, while heptachlor inhibited this effect. None of them affected synthesis of OT in luteal cells and prostaglandins (PGF2 and PGE2) secretion from uterine cells, except PGE2 secretion from endometrial cells was decreased when the cells were incubated with 0.1ng/ml of chlordane. Basal and OT-stimulated myometrial contractions were increased by mirex and decreased by heptachlor. The data show that the insecticides altered secretory function of ovarian cells. Heptachlor and mirex affected also myometrial contractions in vitro, but uterine secretion of prostaglandins were not involved in the mechanism of that adverse effect of insecticides. The data indicate on potential of these insecticides to disturb fertilisation, blastocyst implantation or even the length of gestation.

The adverse effects of aldrin and dieldrin on both myometrial contractions and the secretory functions of bovine ovaries and uterus in vitro

Aldrin and dieldrin are chloroorganic insecticides which are recognised as endocrine disruptors. The aim of the study was to investigate their effect on the secretory functions of the uterus and ovary and on myometrial contractions. Myometrial strips and uterine and ovarian cells from nonpregnant cows were incubated with the xenobiotics (0.1, 1 or 10 ng/ml) for 24 or 72 h. Next, their effect on viability of myometrial, endometrial, granulosa and luteal cells, myometrial strip contractions, the synthesis and secretion of prostaglandins (PGs: PGF2α and PGE2) from uterine cells, the secretion of oestradiol (E2), testosterone (T) and oxytocin (OT) from granulosa cells and the secretion of progesterone (P4) and OT from luteal cells were determined. Neither of the xenobiotics (10 ng/ml) affected (P>0.05) the viability of the ovarian and uterine cells, while both (0.1-10 ng/ml) decreased (P<0.05) the basal and OT-stimulated myometrial contractions. In spite of these effects, neither of the insecticides affected (P>0.05) the synthesis and the secretion of PGs from the myometrial cells. Although they also did not impair the secretion of the PGs from the endometrial cells, they abolished (P<0.05) the stimulatory effect of OT (P<0.05) on the secretion of the PGs and stimulated (P<0.05) the secretion of OT from the granulosa and luteal cells. Moreover, aldrin and dieldrin stimulated secretion of E2 and T from the granulosa cells, while only dieldrin increased (P<0.05) the secretion of P4 from luteal cells. The data show that aldrin and dieldrin stimulated the secretory function of the cultured granulosa and luteal cells and inhibited the myometrial contractions of cows in vitro, which may affect on natural parturition.

Impairment of uterine smooth muscle contractions and prostaglandin secretion from cattle myometrium and corpus luteum in vitro is influenced by DDT, DDE and HCH

The aim of this study was to investigate the effect of dichlorodiphenyltrichloroethane(DDT), dichlorodiphenyldichloroethylene (DDE) and γ-hexachlorocyclohexane (HCH) (10 ng/ml) on myometrial motility and the secretory function of the myometrium and corpus luteum (CL) collected from cows on days 8-12 of the estrous cycle. All of the xenobiotics increased (P<0.05) myometrial contractility. Moreover, the xenobiotics stimulated the secretion of the following prostaglandins (PGs) from myometrial strips: PGF2α, PGE2 and PGI2. DDT and DDE also increased (P<0.05) the release of PGF2α from CL strips, and HCH had the same effect (P<0.05) on the secretion of PGE2 and PGI2. The studied xenobiotics did not affect (P>0.05) PG synthesis, but DDT and DDE increased the mRNA expression levels of leukemia inhibitor factor (LIF), which can stimulate PG production. In summary, the xenobiotics affected PG secretion from cow myometrium and CL, which may contribute to the mechanism of uterine contraction disturbance.

Stimulatory effects of a microbially dechlorinated polychlorinated biphenyl (PCB) mixture on rat uterine contraction in vitro

Microbially mediated reductive dechlorination has been advocated as the first part of a two-stage (anaerobic/aerobic) biotreatment process for polychlorinated biphenyls (PCBs) in sediments, and is generally viewed as a detoxication process. However, previous studies suggest that microbial dechlorination increases the ability to stimulate uterine contractions compared with the original PCB mixtures. Here, we investigate the composition and uterotonic activity of the commercial PCB mixture Aroclor 1260 before and after incubation with microorganisms eluted from PCB-contaminated sediment of the Hudson River. Incubation with microorganisms resulted in a partially dechlorinated mixture (HR1260) dominated by ortho-substituted PCBs with four or fewer chlorines per biphenyl. Aroclor 1260 that had not been incubated with microorganisms had no significant effect on contraction frequency of rat uterine strips (gestation day 10) in vitro, whereas HR1260 dramatically increased contraction frequency to 718+/-134% of the basal rate at a total PCB concentration of 70 microM (p<0.05). The microbial dechlorination increased 2,2',4,4'-tetrachlorobiphenyl and one or more of four congeners that co-eluted during chromatography (2,3,3',5-tetrachlorobiphenyl, 2,3',4,5-tetrachlorobiphenyl, 2,2',4,4',6-pentachlorobiphenyl and 2,2',4,5',6-pentachlorobiphenyl) to 24 and 8 mol%, respectively. However, the uterotonic activities of the latter congeners were modest when evaluated either solely or in a reconstituted mixture and could not fully account for the uterotonic activity of HR1260. Nonetheless, the relative abundance of congeners with three or fewer chlorines increased to 14 mol% as a group in HR1260, suggesting that these congeners collectively contribute to the uterotonic activity even though the abundance of any one congener in this group was less than 5 mol%.

Gestation age-related increase in 50-kDa rat uterine calcium-independent phospholipase A2 expression influences uterine sensitivity to polychlorinated biphenyl stimulation

Phospholipase A2 (PLA2) enzymes catalyze the rate-limiting step in eicosanoid production by liberating arachidonic acid from membrane phospholipids. There is limited information regarding the expression pattern and activity of uterine PLA2 enzymes during pregnancy. Polychlorinated biphenyls (PCBs) are a group of persistent environmental toxicants previously associated with decreased gestation length that are capable of activating PLA2. The purpose of the present study was to determine whether uterine sensitivity to PCB stimulation is dependent on PLA2 expression, comparing rat uterine PLA2 expression in Gestational Day (gd) 10 versus gd20. Western blot analysis revealed a significant increase in the expression of calcium-dependent PLA2G2A and a 50-kDa protein immunoreactive to calcium-independent PLA2G6 antibody in gd20 compared to gd10 rat uterine tissue. The increased expression of the 50-kDa PLA2G6 was associated with a gestational age-related increase in endometrial calcium-independent PLA2 activity that was sensitive to inhibition by bromoenol lactone (P < 0.05). Longitudinal uterine strips isolated from gd10 or gd20 rat were suspended in muscle baths to evaluate uterine contractions following exposure to the ortho substituted congener PCB 50. Exposure to 50 and 100 microM PCB 50 significantly increased the frequency of gd20, but not gd10, uteri compared to solvent (dimethyl sulfoxide) controls (P < 0.05). Pharmacologic inhibition of PLA2G6, but not PLA2G2A, attenuated PCB-induced stimulation of gd20 uterine contractions (P < 0.05). These data suggest that PCB 50 stimulates uterine contractions by activating endometrial PLA2G6. Furthermore, gestation age-related sensitivity to PCB is associated with an increase in the expression of a previously unidentified 50-kDa PLA2G6 in rat uterus.

2,2'-Dichlorobiphenyl decreases amplitude and synchronization of uterine contractions through MAPK1-mediated phosphorylation of GJA1 (connexin43) and inhibition of myometrial gap junctions

The present study examined the hypothesis that inhibition of myometrial gap junctions through MAPK1-induced phosphorylation of GJA1 (connexin43) leads to inhibition of spontaneous phasic uterine contractions by 2,2'-dichlorobiphenyl (2,2'-DCB). Uterine strips from Gestation Day 10-pregnant rats exposed in muscle baths to 2,2'-DCB exhibited increased oscillatory frequency and decreased amplitude and synchronization of contractions. To assess effects on gap junctions, Lucifer yellow was injected into myometrial cells and transfer to adjacent cells was scored. After a 1-h treatment, 100 microM 2,2'-DCB decreased Lucifer yellow intercellular transfer in a concentration-dependent manner. The MAP2K1 inhibitor PD98059 increased percentage of dye transfer to adjacent myometrial cells from 18% in cultures exposed for 1 h to 100 microM 2,2'-DCB alone to 48% in cultures cotreated with 50 microM PD98059 and 100 microM 2,2'-DCB. In contrast, the conventional PRKC inhibitor Gö6976 (10 microM) had no significant effect on 2,2'-DCB-induced inhibition of dye transfer. Western blotting showed about a 4.5-fold increase in phosphorylation of GJA1 at S255, a MAPK1 site, after exposure to 100 microM 2,2'-DCB compared to untreated and solvent controls. However, there was no difference in phosphorylation of GJA1 at S368, a PRKC site. Cells treated with 2,2'-DCB increased phosphorylated MAPK1, implicating the increase of activation of MAPK1. Cotreatment with 100 microM 2,2'-DCB and 5 microM PD98059 reversed 2,2'-DCB-induced modification of uterine contractions and increase of pGJA1(S255) in uterine strips. Therefore, this study suggests that 2,2'-DCB decreases amplitude and synchronization of uterine contractions mediated through MAPK1-mediated phosphorylation of GJA1 and subsequent inhibition of myometrial gap junctions.

Hippocampal long-term potentiation (LTP) is reduced by a coplanar PCB congener

Neurotoxicity of polychlorinated biphenyls (PCBs) is usually ascribed to the ortho-substituted congeners. We have examined the effects of acute perfusion of 3,3',4,4'-tetrachlorobiphenyl (PCB 77), a coplanar, dioxin-like congener, on long-term potentiation (LTP) in the Schaffer collateral-CA1 and the mossy fiber-CA3 pathways in mouse hippocampus. LTP in both pathways was blocked by PCB 77, with a threshold effect at a concentration of 1 microM. LTP is a useful model of learning and memory function in which a patterned stimulation of an afferent pathway produces a persistent increase in the efficacy of synaptic transmission. LTP is reduced by PCB mixtures and ortho-substituted congeners at concentrations comparable to those studied here. These observations provide evidence in support of the hypothesis that dioxin-like and non-dioxin-like PCB congeners are equally potent in causing the cognitive decrements seen in children exposed prenatally to PCBs.

Uterine muscle as a potential target of polychlorinated biphenyls during pregnancy

Because of their once-popular commercial uses, improper disposal and environmental persistence, polychlorinated biphenyls (PCBs) are common environmental contaminants found in many designated Superfund sites. Several epidemiology studies associated PCB exposure with decreased length of gestation. Recent laboratory studies, described in this review, examined PCB actions in uterine muscle in order to investigate mechanisms by which PCBs may stimulate early onset of parturition. Because increased frequency, force and coordination of oscillatory uterine contractions are the defining characteristics of parturition, the laboratory studies used uterine muscle tissue and cells to study PCB actions on uterine contraction. Acute in vitro exposures to commercial PCB mixtures and microbially dechlorinated commercial PCB mixtures increased the frequency of spontaneous oscillatory contractions of uteri from pregnant rats. Increased uterine stimulation was observed with PCB mixtures containing increased abundance of lesser-chlorinated, ortho-substituted congeners. Similarly, in vitro exposures to PCB congeners increased the frequency of spontaneous uterine oscillatory contractions in a structurally related manner, with ortho-substitution of four or fewer chlorines associated with increased stimulation. Moreover, inhibitors of phospholipase A2 prevented stimulation of oscillatory uterine contractions by the commercial PCB mixture Aroclor 1242, suggesting involvement of arachidonic acid in the Aroclor 1242-induced stimulation. Acute exposure to a hydroxylated estrogenic PCB inhibited uterine contraction acutely, but a 42-h exposure increased uterine sensitivity to the uterotonic hormone oxytocin in a manner similar to 17 beta-estradiol, suggesting an estrogenic mechanism by which some PCBs could decrease gestation length. These studies show that PCBs stimulate uterine contraction in vitro, providing biologically plausible mechanisms in support of previous epidemiology findings associating PCB exposure with decreased gestation length. Further conclusions regarding human health should be considered in the context of human exposure and the experimental limitations of the in vitro studies.

Effects of polychlorinated biphenyl 19 (2,2',6-trichlorobiphenyl) on contraction, Ca2+ transient, and Ca2+ current of cardiac myocytes

Polychlorinated biphenyls (PCBs) have been known as serious environmental pollutants, causing developmental delays, motor dysfunction, and decrease in brain dopamine level in humans and animals. We have investigated the effects of a PCB congener, 2,2',6-trichlorobiphenyl (PCB 19) on contractile force, Ca2+ transient, and L-type Ca2+ current (I(Ca,L)) in guinea pig ventricular myocytes stimulated at a rate of 0.25-0.33 Hz. PCB 19 decreased contractile force in a concentration-dependent manner. During the negative inotropic response, the action potential duration at 20% (APD20), 90% of repolarization (APD90), and the action potential amplitude (APA) were decreased concentration dependently: 30 microM PCB 19 reduced APD20, APD90 and APA by 36.7 +/- 3.5%, 22.6 +/- 3.9%, and 2.4 +/- 0.6%, respectively (n = 11, p < 0.01). PCB 19 30 microM decreased the Ca2+ transient and the I(Ca,L) by 46.8 +/- 1.8% (n = 9, p < 0.01) and 47.1 +/- 3.1% (n = 9, p < 0.01), respectively. The results suggest that PCB 19 decreased the Ca2+ transient through inhibition of L-type Ca2+ channels and that the decreased Ca2+ transient consequently caused a negative inotropic effect in cardiac myocytes.

Antioxidants prevent gamma-hexachlorocyclohexane-induced inhibition of rat myometrial gap junctions and contractions

Lindane (gamma-hexachlorocyclohexane) is a commonly used pesticide that bioaccumulates in mammalian adipose tissue. Lindane inhibits gap junctional intercellular communication and oscillatory contractions of pregnant rat myometrium in vitro. The present study investigated the role of oxidative stress in lindane's inhibition of myometrial function in mid-gestation pregnant rat uteri. Lucifer yellow dye was microinjected into cultured myocytes to assess gap junctional intercellular communication. Lindane exposure (100 microM) resulted in a time-dependent, biphasic inhibition of dye transfer. This pattern of inhibition was also seen upon cell exposure to the pro-oxidant, tert-butyl hydroperoxide (100 microM). Lindane's initial and secondary-onset dye transfer inhibitions were reversed by cotreatment and pretreatment with the antioxidants, alpha-tocopherol (25-100 microM), diphenyl-1,4-phenylene diamine (10-30 microM), and superoxide dismutase (100-400 U/ml). D-mannitol (100-300 mM) also reversed lindane's initial dye transfer inhibition. Nitro blue tetrazolium reduction to formazan (measured spectrophotometrically) was elevated upon exposure of cultured cells to lindane or tert-butyl hydroperoxide, indicating the presence of reducing agents. Lipid peroxidation, assessed as thiobarbituric acid-reactive substances, was also elevated in lindane-exposed cell cultures. alpha-Tocopherol reversed this elevation. Finally, uterine contractility was assessed by measuring isometric contractions of uterine strips hung in standard muscle baths. Pretreatment with alpha-tocopherol prevented lindane's abolishment of uterine contractions in vitro. These data support the hypothesis that lindane inhibits uterine contractility and myometrial gap junctions by establishing an oxidative stress environment.

Potential involvement of calcium, CaM kinase II, and MAP kinases in PCB-stimulated insulin release from RINm5F cells

Polychlorinated biphenyls (PCBs) are environmental contaminants that induce release of insulin in rat insulinoma cells, RINm5F (Fischer et al., Life Sci. (1996) 59, 2041-2049). In the present study the mechanisms of this effect were investigated using noncytotoxic concentrations (10 microg/ml) of a PCB mixture, Aroclor-1254, and the pure PCB congeners 2,2',4,4'-tetrachlorobiphenyl and 2,2',4,4',5, 5'-hexachlorobiphenyl. Treatment of RINm5F cells with each of these agents resulted in a rapid increase in intracellular free calcium. The presence of extracellular calcium was required for PCB-induced insulin release because removal of calcium from the medium attenuated the effect. In addition, pretreatment of RINm5F cells with the calcium channel blocker verapamil also blocked PCB-induced insulin release. To determine whether PCB-related insulin release could be associated with the enzyme, calcium/calmodulin-dependent kinase II (CaM kinase II), RINm5F cells were pretreated with the CaM kinase II inhibitor KN-93. PCB-induced insulin release was completely blocked by KN-93. Under similar treatment conditions, PCBs also induced the activity of mitogen-activated protein kinases (MAPK) 1 and 2. However, inhibition of MAPK activation by a specific inhibitor, PD-98059 (10.0 microM) did not prevent insulin release induced by PCBs. The results of the present investigation suggest a role for calcium and CaM kinase II in PCB-induced insulin release. Furthermore, the results suggest that insulin release by PCBs is independent of the activation of MAPKs.

Stimulation of oscillatory uterine contraction by the PCB mixture Aroclor 1242 may involve increased [Ca2+]i through voltage-operated calcium channels

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants associated with spontaneous abortion and shortened gestation length in women and animals. In previous studies, we showed that PCB mixtures and noncoplanar ortho-substituted PCB congeners increased contractions in pregnant rat uterus. In the present study, we hypothesized that the PCB mixture Aroclor 1242 (A1242) stimulates oscillatory uterine contraction in pregnant uterus by increasing intracellular calcium concentration ([Ca2+]i). Pretreatment of uterine strips with ryanodine or thapsigargin, to deplete specific intracellular calcium stores, did not prevent the increased frequency of oscillatory contraction due to 50 microM A1242, whereas thapsigargin effectively blocked carbachol-induced stimulation of uterine contraction. However, 100 microM A1242 was unable to increase contraction in the absence of extracellular calcium or in the presence of the voltage-operated L-type calcium channel blocker nifedipine. A1242 (100 microM) was observed to partially depolarize the cell membrane of myometrial cells from pregnant rats, as measured with a potential-sensitive carbocyanine dye. Changes of [Ca2+]i were monitored in single myometrial cells loaded with the fluorescent calcium-sensitive probe fura-2. Cells exposed to 100 microM A1242 showed a delayed and sustained increase of [Ca2+]i, and this increase was completely blocked in the absence of extracellular calcium or the presence of nifedipine. Therefore, the data suggest that depolarization of the cell membrane by A1242 enabled myometrial cells to increase [Ca2+]i through activation of voltage-operated calcium channels, and the increased [Ca2+]i consequently stimulated contraction of uterine smooth muscle.

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.